Packs, Chargers, Power Supplies and more – Chargers

With my LiPo battery needs recently moving up into the 6S 3-5000mah range I quickly came to the conclusion that my charger was not going to be up to the task.  Not that it wouldn’t work.  I’ve already been charging some of the new 6S batteries with my existing multi-channel charger.  It works just fine, it is just very slow.  I don’t like to charge without being in a position to keep an eye and having it take 2 hours to charge 1-4 batteries made that a painful experience.  I also don’t like to have to keep running to my charger and hooking up another battery every time I fly in order to keep battery packs ready to go for the next flight while I’m out at the field.  That can work if you buy enough batteries and keep your charger running, but having to keep track of which channel is at what point in the charge cycle and continuously feeding the charger just takes away from my enjoyment while at the flying field. Finally, I don’t like the idea of just buying a bunch of batteries to avoid charging at the field as I fully expect my expansion into electrics to just continue and they don’t exactly give these big battery packs away!

Purchasing the right charger with the capability to charge these larger cells quickly, especially if I could be charging multiples, would be great.  So ideally, I’m looking for a way to charge 2 or more 5000mah 6S packs in 60 minutes or less… with 30 minutes being the target.  Let’s look at what it will take to do that.

First, you need to understand that chargers often advertise that they can charge up to a (for instance) 6S LiPo at rates up to 8A per channel.  Unfortunately they often tend to hide somewhere further down in the fine print that each individual charging channel is only capable of charging at a maximum rate of up to 50W.  Those specifications are not mutually exclusive.  The charger can in fact charge at a rate of up to 8A and can handle 6S LiPo cells… just not a 6S LiPo at 8A… What does that mean for you?  It’s really quite simple.  A 6S pack tops out at about 25V.  Since Watts equal Volts times Amps, that means that 2A is about the maximum charge rate you can expect to charge a 6S pack at with this 50W charger… 2Ax25V=50W…  In order to charge at the advertised rate of 8A, the battery being charged would have to max out at just over 6V… 8Ax6V=48W.  So with a charge rate around 2A, for the 5000mah pack the best I can hope for is a charge time of 2.5 hours.  Just to get to a 1C rate of 5A for a 6S 5000mah LiPo would require a 125W capable charger.  For my desired 2C/10A charge rate I would need a 250W charger.  To do two at once I’d need a 2 channel charger with 250W per channel.

So with those numbers in mind I want a charger with at least 250W per channel and I wouldn’t be upset if I could charge at a 4C rate which would require 500W of power!  Occasionally, I’d like to be able to get a pack ready to fly in short order if I happen to have just flown my last battery and need arises.  I don’t recommend doing it often, but most of the packs I am buying these days allow for charging at up to 5C rates!  Another “nice to have” would be the ability to measure the batteries internal resistance and I wouldn’t cry if I had a way to record the relevant details during a charge or discharge cycle.  After reading many reviews and picking through specifications I decided to purchase the FMA Powerlab PL6.  This is a single channel charger that can supply over 1000W of charge power, has a reasonably priced PC control program with nice graphing capabilities and measures internal resistance as part of the charging process.  I was going to spend $175-$225 all in including the charger, control cable and a balancing board but the folks who own these seem to rave about them and with 1000W of power, I don’t expect to be worrying about more power anytime soon.  Here’s a link to the charger itself.

While this is a single channel charger, I have discovered that a lot of folks have taken to parallel charging packs on these high power chargers.  I have actually charged as many as 5 3300-4000 6S packs at a time at 1C rates, so 5 packs done in a single hour!  To do that you’ll need a parallel charging adapter like this.

There are many version of this depending on the type of connector your batteries use.  Since I’ve been using EC-3 in all my larger aircraft, that is the version I show here.

I’ve also pushed to 2C charge rates at the field to get a couple packs back to full quickly.  This means that while it isn’t exactly a multi-channel charger as I envisioned, I have been able to do practically everything I wanted with this new setup.  I’ve also started to work with the PC interface and explored the graphing capability as well as recording the IR measurements.  The piece you need for that is the USB Adapter.


So far, it’s been an excellent charger that I have had almost no complaints about.  That’s not to say that there weren’t some surprises!

First, although clearly documented, I didn’t really pay attention to the fact that the permanently attached wires that are used to supply power to the charger are furnished with an EC5 connector.  This seems odd as most  chargers terminate onto bandanna plugs which are easily plugged into most power supplies.  Not a huge issue.  The first thing I did was to create an adapter which I now wish I had made a bit longer.  The 9 inches or so I did create is just a bit short in many instances.  A couple feet would have been better.  I’d also warn that you want to use at least 10 gauge wire as you may be drawing close to 40A for extended periods from the supply and you don’t want to heat up the wires to much.  I would recommend 2 feet or so as a nice compromise between to long which tends to always be in the way, and to short which causes issues with physical location of the batteries under charge, the charger itself and the power supply it is attached to.

Finally, you should take note that whatever charger you choose for charging larger LiPo batteries will likely require a fairly hefty power supply to feed it.  That is my next post.

Packs, Chargers, Power Supplies and more – Packs

So with my move to bigger E-powered aircraft I have started buying larger packs (mostly in the 6S 3000-5000 range.  These things can easily cost $100-200 and for that kind of investment I wanted to get something that would both perform well and would have a minimum cost in terms of how long the packs would continue to work.  This lead me to a lot of reading and research on internal resistance, C ratings, and care and feeding of batteries… there’s plenty to discuss about all that but for now I will just cut to my understanding.

First and foremost, C ratings on batteries are almost pure marketing.  What most people understand that number to mean… that you can safely draw this number multiplied by the pack capacity until the pack is drained without damage to the battery pack … is apparently NOT what most of the sellers understand.  To be charitable, I would assume they are expressing a number that can only be reached by testing to destruction (in some cases, a very quick and fiery destruction).  In my more pessimistic language, I would say the C ratings advertised are pure bullshit.  Not only will many of these packs not sustain that level of current draw for the amount of time it would take to discharge the pack, but some of them are so ridiculously labeled that the wires would simply melt, the connector would disintegrate and then whatever was in proximity of the pack would likely burst into flames from the heat generated in the pack if you tried.  The consensus among those who have done independent testing seems to be that no LiPo available to us should be labeled above 35-40C continuous.  70C is a cruel prank… 150C is pure snake oil.  I can and probably will write a whole other post or two on this but for now that is all I will say about the C ratings in this post.

Internal resistance (IR) is a much less understood but much more important and useful rating but it is not typically a published specification for most hobby grade batteries.  It is temperature and capacity dependent but is still a very useful tool in comparing batteries and could easily be published as a number of milli-ohms at a certain temperature.  Some folks have suggested a calculated value called FOM or figure of merit which would take into account both the IR at some standardized temperature as well as factor in the battery capacity.  It isn’t perfect, but it would be a much more useful specification than the C ratings published now.  Of course it could be “exaggerated” just like C ratings are but measuring the internal resistance of a battery can easily be done with a few available tools and the FOM can thus be calculated so it would be much easier for hobbyists to spot these exaggerations and react accordingly.  Hopefully the market could then sort it out… but I digress.  The reason IR is so much more useful is simple.  IR is directly related to the current allowed to flow from the battery pack and the amount of heat generated from the battery supplying the current.  Though IR is not the only factor that affects a batteries overall health and ability to provide power to the attached circuit (primarily your motor!) it is probably the most easily understood and has the most direct correlation with these things.  I will likely post more on this later but for now what follows are the basics.

Generally speaking, lower IR is better.  Keep in mind that if you measure IR, you must do so at a constant temperature to be useful for comparison and also keep in mind that only like capacity batteries can be compared.  The relationship between cell size and IR is not linear so no simple way to compare between two different capacity packs is available.  The total IR of a series pack is the sum of the IR of each cell.  This total number is indicative of the current that the Battery can produce overall because the battery IR will cause a voltage drop as the current flows out of the battery.  A battery with a higher overall IR will supply less voltage under load (the loss being “used” to heat the battery).  This results in less power from the battery reaching the motor, which is the real purpose of the whole exercise!  While overall pack IR is important, having each cell in a pack with a similar measurement is equally important.  Having all the cells in a pack with a similar IR indicates a pack that is well balanced and matched and will therefore likely have a longer life.  The reasoning is that every cell will heat up in direct relationship to the IR of that cell and since excessive heat is typically the cause of battery failure, the cell with the highest IR will be first in line to be damaged from the heat thus produced.  The overheating will likely cause the cell to develop an even higher IR over time which will just add to the issue until the cell IR reaches such a high value as to render the pack useless due to the large voltage drop in this weak link or the cell simply fails from the heat.  There are tools available to make this measurement both for the pack as well as each cell and published values and calculations available as a guideline to what is considered to be “good” and how much current you can really expect to draw without damaging the battery so you don’t have to totally re-invent the wheel here either.  If you want to learn more, do some web searches or check in for my further posts on the subject.  If you don’t care that much and just want to know what to buy I will give you some guidance based on my experience a bit later in this post.  If you’d like to measure IR in your packs for yourself so you can start to recognize the good from the bad and become a more informed consumer one of the best tools I have found to do so is available here:

With this device you can measure and compare the IR of each of your LiPo packs.  It will help identify which packs are best used for high current draw versus more routine use and with this an a little math determine how much current is safe to draw from this pack (there is even a webpage that you can enter the result into and get a calculated max draw).  There are several different models so make sure you pick the correct one for your needs.  There are some chargers available that can give you a similar reading but do some research to see if the charger you are considering gives a useful reading.  My research indicates this meter is better than any of the chargers but there are a few chargers that may be good enough for your purposes.

One thing you can do immediately and without spending much/any money is to learn to care for you LiPo batteries correctly.  Care and feeding of LiPos is actually pretty simple.  Avoid physical abuse (punctures or compression may cause a fire).  Always balance charge your packs with a charger that is made for the task at an appropriate rate (1C when possible for longer life, even if the battery says you can go faster).  Don’t discharge them to fast or to far if you can help it (85% discharge is a nice goal).  Store your packs at a 40-50% charge level and in a cool/dry place (the fridge is almost perfect but you will need to watch out for condensation and allow them to warm before use) whenever you can.  Avoid extreme heat and extreme cold pretty much always.

Other than the physical abuse and charging rules you can violate just about any of the other rules with the understanding that you are taking a bite out of the life of your battery and sooner or later you will pay for it!

For now suffice it to say that I own a single E-Flite 6S 3200mah 30C pack that I bought with my Carbon Cub…, a G-Force 6S 3700mah 45C pack, and 4 Glacier brand 6S packs in 30C rating.  2 each of the 3300mah and 4000mah variety.  Here are my feelings on each based only on my personal experience.

The E-Flite is a mediocre pack that I believe would be destroyed if asked to deliver the 96 amps it advertises for any length of time.  It does fine in the Carbon Cub which only draws a max of 70A on occasion and for very brief intervals, but I wouldn’t try to pull more than about 60A from it for a sustained period.  (Just in case you’re wondering, that means the battery is about a 20 C pack or at bit less if you subscribe to my definition of C ratings as expressed earlier).  The cells do not seem to be exceptionally well balanced (IR varies quite a bit between cells in the same pack).  In short this pack simply doesn’t measure up.  I don’t consider it a terrible battery, just not a good value.  There are many packs out there that are as good or better for at least 30% less… I will say the folks at Horizon (who sell this pack) have great customer support so I would be confident that they would take care of me if a quick failure occurred.

The G-Force pack is somewhat similar in that it is more than adequate for the Cub but it’s ability to deliver current I would estimate to be far below (half or so?) the C rating posted on the label.  The difference is that the G-Force is significantly less expensive so it is a little easier to swallow the limitations.  It is also quite a bit better balanced from cell to cell than the E-Flite pack.  I have flown it in both the Carbon Z and my Aeroworks Extra 260 powered with an E-Flite power 60 motor and found it adequate in both.  I don’t know what kind of warranty service I would get from the manufacturer/reseller, so it is hard to give a solid final opinion.  Overall I wouldn’t rush out to buy more at this point but at least it is more reasonably priced and compared to the E-Flite is a better value.

The 4 Glaciers are my favorites so far as they are some of the cheaper packs I have purchased and yet outperform (provide all the needed current and barely get warm!) my other packs and purportedly are as good as the best out there.  They certainly test out as excellent when I use my own internal resistance meter and according to my calculations they are the only batteries I have any personal experience with that might actually be able to sustain the rate that is implied by the label.  In addition the balance (measured IR) between cells is very close.  All this and they are in the same price range if not cheaper than the G-Force packs mentioned above.

Here’s a link to the web page where you can find these packs… Buddy RC

I have also had some limited exposure to Admiral and Thunder Power Packs in this range and the Admirals seem to to be on a par with most of the other packs out there and are in that same average price range.  The Thunder Powers I have experience with have been disappointing so far.  I am withholding final judgement as I have not had a chance to test a new TP pack in this range but the used ones I have played with have not measured up.   The price on them is premium and while I have always heard good performance reviews, my measurements and experience with some slightly used 70C (hah) 4400s gives me the impression that the 30C Glaciers are just as good if not better.  I do know from second hand reports that the TP folks will take care of their customers but that excellent service comes at a very steep price.  I’d love to say it’s worth it… If I have the opportunity to test some new packs I’ll be happy to report back but right now they won’t be getting any money from me.

On to some other concerns that I think are worth noting.  Firstly, you obviously want to make sure whatever you buy will physically fit and isn’t so heavy as to cause an issue.  In smaller planes, weight can be critical, so take this into account but for what I fly I haven’t seen a huge or at least unexpected difference.  Sure the Carbon Z Cub doesn’t have quite the straight up pull with a standard 4000mah pack as it does with a 3200… you do give up something for that weight.  But it’s still pretty spritely and it can fly for 15 minutes on the 4000 versus about 10 on the 3200.  One thing the C rating is good for is it seems that higher C rated cells tend to be heavier, so keep that in mind.

Second, take a good look at the gauge and type of wire being used to build these battery packs before you purchase.  I can tell you that if the balance leads are not very flexible, they are likely to break off at some point and now you have a potentially dangerous (to your personal property as well as your health) problem.  That loose wire can contact another terminal of the battery and cause a short or simply cause the charging of that cell to fail.  Next stop is a forced landing in a bad place or worse.  At a minimum you will be trying to repair that connection very soon and that means some fairly demanding dis-assembly and re-assembly of the pack.  It is not a task I would recommend to anyone who isn’t both knowledgeable of pack construction and fairly experienced with a soldering iron.  The main leads need to be both flexible and heavy enough to handle the current load as well.  The gauge of the wire is usually adequate in my experience but I have run across some that were made from very stiff wire which makes them difficult to connect and position properly in the aircraft.

Lastly, pay attention to the balance and load connectors on any pack you consider purchasing.  Of course it has to work with your charger and speed controller or you will need to adapt it to fit.  I don’t like using adapters on the load connector (in flight) as they just add another voltage drop and possible failure point so can affect both longevity of the model and performance.  I eventually will swap out whatever comes on the battery for whatever I deem appropriate for my use.  I am currently using some JST 2 pin (red) connectors on my smallest aircraft, Deans ultras on my mid size birds and EC-3s almost exclusively on my larger aircraft.

Great-Planes-MM3107-Female-2-Pin-Bec-Connector-22 Pin Red JSTs

Deans Ultra

Image result for ec3 connector

EC-3

The EC-3s are reasonably easy to assemble, make a good secure connection and are rated at 60 amps of continuous current flow.  So far I have only seen 70-75A for very short periods on my larger craft so these seem to be quite adequate.  Many folks favor the Deans, but they are only rated at 40A continuous and I find they become difficult to get soldered to 10 gauge wire without melting the housing and just about impossible on anything larger.  They work well for 12 gauge and smaller wire and I use them almost exclusively on my 3S powered craft where smaller wire and ~30A draws are more the rule.

On the balance connector pretty much everything I own uses the XH style connector.  It’s not my favorite in the world but it is almost universal these days which is a nice change.  I think Thunder Power is one of the few holdouts on this which I really don’t understand.  At this point they need to just concede the point and move to the XH with everyone else.

Big Electrics need big power… Packs, Chargers, Power Supplies and more

Recently, I’ve been spending more quality time with my electrics… especially my newer/larger electrics like the Carbon Z Cub and the AW Extra 260.  Both of these planes are a blast to fly and the AW is, if anything, even better since its conversion to electric.  I’ve almost gotten to my goal of only flying either electric power or gas (no glow fuel for me).  I recommend the AW Extra for a nice mid-size electric acrobat and the Carbon Z has a wide flight envelope combined with the ability to fly off floats, tow gliders and fly anywhere from wild to mild.  Both are great.

The only drawback to this whole scenario is that these bigger electrics need bigger batteries.  Bigger batteries need a bigger charger to charge them up and bigger chargers have bigger power needs…  In short a whole new series of challenges arise when you get into large electrics.  I’m working my way through all of them and have done a bunch of research and some experimentation of my own that I’d like to share.

First, let’s try to put some parameters around the size of the issue…  In my case, I started out in what I would call “large” electrics with the Carbon Z Cub.  This airplane uses 6S LiPo power with a recommended capacity of 3200mah.  Many folks fly larger capacity batteries in the cub to get some longer flight times with sizes up to 5000mah being common.  Two other conversions currently underway will use similar size power systems.  To charge a single 6S pack at a 1C rate takes a considerable amount of power.  For instance a 5000mah 6S pack means charging at 5A and ~25V.  Since power (expressed in watts) is equal to current in amps times volts that means about 125 Watts of power are required to charge just one of these batteries at a standard 1C rate which takes about an hour.  You can charge slower or faster of course.  If you don’t mind a 2 hour charge you only need 62.5 Watts… if you want a 30 minute charge than you need 250 Watts of charging power.

I was hoping to be able to charge 2-4 such batteries at once which means drawing as much as 500 Watts from my charger and power supply system for a 1 hour charge and up to 1000 if you want to get it done in 30 minutes!  Keep those numbers in mind.

My mainstay charger to this point was the Hitec X4.  This charger has 4 separate channels (independent charging outputs) which can each charge at a 50W rate.  For my previous usage where I would sometimes charge as many as 4 of the 3S 2200mah packs, this was not a problem.  At around 12V, the 2.2 A charge rate only required ~27 Watts….  No problem.  Four batteries charged in an hour with only a little over 100W of input power was easy to take care of.  Even pushing all four to double the charge rate (or nearly so) was within reach at the max 200W combined output of this charger.  A small 12V supply capable of 20amps or so was more than enough to supply the needed power and the 200W load was easily supported by my existing 900W cheap-o generator.  Unfortunately this is clearly inadequate for these 6S packs.  At the maximum output of a single channel of the Hitec, the maximum charge rate into the 6S pack is about 2A.  A 5000mah pack is going to take 2.5 hours to charge.  That’s a long way from the performance I’m looking for.  For smaller jobs, the Hitec is still a great charger that I expect to continue to use and highly recommend.  If 3 or 4 cell 3000mah or smaller packs is all you need… it is a fine choice.  The one I have linked to here is a slightly newer and higher power version of what I have and would work reasonably well for up to 4 cell 5000mah packs or even 6 cell 3000mah packs at 1C charge rates.

Since I already know I want to run 6S 5000mah (max for now) batteries and I want to charge 2-4 packs in 30 minutes, I can start shopping for a charger, power supply and generator (if needed) and of course a few extra flight packs!  I’ll try to do a few posts in the near future outlining the buying decisions I made in each case and how they affected each other.  Let the fun begin.

 

Taft Hobby DO-27… First Flight!

If you read the first look post on this plane you will recall that we ran into problems trying to install the first wing set due to (apparently) a misaligned tube in one wing.  Once again the folks at Falcon took good care of their customer and shipped out a new wing set and tubes.  The new set slid right into place but at this point we noted another issue.

2015-04-28 18.13.27

 

As you can see one of the servo leads in the wing is so short that it is very difficult to plug in at all when you are assembling the aircraft.  You don’t have a lot of wire coming out of the wing root either, though it is adequate.  The problem is you can’t hold onto this servo lead and apply any pressure to assemble it…  Forceps are NOT optional!  This is an annoyance, but not a showstopper.

Finally, the last complaint I have about the Taft DO-27 is the hinging of the control surfaces.  The folks at Taft obviously know these things are a bit fragile as they include a bag of hinge points to install in case the molded in hinging fails.  We added some wound tape in the aileron hinge line on Steve’s plane and we will see how it goes but both the returned wing set and the new set are already showing signs of hinge failure so I think I would consider adding tape to all hinge lines or cutting them loose and installing the hinge pins from day 1 if it were my airplane.

The good news is, once we got the plane assembled and at the field… It looks good and flies really well.  The scale details really add to the look and the lights are a nice touch as well.  Taxiing on our grass field was easy and with almost no wind and a short takeoff run the DO-27 picked itself up and climbed quickly.  Steve shortly had it doing loops, rolls, snaps and more.  Power was good and flight times look to be 8-10 minutes of general sport flying… maybe longer with some throttle management.

I’d like to rant about how nice the plane is and in the air it really is.  Flying characteristics (based on the two flights so far) seem to be excellent.  Plenty of wing, good roll rates, just a generally good flying airplane.  Looks too are a plus with nice lights and a distinctive shape and color scheme with a few details thrown in makes for a nice combination.  Assuming the wing tube problem is unique, you have to deal with a few issues… First rearrange things to get the tail linkage setup correct.  Second, you should probably get some short extensions to permanently attach to the 2 shorter servo wires and make them easier to connect and disconnect.  Third, get out your hinge tape or go ahead and install the hinge points day 1.  With those 3 things out of the way, the airplane should be a winner.  Time will tell for sure.

Taft Hobby DO-27… First look

During his recent trip to the Weak Signals show in Toledo, my flying buddy Steve made an “impulse buy” from the good folks at Falcon Hobby Supply and came home with the Taft Hobby DO-27 in Red and White.

THLTP-03C-2

The purchase started out with a bit of  misstep when the folks working the booth there assured Steve that the plane would accept the 6S LiPos that he had on hand.  This is not the case!  The DO-27 is setup for 4S use and I very much doubt the speed controller or motor would last long if a 6S was installed!  With no 4S batteries in his inventory, Steve was considering returning the aircraft but the folks at Falcon stepped up and offered to send a free battery at no charge.  Shortly thereafter Steve has a 45C Pulse Ultra battery in hand and is looking forward to flying his new airplane.

Today, Steve brought the DO-27 over and we started unpacking and assembling.  Visually the airplane is striking with a nice paint scheme, quite a bit of scale detail and a very distinctive look.  Packaging seemed to be excellent with no damage noted and everything held tightly in place.  The model is also very complete with everything needed including a nice wood prop, spinner, nice looking wheels, etc…  Assembly is very simple with only a few steps to complete but during the process we did note a couple of issues.  Two were especially troublesome.

First, the front wing tube in the port side was impossible to install.  It went in an inch or so and then became very stubborn.  After forcing it a bit further it just continued to get more difficult to slide in.  Visual inspection seemed to indicate the tube was misaligned with the plastic wing root as a lip can be seen on one side.  With no way to move the tube (it seems to be quite securely installed) we tried using a drill bit to open up the entry to the tube and eventually managed to get the tube in place but it is very difficult to install and I think another call to Falcon is imminent!

Secondly, when Steve attempted to connect the linkage to the tail surfaces we quickly realized one was far to short and the other far to long!  It was quickly decided that the linkages were simply swapped at the factory so we traded them out and things looked a bit more promising until we realized that both were now to long…  a bit more head scratching and we realized that if we physically reversed the servos, essentially moving the output shaft forward a bit, we might have something that would work.  With that done, we got to a workable linkage layout and all seems well.

Another minor issue was clearance between the landing gear blocks and the foam hatch that screws on over it.  Once the straps were added to hold the landing gear in place, the belly hatch was held slightly away from the body of the plane.  Some simple trimming in the area took care of the problem.

We still have high hopes that solutions to all the issues will be found and Steve will get to actually fly the bird soon.  With any luck it will fly as good as it looks and we can leave the issues behind.  More to come….

Lots of LiPos… maybe parallel charging is one answer?

I recently picked up a higher power charger… In my case, I chose the Revolectric FMA PL-6.  This is a very highly regarded charger and I did not pick it for just the power but that was a basic requirement in the decision making process.  So far, I am enjoying it and I will have another post up shortly with more info on that product.  The important plot point for now is that this is a single output charger that can crank over 400W of charge power at 12V and over 800W at 24V.  Compared to my previous chargers that have always (at most) been limited to 50W per output this thing is a real power house… but I was thinking I had to trade off quite a bit to get the big power.  For instance…

The first big trade off when looking at these higher wattage chargers is that they typically have fewer outputs.  On my old trustworthy Hitec X4 I have 4 outputs, each capable of 50W of charging power.  When you start looking at chargers with 400W or so you usually get 1 output or occasionally 2 outputs with 200W of power each.  By the time you get to 600W or higher you are typically going to get one output.

This was an acceptable trade off for me because my main goal in purchasing this charger was to allow me to charge my 6S 3300-4000mah LiPos in a reasonable time.  A 4A charge (one hour recharge for the 4000s) at 25V (approx.) requires a 100W charger.  With my 50W, charge times were in the range of 1.5-2 hours.  With my new charger I can charge at 2C (8A) which at 25V is 200W and charge in 30 minutes or less.  Not bad!  In a pinch I can even charge faster as the batteries are rated for 5C (20A) max charge rate which would bring me to a 12 minute charge provided I have at least a 24V supply!  I don’t like to push the batteries that hard normally but it’s nice to have that ability.

The problem, it would seem is that I now can only charge one battery at a time so if I charge at 2C or so I could charge another battery every 30 minutes.  That’s great but it sure would be nice to be able to charge multiples… Oh well, I guess I have to give up something for progress… or do I!  As it turns out there is a way to get there, and it really isn’t that difficult.  Enter the parallel charging board…

2015-04-16 21.03.15

With this nifty little board plugged into the 6S balance port on the included balance board as well as the main charge ports of the PL6, I can now connect up to 6 similar batteries at a time and using the high power charging capabilities of this charger I can charge all 6 at once!!    There are many versions of this board with various types of charge plugs, so be sure to get the version that is right for your batteries.  It’s really fairly simple to use and quite effective.  Basically as long as the batteries are all similar cell counts and are starting the charge cycle at fairly similar states of charge, you can simply plug all of them into the board (main charge lead first, then the balance plug from each battery) and you’re ready to charge.

As an example, let’s say I’ve flown 6 flights on my T28 using 3S 2200 mah LiPo batteries.  Assuming I’ve run them all down near exhaustion I simply plug in the main leads and then the balance plugs to the balance board, set the charger for 2200mah charge rate as normal but specifying that I am charging 6 parallel batteries.  The charger will then multiply the charge rate and start charging at 13.2A.  In an hour or so, all 6 will be charged.  If all the batteries can handle a 2C charge rate of 4.4A then we could charge them all in about 30 minutes as the charger would be pumping out 26.4A.  26.4A at 12V (all approximations) would require a bit over 300W which is easily attainable with even a fairly modest 12V power supply or battery.

There are a couple things to keep track of when parallel charging.  You should take it seriously when I say that the batteries need to start the process at near similar charge levels.  Any difference in voltage between the packs will equalize by current rushing from one pack to the other through whatever connections are available (thus the advice to connect the main load connectors first since they can handle more current).  This rush of current if pretty much unrestricted and could overheat another battery or smoke the balance board if the difference is to great.  Also, note that all the packs need to be of equal cell count so no mixing 3S and 6S etc…

When this really gets to be impressive is when you look at what happens if I want to charge up all six of my 6S batteries.  I have 2 4000mah, 3 3300mah and 1 3700mah 6S packs for use in several of my planes.  Using my old 50Wx4 charger getting all 6 packs back to charged state after a full day of flying would take at least one full charge cycle of 1.5 hours (at least) for the first four and an additional 1.5 (or more) hours for the second batch of 2.  This is 3-4 hours of charging.  Now, I can hook up all 6 packs in parallel and even if I pick a modest 3.3A charge rate the charger will then do the match and start charging at about 20A (assuming adequate DC power).  The charge cycle will likely take only a bit over an hour and all 6 packs will be race ready again!

I’m not sure I’d want to do this with packs that were hugely different in capacity… have to think about what will happen and whether this might cause issues but I’m not concerned with this particular scenario.  Of course parallel charging is possible with other chargers… this is not something only this charger can do… but to be useful the charger needs power to spare.  Your average 50W charger need not apply…  Here are links to both the charger and the  balance board in case you are interested in purchasing one or both for yourself.


 

 

“Wax” coating for foam airplanes…

As I have ventured into more Electric powered flight I have acquired more and more foam aircraft.  Foamies are great as they are durable, easily repairable in most cases and very light.  Foam is also easier for manufacturers to shape into all sorts of shapes and allows them to mold in a lot of intricate detail if desired.  Sometimes the downside of foamies is that the foam tends to get dirt and dust embedded in it, grass stains and other scuff marks etc… As well, whatever paint has been applied often wears away quickly.  That’s not a big deal when the plane is the $30 variety but as the foam and electric planes get bigger, more detailed, and more expensive, you tend to become more interested in preserving them.  Even my T28, which is cheap at twice the cost (but don’t tell Parkzone) gets dirty and ugly far to fast in my opinion.  I am on my third and have probably 1000 total flights on them, and wanted a way to protect the latest edition.

I have seen folks using a clear spray coating of either urethane or something similar but it can damage the foam (either the spray itself or sometimes the propellant used).  As well, many of these eventually yellow and are hard to remove once that occurs.  Looking for something better, I ran across some information recommending a coating of Pledge Future floor polish to help preserve the foam and whatever finish has been applied to it.  I hunted a bit and found the product had since been renamed and re-marketed as Pledge Multi Surface Floor Cleaner so I went out an hunted down a bottle and first did a test coat on a scrap of foam with promising results.

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I have since coated part of my FlyZone Tidewater and all of my Parkzone T28 with it and I have to say the surface seems to be quite tough and very slick and shiny.  In both cases I covered the airplanes by simply painting it on with a foam brush but you really can’t tell that by looking at them.  I have read that many folks have applied it with an air brush with great results as well but aside from giving you a thinner and lighter coating (which may be important to you if weight is a critical in your application), I don’t think you will be able to tell the difference in finish as the product seems to be self leveling in nature and I ended up with a very smooth, slick finish on both aircraft.  Here’s a view of the T28…  it may be hard to tell from this but the finish is much slicker now than it was before.

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So aside from a small amount of weight there are a couple possible downsides to watch out for.  As I learned first hand on the Tidewater, the paint on your foamy may be soluble by the coating!  Yep, the paint on the Tidewater started running as soon as I applied the “Future”.  So test first with a very small amount of finish in an unobtrusive spot before applying widely.  With care, I did manage to coat all of the colored areas with a minimum of runs (a bit of dabbing with a paper towel works wonders).  On the plus side the T28 finish had no issues at all.

Secondly, while the viscosity of the product (just a bit thicker than water) lends itself well to application via foam brush or airbrush, it also can run easily so apply lightly.  The good news is a little reapplication will often soften the area and allow the aforementioned self leveling to occur.  If worse comes to worse, ammonia based cleaners will take it off so you can start over!  Keep this in mind while cleaning the aircraft in the future as many window type cleaners will contain ammonia and dull or remove the finish.

Based on my experience so far, I’m planning on having a buddy do a coat of Future with an air brush for my Carbon Z Cub.  He has more experience with air brushing than I so once I do a little bit of customization/decoration I plan on handing it off to him for the actual application.

If you need to get some Pledge Multi Surface to try it out for yourself and can’t easily find it locally, here’s a link to Amazon for the correct product.  Pledge Floor Care Multi-Surface Finish

It’s cheaper there than I found it locally, even with shipping!  I’ll update this post with my experience once flying season is in full swing.  Please comment with your own experience here as well.

Carbon Z Cub – First changes/modifications.

I’ve spent a fair amount of time scouring the forums and am currently up to about page 400 in the 1000+ page discussion of the E-Flite Carbon-Z cub on RC Groups.  If you care to read all about it click here.  Just to be clear, the cub doesn’t necessarily NEED any modification to fly well.  It appears quite capable and fun to fly right out of the box but I’m one to “tweak” a bit on every plane in order to get a bit more out of the plane, increase the fun factor and hopefully the life of the airplane.

Using input from the discussion group and based on my own experience with this model as well as others, here are three areas where I’ve made changes to the airplane so far.

1.  I continue to be disappointed with the paint.  Just normal handling, battery insertion, etc.. has caused 3 or 4 areas of paint flaking off already.  My first step in combating this was to head to the local home improvement store and get computer matched blue and gray, satin, interior house paint samples.  Each is a half pint (probably a lifetime supply barring drying up) and cost is only about $3.  It was suggested to take the two hatches in to have them computer matched… but of course I forgot and left them at home so had to find the pictures in the forum on my smart phone and have them mixed off the numbers on the labels that someone was kind enough to post.  I suggest you do your own computer match instead as that has a better chance of exact matches to the paint on your cub but mine came out excellent… I was lucky.  Using this paint I have already touched up 4 spots on the cub and other than a very small difference in “sheen” I’d say it is an excellent match.  It does take two coats of blue to get the color perfect over bare foam.  Also, it does look bright when you apply it but after drying it is a great match.

2.  Bought and static tested an APC 15×6 E prop which has received some good reviews on line… Static tests indicate that a full charged stock E-Flite 3200 6S 30C pack with the stock 15×5.5 propeller is drawing 59 Amps right off charge.  The cells sag to maybe 20V which equates to about 1200 Watts.  1200 Watts with a sub 9lb airframe equates to ~133 Watts per lb.  For a cub… that is somewhere between high and rocket powered!  In addition, 59 Amps is just under the 60A continuous rating of the speed controller and well under the 75A peak allowed so all is well with this setup.  Static testing of the new APC propeller had it pulling only 54 Amps.  Flight testing and perhaps some static thrust measurements will be interesting.  If the APC can produce as much thrust as the stock setup and use less amps it would prove that it is simply a more efficient airfoil… If it does not produce equal or better power than I may stay with the stock prop for at least a while longer.  Stay tuned on this one.  Propellers are often a quick and easy upgrade and this test so far proves that you cannot use diameter and pitch measurements to compare propellers across brands.  The airfoil design is key and the listed measurements from the manufacturer are to be taken with a grain of salt.

3.  I purchased some DuBro 6″ inflatable tires to replace to stock foam tires.  The stock tires are considered by most to be acceptable for grass fields only.  I don’t even really like them on grass as they seem to have almost zero cushioning capability and the heavy wire landing gear is mounted into foam and plastic which seems like a possible weak spot.  In order to protect that mounting, I am going to try the DuBro wheels with minimal air pressure.  They are almost 3/4 of a pound heavier than stock so I will lose a little power/weight ratio but I can compensate somewhat by keeping to smaller battery packs (folks are running up to 5500 mah packs… so far I’m staying with 3300-3700).

I’m considering quite a few other additions, modifications, updates, etc. that I’ll discuss as I decide on and implement them.  Most likely there will be telemetry installed as well as some personalization of the color scheme, flap/elevator mix testing, and more.

Right now I’m getting prepared to go flying on new years day which is currently being predicted to be a balmy 20-25 degrees(F) and 10-15mph winds…  First to explore is whether I can get the Cub into the trailer fully assembled to avoid freezing fingers having to assemble in the cold!

Hitec X4 Micro AC/DC 1 cell LiPo charger

I have taken to doing some indoor flying over the past couple of winter seasons as the bitter cold and snow of Indiana this time of year is not particularly conducive to just hanging out at the field.  It’s a lot of fun, but is yet another specialized endeavor within RC which means there is some specialized gear available to help you get the most out of your time spent.  I.E. More toys!!

For instance, most of the small indoor aircraft use a single cell LiPo in the 30-200mah range and tend to eat up those precious little milli-amps in a short 4-8 minute flight.  That means over the course of a 3 hour indoor session you can run down a BUNCH of batteries.  I tend to take some pictures, talk with the other pilots about their aircraft and find other ways to distract myself for much of the time but I can still run short of charged batteries in a hurry.  This is especially true when flying a little quad that can use up a battery in 4 minutes.  Along with buying ever more batteries, I’m doing a fair amount of recharging at the gym.

At first, just using the single chargers that come with many of these airplanes was OK, but those chargers can be slow, are sometimes bulky and they either have to plug-in to an AC outlet or run off AA batteries depending on the whim of the manufacturer.  It’s easy to end up with nearly dead AAs inside those chargers at the worst time and there is never enough space on my 2 wheel cart going in and out of the gym so my array of 4 single cell chargers (powered by 16 rechargable AAs) had to go!

At first my solution was simple.  I have a couple of buddies who each have one of the Thunder Power Quad Port AC/DC chargers.  I would just borrow a charge port or two from my flying buddies!!  This works alright and they don’t mind sharing (not much anyway) but there were never enough charge slots available and I was hoping for something a bit better.  I tried to drop hints that those guys needed to upgrade their chargers but I’m the gadget guy of the bunch… I like buttons and switches (if they serve a purpose) and they were happy with the simplistic but effective little Thunder Power.  Here is the little TP with a link to see it on Amazon.

 Thunder Power Quad Port Charger

After a little research on the web, I decided to pick up the Hitec X4 Micro.  At a bit over $50 it’s a bit more expensive than the TP but it has several nice features.

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X4 Micro AC/DC 1C LiPo Charger  <- Click here to see/purchase this on Amazon

The Hitec can not only charge 4 batteries simultaneously at anything from .1 to 1 A rates, but it has a separate LED display for each of the four charge circuits so you can tell what is going on with all 4 with a glance.  To charge just plug in to any of the 4 sockets as appropriate for your battery connector type, dial up the rate you’d like to charge and push down and hold the red start/stop button for a few  seconds (until the led lights solid and you hear a longer beep) and you are charging.  If you just momentarily tap the button before charging you will be shown the current cell voltage (and hear a short beep).  During charging the display sequences through showing you the current charge rate, the current cell voltage and the amount of charge taken (in ma).  When the charge is complete you are treated to a green light along with a series of 5 beeps and the word FULL on the screen.  This alone may be worth the price of admission for some.  One of my flying buddies is effectively red/green color blind so you can imagine that seeing FULL displayed might be more helpful for him than just a red or green LED.  With FULL displayed you can tap the button again and get a cycling display showing the end voltage, the total milliamps provided to the battery during the charge cycle and the FULL display.  With AC or DC input options, along with an AC cord and DC connection with alligator clips all supplied, this little charger is at home and ready to work on the bench or at the gym.

While the Thunder Power is a fine little charger (and it is much smaller than the Hitec which can be an important plot point) it can’t compete in my mind because of what for me are the two big pluses afforded by the Hitec.  First is the array of information available to me when using the Hitec.  The TP just tells me charged or not via the red/green LED.  The Hitec keeps me informed from start to finish. Secondly is the ability to control the charge rate.  This is handy in both protecting my batteries from being “beat up” by a to high charge rate and to take advantage of faster charge rates when I want to based on the capability of the battery under charge.  Most of the little 1 cell chargers do so at a fixed rate… in the case of the TP for instance .3A… period.  Want to charge your 30mah cell?  Hope it likes to charge at 10C cause that is what it is going to get.  Fast but brutal!!  How about your 200mah?  You guessed it, .3A and I hope you aren’t in a big hurry cause it’s going to take 40 minutes or so.  Don’t get me wrong, chargers like the TP are fairly inexpensive (Around $35 at the moment) and work pretty well for most applications, but I like to have more control over the charge process and know a little more about what is taking place.  With the Hitec I can charge my 150mah E-Flite at it’s max charge rate of 3C (450ma) for a quick 20 minute charge when I really want to get back in the air fast but when the session is over and I’m back on the bench getting things ready for the next fly, I can just as easily drop down to a leisurely 150ma 1 hour charge.

I will say that the Hitec does require you understand a bit more of what you are doing in order to be used correctly.  You have to pay attention and set the charge current accurately to get maximum benefit from the box (easy to do with the display and just a little knowledge).  In my book that’s just another part of the hobby and one I enjoy actually so this is my kind of tool and for $50 I think the price is reasonable.

The other price you pay for the extra features of the Hitec is a little bit of bulk.  The Hitec is pretty compact for what it can do (especially for an AC or DC unit) but your not going to stick it in your shirt pocket either.  Still compared to the single cell units I was using this will take up the same space as one, and do the work of 4 so all in all I expect this thing is going to work out well for the intended job.  I’ll update as I get more experience if anything changes my mind but at the moment I’m thinking the Hitec X4 Micro is a keeper.