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.