Don talks about charging Li-Poly batteries!

From : Don Stackhouse

The Apache chargers made by E-tec are designed to run off of a car battery. There is a little one for 1 to 2 cells and a bigger, fancier one that handles up to 4 cells. The big one is a little more expensive than the Plantraco, somewhere around $80 if I remember correctly. I think the little one is around $30-something. We don't have either of these in stock at the moment as far as I know, but we can order one for you reasonably quickly.

OTOH, my own experience is that the flight time on a Li-poly pack is so long that there normally isn't a need to recharge during a flying session. To PROPERLY recharge a Li-poly battery takes about 1.5-2 hours, not really an attractive proposition in the middle of a flying session. Most folks don't fly for a half hour anyway, they'll fly 10 minutes, land and socialize for a while, fly another 10 minutes, land and socialize some more, etc.. By the time you've accumulated half an hour of flying it's usually time to go home anyway. Also, since Li-poly batteries will hold a charge literally for months, you can recharge as soon as you get home and be all ready for the next flying session. It's not like the old NiMH cells that lost a big part of their charge in just a few days of sitting on the shelf and ideally needed to be "re-peaked" immediately before each flight.

With that in mind, rather than investing in a DC to DC adapter for your car, it might be a better use of your money to buy some extra batteries, then mount them on the model such that they can be removed for charging (an excellent thing to do for safety reasons as well), and switched at the field. This would actually give you more flying time than that same money spent on a field charger setup, since you would not have the down time associated with the recharge cycle (assuming you really needed that much flying time per session in the first place). I am working on some "quick release" screw-retained battery mounts this week, and hope to have parts available in a few weeks. These will allow you to remove or swap batteries just by loosening two small screws.

One other VERY IMPORTANT thing I need to tell you about while we're on the subject of chargers:

The Plantraco chargers has safety features built-in for most human errors. However, as a friend of ours found out the hard way last Saturday morning, the Plantraco can't tell the difference between a discharged 3 cell pack and a nearly fully charged 2-cell pack. It figures out the number of cells by measuring the pack's total voltage, and unfortunately the discharged 3-cell and the fully charged 2-cell BOTH are about 8.1 volts! If you have the charger's rotary switch set for 3 cells, and try to "top off" a nearly charged 2-cell pack, the charger will not know the difference. It will overcharge the 2-cell pack, causing a serious explosion and fire. Our friend had been recharging some 3-cell packs, and forgot to reset it to the "2 cells" setting . I've attached a photo of the remains of his B-17. Note, you can see in the photo that the charger is set for 3 cells (the plane had a 2-cell 1200 mah pack in it). Fortunately it was on a wood-burning stove when it blew, and someone was watching it and immediately took it outside and extinguished it. It did not burn down his house, and believe it or not, the plane is repairable. It could have been much worse.

It should be obvious that you must be EXTREMELY careful to set the number of cells switch correctly for EACH CHARGE. I'm personally going to get in the habit of always turning the switch to the "1 cell" setting every time I take a battery off the charger, so that it forces me to reset at the beginning of the next charge.

I hear the folks at Plantraco have a new version coming out soon that can tell the difference between 2 and 3 cells. However, that doesn't help folks like you and I who already have the old version. I don't know if they will have any sort of "upgrade program" available.

The E-tec "Apache" chargers I mentioned above do not have this problem. They have a fairly elaborate internal test procedure that can tell the difference between 2 and 3 cells. However, just to add another level of safety, I'd still recommend getting in the habit of always resetting those to "1 cell" at the end of each charge cycle, and that advice is probably good for any other chargers as well.

Don Stackhouse
DJ Aerotech