dazzassj6 said:
ok i just found these li-po batteries but not sure if they are too powerful or not.
im looking at:
2 x 2 cell 7.4v 10aH 12C Lipo batteries. its about 530gm each.
http://i278.photobucket.com/albums/kk89/baqiest/Parts/10000mAh.jpg?t=1215595694
Im waiting for his reply if he can rig it up in parallel for me before he sends it.
i was looking at another which was 7.4v at 5aH. But if i doubled that it would be around the same price as this 10aH one. But does it matter if i picked the 10aH one?
yeh my main battery is only 10aH, that means if i rig it up with this booster pack it would become 50.8v 30aH, i dont know the amp discharge from my main battery though. Does anyone know what the 12C mean? is 12C too powerful ?
Okay, a few things. You want your booster pack to be either 3 or 4 cell (11.1v or 14.8v). To use the "2 x 2 cell 7.4v 10aH 12C Lipo batteries", you want them wired in series, not parallel. Series adds voltage (V), parallel adds capacity (Ah).
If you got 4x 7.4v 5Ah packs and wired them correctly you would have pretty much the same thing as 2x 7.4v 10Ah packs, wired in series for 14.8v. Electrically they're be very similar. However, if they cost just as much, you might as well go with the two larger ones than four smaller ones, since they will need less wiring, involve a little less complexity, and hopefully be slightly more compact.
With a small booster pack, you don't need to worry about weight. Those RC LiPos are designed for airplanes, and if you're putting it up in the air you often need to know the weight down to the gram. For a bike, where after frame, motor, batteries, and rider it'll definitely weigh over 100kg, 500g is nothing.
And, importantly, about the amp discharge. The most important thing you need to remember is that any RC LiPos are going to be able to discharge more amps than your main battery. As long as your main battery is safe, your booster pack will be more than fine. It would be prudent to find out how many amps your main battery can safely provide. Try to find out what sort of cells are in your main battery. Look for any numbers and markings, note the shape of the cells (rectangles, cylinders, flat like LiPos, ets). Take pictures and post them here, and we can do our best to tell you what you have.
Let me explain the C ratings. The higher the C, the more amps the battery can safely provide. The C rating, multiplied by the capacity in Ah, is how much current the battery can provide (in Amps). So a 12C 5Ah battery is good for 60 amps (which is a whole lot). Even with high-powered 40mph+ ebikes, using more than 50A is uncommon. The flip side of the C rating is it tells you how fast you can drain a battery. A 1C battery shouldn't be discharged in less than one hour, a 2C shouldn't be drained in less than half an hour, and so on. A 10Ah 12C battery, though, can be safely fully discharged in as few as (60min/12C=) 5 minutes, and for those five minutes can provide (10Ahx12C=)120 amps! That is great for large planes, though, when you might need a lot of power for a very short flight.
C ratings are maximums. Just because a 12C battery can be safely discharged in 5 minutes doesn't mean you have to or want to; you could just as well slowly drain it so that it only runs out of juice after a few hours. If your main battery is, say 2C, and your booster pack is 12C, your booster won't be "too powerful" to work with the main battery, as long as you don't need more amps than the main battery can give.
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