RC-Monster Forums - View Single Post - Maxwell Ultra-Cap's/Lithium cells hybrid pack

BrianG · 12.03.2006, 04:58 PM

The capacitor idea is nice, providing the weight and size could be reduced. If the caps are the same size/weight (or more) as simply adding a parallel set of batteries, you'd most likely get more bang for the buck with the added batteries. This is why I said use something like a 2-5F cap; it still will offer substantial help with the high current pulses while remaining relatively small and lightweight. Even 1F will help a lot for 1,000 watt loads.

5 mOhm is actually not bad. That's only a 0.5v drop at 100A. Don't forget, that's just the voltage drop of the cap. The batteries will reduce that 0.5v drop to a lesser value because they are in parallel.

Also, if these caps are hooked in series, it add the voltage values, but halves the capacity. So, if you took two 2.5v 10F caps and hooked them in series, you'd get a single 5v 5F cap. You put 10 of those in series, and you get a 25v cap rated at "only" 0.5F.

I am absolutely sure using these is good for the batteries and provides a more stable voltage with substantially less sag at high current, but when used in an R/C, it's going to become a compromise of cap/battery performance vs total size and weight.

	(#29)
BrianG RC-Monster Admin Offline Posts: 14,609 Join Date: Nov 2005 Location: Des Moines, IA	12.03.2006, 04:58 PM The capacitor idea is nice, providing the weight and size could be reduced. If the caps are the same size/weight (or more) as simply adding a parallel set of batteries, you'd most likely get more bang for the buck with the added batteries. This is why I said use something like a 2-5F cap; it still will offer substantial help with the high current pulses while remaining relatively small and lightweight. Even 1F will help a lot for 1,000 watt loads. 5 mOhm is actually not bad. That's only a 0.5v drop at 100A. Don't forget, that's just the voltage drop of the cap. The batteries will reduce that 0.5v drop to a lesser value because they are in parallel. Also, if these caps are hooked in series, it add the voltage values, but halves the capacity. So, if you took two 2.5v 10F caps and hooked them in series, you'd get a single 5v 5F cap. You put 10 of those in series, and you get a 25v cap rated at "only" 0.5F. I am absolutely sure using these is good for the batteries and provides a more stable voltage with substantially less sag at high current, but when used in an R/C, it's going to become a compromise of cap/battery performance vs total size and weight.