Servo packages say "Ni-Cad only" Why?
12-28-2004, 09:14 PM
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Servo packages say "Ni-Cad only" Why?
A few of my servo packages say to use "Ni-Cad only" Why is this? I just spent a bunch of money on new Nimh batteries, and I wont be able to use them in planes with these servos ( 9451 for example)? They charge the same, and they seem to be a better battery.
Thanks,
Blair
Thanks,
Blair
12-29-2004, 02:12 AM
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RE: Servo packages say "Ni-Cad only" Why?
NiCd batteries can supply higher currents without experiencing a reduction in their voltage while under load -- this is because NiCds have a lower internal resistance.
Earlier in the development cycle of NiMH cells their internal resistance was markedly higher than that of the equivalent NiCd pack but these days that gap has narrowed somewhat -- which makes Futaba's recommendation a little less critical.
I no longer use NiCd packs, having switched entirely to NiMH for all my planes and despite this I regularly run hi-torque (hi-drain) Hitec digital servos (HS5945 and HS5925) without any problems at all.
The caveat on that would be that you should replace like-size with like size rather than like-capacity with like-capacity.
I use 1650mAH NiMH receiver packs which are the same size as 600mAH NiCds and seem to have almost the same internal resistance. These work just fine and dandy with those current-hungry hi-torque servos.
However, I would *not* dare to use a 600mAH NiMH pack to replace a 600mAH NiCd pack and expect to run the same hi-torque servos.
So, if you're using *good* quality NiHM receiver packs with enough capacity (1650mAH would be a minimum) then I can't see why you would encounter problems unless the Futaba servos are somehow more hungry or sensitive to small levels of voltage drop than the Hitec ones (which I doubt).
I get my NiMH receiver (and transmitter) packs from Radical RC and have never had a single problem.
I suspect Futaba are playing safe so as to avoid the situation where someone tries to replace a standard NiCd pack with a tiny NiMH one of the same mAH capacity.
Earlier in the development cycle of NiMH cells their internal resistance was markedly higher than that of the equivalent NiCd pack but these days that gap has narrowed somewhat -- which makes Futaba's recommendation a little less critical.
I no longer use NiCd packs, having switched entirely to NiMH for all my planes and despite this I regularly run hi-torque (hi-drain) Hitec digital servos (HS5945 and HS5925) without any problems at all.
The caveat on that would be that you should replace like-size with like size rather than like-capacity with like-capacity.
I use 1650mAH NiMH receiver packs which are the same size as 600mAH NiCds and seem to have almost the same internal resistance. These work just fine and dandy with those current-hungry hi-torque servos.
However, I would *not* dare to use a 600mAH NiMH pack to replace a 600mAH NiCd pack and expect to run the same hi-torque servos.
So, if you're using *good* quality NiHM receiver packs with enough capacity (1650mAH would be a minimum) then I can't see why you would encounter problems unless the Futaba servos are somehow more hungry or sensitive to small levels of voltage drop than the Hitec ones (which I doubt).
I get my NiMH receiver (and transmitter) packs from Radical RC and have never had a single problem.
I suspect Futaba are playing safe so as to avoid the situation where someone tries to replace a standard NiCd pack with a tiny NiMH one of the same mAH capacity.
12-29-2004, 10:34 AM
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RE: Servo packages say "Ni-Cad only" Why?
Hi BR289,
Please see our FAQ's at:
http://www.futaba-rc.com/faq/faq-battery.html#q783
Thanks, Krysta
Please see our FAQ's at:
http://www.futaba-rc.com/faq/faq-battery.html#q783
Thanks, Krysta
12-29-2004, 02:16 PM
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RE: Servo packages say "Ni-Cad only" Why?
Hello,
I read the faq, but how do you tell whether or not they can handle them. The batteries are Hydri-Max...distributed through Great Planes. For example, I have a Funtana that has three 9451 servos in it, and I think a 9151 too. I put a 2000Ma Nimh battery in it....what will happen if I flight test this plane with this battery?
Thanks for your input.......
Blair
I read the faq, but how do you tell whether or not they can handle them. The batteries are Hydri-Max...distributed through Great Planes. For example, I have a Funtana that has three 9451 servos in it, and I think a 9151 too. I put a 2000Ma Nimh battery in it....what will happen if I flight test this plane with this battery?
Thanks for your input.......
Blair
