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ni mah question

Old 02-14-2003, 03:06 AM
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powerglide
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Default ni mah question

had real good luck with nicads re electric flight, got a hold of 8 nimah 1000 mah. anyway almost wasted a new model when it lost all power including control surfaces after only 4 min. up with full throttle on a speed 400 direct drive, do these nimahs have a drastic drop rate?? I know the nicads drain off at a slow rate and dont just fall off>>>>>>>>>>>>>so need some input
Old 02-14-2003, 11:10 AM
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Steve Lewin
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Default ni mah question

NiMH don't drop off much quicker than NiCds under normal use but it's possible you are simply trying to drag too much current out of the battery. Not all small NiMH cells can cope with a DD S400. and if it was really 4 min on a fully charged 1000mAh battery that's an average current draw of 15A. That's a heck of a lot for a Speed 400 and even more for small NiMH cells.

But if you lost all power including to the radio you may have another problem. I assume you're using BEC. The ESC should stop the battery getting that low by shutting off the motor while still leaving plenty of power for the Rx/servos. Something is not working properly.

Steve
Old 02-14-2003, 02:51 PM
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TLH101
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Default ni mah question

Nimh batteries need a couple of cycles on them to get full capacity. You will also need to add one cell to get the equivelent voltage under load of nicad, on packs with four or more cells. This is due to internal resistance.
Old 02-14-2003, 03:50 PM
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Matt Kirsch
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Default ni mah question

You will also need to add one cell to get the equivelent voltage under load of nicad
This used to be true, but modern NiMH cells can stand right up there voltage wise with NiCd.

The key to converting from NiCd to NiMH is to use cells of the same physical size. That ensures that the discharge characteristics (e.g. current producing capability) will be similar. NiMH's main advantage is increased capacity, not weight savings. If you try to save weight by using, for example, a 600mAh NiMH in place of a 600mAh NiCd, you'll find that the batteries can't keep up with the demand, and will drop off pretty quickly.

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