Hi James,
NiCD's will deliver the most PWR on demand, but offer the least watt/Kg. THis may require recharging at some point in the day.
AA NiMH's have significantly higher internal resistance (lack of reactive surface area in the form factor), and will demonstrate a lower voltage under a similar load. Add to this they discharge at almost double the rate compared to NiCD just sitting waiting for the next flying day.
Contrary to the suggestion NiCD is history, this technology will be around for a long time to come. No other technology at present can offer similar PWR demand for as many cycles. NiMH still has a long way to go to meet NiCD specifications in the areas of actual service life, charge degradation due to being endothermic by nature under a charge regime, and the obvious higher internal resistance to start with.
Also be wary of AA NiMH cells claiming in excess of 2000mA. The manner in which these cells are rated is at relatively light loads...which means they deliver significantly less under loads in the manner we might subject them to.
If you perform light-duty casual flying, NiMH may suffice. If you want maximum electrical performance, then employ NiCD's.
On Apr 17, 2005, at 11:41 AM, James R MacLean wrote:
Its too windy to fly here on the east coast of Florida, so maintanence
time. (Yes, I know, what a wimp. I can and have flown contests in pretty
bad wind but why risk a plane when there will be better days soon.) The
question is about batteries. I need to replace a number of sailplane
batteries. They all hold a square pack of AA size. It appears to me
that there are only two packs which make sense: the 1100MAH NiCd and the
1650 NiMH. Both are nearly identical in cost, weight and size. I have
the appropriate charger which is rated for either and does a good job in
a reasonable time. Both cells are made by Sanyo which usually means
excellent reliability and service life. Sailplanes generally don't draw
extreme servo currents so I expect the hydrides to be sufficient in that
respect - the nicads are usually superior in high current applications.
What do you think? Any data / experiences to suggest the better choice?
Thanks for your thoughts, Jim MacLean
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Simon Van Leeuwen RADIUS SYSTEMS PnP SYSTEMS - The E-Harness of Choice Cogito Ergo Zooom
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