Other than cost, is there any reason why NiCds are still the default for airborne batteries. At home for cameras, phones, etc. I have switched over to NiMhs since they last so much longer. Seems like this would avoid a lot of low battery problems or save weight without the cost of LiPoly.

Thanks,

John

Tradition.

When I first stared using NiMh there were only a few of us using them at my club and I got a lot of grief from some of the established members. They told me that you I to be extra careful charging them, that they would die halfway through a normal discharge without warning, that they were prone to exploding.

Sometimes it takes a while for new stuff to catch on.

Taken from Red's web site:

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Nickle Metal Hydride - the picture today.

The Ni-MH that are available to us today from Sanyo/Panasonic may be treated essentially the same as Ni-Cds –EXCEPT FOR PEAK CHARGING. You have to be careful here. Some chargers will accommodate them, others won’t - and end up severely overcharging them to the point of destruction.

In a given cell size Ni-MH has on the order of 20 to 30% more capacity than Ni-Cds. They have slightly higher internal resistance, but not enough to concern us in most R/C control applications. This higher internal resistance can be of concern in electric flight operations where it is common practice to add an additional cell to compensate. They have a shorter cycle life in general, but again not enough to be of real concern. Most people run out of calendar life before cycle life in flying R/C. Meaning that the separator system in the battery (same for both types) fails (shorts) before the cells fade away in capacity delivery ability. Ni-MH are less tolerant to abuse (excessive high rate discharge, excessive overcharge, vibration, cell reversal) than Ni-Cd – but again, it seldom becomes an issue if reasonable care is given in the installation and maintenance of the packs. Ni-MH capacity falls off with cycling whereas Ni-Cd stays pretty constant, seldom going below 80% before shorts develop. Ni-MH has a higher self-discharge rate (3-4%/day) than Ni-Cd (1%/day). Ni-MH cost a bit more per Ah of capacity.


Red S.
Red’s R/C Battery Clinic
http://www.rcbatteryclinic.com

Updated 2/04

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While highly "un" scientific, I also have had issues with them providing proper voltage when extremely cold (in the 30 degree F and lower realm), but still use them regularly during the rest of the year.
Dennis-