[Elecraft] NiMH Battery Question

[Clark Wierda]

On Mon, 4 Jul 2005 n2htt at optonline.net wrote:

> I've been looking around for this info and throught someone on the list must know:

Google on nimh discharge curve for plenty of info

> 1) What is the full charge voltage for a AA NiMH battery? I'm guessing 
> about 1.275v, since the pack of 8 I just got for my K1 had a starting 
> voltage of 10.2v or thereabouts.

That appears to be correct.

> 2) At what voltage is it recharge time? The pack has dropped to about 
> 9.8v after about 6 hours, seems to be still going strong.

Depends, 9V is probably a good point.  Also, you don't need to wait for 
them to be discharged before recharging.  Shallower discharges tend to 
result in longer service life.

> 3) I have a solar panel that puts out 250ma in full sun. Since these 
> batteries are rated 2000mah, can I just hook the pack up to the solar 
> cell to charge. I've done some reading and that seems to be the 
> conclusion, but somehow it seems too easy.

Not recommended.  There are some small charge controllers out there, but a 
relay configured to open when the battery reaches full charge is the 
simplest.  If the rated current on the solar panel is less than 3% of the 
battery rating you can get away with a direct connect, but this is 
basically a maintenance charge.

> Thanks for the help
> Mike N2HTT

Hope that helps,

Clark B. Wierda, cbw at io.com
N8CBW