[Elecraft] NiMH Battery Question

[Don Brown]

Hi

Yes the full charge voltage is in that range although under charge or right 
after removing the charger the voltage will be higher around 1.35 volts. 
This will drop quickly under load to about 1.25 volts and remain fairly 
constant until discharged. NiMH batteries can be charged with a constant 
current charger (solar panel). Most NiMH batteries can be charged almost 
indefinitely as long as the charge current is kept below 1/10 of the full 
rated current of the battery or 1/10C. Your battery is 2000 mah so 200 ma is 
1/10C. It is unlikely you will get 250 ma out of the panel all the time so 
this setup will work safely. At this rate it will take about 14 hours to 
fully recharge a discharged pack so it would take more than one day to 
charge the pack. Most 12 volt solar panels will output 15-20 volts and act 
like a constant current generator. That is the same current will flow 
regardless of the number of cells as long as the battery voltage is less 
than the panel voltage. All you need to do is connect the battery pack (1 to 
12 cells) to the solar panel through a 1n4002 blocking diode. This prevents 
discharging the battery if the panels are not producing enough power to 
charge the battery when in the shade or a cloud passes over. Charging at 
higher rates or charging a sealed lead acid battery will require a charge 
controller or you may damage the battery by over charging it.

Don Brown

KD5NDB


----- Original Message ----- 
From: <n2htt at optonline.net>
To: "List Elecraft" <Elecraft at mailman.qth.net>
Sent: Monday, July 04, 2005 11:07 AM
Subject: [Elecraft] NiMH Battery Question


> I've been looking around for this info and throught someone on the list 
> must know:
>
> 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.
>
> 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.
>
> 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.
>
> Thanks for the help
> Mike N2HTT
>
>
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