NiMH Battery Question
Locked
 
|
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 _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
|
|
On Mon, 4 Jul 2005 [hidden email] 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, [hidden email] N8CBW _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
|
|
In reply to this post by n2htt-2
In a message dated 04/07/05 19:56:32 GMT Daylight Time, [hidden email] writes: There are some small charge controllers out there, but a relay configured to open when the battery reaches full charge is the simplest. Reply:------------------------------------------------------------------ The problem with using a relay for solar charge control is the current needed to activate the coil of the relay. This could be as high as 100mA and with a charge budget available of only 250mA you would have to select the relay used with care. If a solar charge controller was seen to be necessary I would have thought a solid state version similar to the type Don Brown is making the kit for would have been a safer bet for minimising power losses in the control mechanism (pity these are only available in the USA as I could have used one). The usable solar power available for solar panels is usually calculated at 8hrs per day, though does depend on the seasons further away from the equator. With 8hrs @ 250mA that would equate to 2000mA per day which is the total rating of the NiMH cells being used. The charge needed would depend on the initial state of the batteries and what the consumption of the radio was to offset the available charge. Some device to monitor the battery voltage and an on/off switch would also work as a charge controller in this case at probably even less cost. With regard to the point when full charge is reached with NiMH cells, I was checking out a motorcycle racing ignition pack last week and using a commercial charger built for the purpose, the end voltage for a 6 NiMH pack was 8.40V, which equates to 1.40V per cell. These guys can get exceedingly upset if they are leading a race and the batteries die, so had to ensure that all was OK. The point with this type of cell and many others including gel cells is that the initial voltage at the end of charge is higher than the nominal voltage of individual cells, though the voltage soon droops with use to the nominal voltage of approx 1.20 to 1.25V per cell. This carries on pretty well constant until the battery is almost empty then there is a rapid fall as the battery dies. Under these circumstances using NiMH cells it would be better to maintain the charge to prevent the voltage falling as was recommended. Understand with the earlier NiCADS it was better to take them as far as possible before recharging otherwise cell capacity could reduce. Bob, G3VVT _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
|
|
In reply to this post by n2htt-2
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: <[hidden email]> To: "List Elecraft" <[hidden email]> 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 > > > _______________________________________________ > Elecraft mailing list > Post to: [hidden email] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
«
Return to Elecraft
|
1 view|%1 views
| Free forum by Nabble | Edit this page |