Author Topic: Charging 9V NIMH batteries  (Read 2794 times)

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Offline sean0118

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Charging 9V NIMH batteries
« on: March 03, 2015, 07:28:51 pm »
Hi everyone,

I bought some rechargeable 9V NIMH batteries, only problem is my charger can only charge AA and AAA.  |O

They are 200mAh and list the standard charge as 20mA for 16 hours. Do you reckon I could charge these using a lab power supply with current limiting?


Also, for a longer term solution, does anyone have a simple charging circuit that would be suitable? Bonus points if it charges from a solar panel...  (I have some spare ones from garden lights)  ;)
 


Offline BradC

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Re: Charging 9V NIMH batteries
« Reply #2 on: March 03, 2015, 11:01:32 pm »
Hi everyone,

I bought some rechargeable 9V NIMH batteries, only problem is my charger can only charge AA and AAA.  |O

They are 200mAh and list the standard charge as 20mA for 16 hours. Do you reckon I could charge these using a lab power supply with current limiting?

Absolutely. I do that all the time for custom NiMH packs.
Also, for a longer term solution, does anyone have a simple charging circuit that would be suitable? Bonus points if it charges from a solar panel...  (I have some spare ones from garden lights)  ;)

Don't stuff around with other chargers. This is the one to get,

http://www.mahaenergy.com/mh-c490f-9v-charger/

I switched to 9V (8.4) NiMH for my guitar wireless back in 2006. I went through a lot of batteries before I recognised that the chargers were destroying my batteries. I bought the c490f in 2010 and I've not lost a battery since (I have 4 batteries and average one a week - so that's about 52 cycles each thus far).  I have a MH9000 for AA & AAA cells and I love that also, but the c490f is a winner. I bought some 9.6v powerex LSD batteries recently and man what a difference.

The c490f will charge from a car battery (so ~11-16v) so you'd probably be ok on a solar cell.
 

Offline macboy

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Re: Charging 9V NIMH batteries
« Reply #3 on: March 04, 2015, 03:17:59 am »
Hi everyone,

I bought some rechargeable 9V NIMH batteries, only problem is my charger can only charge AA and AAA.  |O

They are 200mAh and list the standard charge as 20mA for 16 hours. Do you reckon I could charge these using a lab power supply with current limiting?


Also, for a longer term solution, does anyone have a simple charging circuit that would be suitable? Bonus points if it charges from a solar panel...  (I have some spare ones from garden lights)  ;)
You don't even need current limiting, just a series resistor and a good stable voltage. The resistor will limit current to I = (Vpowersupply - Vbattery) / R. As a bonus, as the battery voltage rises due to charging, the current will decrease due to a lower voltage difference, so you can get a nice taper down to a constant trickle charge by choosing an appropriate V & R.
 

Offline sean0118

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Re: Charging 9V NIMH batteries
« Reply #4 on: March 04, 2015, 02:13:21 pm »
Thanks for the replies guys.  ;)

You don't even need current limiting, just a series resistor and a good stable voltage. The resistor will limit current to I = (Vpowersupply - Vbattery) / R. As a bonus, as the battery voltage rises due to charging, the current will decrease due to a lower voltage difference, so you can get a nice taper down to a constant trickle charge by choosing an appropriate V & R.

I ended up doing this because a 20mA current limit is too small for my power supply to accurately regulate. It would limit at 10mA then jump up to 30mA, so I left it at 30mA and placed a 150ohm resistor in series. It's very close to 20mA now.
 

Offline FreddyVictor

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Re: Charging 9V NIMH batteries
« Reply #5 on: March 04, 2015, 09:04:16 pm »
can use LM317L in constant current mode - example circuit here
 


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