Charging Pattern for NiMH cells?

Timothybil

Flashlight Enthusiast
Joined
Nov 9, 2007
Messages
3,662
Location
The great state of Misery (Missouri)
I am in the process of charging some AA NiMH cells I had in my AM/FM/Shortwave portable radio. I don't use it much, but the LCD display is always active, which acts the same as parasitic drain in a flashlight. When I went to use the radio today, it played for about ten minutes, then stopped. The battery indicator showed totally empty.

I put the cells in my Xtar VC4 charger, and all three read 1.0v, and a aggregate charging current of 0.5A. Now, about 20 minutes later, the [cell voltage] charging current is reading ≈0.1A. My question is, what is the standard charging method and pattern for NiMH cells, and are these readings what I should be seeing.
 
Last edited:

SilverFox

Flashaholic
Joined
Jan 19, 2003
Messages
12,449
Location
Bellingham WA
Hello Timothybil,

I am confused...

A voltage reading can't show amps. Please correct your comment about the cell voltage is reading 0.1A.

A charge rate of 0.5 amps is OK and should result in a cell fully charged showing a voltage of somewhere around 1.45 - 1.50 volts. Removing the cell from the charger will allow the surface charge to bleed off and it should settle down to somewhere around 1.40 volts.

Did the cell get hot during the charge?

If all else fails, try to charge again and watch to get a better idea of what is going on. You have a mystery in your hands... :)

Tom
 

ChrisGarrett

Flashlight Enthusiast
Joined
Feb 2, 2012
Messages
5,725
Location
Miami, Florida
Try a new set of batteries and see what happens.

I have a TecSun PL-390 that has on board NiMH charging if I use them, which I do.

It does a decent job of charging, but I've had some recent NiMH (hi-cap Duracell Ion Core) start to fail on me, which isn't the charging module's fault.

Chris
 

Timothybil

Flashlight Enthusiast
Joined
Nov 9, 2007
Messages
3,662
Location
The great state of Misery (Missouri)
Try a new set of batteries and see what happens.

I have a TecSun PL-390 that has on board NiMH charging if I use them, which I do.

It does a decent job of charging, but I've had some recent NiMH (hi-cap Duracell Ion Core) start to fail on me, which isn't the charging module's fault.

Chris
Mine is a CountyComm GP 5/SSB, and it will charge in situ as well, but it takes a mini-B connector so I am going to have to try and find mine or acquire one.
 

iamlucky13

Flashlight Enthusiast
Joined
Oct 11, 2016
Messages
1,139
As I understand it, charging out of the device in smart charger with individual channels should be better for the longevity of the batteries than in series in the device. However, my impression is that serial charging at low currents is not a major concern, so it's pretty reasonable to charge in the device for convenience. Since it's relevant to this topic, I'd be interested if anybody knows enough to clarify.

Empty AA batteries dropping from 0.5A to 0.1 after only 20 minutes sounds wrong. Did all the batteries show the same effect?

I took a look at HKJ's review of the VC4 to see if it provides any hints:
http://www.candlepowerforums.com/vb/showthread.php?400085-Test-Review-of-Charger-Xtar-VC4

When the voltage is below 2V, he says the VC4 starts with a 0.1A precharge for 10 minutes, I assume in case it's a lithium ion battery.

Is it possible that the 0.5A observation was just the charger's programmed charge rate, and then when you checked it later you saw the actual rate, still in the precharge phase?
 

ChrisGarrett

Flashlight Enthusiast
Joined
Feb 2, 2012
Messages
5,725
Location
Miami, Florida
Mine is a CountyComm GP 5/SSB, and it will charge in situ as well, but it takes a mini-B connector so I am going to have to try and find mine or acquire one.

Mine is the same Mini-B, which is the 'odd connector out.' Luckily (and I've bought spares) my Play Station 3 uses the same connector for its game controllers, so it's not an issue.

Chris
 
Top