NiMH batteries and chargers

[Guest Point2Point]

Okay, this is more of a battery question than a GPSR question, but I need some help.

 

I have a Radio Shack battery charger that I have used with the same Radio Shack 1200 mAh NiMH batteries for over 2 years with no problems. But recently I bought some Nexcell and Sunpak 1600 mAh NiMH batteries that get extremely hot during charge. Worse yet, the Nexcell batteries have started to die (won't hold a charge) after only a dozen or so charges.

 

So - how hot should NiMH batteries get when they charge? I mean how hot is too hot? Is my charger putting out too much juice for the 1600 mAh batteries and frying them? Why do the Radio Shack batteries recharge without getting so hot? Does Radio Shack have some kind of conspiracy going on?

 

(I'm sure I'm not the only one that has asked that last question - I mean, really, why does Radio Shack ask for my address when I'm only buying batteries??? So they can secretly program the charger at my house to work only with Radio Shack batteries??? - hmmmm???)

 

Any advice/experience would be greatly appreciated.

 

Thanks.

[Guest Fotogg]

ave, I use the 23-335 charger/conditioner and have no problems.

 

Steve

[Guest Point2Point]

I have a model 23-405 charger, rated at 900mA. It has the switch for NiMH / NiCD which I keep in the NiMH position. This charger has a red LED that stays on when the batteries are charging and goes out when the batteries are charged - supposedly you can't overcharge with this unit.

 

I just can't understand why the Radio Shack batteries don't overheat but the others do. And when I say overheat, I mean I can't hold them in my hand tightly - they are too hot.

 

I'd hate to buy a new charger and have the same problem,, also don't want to fry any more batteries. Not sure what to do.

[Guest peter]

The high temperature is a sign of overcharging and definitely harms the cells.

Most 'smart' chargers look at the change in voltage of the charged cells and cut off the charger (or switch to a trickle level) when the voltage stops rising or dips a little - signifying a full charge. Sounds like your charger is expecting a more pronounced voltage dip than shown by your new cells and therefore it doesn't shut off.

I've had good luck with the Maha C204F charger with a variety of NiMH and NiCd cells.

[Guest k2dave]

Nexcell's are known to have problems with some chargers - IIRC their advantage is they can be left on a trickle charge for up to a year w/o dammage, so I guess they like a slow charge due to higher internal resistance. I don't know about sunpack.

 

Some advice that might help

 

Leave the cover of yur batt charger open and maybe have a fan blowing air over it.

 

if this is the type of charger that does NOT require you to press a button to start charging then buy a timer that will allow you to turn on and off a electrical device. You can set it to charge for 1/2 hr then off for 1/2 hr - maybe they have 15 min intervals now or digital so you can control the intervals. These timers are not really made for such cycling though - they are really made to turn on a light when it gets dark and off in the morning so the digital device might not have enough setpoints. The one I have has 48 'pegs' that I can move up or down to turn on or off the device every 1/2 hr.

 

finnally buy another charger - it will cost you less to get a good charger then overheating yoru batts.

[Guest Fotogg]

It might be best to try a new charger. I paid less than $15 for my RS. If anything just to try it out to see if it fixes your problem. You can always return it.

[Guest Point2Point]

Fotogg - I looked up specs for 23-335 charger and 23-405 charger on RS web site. Seems that the 23-335 output is much less than the 23-405 (250mA vs. 900mA). From what the rest of you guys are saying, seems like the Radio Shack 23-405 charger is trying to pump a little too much current into the Nexcell and Sunpak batteries and frying them. Can't find any specs for recommended charge rate for Nexcell or Sunpak batteries on the web, but apparently all batteries and chargers are not created equal.

 

So, I am going to buy one of the 23-335 chargers today and see if that solves the problem. Just wanted to post this information for those following the thread.

[Guest Fotogg]

It should work fine for you, I think it's a great little charger/discharger. I looked at the specs and they consider it a 5hr charger in the standard mode @ 200mA, and 8hrs in the high-capacity mode @ 250mA, (.50mA ?) They list a standard capacity range for AA batteries as 1100-1300mAh, and high capacity from 1301-up.

 

Your charger would still work but it sounds like it's not an "intelligent" type charger. You would have to closely monitor the batts while charging. Probably full charge in less than 2 hrs. I prefer intelligent type chargers mainly so I can do other things and not worry about the charge status. Usually put them on charge when I go to bed and when I wake up there all charged.

[Guest badbitbucket]

According to the manual for my Rayovac charger, NI-MH batteries get very hot during charging. and they emit gases, hense the very small vents aroung the positive end of the batt's.

 

the manual says to leave the lid open on the charger when charging HI-MH batt's because of the heat issue.

 

so heat isn't necessarilly a sign of something wrong. even my rechargable alkalines get a little warm during charging.

 

-BBB

[Guest k2dave]

a little warm ok, maybe you would consider it hot but it shouldn't get so hot you can't hold it.

[Guest SteveL]

I have a bunch of Nexcells and Yuasa Ni-MH batteries that I use for my Nikon 950, my FSR radios, and my Garmin Venture. I use a Maha Communications MH-C204F rapid charger as well as the MH-2A4 trickle charger - both with excellent results. In the C204F the batteries can get warm, but never hot. Heat will KILL your cells - if they got very hot during a charge, that is why the no longer hold a charge.

 

SteveL