NiMH charger efficiency?

[Doug Owen]

I've been thinking of something I hope someone in CPF land can help with. I want to know what's the most efficient charger for NiMH AA cells. Not the fastest, but the one that uses the least power to charge.

Since most chargers seem to work on 12 Volts (makes car use easy), this would seem like an easy thing to figure out. However, it would not seem so. I'm thinking what I need to do is something like charge a gel battery that's charged to a fixed state, then discharged into the NiMH charger until the gel battery gets to a given voltage (say 11.0 Volts). The number of fully charged cells produced will determine the winner.

Anyone have any thoughts?

TIA

Doug Owen

 

[brickbat]

Maybe I'm over simplifying this, but why not treat the charger as the switching DC supply that it is? Measure its input current and voltage as well as its output charge current and voltage at several points throughout the charge cycle. Compute input and output power at these points and strike an average from them. Another thought might to be to just measure the AC input energy with a watt-hour meter. (though it wouldn't give you the efficiensy, you would know how much energy each charger used) One of these would do the trick - and they're handy for lots of other stuff:

http://www.p3international.com/products/special/P4400/P4400-CE.html

 

[Doug Owen]

Thanks for the thoughts. I'd tried that in fact.

There are several problems. First off, input current isn't always constant from moment to moment, it runs in cycles or pulses in some cases. And it declines as the charge progresses in many. I could find no 'average input current' value I trusted.

As far as measuring mains input power, while easy, it's not useful really. It includes the wall wart (often hotter than the charger) as well. As the end use is 12 Volts from a gel battery, I think that's the input that matters.

Doug Owen

 

[Brock]

Funny you should bring this up.

I have the Ccrane charger, a Vanson 1HU and the MAHA 401. The 401 in slow mode uses the least amount of power to get the cells charged. The vanson was a close second and the ccrane used the most. Actually the 401 in fast used the most, but I rarely charge in that mode. I charge all my batteries from my 12v bank that is charged via solar.

 

[Doug Owen]

Brock,

Super, just the sort of information I'd hoped for!

You wouldn't by any chance have any numbers to go with that useful information would you?

TIA

Doug Owen

 

[Brock]

I should have written it down. I had 12 cells all depleted at about the same level, then charged them in sets of 4 in my chargers. I put a fluke 87 on averaging on the input side at 12v and let it run for 6 hours exactly on each. I just did it to see which charger I should use the most. I should have written it down, I can't even remember how much power actually went in to the batteries vs. their size. I want to say it was about twice what I thought. Like the 1800mA batteries each took about 2000mA to get charged from about 1/2 dead. But that is just a guess from last year.

 

[Doug Owen]

Brock,

A meter with *average* reading? Cool. That should do it. That, coupled with a 'battery analyzer' to measure the actual charge delivered into the cell.

Thanks very much.

FWIW, I use the same two chargers (401 in slow as well), but got hung up on the current pulse nature of the 1HU...

Doug Owen

 

[Brock]

I am pretty sure the 401 pulses also. Maybe not the same way. But if you put one cell it uses the same amperage from the 12v source, it is just of for 1/4 of the time. If you listen really close you can hear the clicking in the 401. If really freaked me out the first time I measured the current feeding it. Then I put all 4 cells in and it was consistent /ubbthreads/images/graemlins/smile.gif

 

[RussH]

These pulse type chargers interfere with my AM radio. Put them near an AM radio on a weak station & you can hear static when current is flowing. I agree with Brock on the C401fs.
Hey, my CCRane charger conked out on me the other day. I haven't made my mind up what to do with it. I'm pretty sure I could fix it but my time is limited. I'd much rather be modding flashlights. I'll either buy another or perhaps if something for C & D size is recommended as more efficient I'll consider that....I keep hoping CCRANE will come out with a new and improved model (more current). Does anyone have a reference for the circuit details if I choose to mod it?

 

[Brock]

I have a feeling CCrane is going to come out with a new or at least updated version since they seem to be selling them off lately, both on eBay and their site. Although I could be wrong and they are just making them cheaper, but I hope a new and improved version comes out /ubbthreads/images/graemlins/smile.gif At least slightly larger to hold the D cells without really pushing /ubbthreads/images/graemlins/wink.gif