Pulse or CC for NiMH Cells, whats the advantage?

[netprince]

I have been wondering about this for a week or two, and I cant seem to find a definitive answer, perhaps I dont know the correct search terms...

Pulse charging is better for NiMH cells right? Why exactly is it better? (I sort of recall something about reducing memory issues)

I was reading about the CH-UN180, and it doesn't say anything about pulse charging, should I assume its charging with constant current?

Finally, I am interested in a hobby charger that will safely charge and balance LiON cells, as well as pulse charge NiMH cells. Most of them dont list much about how they charge NiMH. What do you fellow CPF'ers recommend?

Thanks!

 

[T24]

In my opinion, pulsecharging ist just a maketing gag. :oops:

I have plenty of NiMh, thats the reason, i also use them in my flashlights. I use a good charger, CC charging with dU 3mV/cell. That works really good.
Some old packs (8 years), frequently used, still have 90% capacity.

Most important: Do not overcharge! Overcharging is the worst thing, to treat your NiMh.
memory issues and NiMh? Not really...
anyway, discharging every 50 cycles would be a good idea :)

 

[45/70]

Pulse, or "burp" charging by PWM, is a much cheaper way to build a charger circuit than utilizing constant current. The same is true for flashlight driver circuits. That's why most chargers use PWM, it's cheaper.

If you do a search on the "burp" method, you will find that originally, it was pretty much just a marketing idea, than anything else. As this article points out though, it doesn't hurt anything, but there's no reason to prefer it over a CC charger.

Dave

 

[uk_caver]

Even with an essentially constant current charger, a smart charger may well have brief 'off' periods to do voltage measurement, and if the people involved think that 'pulse' sounds like good marketing, they may well describe their charger that way.

 

[45/70]

Brief "off" periods would be a form of PWM, would it not? :D

Dave

 

[uk_caver]

In a sense, though it's arguable they're not really PWM as such - there's no message in the modulation, the 'off' periods aren't necessarily there with the intent of regulating the average current.

In the chargers I've built, I have something like a 5% 'off' time, inbetween spells of constant-current.
I could probably get away with a briefer off-charge time without affecting the accuracy of the voltage readings, but it hardly seems worth finding exactly how short a period is feasible when at best I could only reduce overall charge time by a few percent.

 

[45/70]

I was just kidding a bit there, uk. :)

Dave

 

[uk_caver]

That's fine.

You did set me thinking though.
I just realised how cheap it would be to add a tiny discharge pulse to my charger, so I could then call it a burp charger. I have pins free on my MCU, so one little resistor, one tiny FET (it'd hardly ever be on), and a few lines of code would sort it.
However, on the other hand, I'm not sure anyone I sell to would be too bothered what I called the charger.

There does seem to be the suggestion around that burp charging might lower charge temperature a little, and there was a NASA paper which gave the impression it might have small advantages with no obvious disadvantages.

At the very least, as a iny extra cost, it'd be interesting to play around with, though I guess I'd probably better get the datalogging side of my charger/analyser testbed implemented first.