Charge AAA NiMh - teory & practice

[bigge]

I try to fast charge many AAA NiMh 700 packs for the MiniZ wonderful car, but with no result.

I'm using a Tekin BC112 charger, H27 version firmware that seems good to worh with NiMh batteries.

I try different Amp from 0.4 to 0.8, in the 'normale mode (P0)', with powerflex activate. But after a few minutes, 3/4, the charge ends.

Could someone help this MiniZ fanatic racer ?

The batteries I'm using are four Sanyo AAA 700 Mah Nimh.

If someone knows the 'theory' about the fast charging mode, it will be appreciated for me.


Thanks in advance

Enrico

[jeepinator]

You need to be charging with more juice.
I understand these are sensetive NIMH cells, but .4 to .8 may be too low.
In Nicad land, 3 times the capacity for a charge rate is normal.
Ket's make it 2 times since these are small, NIMH cells.
That would be 700*2 or 1.4 amps.
The Tekin chatgers will not do the pulse thingy under 1 amp, FYI.

On the first run at this current level I would watch the temp very carefully. Keep touching them once a minute or so. If they get more than mildly warm, back down the current .2 or so.
I have top of the line cells and I charge them at 1.4 amps all the time. They have survived many charges thus far ;)

[Railman]

I can't seem to get my 1,000 mha, nmh's hump pack to charge at much over 1/2 amp. They keep kicking the charger off. From what I've read on various sites, this is fairly common. I would think that your problem is due to too much amperage. If you want to fast charge I'd suggest using nicads. The sub c nmh batts are a new, specially developed cells, for RC use. The aa & aaa nmh cells are not up to the fast charge task yet. I'd try maybe 1/4 amp, & see what happens. I would not use the power flex on nmh batts, as it doesn't help them, & they don't develope memory like nicads.
Joe

[ 09-16-2001: Message edited by: Railman ]

[jeepinator]

Maybe the difference is the charger ?
I use a Tekin BC112a.

Just for the heck of it, I charged 4 AAA cells. 1.4 amps may indeed be too high (they got kinda hot). It false peaked once, but finished normally on the second try.

Maybe try like 1 amp. Or, go the opposite way like Railmaster suggested. For me, it'a all about time. I have 2 sets of four for my Mini Z. Last winter we played with those things until the wheels fell off. I was allways in a hurry to get them charged, so I used high charge rates.

Seemed to work before ... but then again there was a keg in my garage for a few weeks ... you never know what I actually may have done ;)

http://www.theshreves.com/pics/kegingarage.jpg


Heheh !

[Railman]

Jeep, Those were aaa nicads that you charged at 1.4 amps...right? We routinely charge our aa's at 1 3/4 to 2 amps without any problems. Nmh's are another story, unless they are the special sub c cells. We have 4 tekin chargers; 2 112c's, 2 112a's along with a 350 discharger, & two old style Integy high amp dead short trays for all those packs! :p :D
Joe