sharpcroft

Hi all, first let me introduce myself.
Im a 40 something year old who has dabbled with RC on and off for over 20 years.
Started with a kit Tamiya Monster Beetle and then have been through, in order, Mardave Ministock, Traxxas Rustler (old style kit with 3 speed controller!!), Mardave Cobra and have just gone out and bought a Traxxas Slash (2wd brushed).
My question is regarding batteries and chargers as long gone are the mechanical timer type nicad chargers i used to use.
I went out a bought a Etronix Powerpal h**p//w w w.etronix-rc.com/etronix-powerpal-ac.php and a couple of EP3600mah Nimh's from ebay h**p://snipurl.com/epbatteries
The manual that came with the Etronix is minimal to say the least???
Anyway i charged up the batteries and run them to almost stand still in my Slash but when i charge them on the Powerpal (using "auto" and current limit 3.6a) it reports full but has only put in around 3000mah?? if i disconnect the battery and then reconnect the charger puts in another 300-400mah and then reports full which im guessing is probably about right.
Why would the charger stop prematurely??
In the menu settings i can set D.Peak sensitivity, at the moment its set to DEFAULT (7mv) would a change to this setting make any difference??

FYI the battery and charger are using self soldered "deans" style connectors sourced from ebay.

Thanks for your help and patience (sorry about the URL's but rules is rules )

Sharpcroft

Duster_360

iTrader: (21)

Auto is not the best way to charge NiMh imho. You have no control over the size if the NiMh peak the charger is looking for when set to auto, suspect you can't find out either with the minimal manual. Charger was prob looking for a 'smallish' voltage rise and triggered charge termination on what was really a false peak relative to being completely charged.

Auto only gave you this good of a charge because your pacs are new. It will do an increasingly poorer job as the pacs get older. Try a manual setting with peak sensitivity of 3-5mv/cell. When I was actively using these, I got good results with 3mv/c on new pacs and then bumped it up as the packs got some cycles thru them.

What you did thus time will obviously work as well, its just a pia and requires more time than being able to charge all the way thru...

sharpcroft

Hi Duster, thanks for the reply.
The only thing that confuses me is that the (minimal) manual tells me that default peak detect for NIHM's is 7mv, this is what i have it set to, would not setting the peak detect to 3-5mv mean it would cut off even earlier??

Sharpcroft......

Duster_360

iTrader: (21)

With 7mv/cell, you're telling charger to look for a 42mv rise (using a 6 cell pack as example) and that's obviously much bigger than a 4mv/cell setting would require (24mv). This bigger peak rise should mean charger will charge longer than it would have for a 24mv peak and this can overheat the cells. So yes, a lower setting would mean it would terminate earlier.

The objective is not to stuff mah into the cells, its to optimally fill the cells based on NiMhs characteristic voltage rise when they are full. 3000mah into a new 3600mah pac would not have caused me any concern. NiMh has a breakin and they should show a little increase in capacity thru 1st dozen or so cycles.

One thing I've always been told is to adjust sensitivity based on how hot the cells are getting when they peak, they should not be getting hotter than 120-125F. It does no good to pump a higher mah amount into the cells if you're overheating them and compromising cycle life.

It may be this is just diff for this charger (compromises in design of electonics capabilities to measure small voltages accurately), how hot were your cells when they peaked the 1st time?

sharpcroft

Hi,
Yeah they got pretty warm, not to hot to pick up and hold but not far off it.
There is an optional temp sensor to go with this charger so i may as well get it (£5) as a fail safe, the cut off temp is adjustable so would you recommend about 120f?

Duster_360

iTrader: (21)

If you're serious about using the temp probe as a cutoff, it needs to be set lower since for NiMh, some of these probes seem to lag way behind pack temp. The prob is the probe making contact with the pack - if this is a curved probe that will lie flat on the curve of the cell put it on cell nearest to the batt connections - thats at least better than the stick kind of probe that just sits there with marginal contact with the cells.

I would try 110F (or lower) and watch the next charge. If it terminates on temp, then bump it up a little. If this temp probe is like the stick style one I had with my Ice or TC1030 charger, its slow to react and reads way low compared to an IR temp gun. If you set it at temp pack should reach, it'll let pack opverheat before it cuts off.

I personally wouldn't invest in one if its the stick type. I don't know which style they sell for this charger.