on my powerlab 8 i all ways get one ir reading higher than the other but thats on turnigy's a guy aslo mentioned it at my field as well with his powerlab i think they brought out a update to fix it but i dont have the usb cable to update and see if it worked

but i do think its just the powerlab not your packs ( i could be wrong tho so please correct me if i am )

Im running the latest firmware though?

I think the incorrect Ir on the PL8 was shown on the last cell. If it's in the middle Martin I reckon it's correct. Although the IR readings on the PL8/6 have been shown to be a bit off. A couple of the guys are using a more accurate way of measuring it and this has shown chargers IR readings to be a bit suss

Martin Are you using pitch Boost on vbar and rinsed out your pack!!!

ohh i arnt sure then sorry about that i just thought it was a software bug as the another guy i know his powerlab was doing the same i will have check my lipos then and get it updated

version v3.31

***VERSION 3.31 2-24-12*** Fixed MPA internal resistance reading.
so the charger says

As Dave says, this was a problem affecting typically the last cell, and then only when using a balance board that needed XMA wiring mode.

If you see a cell in the middle that is significantly different then the odds are something is not right.

One thing though is do make sure the pack has a chance to settle at room temperature before testing. As an example if you were to hold the pack so you warmed up the outer cells in the pack then test you would find the middle cells had a higher resistance.

Just leave the pack in the room for a couple of hours then charge, if you are seeing the same then I'd talk to OptiPower as a difference that high will just result in the pack degrading over time.

Mine was reading exactly the same until I installed the latest 3.31 firmware Martin.

All is well now after updating.

We had a similar problem a few days ago that was cured by cleaning the balance connector. (Much to my annoyance as it shouldn't make that much difference, but it does in some cases). A cell with high ir will warm up quicker and its ir will drop. The other cells will act as a heatsink. Mark mentioned a thread about it. If it is a real effect then that cell will not last as long as the others. I would borrow a Wayne-Giles meter or use an I charger to check.

I doubt if it is a real problem, it is too big a difference. If it is real you are covered by the guarantee. You can get a rough estimate of ir by checking how the cell volts change as a current changes. If you start charging at 5 or 10 amps you will see a big change in cell volts. If your cell really has an ir 3 times more than the others then the change will be three times as big.

ir comes from change in voltage divided by change in current. A 1 milli ohm ir means a 1mv change for a 1 amp change. We should call it partial dv/dt with other parameters held constant. Calling it ohms is pretty close to the truth. So you should see a 10mv change in cell voltage when charge current is changed from 0.1 to 10.1 amps on a 1 millohm cell and 30mv change on a 30 milliohm cell. This time contact resistance shouldn't make a difference, unless the charger uses a lot of current to measure voltage.


It might be worth looking at the crimp on the cell that is giving a problem. It may not be pushed in far enough and held by the finger, or it may be gripping too much insulation. There may be a dirty pin on the connector.

Hi Martin , not sure bout the update fixing things as I ain't done it yet , but you will get a higher ir reading on cell 3/4 because of the "joint" that opti and others put in ( between cell 3&4)to get round air travel limits on cells , as in when you go to say rc hotel etc

+1 on the above

my 6s 5000s are reading 0.9 which i thought was pretty damn good. This is on my cellpro 10s, not sure how accurate the reading is though?

No mate I don't use pitch pump on the vbar but the packs are being pushed hard lately on my 550