liveforphysics wrote:The iCharger sadly can't check Ri below about 50mOhm with even a shred of accuracy. I've got a $3500 Ri meter here at work, and the iCharger can read 15mOhm with the actual Ri is 3mOhm, or sometimes visa-versa.
So, if you want to check the Ri of a single cell, or likely even the stack of 6, it's not really the tool you want to use for these fairly low impedence cells.
I would check resistance by leaving them paralleled and floating a charge, so they are all at the identical state of charge, then 1 by 1, measure resting voltage, apply some known load (like a 10ohm resistor), and measure the voltage sag after 10 seconds, and record this.
I think the iCharger does very accurate charging/balancing so I was surprised to hear its IR readings are essentially useless. Richard's Cadex analyzer is very expensive so that's even more surprising.fechter wrote:Sounds like the IR measurement on the iCharger is just like my Cadex. Useless in the range where these batteries run.
The 10 second drop measurement is what I proposed before. This will give you the best indication of a bad vs. healthy cell as far as I can tell. It will be essentially the same as a relative IR measurement. This is what the Prius guys do.
Its good to know that there is a work around but an absolute IR measurement would be more useful than a relative IR measurement and it would be nice not to need to put all the cells you want to check into an identical state of charge.
Are there any accurate affordable RI Meters (dedicated or in RC chargers) available?
Since affordable is relative a better way to phrase the question might be what is the least expensive piece of equipment that can measure IR accurately with low impedance Cells?
If there are not any accurate affordable RI Meters available new, how about used on Ebay? What should we look for?