Milliohmmeter to measure battery internal impedance?

Archive SparkFun Site Questions/Comments
1

This is my first post, so I hope I directed this to the right forum.

I was curious if anyone had a meter or circuit that they reccomend for milliohm impedance measurements?

I’m aware I can use a discharge curve to caluculate this value via ohm’s law, but I’d like to do quick measurements on many different cells, without applying a load to each one for 1+ hour.

One meter I’ve seen reccomended for this purpose is the the Hewlett Packard 4328A Milliohmmeter, but it is rather pricey an a difficult piece of equipment to find (has not been manufactured for many years). The newer version of this HP instrument is several thousand dollars. So, I’m wondering if there are any alternatives that I am missing (?).

thanks,

ian

2

I think using a milliohmmeter would be the wrong plan here. The meter is probably expecting a pure resistance and the DC offset from the cell will throw it off. Unless of course, it’s just doing an AC impedance measurement.

You can research a quicker way to measure cell impedance online. Going from memory:

  1. Measure open circuit cell voltage; V1

  2. Apply fixed load for short period: say 2 seconds or until measured voltage droops about 10%

  3. Remove load and immediately measure open circuit voltage before cell has a chance to recover; V2

  4. impedance is (V1-V2)/Iload

Google this to be sure. It’s been a while since I did it and I may have something wrong.

3

Thanks for the response. I wrote a follow up several days ago, but it appears to be stuck in some sort of moderation queue. I then sent a PM to the site moderator: phalanx - but never received a response. I have no idea why the post was pushed to a moderation queue, but hopefully it gets posted. Thanks. Anyway, in summary: For various reasons, I’d like to use an AC impedance measurement.