IR testing with OPUS

graham

Member
Joined
Jan 5, 2018
Messages
30
I am in the process of capacity testing secondlife cells for a 7s60p with an Opus BT-C3100. (and another on the way)
I understand that the Opus can be a bit off when it comes to IR testing, but by how much? and what sort of figures would be acceptable using an Opus for IR readings?

Thanks in advance
 

Wolf

Well-known member
Joined
Sep 25, 2018
Messages
1,390
bit off when it comes to IR testing, but by how much? and what sort of figures would be acceptable
A bit off, is an understatement. Most all comercial reasonably priced Battery Chargers/ analyzers measure battery internal resistance (IR) using a dc voltage drop method. Calculate the IR by measuring Vdrop against a known load. Unfortunately to measure such a low resistance you really need to incorporate a 4 wire kelvin method of measuring the IR accurately of a cell. The opus manual even states that the readings can vary 10% to 20% and that you need to subtract 30mΩ from the reading due to contact resistance. There is absolutely no correlation between actual IR of a cell and what the Opus gives you other than that it is wrong. Get yourself a proper IR meter RC3563 or a YR1035+ and you will have a proper IR reading you can trust the first time. No need to check it two or three times and hope you get a reasonable reading that is wrong anyway.
Wolf
OPUS IR.jpg
 
Last edited:

graham

Member
Joined
Jan 5, 2018
Messages
30
Thats great thank you for your advice, i'll get myself an IR tester and start again with readings.
 

daromer

Moderator
Staff member
Joined
Oct 8, 2016
Messages
5,573
The Opus can vary up to 100% easily and i have shown that in videos. This due to contact resistance not being equal between tests and the spring does not apply equal force.
 

deswong

New member
Joined
Jan 20, 2021
Messages
19
I am in the process of capacity testing secondlife cells for a 7s60p with an Opus BT-C3100. (and another on the way)
I understand that the Opus can be a bit off when it comes to IR testing, but by how much? and what sort of figures would be acceptable using an Opus for IR readings?

Thanks in advance

I can't even trust it - I put in a cell and it came up as 68, then changed the mode setting to charge, then back to quick test, to get a new value of 158...

Definitely get yourself an IR tester - this way you can also test reliably without having to have the battery charged!
 

Overmind

Active member
Joined
Jan 16, 2019
Messages
416
Bypassing the spring internally helps. A good copper lane or something should definitely make things significantly more accurate.
 

deswong

New member
Joined
Jan 20, 2021
Messages
19
Bypassing the spring internally helps. A good copper lane or something should definitely make things significantly more accurate.
Aren't the spring ends insulated? So it doesn't touch the battery? The tracks seem to be on the front where the negative terminal is attached, so if anything wiring against the negative connection and the track endpoint would be the way to go, but it is a pain to mess around with, and have to use some super flexible wire to cope with the strain.

I can't remember now as it has been a while since I pulled mine apart, but measuring resistance from the negative connector to the spring I got an open circuit on all 4 so I didn't bother with the "Spring Wire mod" others have done.
 

Wolf

Well-known member
Joined
Sep 25, 2018
Messages
1,390
"I did the OPUS wire mod and it made absolutely no difference in the readings."
It may be sad but it is true in my case as well. But then again why would you use the OPUS for an IR meter in its own admission just contact resistance will add ≈30mΩ to the results. As far as any off the shelf Battery Analyzer/Tester that claims it does IR is just hoodwinking you.
The only proper way to test resistance that low is with the proper 4 wire kelvin methode, PERIOD.

You cannot get a proper IR reading with slide contacts and without 4 wire, you get a guestemate and it is not repeatable.
A proper IR tester such as the YR1035+ or RC3563 will give you the proper IR of the cell and it is repeatable.
Wolf
 
Top