If your Opus BT-3100 charger is reading 0.05V higher on the display than reality....

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jm1

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Dec 14, 2017
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Hello Guys,

I have a couple of Opus chargers, one of them was consistently reading higher voltages than the other. For example, my cell would read 4.19V on my Fluke multimeter and also on one of my Opus chargers. If I popped the cell in the other Opus it would read 4.24V which was not reality. This caused all cells to start the discharge cycle from 4.15-4.16v since the display showed that as 4.20V.

I opened the back of the charger and desoldered the J1 jumper which is described as a "voltage compensation" by the Opus manufacturer. Once I did this it now reads accurately and matches the |Fluke meter as well as the other Opus charger.

Just putting this out there in case anyone else notices this 0.05V higher voltage reading on the Opus display.

James


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Korishan

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Jan 7, 2017
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I wonder if this could be one of the reasons it reads consistently about 10% off on capacity tests. Perhaps instead of leaving it disconnected, put a POT on there instead so it can truly be calibrated accurately.
Wonder what else can be so easily be fixed with these things.
 

jm1

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Dec 14, 2017
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Korishan said:
I wonder if this could be one of the reasons it reads consistently about 10% off on capacity tests. Perhaps instead of leaving it disconnected, put a POT on there instead so it can truly be calibrated accurately.
Wonder what else can be so easily be fixed with these things.

A POT might help, right now it seem to be reading within 0.01V of my Fluke so Im pretty happy now. I did some extensive Googling and found info online from 2014 about the J1 jumper needing to be desoldered if the Opus reads pretty much exactly 0.05V over the real voltage.
 

Korishan

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Perhaps you can do a test of a known cell and see what it does with and without the jumper in place. How far off are the capacity readings.

Would be interesting if that is the sole reason for it being off. Something everyone with an opus could do as a permanent mod to get it more accurate.
 

not2bme

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Oct 16, 2017
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I just returned one because of that. The replacement isn't any better, it's .03v off, which isn't so bad, but the big thing is that it charges and discharges much slower than my original unit. It's about 20 mins longer. Hope this might have something to do with it.
 

daromer

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Both 0.03 and 0.05 is within what that device can do :p Its cheap of a reason but with that said you can tweak it a bit but it wont do that much on capacity since its already showing to high capacity to how it measure.
 

jm1

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Dec 14, 2017
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daromer said:
Both 0.03 and 0.05 is within what that device can do :p Its cheap of a reason but with that said you can tweak it a bit but it wont do that much on capacity since its already showing to high capacity to how it measure.

In my case I made the change so that all my Opus chargers are reading the same or extremely close to the same which is now the same as my calibrated Fluke meter.Having one charger with a constant 0.05V difference was making a difference in the mAh rating I was writing on each cell out of this charger because of the fact that it started its capcity test when the real cell voltage was only 4.15-4.16 instead of 4.20 as the other Opus charger was doing. The means all cells from one Opus charger always had lower mAh values compared to running those same cells on the other Opus charger because there is more mAh to be gained from 4.15-4.20 then there is at the bottom end 2.75-2.80.

So now they both read consistently high ::)ut at least I can separate my cells by mAh properly.
The info on desoldering the bridge at J1 came right from the designer of the Opus charger, many owners discovered this exact 0.05V difference and he said "desolder the J1 jumper".
 

Overmind

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Jan 16, 2019
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Mine seem also to indicate values higher than normal, since cells charged with different chargers when put in for discharge tests show voltages of 4.23. I will test this with my Extech to be sure.
 

LEDSchlucker

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Dec 20, 2018
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On one of my Opus chargers I measured 4.19V with my DMM while the Opus itself said 4.20V. (the J1 is connected)
I'll test the other one after the DC-Test is done.
 

Wolf

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Sep 25, 2018
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Yep they definitely are not the perfect Voltmeters out there. :D


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Wolf
 

Mazlem

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Aug 8, 2017
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So where might a pot got to dial in the voltage? I bought some small ones months ago but never got as far as figuring that out.
 

hbpowerwall

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Well done James!
 

DCkiwi

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Sep 11, 2017
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All Opus users need to know about J1 --> inside the Opus is a labelled solder bridge on the PCB which substantially (60-70mV?) alters the voltage sense on all slots. Cheers jm1 for starting this thread, with pictures.

If it is open, it reads low[er] which is optimal if you want the cells to be recharged AND topped off by the Opus. If it is closed, it reads lower on all slots, which is optimal for testing cells, as it doesn't 'hang' on (try to top off)cells which are 'only' 4.16-4.19V, it just gets started testing (discharging), as it thinks they are 4.22V already.

All of mine now have J1 joined. I think it matters far less which way you set yours up, so long as they are all set the same.

Do not assume that if you order two at a time that they will be the same out of the box. Mine weren't.
 
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