Can I correct the voltage calibration my 75/10?

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mprowe asked May 22, '19

Can I correct the voltage calibration my 75/10?

The Victron Connect App is reporting the voltage on my battery as approximately 1 (one) volt higher than it really is. By "really is", I mean that I am witnessing the battery voltage, firstly on the in-built voltmeter on the Motor Home control unit and again (using a good quality) voltmeter at the "BAT+ & BAT-" terminal of the 75/10.

The image below, hopefully shows my test layout. There is also a video.

My assumption is, that if the 75/10 is "miss-informed" on the actual battery voltage, all management functions are probably in error too? For example, when the 75/10 thinks that my battery is at 14.2v - it is not! It is only at 13.2v etc.

How can this be corrected?

Best regards, Martin

VEConfigure 3 voltage

layout.png (24.5 KiB)

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Answer 1 · 2019-05-29T13:51:37Z

Paul B answered · May 29, 2019 at 01:51 PM

I would be looking are replacing the wire between the battery and the MPPT REG reg as its more than likley TOO SMALL or theres abad connection and you are loosing voltage because of that

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Answer 2 · 2019-06-01T07:37:44Z

mprowe answered · Jun 01, 2019 at 07:37 AM

Thank you for your suggestion Paul,

However, I think you are looking at the problem the wrong way round?

Three independent measurements (voltmeter at the battery, MH distribution voltmeters and lastly a voltmeter at the Victorm BAT+ BAT- terminals) say the battery voltage (in this test setup) is 12.8v. While the Victron, INTERNALLY thinks it is 13.8v.?

By my understanding, the Victron's internal ADC is reporting one volt higher than reality.

OR... it could be that the internal voltage determination is perfectly fine BUT the display (via the Connect App) is in error? But I think the liklyhood its the latter, is diminishingly small!

Regards, Martin

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Answer 3 · 2019-06-01T08:48:12Z

dwmarine answered · Jun 01, 2019 at 08:48 AM

Do you have time to do a couple more tests for us please? You may already have the answers.

Does the discrepancy show up more under load? i.e. when the 75/10 is working fairly hard?

Are all the voltages the same at night, when there is no solar generation?

Every connection adds a little resistance and this will compound under load, as Paul B noted.

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mprowe commented · Jun 06, 2019 at 08:09 AM

Sorry for the delay responding to suggestions...

Under all test scenarios I can think of, this discrepancy is evident. To do a "No Load" test, I am using the Victron Connect App to "Turn Off" the charger. This is the layout and the figures quoted are "as recorded".

Regards, Martin

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