question

joeoffgrid avatar image
joeoffgrid asked

BlueSolar voltage accuracy issue

I just noticed the voltage display via the app in my blue solar is quite off.

It tends to show battery voltage about .2V higher than what I measure right at the terminals of the charger. That is comparable to my worst Chinese charger...

Someone else got similar findings?

It might be related to the recent update?!

charger
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6 Answers
joeoffgrid avatar image
joeoffgrid answered ·

How are you guys with voltage deviations connecting to the charger? I suspect now it is my non-Victron Prolific TTL device connected to the MPPT's VE.direct port which is supplying power on the 5V side to the blue solar that might be causing the deviation.

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mvader (Victron Energy) avatar image
mvader (Victron Energy) answered ·

Hi all. in this (lengthy) thread, two units were reported to be inaccurate in their battery terminal voltage measurement. Both have been investigated; and there are no issues with voltage accuracy.

Joe received a new unit from us; his unit was sent to us; tested found to be Ok.

Dean also reported an issue; this was looked into; and also there is no problem with the unit. It measures just fine; unit is Ok.

For all the details; happy reading!

I’m considering this case closed now. Thanks for your help.

Have a good day, Matthijs

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thanar avatar image
thanar answered ·

Does the delta fluctuate according to the current going through to the battery?

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straightup avatar image
straightup answered ·

@JoeOffgrid

Victron units are well known at this point for having poor accuracy across the MPPT range.

At this stage, the response from the company seems to be "this is normal, live with it", and the response from much of the forum community is generally to attack people who bring it up too much (just so you're aware).

A friend of mine (@Solvan) recently returned his unit because of poor current accuracy (and other issues), and when testing with his vendor, found their entire stock was subject to varying degrees of error. His posts were subsequently deleted and I believe he has now been banned from posting.

In short - nothing you can do. This is the Victron standard of quality. I live with it and rely on an accurate battery monitor to compensate (at least for that problem).

See also:
https://community.victronenergy.com/questions/7861/innaccurate-and-poor-absorption-on-smartsolar-an-u.html

https://community.victronenergy.com/questions/322/inaccurate-dc-input-current-readings-from-multiplu.html


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mvader (Victron Energy) avatar image
mvader (Victron Energy) answered ·

Hi @JoeOffgrid, 0.2V deviation is indeed too much. I’ll contact you from the helpdesk email to resolve it further / ask for serial number details etcetera.

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deandavis1 avatar image
deandavis1 answered ·

I hope the following might help some users. Firstly thanks to the Victron team for their assistance here its been very helpful. Secondly I'd like to point out that the conclusion I've reached regarding voltage accuracy has all been tested on cloudy days and I want to confirm my findings on a sunny day.

My belief (like others) that the Victron MPPT 100/50 controller over stated the battery voltage was due to measuring the voltage at the battery and finding it lower than what the controller was reporting.

If anything I was expecting to see a higher voltage at the battery due to any voltage drop, but after testing the voltage at the controller terminal I found this was in fact higher at the controller than the battery.

There are three main aspect of the system worth considering here.

  1. The voltage at the battery.
  2. The loss introduced by the BMS (ie cables, switches, fuses, shunts etc).
  3. The voltage at the Victron MPPT controller.

Because the controller is generating a charge the voltage drop as a result of resistance in the BMS drops from the controller to the battery. Hence by testing the voltage at the controller (as the controller software does) you get a higher voltage reading.

Perhaps a more accurate label here would be MPPT Controller output voltage rather than battery voltage.

One way to address this problem would be for the controller to test the voltage directly on the battery (ie bypassing the BMS) and this is exactly what the additional Smart Battery Sense Victron module does if its installed.

Otherwise the work around is to increase the voltage settings in the controller to compensate for the loss. This will still report the wrong "Battery Voltage" but at least the batteries will get fully charge. Obviously this has its dangers especially as the value can change with current (ie V=IR), but measure the actual install resistance (or voltage drop) or with some small incremental tweaking the results are pretty good.


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