Voltages on different devices not accurate

Q&A and troubleshooting
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1

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I have inherited this problem from another installer.

You will notice that of the devices in the picture the voltages of the BMV and MPPT are very close but the BlueSmart charger is significantly higher.

At first I suspected voltage drop so I busted out the multi meter.

If I meter at the battery terminals I get the 13.68 V just like the BlueSmart is showing.

If I meter at the MPPT terminals and the shunt positive to battery negative I also get 13.68 V.

Essentially all the devices are the same 13.68V at their respective terminals.

So why are the voltages showing differently in Victron Connect?

It seems also that if the BMV is using its inaccurate voltage it will not yet have reached the 14.2V “charged voltage” when the charger has completed its bulk cycle. I would need to set the charged voltage lower to accommodate for the inaccuracy and get the shunt to calibrate to 100% at the right time.

The BMV and MPPT are networked wirelessly and therefore sharing voltage. Could this be part of the problem? Maybe I will remove them from the network and see what happens. I can not network them with the BlueSmart because its mine and wont be part of the permanent installation.

2

Are there dc consumers at the same time? I see a 1Amp difference between the charger and the shunt as well.

So a 0.14 of a difference. Interesting. The charger is an HQ21 is there any corrosion on anything (it has a few years in service)? Everything properly tight?

3

If the charger is pushing 30a through a cable, there will be some voltage drop. Better measure that at both ends again under load.

Another thing to check would be to check the fuse and fuse holder of the BMV 712. The fuse should be a 1a, not less. The fuse should be clean and shiny. Likewise the brass contacts in the fuse holder should be clean and shiny. The spring should be free to apply pressure to the fuse, check the cables allow enough movement.

4

The BlueSmart terminals are in great shape but I will go ahead and run through these items you have suggested.

Interesting update. Last night when the charger went into absorption the voltages all matched. They matched this morning too. Then I put a load of around 5 amps on the system for 30 min or so, turned on the solar to charge and the voltages are off again like yesterday. Again they meter the same at all the terminals but show off in Victron Connect.