Victron Solar Charger Controller misreading battery voltage?

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marcop asked Jan 30, '20

Victron Solar Charger Controller misreading battery voltage?

I have the 20ah solar charger and a smart bmv monitor. Usually things work at expected - hit float sometime most afternoons around 14.2v and sunrise around 12.3v. However every now and then I'll notice the charge controller reading the battery at float in the morning and not charging all day. Example attached. The BMV reads the actually battery voltage correct. I've reset setting to factory, turned off charger and turned back on via the Bluetooth battery settings, checked wires, and nothing seems to fix the issue (the charge controller reading the batteries at float when they are far from it. Current firmware. Any pointers or ideas?

voltage

bmv.png (143.2 KiB)

cont.png (123.0 KiB)

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Answer 1 · 2020-01-30T11:53:27Z

klim8skeptic answered · Jan 30, 2020 at 11:53 AM

Your main battery and start battery read the same voltage on the BMV.

That's odd.

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marcop commented · Jan 30, 2020 at 12:16 PM

Not so odd in this case. There is 2 banks - but they are joined as 1 on the battery selector switch (both). Each should have the same charge.

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Answer 2 · 2020-01-30T12:16:25Z

Guy Stewart (Victron Community Manager) answered · Jan 30, 2020 at 12:16 PM

As @klim8skeptic noted, I would confirm the accurate reading of both by using a multimeter on the battery terminals themselves and confirming before doing anything else.

BMV is currently reading the same voltage for main and starter battery, which is very unusual when wired correctly.

Once that has been checked though, have you enabled VE.Smart networking? That will send the BMV-712 voltage to the SmartSolar MPPT and improve its accuracy.

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marcop commented · Jan 30, 2020 at 01:21 PM

Yes confirmed BMV is accurate on the batteries. For whatever reason the charge controller is sensing a completely different voltage not even close. Odd part is the voltage is correct most days and every night It reads the correct voltage, but some days when the sun rises, it thinks it's already at float and doesn't charge at all. This is the third time in 6 weeks.

Not using VE smart networking, but thanks for the idea - will try it tomorrow!

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Guy Stewart (Victron Community Manager) ♦♦ marcop commented · Jan 30, 2020 at 09:48 PM

Take the measurement at different points in the system with a multimeter. Is the battery voltage also rising at the MPPT terminals, at the fuse, on the bus, or somewhere else.

Does the multimeter measurement match the display on the MPPT. Where does it begin to deviate and what can be done to improve it?

Rising during the day sounds like a voltage rise due to undersized cables or poor connection, and should be investigated as it may lead to heat and damage to the connections.

Just correcting the voltage (by reading it from the BMV to the MPPT) by adjustment would not be a good idea until you understand why the voltage is appearing higher.

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Answer 3 · 2020-01-30T17:44:04Z

kencor answered · Jan 30, 2020 at 05:44 PM

I have a similar issue. I have 3 separate controllers all linked to one battery bank, two of them (100/30s) are reading the correct voltage and charging the batteries, the other (100/50) thinks the batteries are at 13.80V and at float and will not charge (note there is 13.80V at the controller). Also the 100/50 does not show up on my bluetooth linked VictronConnect, I disconnect power from it reboot and it works then but not the next day....

Any thoughts on what the issue may be , or further tests to check?

Many thanks

Ken

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dazey77 commented · Jan 30, 2020 at 09:42 PM

I witnessed the same here, two smart solar 75/15, both on the VE network with a BMV712. One smartsolar was reading the same as the BMV (13.5ish) and the other was reading about 13.8 ignoring the BMV.

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Answer 4 · 2020-09-30T03:34:39Z

jaydub answered · Sep 30, 2020 at 03:34 AM

I am having the same problem. MPPT 75/15 goes into float way too early. It thinks the battery is at 13-14 volts when in reality the battery is only at 12.4. When I disable the MPPT charger via the app, it reads the voltage correctly at 12.4. Because it jumps to float to soon, my bank is not getting charged.

Did you ever figure out what is going on? I am starting to think my MPPT has gone bad.

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wkirby ♦♦ commented · Sep 30, 2020 at 07:47 AM

You seem to be experiencing a large Voltage drop over the cabling.
When charging the MPPT will have a higher Voltage than the battery which causes a current to flow from the charger to the battery. When a current flows through a wire there will be a Voltage drop. The ammount of Voltage drop depends upon a) the resistance of the cable and b) the ammount of current flowing.
When zero, or almost zero current is flowing through the cable then the Voltage drop will be zero (or almost zero). You are also seeing this, the Voltage reads correctly when the charger is disabled.

If you are experiencing a high Voltage drop between the MPPT and battery then either the wiring is too small or there is a bad connection somewhere along the way, switches, fuses, connectors etc.

Please check that the wiring is of an adequate rating and that there are no bad connections.

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