Inaccurate voltage readings across Victron Smart solar and bmv-700

[Yurtdweller]

I have a Victron Smart solar 150/100, a bmv-700, and a LiFePo4 bank @12v, 560ah.

Each device gets different battery voltage readings with the cc getting the most innacurate readings of the system.

For example, I am currently charging, and here are some readings:
13.61 voltmeter(Klein Tools cl-390) at bank
13.85 bmv-700(no Bluetooth)
14.03 smartsolar mppt cc

Each battery in the bank has it's own jbd BMS. They read:
13.54 and 13.57

Currently, all devices are wired to main buss bars except, of course, for the bmv-700.

Can I set up the Victron charge controller to read battery voltages off the bmv, either through the monitor head, or directly off the shunt, or by some other, more direct, method?

I'd prefer not to buy a smart shunt at this time.

I have fudged the settings to account for the different readings, and the batteries are staying within recommend ranges, but I'd prefer more accuracy between the battery and the cc.

Thanks

 

[sunshine_eggo]

BMSes, BMV and CL-390 are reading open circuit voltage (OCV), i.e., the voltage with no current passing through the sensing circuit.

The MPPT is reading the voltage as it's reacting to the charge current, so it should be higher when charging.

What do the 5 devices report when there is no charging and low discharge?

The only way you can get a BMV-700 to pass voltage data to the MPPT is by buying a GX device, connecting both to it via VE.Direct cables and enabling shared voltage and current sensing in the GX device. Spendy.

Recommend a smart battery sense. It measures both OCV AND temperature and can be VE.Smart networked to provide data to the MPPT.

 

[Bud Martin]

'What do the 5 devices report when there is no charging and low discharge?'
+1, good question.

 

[newbostonconst]

Look at the bright side you got one of the 4 digits to match....

I would loosen and tighten every connection and if that didn't work check for a voltage drop at each connection. Ask if you don't understand how to check for a voltage drop under load.

 

[Yurtdweller]

'What do the 5 devices report when there is no charging and low discharge?'
+1, good question.

I will check on that. But it will mean getting out of bed in the cold:/

 

[Yurtdweller]

No charging, no draw, pretty consistent.

13.26 cc
13.28 bms
13.27 bms
13.29 bank
13.24 bmv-700

 

[Yurtdweller]

It's really only proper charging that concerns me. I don't want to overcharge by a half volt, but not at all concerned about undercharging a half volt. I guess I'm good. Just curious. Thanks for the help. I'll probably get a smart shunt someday.

 

[newbostonconst]

You really need to check for voltage drops across each connection. That includes from nut to stud to connector at each connection.

 

[sunshine_eggo]

No charging, no draw, pretty consistent.

13.26 cc
13.28 bms
13.27 bms
13.29 bank
13.24 bmv-700

CL 390 is the "bank"?

This means that ALL devices are correlated, thus any deviations you see are real and likely associated with increased electrical resistance in the circuit.

If you care about accurate charging, I implore you to get the smart battery sense to ensure your MPPT is getting a good voltage reading.

You really need to check for voltage drops across each connection. That includes from nut to stud to connector at each connection.

This.

You need to go through every single connection and ensure it's properly torqued and that no component/wire has excessive voltage drop.

 

[HRTKD]

You need to go through every single connection and ensure it's properly torqued and that no component/wire has excessive voltage drop.

I'll add that every connection should be taken apart, cleaned and verified as being sound (no burrs, bends, etc). Check every crimp to make sure it's solid.

 

[Yurtdweller]

I'll add that every connection should be taken apart, cleaned and verified as being sound (no burrs, bends, etc). Check every crimp to make sure it's solid.

I will try tracing the whole build. The crimps are correct. I have good specialized crimpers, and have cut several crimps apart to make sure. I also have adhesive-sealed marine grade heat shrink. These are awesome. All the bars are clean. No burrs. I did not use a torque wrench, though. Might have to spring for one. I don't think the long-bar torque wrench I already own will work, unfortunately. I'll be building my crate soon, and will run through everything when put my 15KWh pack together.