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kaypea avatar image
kaypea asked

Anyway to calibrate voltage readings?

Victron Easysolar 2 GX system, 130a/h lead calcium batteries (24v). Short 50mm cables to batteries.

Are there any settings/adjustments to be able to bring the solar and system voltages closer to the real battery voltage?

I have a calibrated fluke multimeter on the battery which measures 26.01v - I have a chart recorder connected to the battery which also says 26.01v - I have a cheap ebay KG140 meter which reads 25.96v (50mV error) and then the Victron VRM remote console which measures 26.3v (299mV error).

I would have expected the Victron to be fairly accurate, but when the batteries are getting low at night, the battery voltage reads 24.1v and the victron system reads 24.4v. These measurements are when loads are quite light on the system.

Yes, I have connected the remote sensor terminals to the battery, but ithe Victron system always reads 300mV too high.

In a system where 300mV error is a big deal for a lead/calcium battery, I could do with being able to calibrate to account for the difference. Is this possible? Have I missed something?

EasySolar All-in-One
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3 Answers
nickdb avatar image
nickdb answered ·

What your post doesn't clarify is, whether or not you did meter readings at the mppt/inverter terminals at the same time and if they agreed with the battery readings?

Differences are not uncommon but usually related to cabling losses, though these should be measurable, especially under load.

As mentioned elsewhere, you can use vsense inputs on the inverter or configure SVS on DVCC so an external reference is used for charging.

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kaypea avatar image
kaypea answered ·

The readings were taken at the battery under a very light load. Cables are a combination of 35mm and 50mm but very short. The readings were the same at the MPPT terminals.

The vsense inputs are connected, but you said about configuring them on DVCC - Maybe thats the issue - I will have to check if that bit is configured correctly. EDIT - Just checked and all the DVCC settings for SCS, SVS, and STS are turned on...

The load on the system was only 3amps when the voltage checks were done - battery system is 12v lead/calcium (two in series - three sets in parallel for 520a/h capacity).

Thanks for your reply.


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nickdb avatar image nickdb ♦♦ commented ·

It's challenging when you can't see how a system is setup, if you're using a shunt and that is configured for DVCC with SVS, if your devices are physically connected to the GX and under external control then that is what will be used for charging, irrespective of what they independently report.

If you are using the ports on the multi, the following from the manual applies:


4.4.5. Voltage sense (connection terminal J, see appendix A)

For compensating possible cable losses during charging, two sense wires can be connected with which the voltage directly on the battery or on the positive and negative distribution points can be measured. Use wire with a cross-section of 0,75mm².

During battery charging, the MultiPlus-II will compensate the voltage drop over the DC cables up to a maximum of 1 Volt (i.e. 1V over the positive connection and 1V over the negative connection). If the voltage drop threatens to become larger than 1V, the charging current is limited in such a way that the voltage drop remains limited to 1V.

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kaypea avatar image kaypea nickdb ♦♦ commented ·
Hi Nick - I am already using the battery sense terminals, and can understand the voltdrop scenario. I did the measurements at very light load (around 3amp from the batteries and before it got light this morning) using my calibrated Fluke meter, and the difference was around 300mV between the system, solar and Fluke readings given on the VRM console - bearing in mind I do have the sense wires connected to the Victron.


The system is the Easysolar 2GX which has everything built in including the measuring shunts, MPPT 250/70, GX device etc. There is nothing else connected apart from the Victron battery balancer which is completely seperate. Its all prewired so everything should be compatable with everything else?!! That was my question to get the reported voltages aligned better as 300mV is a big difference when you are only talking about two volts from battery charged state to flat state.I can of course compensate for the error by setting float and absorption voltages incorrectly, but thats not the point with a quality bit of kit!


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nickdb avatar image nickdb ♦♦ kaypea commented ·

The official line (that has been discussed on other topics, so I am paraphrasing) is that the chargers aren't measuring devices, they are sufficiently accurate for their purpose. The shunt is accurate and has a defined tolerance, so while that is configured for use, everything should charge accurately, the internal readings would be ignored as long as the GX is active and coordinating everything via DVCC. In most installations this shouldn't be an issue as an accurate reading, via shunt/BMS etc, is used as the primary reference.

You also need to consider that readings are at their least accurate with low power usage.

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kaypea avatar image
kaypea answered ·

I have an update to my question from over a year ago. My original problem with the system was about the voltage readings being 300mV too high from the MPPT charger... Today I expanded my system with a 2nd MPPT charger and guess what? The voltage reads correct from that one, but the original MPPT reads 300mV too high even though they are connected to the same battery. So it looks as though my orginal MPPT has a fault giving the voltage reading 300mV higher than it should be.!!!!

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