Victron SmartShunt

[ShedPower]

Hi

Ive just installed a Victron smart shunt and have some voltage discrepancies. The shunt is saying 12.5v a multimeter is saying 12.4, and I have a automatic transfer switch that says 12.3v. all connected directly to the batteries, which are 3 130am in parallel using two bus's to join the batteries together. It is perplexing and important as I have to set the transfer switch at the voltage that it will transfer to grid power. I usually have that set to 12.2v, If it transfers too soon it defeats the whole object, if it transfers too late it will harm the batteries.

Any advice appreciated. Thanks.

[Bala]

Use the victron shunt to find the dod you want to set the transfer at.

So if you decide its 75% state of charge on the victron see what the volt reading is on transfer switch and set it accordingly.

[ShedPower]

Thanks. I am confused though how the batteries can be 99% full and now be 12.4v. It doesn't seem possible, does it? The batteries were all fully charged when I installed the shunt. The batteries were brand new but they were quite cheap so I am a bit suspicious if they are really poor quality and not fit for purpose. I just don't know.

[Bala]

Voltage is not a great indicator of Soc.
if you have any load on the battery it will bring the voltage down. This is where the shunt helps with its Soc %

For the shunt to be calibrated you need to fully charge the batteries with the shunt connected. Anytime the shunt or battery is disconnected and reconnected the shunt will read 100%. You again need to do a full charge to calibrate.

[ShedPower]

Thats helpful, thanks. I think I am panicking about voltage too much.

[Bala]

The only way to get accurate v readings is to buy a quality meter like fluke and pay to have it calibrated. I don't bother for lead acid and drop in lithium.

[chrisski]

I would not spend too much time worrying about three different readings within .1 volt of each other. Too much work would be required to calibrate the equipment and the cost would be a bit much. Just work with what you have. Sometimes its equipment not called. Could be normal voltage loss if measured at different places, and this depends on current and size of the wire when measuring different places.

I agree that the voltage is not a good way to measure battery SOC, but if you need a voltage to activate the transfer switch that tidbit does nothing to help you.

The only thing i would recommend looking into is the victron shunt has an option to power a relay based on SOC. If your transfer switch allows an electric input for on and off in addition to a voltage, this could work.

For the shunt to be calibrated you need to fully charge the batteries with the shunt connected. Anytime the shunt or battery is disconnected and reconnected the shunt will read 100%. You again need to do a full charge to calibrate.

I have the Victron shunt and my 712 BMV does not do this. I turn off the batteries with a blue sea switch a lot and the SOC remains accurate. If you’re talking removing the voltage sense wire, than perhaps that will do what you’re saying but i don’t understand why that wire would be disconnected.

[Bala]

I have the Victron shunt and my 712 BMV does not do this. I turn off the batteries with a blue sea switch a lot and the SOC remains accurate. If you’re talking removing the voltage sense wire, than perhaps that will do what you’re saying but i don’t understand why that wire would be disconnected.
[/QUOTE]

For my caravan i have a switch on the earth and shut the complete system down when not in use. The bmv has self consumption that is not measured in soc% so gradually drains the battery.

[chrisski]

For my caravan i have a switch on the earth and shut the complete system down when not in use. The bmv has self consumption that is not measured in soc% so gradually drains the battery.

That I have seen. After a couple of months of storage between the 5 mV the Victron Shunt uses and the normal battery drain, the batteries are at a lower SOC, but the meter still reads 100%.

[jflorey2]

Thanks. I am confused though how the batteries can be 99% full and now be 12.4v. It doesn't seem possible, does it?

If you fully charge a lead-acid and then put a moderate load on it you will see about 12.4V.

[ShedPower]

That’s very reassuring! Thanks.

[ShedPower]

A battery question on this system. I have 3 x 130ah lead acid leisure batteries in parallel. I have 360w panels on my shed roof but while its overcast they are struggling to charge the batteries. Two days and still not fully charged. So tomorrow I am buying some larger panels, 3 x 410w panels. The new panels will have their own Victron charge controller because of bigger volts and amps.

My question is, how many amps could, in general, 3 lead acid batteries in parallel cope with when charging? The most I have had out of the 360w panels when its sunny is 15 amps. With the new panels, im guessing there would be (from all panels) about 30-40 amps. I don't want to fry the batteries! I have had no success trying to get any information from the ebayer I bought them from and the batteries have no brand names on them. Thanks.

[Bala]

Generally around 10% of battery capacity for charge amps.

For off grid systems a generator and charger are used for extended overcast weather. You have mans power so you could just get a charger and plug it in.

[ShedPower]

Thanks, 10%, thats helpful. So about 39 amps max. I have an automatic transfer switch that switches back to mains power when battery voltage reaches 12.2, or whatever it is set to.

What im wrestling with is having two charge controllers on the same system both independently pumping amps into the batteries. They are victron, so I could get get a Cerbo GX which would supervise the overall current going into the batteries, but I am spending way too much on this system at the moment!

[Bala]

As far as expenses, it depends on why you have thus system when you have mains power.

it is possible to run multiple controllers How well they play together depends on tge settings available.