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cranky-yoda avatar image
cranky-yoda asked

MPPT charger taking voltage from SmartShunt instead of SmartSensor

The MPPT charger gets voltage value from the SmartShunt, if the shunt is added to the network.

But we can do better, with the SmartSensor, so it's a more precise "four wire" measuring, and that way also it disregards voltage drops along the cables and bus bars and so on.
So I have the Smart Battery Sense connected right at the battery terminals, I add it to the network, and it says sending battery voltage and temperature "to the network". Great.
I go back and check the MPPT charger and now it says it's taking temperature from the Smart Battery Sense, but still says it is taking voltage from the Smart Shunt. And I don't see a way to fix that.
The only way to have the MPPT charger to take both, battery voltage and temperature from the Smart Sensor, is to remove the shunt from the network. I am fine with that, as I think the most valuable function of the shunt is to tell me, the SoC of the battery, but I wold think SoC would be valuable data the MPPT could use.
MPPT ControllersSmartShunt
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4 Answers
snoobler avatar image
snoobler answered ·

This statement:

"it's a more precise "four wire" measuring, "

The shunt is a "four wire" measurement. It's measuring (-) at or very near the (-) terminal, and the (+) should be connected at the (+) terminal. Thus you have a "four wire" measurement.

Any difference in OCV readings between a SBS and a SS/BMV will be negligible unless you have created an unfavorable configuration.


Please read Section 5:

https://www.victronenergy.com/upload/documents/Manual-VE.Smart-Networking-EN.pdf


This statement:

" I think the most valuable function of the shunt is to tell me, the SoC of the battery, but I wold think SoC would be valuable data the MPPT could use."

No. SoC isn't relevant to the MPPT. The MPPT is driven by voltage and temperature. Any meaning SoC might have to the MPPT is manifested as voltage and/or temperature.

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cranky-yoda avatar image cranky-yoda commented ·

Thank you for confirming that. I will then use the Battery Smart sensor just as a temperature helper, and make sure I connect the fused little red wire from the shunt directly to the battery (+) terminal, and not after all the cables, buss bar, switch, fuse... Still, there is one cable from battery (-) to bus bar, and bar to the shunt, that could cause a voltage drop affecting the reading. Those cables need to be well dimensioned, short as possible and bolts well tight, as a few mOhm could result in a 600mV drop at 200 Amp.

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snoobler avatar image
snoobler answered ·

You seem to be focused on minutia you're using to justify your bias. If a system permits a 0.6V drop @ 200A current, it is a poorly designed system and where the shunt is connected or whether a SBS or BMV is the better choice are the least of your concerns. Even a puny 6" 2awg cable would only produce a 30mV drop @ 12V/200A.

I personally used a SBS with my MPPT because the sides of my ailing FLA batteries were notably warmer (10-15°F) than the terminals, and I wanted more accurate temperature compensation than my BMV sensor yielded. Once I replaced the ailing batteries with a new Li-NMC, the SBS is sitting on a shelf, and the BMV is the STS.

Unless you have a special situation, I can't see that there is any advantage whatsoever of using a SBS over a SS if you already have both. The reasoning you presented is irrelevant as proper sizing and connection quality are critically important for every single component in the system. The wire between the battery and shunt aren't a defensible choice for the SBS.

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ako avatar image
ako answered ·

The Smart Shunt takes precedence over Smart Sense so Voltage will come from Smart Shunt and with no Temperature Sensor attached to it then the Temperature will come from the Smart Sense . The Smart Sense doesnt take its temperature via conduction through the battery case so that is of no benefit .

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cranky-yoda answered ·

I agree. I have four LiFePO4 batteries so the Smart Sense, makes not sense, Lol. I still have it in the battery compartment which is ventilated with outside air so I can I look at the app and I know what's the "outside" temperature "near" the batteries, but it is no longer on the VE Smart networking.

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