question

lawrence-craig avatar image
lawrence-craig asked

Float voltage different from setting

Hi there.

I have 3 x SmartSolar MPPTs connected to a bank of Lead Acid batteries with a SmartShunt, Multiplus and a Pi running Venus OS. The Multiplus is off and the MPPTs are using VE Smart Network to sync.

Even though the float setting on all MPPTs is 13.6V, the float voltage on the battery bank is being held at 13.2V. This is even if I take all loads off of the batteries. Can anyone explain why there is this difference?

Many thanks.

MPPT ControllersVenus OSSmartShuntVE.Smart Networkfloat
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6 Answers
seb71 avatar image
seb71 answered ·

smart networking is on

Do not use VE.Smart Networking when you have a GX device.


Set all the MPPTs the same (same battery charging settings).

Set the SmartSuhunt as the Battery Monitor in GX.

Enable DVCC in GX.

Set the temperature sensor in DVCC.

Enable SVS, SCS and STS in DVCC.


See how it goes.

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kevgermany avatar image
kevgermany answered ·

Probably automatic temperature compensation. Voltages are lowered for AGM batteries when temperature rises. If this isn't done, battery life is much shorter.


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Peter Buijs - NL avatar image Peter Buijs - NL commented ·
For a 12V bank the battery spec state about 3 till 5 mV/cel temperature compensation.

This is 18mV - 30mV /degree Celcius for the bank. When the compensation lowers the voltage 400 mV this would be how many degrees Celcius?


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kevgermany avatar image kevgermany ♦♦ Peter Buijs - NL commented ·
Is this 6*2V batteries in series?

You don't say what the actual charger setting is.

Base temp is 25C. So at 400mV reduction, 400/30=13.3C, so this equates to 38.3C.


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Peter Buijs - NL avatar image Peter Buijs - NL kevgermany ♦♦ commented ·

With 3mV/cell it is even 400/18 + base temp that is 48.22 C not a healthy environment for a battery bank that is fully loaded and in float. With no no loads connected!

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lawrence-craig avatar image
lawrence-craig answered ·

I understand this might look like temp correction. But I am currently in Greece where the current batt temp is 25C and the evening temp is 25C. Temp correction is -16mv/C. Therefore wouldn't expect as much as a 0.4V difference unless I am understanding this wrongly.

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kevgermany avatar image kevgermany ♦♦ commented ·

Is DVCC on? What are the battery settings?

If DVCC is off, what are the battery/charging settings in the multi and MPPTs?

Screen shots are most helpful.

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lawrence-craig avatar image lawrence-craig kevgermany ♦♦ commented ·

DVCC is off but smart networking is on. Multi is also off. Attached screenshots.

screenshot-2022-07-13-at-175555.png

screenshot-2022-07-13-at-175720.png

screenshot-2022-07-13-at-175437.png

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kevgermany avatar image
kevgermany answered ·

Thanks. Multi can only control the MPPTs if DVCC is on.

MPPT is in float, which suggests your float voltage setting in the MPPT is low er than the multi. You should see it a cog icon top right on the MPPT screens, what are the battery settings there?

Another possible problem is that the panel voltage isn't that high. For charging to start it must be 5V higher than actual battery voltage and must remain 1V higher than the battery to continue charging. As it's generating current, it's probably ok, but you need to check tomorrow.

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lawrence-craig avatar image lawrence-craig commented ·

Mutiplus is off as I am offshore, I only use Multiplis to charge onshore or to use inverter. So will that still be impacting the MPPTs? MPPT settings are the ones I just sent above (abs 14.4, float 13.8). I sent the multiplus screen to show the Batt temp.

Panel voltage might be low in this instance, but looking at VRM above, the float is strangely still less than 0.4V below set point and is maintained there, that's what I don't understand.

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kevgermany avatar image
kevgermany answered ·

DVCC is in the GX device, not the multi.

Unless you have smart batteries (your lead acid are not smart), settings in the MPPTs control float, NOT DVCC or the multi.

At setup the MPPTs should have been configured individually whether or not DVCC is enabled.

DVCC will control charge currents across the system.

What is the temperature source set to? MPPTs have internal temp sensors and can give higher readings than you'd see elsewhere.

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lawrence-craig avatar image lawrence-craig commented ·

Yes, the MPPTs have been configured individually and the same. Temperature source is set to the Multiplus Temp probe which is showing in the previous screenshot.

As I understand it, with Temp Compensation being -16.2mV/C, for the voltage difference to be 0.2V from Set Point (13.6 float vs 13.8 set point), the MPPT internal temp sensor would need to be 12C different (200mv/16.2=12C). That seems a lot considering I am on a boat in Greece right now where the temperature is pretty consistent.

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lawrence-craig avatar image
lawrence-craig answered ·

I get that you can't use Smart Network and DVCC together. But why not use Smart Network?

I've turned on DVCC and it fixed the issue interestingly is fixed so maybe an issue with smart networking.

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seb71 avatar image seb71 commented ·

VE.Smart Networking should not be used at all when the system is controlled by a GX device.

VE.Smart Networking has some of the capabilities of a system with a GX device (some similar capabilities), without having to buy a GX device.

It's at no cost (if you have the proper devices), but far less capable than a system controlled by a GX. For small systems, a GX device might not make much sense price-wise.

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