question

karlosclaco avatar image
karlosclaco asked

Mppt and Shunt

Hello there,

I'm not sure if this is an issue or just me getting used to using this system full time.

I have the 100/50 blue MPPT and the 500a smartshunt. The smartshunt is showing my batteries are down at 32%, which with the weather could be accurate, however the MPPT history is showing that it entered absorption mode at some point during the day. Does this mean the batteries are actually much higher in charge than the shunt is telling me, or can the MPPT enter absorption for other reasons?

Any advice would be much appreciated.

MPPT SmartSolarSmartShunt
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2 Answers
Mike Dorsett avatar image
Mike Dorsett answered ·

If the MPPT enters absorption during the day, this just means that the battery voltage measured by the MPPT got to the setpoint. This should mean the battery is 80% charged, but this could be affected by volt drop in the MPPT cables. What does the voltage trend of the shunt give for the voltage during the day? This could just be a synchronisation issue - if the shunt has not reached the sync voltage for several days or more.

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karlosclaco avatar image karlosclaco commented ·
The voltage from the panels tends to stay steady throughput the day.

Is there a way to set the sync voltage or is that related to the absorption voltage?

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pwfarnell avatar image pwfarnell karlosclaco commented ·
The absorption voltage is set on the MPPT and the sync voltage on the Smartshunt. The sync voltage is best set a little bit below the absorption voltage, but you also need to set the sync current, which if I remember correctly is set as a %age of the battery capacity. It might be that you are getting to absorption but not a low enough current. You could let us know your voltage settings on the MPPT and sync settings on the shunt and what voltage you normally get to.

It could also be the case that you are not putting enough energy back in, days are becoming shorter if you are in the northern hemisphere.

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karlosclaco avatar image karlosclaco pwfarnell commented ·

These are the settings. Im also only using the van during the evenings so during the day its mostly just charging, van is parked in full sun light all day.screenshot-20220908-063508.jpg

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karlosclaco avatar image karlosclaco karlosclaco commented ·

Shunt settings

screenshot-20220908-063424.jpg

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karlosclaco avatar image karlosclaco karlosclaco commented ·

Solar history

smartselect-20220907-161249.jpg

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pwfarnell avatar image pwfarnell karlosclaco commented ·

@Karlosclaco the information you have provided goes some way to answering the problem, your absorption voltage is 14.2V on the MPPT and you reach that. However, the Smartshunt "Charged voltage" is 14.6V so the Smartshunt will never reach this. Set the "Charged Voltage" to 14.0Vand if that does not work then try 13.9V. This will mean that when you do get full the shunt will reset to 100% and what you have been seeing is some build up of errors.

The MPPT believes that the batteries are full as it is doing some absorption each day, but make sure you have thick enough cables so that the batteries see the same voltage as the MPPT.

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karlosclaco avatar image karlosclaco pwfarnell commented ·
Thank you very much for confirming that! I was convinced the batteries would be higher in charge based on the MPPT hitting absorption, suspected that the shunt wasn't displaying correctly. I will change the charged voltage and see how I get on with that, hopefully the shunt will reset once it hits that next time! Thanks again.
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karlosclaco avatar image karlosclaco pwfarnell commented ·

@pwfarnell Update from today. The batteries are currently reading 12.9v which I understand is low, as only the fridge and fan are running. However the solar has once again hit absorption. Although right now it's on bulk with no charge coming in. Does this mean anything?screenshot-20220908-124213.jpg

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karlosclaco avatar image karlosclaco karlosclaco commented ·

@pwfarnell

smartselect-20220908-124656.jpg

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klim8skeptic avatar image klim8skeptic ♦ karlosclaco commented ·
You dont have enough solar yield to charge your 300ah battery from 10.5v to 14,2v.


Something really bad is going on.
Post the "status" tab for the smart shunt.

Post some photos of your system, battery bank, smart shunt, breakers/fuses, everything.

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karlosclaco avatar image karlosclaco klim8skeptic ♦ commented ·
@klim8skeptic I will post all those pictures below
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karlosclaco avatar image karlosclaco karlosclaco commented ·

Let me know if you need any more

screenshot-20220908-152330.jpg20220908-152535.jpg20220908-152450.jpg20220908-152516.jpg20220908-152444.jpg

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klim8skeptic avatar image klim8skeptic ♦ karlosclaco commented ·
3 things look questionable between the mppt and battery.


Those 3 circuit breakers are known to trip well below the labeled limit. Replace the mppt one with a better quality unit, or fuse.

The ferrules on the battery output of the mppt look solid and way to small diameter to make proper contact.

There is a join in the cable between the mppt and battery breaker, check the join.

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pwfarnell avatar image pwfarnell karlosclaco commented ·
@Karlosclaco Getting a bit out of my experience here with lithium, are the batteries full and somehow shut down the MPPT. Hopefully someone else will be able to help further.
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karlosclaco avatar image karlosclaco pwfarnell commented ·

Thanks anyway @pwfarnell. Looking at the voltage they can't be full, but then I can't understand why it's going into absorption

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pwfarnell avatar image pwfarnell karlosclaco commented ·
As above, high resistance contact between the MPPT and the batteries, MPPT measires 14.2V but voltage drop at the poor connection so batteries see only 12.8V. I will back up previous comment, those breakers are very poor and known for problems. Get a digital multimeter and measure all voltages everywhere, screw terminals on the MPPT, ferrules on the MPPT, either side of the breakers etc until you find the voltage loss.

I believe if you read the MPPT installation instructions it tells you to put the wires direct into the screw terminals and use fine stranded wire for good contact. Make sure that they are properly torqued.

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karlosclaco avatar image karlosclaco pwfarnell commented ·
Thanks @pwfarnell & @klim8skeptic, I will have a look at addressing all of those issues and see if I get an improvement!
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karlosclaco avatar image karlosclaco pwfarnell commented ·

@pwfarnell I don't have the correct cable size yet to swap it out but I've checked the voltage on every connection, terminal and ferrule and the voltage is identical down to 2 decimal points. This was only on the positive side though, does the negative run need checking too.

I did manage to catch a voltage difference earlier though which I will post below.

@klim8skeptic

screenshot-20220909-125554.jpg

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pwfarnell avatar image pwfarnell karlosclaco commented ·
Yes you have to check the negative side as well for voltage drops.
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klim8skeptic avatar image klim8skeptic ♦ karlosclaco commented ·

Have a look at Wiring Unlimited for some inspiration.

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pwfarnell avatar image
pwfarnell answered ·

Where is the negative cable from the MPPT connected to the shunt / batteries, we see lots of people reporting that their SOC is falling because they have connected the MPPT negative direct to the batteries so the shunt never sees the charging current so does not count it. The negative from the MPPT must be connected to the "load" or "system" side of the shunt, not sure what it is called on the Smartshunt, the opposite side to the batteries.

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karlosclaco avatar image karlosclaco commented ·
The negative is connected to a busbar with every other negative, then goes to the load side of the shunt. I can see on the shunt when it's receiving charge by the wattage and Amps reading positively.
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Related Resources

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SmartShunt Product Page

SmartShunt Installation Manual

SmartShunt Quick Installation Guide

SmartShunt Datasheet