question

emmakrieg avatar image
emmakrieg asked

Solar hitting abs. When battery not full. MPPT registering wrong voltage

Hello,


Our system is reporting inaccuracies in battery voltage and as a result solar not charging battery full. For example, today our battery was at 13.44V (consistent with BMV and BMS) but MPPT showed 13.8V. MPPT then ended up going into absorption well before battery was full. I noticed that the difference was greater when a higher wattage was coming in from solar. Eg, 300w There was a difference of 0.2-0.3 volts but when only 100w coming in they were showing similar volts. MPPT history also shows we hit 14.73V which is really inaccurate.

We have checked the connections and had to make a reconnection but issues still happening. We have not synchronised SOC yet as hasn’t hit 14.2V.

Any help appreciated! Thank you

MPPT Controllers
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2 Answers
klim8skeptic avatar image
klim8skeptic answered ·

You could set up a smart network between the b m v and the mppt, to enable temp and voltage compensation.

Are your batteries terminals really that hot?

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emmakrieg avatar image emmakrieg commented ·

Thanks this has helped for now but I guess we still need to work out why it’s reporting that voltage. Nothing felt hot - what temp should the battery be?

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klim8skeptic avatar image klim8skeptic ♦ emmakrieg commented ·

Your mppt is recording higher than actual battery voltages due to voltage loss on the cables/connections between the mppt and battery.

Your battery/terminals should only be a few degrees above ambient, unless you really are charging/discharging at high C rates.

Clean/tighten your battery terminals.

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wkirby avatar image
wkirby answered ·

It seems that you have a bad connection somewhere, probably close to the battery terminal given that the temperature sensor is reading very high.

The more power you drive through a circuit, the higher the Voltage drop will be, that's physics. However, 1-3V is too high. Again, this suggests a bad connection somewhere. You are losing 75W in that bad connection. If that is inddeed somewhere near the temperature sensor then that could explain that very high temperature there.

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emmakrieg avatar image emmakrieg commented ·

Thanks for the reply. Sorry that was a typo, it is 0.2-0.3V out. How high should the temp be? I felt around but nothing felt very hot.

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