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berwick avatar image
berwick asked

MPPT charger voltages are higher than expected

I have 3 MPPT 75/15 solar controllers from 3 different panels on a sailboat. The absorption voltage is set for 14.82V and float to 13.5V. I also have the temp/voltage remote sensor running into the VE network. They are not always in absorption or bulk at the same time and understand this will be fixed in the next firmware update. There are times that my batteries measure and show on a battery monitor up to 15.1V. Why is this? Should it not be limited to 14.82V, worried about frying the batteries. Even if one of the controllers was still in bulk I don’t believe it would go this high?

Thanks, Richard

MPPT Controllers
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Alexandra avatar image Alexandra ♦ commented ·

@berwick are the batteries lithium or lead based? It may be that there is an equalization charge happening? Not sure if you enabled or disabled this feature? Is temperature compensated charging enabled?

The other thing could be voltage drop over battery cables from mppt to the batteries. Is the BMV shunt closer to the batteries or the chargers?

Not knowing much else about your setup, like how the batteries are connected together and where in the bank the sensor is, these are just points I would start checking.

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espen avatar image
espen answered ·

The absorption voltage you have set( 14.82V), is at 25 degrees Celsius. If you're using the default temp. compansation, 16mV/C, then 15.1V should meen that the MPPT is measuring around 7.5 degrees Celsius.

So first check your temp.comp. setting, and do a calculation with the correct temperature to see if the MPPT is working as it should, before looking for faults.

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berwick avatar image berwick commented ·

Espen, you are right on the money, as the temperature went up in the battery compartment the voltage kept going down til it was spot on, I never thought of that. Trojan batteries say 5MV per cell per C so I guess I will change the temp compensation to 30 mv/C vice 16.2 mv/C.

Also the firmware updated today and so now all of the chargers are linked together and are on the same charge level!!! My

thanks, Richard

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berwick avatar image
berwick answered ·

They are Lead acid, equalization is off and has to be selected manually. The temp/voltage sensor is located in the battery compartment and on the middle of 3 parallel batteries and it is shown that it is being read by the MPPT controllers. I am measuring battery voltage directly on the battery and even the MPPT controller is showing 15.1 volts even though it's programmed for 14.82 absorb, Doesn't make sense, shouldn't 14.82 be a hard wall high limit?

Richard

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klim8skeptic avatar image klim8skeptic ♦ commented ·

Temperature compensation?

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Alexandra avatar image Alexandra ♦ commented ·

@berwick And are all the batteries at the same voltage? Is it just the one charge controller and battery? I recently had to take one out of a bank because it was not charging correctly and charge it separately and load test it before returning it to the bank. How old are the batteries?

If age is not a factor and they are all balanced, then maybe take the temp/voltage sensor off and see if it affects anything.

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