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wsconner avatar image
wsconner asked

75/15 mppt not controlling voltage?

I just installed the BT version of this controller with a 110watt panel. I updated the firmware. I'm charging a three battery bank of Northstar 31AGMs and set the bulk charge voltage to 14.7v and the float to 13.6v. The controller seemed to be workingas I was getting 14.5V and ~2amps (cloudy), but when it went from bulk (solid green) to absorption (solid orange), the battery were showing 15V+s (?). I would have thought the controller would have maintained voltage at 13.6v?

I took readings directly from the battery and the software app, and both had the battery voltage at 15v+. Any ideas are appreciated. thx.

MPPT Controllers
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klim8skeptic avatar image klim8skeptic ♦ commented ·

Temperature compensation?

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Jack Peters avatar image Jack Peters commented ·

Check the battery voltage setting is 12V and not 24V.

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Stefanie (Victron Energy Staff) avatar image
Stefanie (Victron Energy Staff) answered ·

Hi @wsconner,

the MPPT controller has a temperature sensor built in. As far as I remember temperature compensation is set on by default at -16.2mV/°C. As soon as ambient temperature inside the housing of the MPPT drops below 25°C, temperature compensation is in effect. That might explain your higher voltage.

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wsconner avatar image wsconner commented ·

ok, thanks very much. so the 16mV value in the compensation settings is the max bulk charge voltage that accounts for temp differences? If so, if I lower that value to my batteries recommend charge voltage (14.7) I'd effectively negate the purpose of the setting?

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Stefanie (Victron Energy Staff) avatar image Stefanie (Victron Energy Staff) ♦♦ wsconner commented ·

Exactly. When you set temperature compensation offset to 0mV/°C, there is no temp compensation and the feature is disabled.

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wsconner avatar image wsconner Stefanie (Victron Energy Staff) ♦♦ commented ·

Ok, makes sense now. appreciate the help. thanks.

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