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Russ Smith avatar image
Russ Smith asked

Solar Controller PV Input drops when inverter is running

I have a Victron 150/45 MPPT charge controller and a Victron smart shunt that connect into negative and positive bus bars. The bus bars also connect to a 24v 100ah lifepo4 battery bank and a 2000w inverter. Everything worked fine until I expanded my solar array. When there is full sun and the array is charging at 44 amps and no load is running everything is fine. When the inverter is drawing a load then the Solar Controller will constantly cycle where the watts will drop to zero then will go back up and run for a bit and then go down to zero and then back up.

I can fix the issue by dropping the Max Charge Current of the Solar Controller down to 41 amps then it works fine. I checked all the lines with an AMP meter and nothing seems wrong. Does anyone know why the inverter is causing these issues with the solar charge controller?

MPPT SmartSolar
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JohnC avatar image
JohnC answered ·

Hi @Russ Smith

Not much to go on here, so looking for clues. "I expanded my solar array" is one.

Might your new array be tracking to a lower Vmp? This is consistent with a low load allowing Vpv to rise, then when called to deliver that V will drop closer to Vmp. It must remain higher than Vbat plus 1V, and if dropped out, plus 5V to restart.


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Russ Smith avatar image Russ Smith commented ·

I now have enough solar capacity to get near the 45 amp limit of the solar charge controller. When the inverter doesn't have a load running everything is fine. I can charge at 45 amps. However if I'm charging over 42 amps and then I put a load on the inverter the charge controller input wattage will keep dropping to 0w and then recover and do this over and over again. If I limit the controller to 42 amps then everything is fine.

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JohnC avatar image JohnC ♦ Russ Smith commented ·

@Russ Smith

Look to your Solar Panel Voltage (Vpv) while this is happening. If it's getting to within 1V of your Battery Voltage (Vbat) then the mppt will cease producing. Vpv will then rise, until it reaches >5V above Battery Voltage (Vbat) and it will then recommence production (and continue the cycle). I suspect your imposed Amp limit is keeping Vpv high enough for it to continue producing.

IF this is happening you'll need to rewire your panels to give a higher V, in the range up to the mppt's 150/ hard Voc limit.

It should make no difference whether the load is an inverter or a dc load. And you may experience similar at dawn or dusk when Vpv will usually be much lower anyway.


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Russ Smith avatar image Russ Smith JohnC ♦ commented ·
My panel voltage is over 80v and my battery is 24v. I think I might have a lead on what is happening. When the Solar Controller is running below the 45 amp limit for instance its running at 41 amps then I turn on the inverter it will go up to 43 amps. When I turn off my battery my DC to DC converter will still run because I suspect the inverter is back feeding from its capacitors. I suspect the inverter when running is back feeding and affecting the Solar Controller. I plan to add a 100amp diode inline on the positive connection to the inverter to see if it prevents back feeding and resolves the issue.
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