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chris-kegel asked

Fluctuating under load

I have a 100/50. I have 4x 180 watt panels. I had them in parallel to minimize possible shading issues. They are on an RV. I wanted to see if now that I am in full sun for a while whether they would perform better in series. What I am finding is under heavy load the voltage jumps up, as it should but the amps won't "lock in". The watts wildly fluctuate from 10-300 watts. It will do this forever. I tested with the electric hot water. This never happened in parallel. Any ideas?

battery charging
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I have a 100/50. I have 4x 180 watt panels

In the old days, a 180 panel had a Voc of about 45v.

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chris-kegel avatar image
chris-kegel answered ·

img-20220625-130553415.jpg

Here is the culprit. While testing with the hot water heater I noticed the terminals on this starting to get warm. After a minute they were too hot to touch. I checked the connections and all was tight. Removed this and bolted the positive directly to the busbar and now the connection does not even get warm. This is an Amazon find and I believe it was rated at 300 amp continuous. Obviously not working as rated. Are the Blue Sea switches the best option?


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trevor-bird avatar image
trevor-bird answered ·

The voltage of these panels in series may exceed the 100volt maximum input to the MPPT controller causing it to shut down. Try wiring them in series parallel. Two strings in series paralleled together.

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chris-kegel avatar image
chris-kegel answered ·

It is not an over-volt issue. I removed 2 panels in the series and it still happens.

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Still, what is the Voc of one panel?


If now you put all panels in parallel, the charger still works as before?

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chris-kegel avatar image
chris-kegel answered ·

The open is about 25V. I have not returned them to parallel to test. Other than when I run my coffee maker or hot water heater, they seem to operate better in series.

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elvis avatar image
elvis answered ·

I understand you said its on an RV but by chance do you have a multiplus and "Grid feed-in" enabled? and if so, is it limited under the feed-in options?


I only ask because I experience something similar while limited "Feed-in" is enabled.

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chris-kegel avatar image
chris-kegel answered ·

I believe you are referring to setting in the inverter. I do have the controller wired into the inverter and a global charge setting that includes both grid and shore is limited to 70 amps. This is so I am not sending too many amps to the battery. However, I am not plugged in to shore at this time. I am planning on moving the mppt to the bus bar connection to see if that changes anything.

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chris-kegel answered ·

One test I did do was when the controller was in float I turned on some low watt devices to see what would happen. Turning on 12 volt sources did not seem to shut down the controller. The contoller compensated by increasing its output. These are much smaller loads than the 120V loads. So I need to remove the inverter from the equation, as the controller is wired into the inverter\switch\charger unit.

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