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svzootoo avatar image
svzootoo asked

MPPT 75/15 low output

I've been using a BlueSolar 75/15 for 4 years. The solar input is 2*110W panels in series. On a sunny day they generate 40-44V, which should be enough to max the controller output. The controller charges 2 victron agm 110Ah 12V batteries. The batteries are about 1 year old now. I typically run a fridge 24hours (~ 0.5 - 1A). For the last year, if I check battery voltage in the middle of a sunny day, I see ~13.5V

Rather suddenly, this week I see 12.6-12.8V in middle of sunny day. The panels are still producing 43V. When disconnected from the batteries, output is 14.2V. But it's not getting the batteries up to 13V even after several hours of charging. When I tried connecting shore power, I see 13.6V on the batteries after a short charge.

Is there something wrong with the MPPT? I there something I can do to get the charging back to what it was for the last few years?

MPPT Controllers
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4 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Did you check the fuses?

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svzootoo avatar image
svzootoo answered ·

Yes, the fuses are fine

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Matthias Lange - DE avatar image Matthias Lange - DE ♦ commented ·

Also the fuse directly at the MPPT(red)?

Your BlueSolar don't have build-in Bluetooth, so you need a VE.direct BT dongel. The VE.direct port should be below the fuse(green).

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mppt-fuse-vedirect.png (212.4 KiB)
Rob Fijn avatar image
Rob Fijn answered ·

Hello, it sounds like you need to check your Solar panels and cabling. You say that when you disconnect the load, the battery voltage goes up. This is what your MPPT is doing, that is good. But it seems that there is not enough energy coming from your solar panels... starting from the wire terminals PV on the MPPT to the panels..

If you would be able to connect with VictronConnect to the MPPT you can see this immediately.

Let us know what you find.

Regards, Rob

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svzootoo avatar image
svzootoo answered ·

Hello Rob, thanks for the comments. I downloaded Victron Connect but it doesn't pick up the MPPT device. It's a 4+ year old unit and I don't have a dongle (in fact, I don't see where to connect one either). I would be surprised if the solar input is low since the cables are showing 43V (15% over the rated voltage for the series) at the point the connect to the mppt.

Today I rechecked everything - with no charging and no load the batteries were at 12.75V. With no charging + fridge they showed 12.6V. I disconnected all cables from the mppt, then reattached them to mppt and battery. I was seeing 12.9 and increasing on the terminals with no load on batteries.. Restarted the fridge and was seeing 12.8V and increasing. That ran for 1-2hr before darkness. MPPT showed bulk the whole time. With no charging and fridge on, batteries showed 12.7V. After 2 hours with fridge they showed 12.45V.

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