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khave avatar image
khave asked

Why is my MPPT 150/35 cycling and not charging?

New 2023 Airstream trailer purchased in January with a Victron MPPT 150/35 and 300W solar + 200W added by dealer. I installed 4 12V BattleBorn LiFePO4 100Ah batteries in parallel, with a Victron smart shunt. Everything worked great for months, solar kept the batteries charged with electric fridge, fan and lights all running, no problem. About 6 weeks ago the solar controller started cycling, ramping up power to max then shutting off every 40 seconds or so. Right before it shut off I'd see PV current spikes of 500A or more on my VE Direct Smart, which of course is not possible given the PV short circuit rating of around 5A per panel. With this cycling, there is no battery charging and they'll run down as far as I'll let them.

I filed a claim with Victron, who connected me with an Airstream dealer in Ohio (I'm in California). They weren't helpful in troubleshooting, but eventually agreed that the controller was bad and sent me a new one. I connected it up, and it worked fine initially but started cycling again liked the original once the sun was fully out. I next tried upgrading the firmware from v1.59 to v1.61, and now the controller is unresponsive. The PV input voltage matches the battery voltage (currently 13.42V) and the charger stays off, with the bulk charge light flashing every few seconds, so the charger thinks there's insufficient solar power. When I disconnect the PV wires I get 20.9 volts open circuit, and I see the expected current when I connect a load, so the problem is not with the solar or solar wiring. For reference, the absorption voltage is set to 14.2V and battery charged voltage is 14.0V.

Somewhat disappointed that Victron pushes support off to (untrained) dealers, which wastes a lot of my and their time going in circles, whereas a knowledgeable tech could probably quickly get to the bottom of the problem. So I'm posting my problem here in the hopes that someone can shed some light on the issue. Thanks!

- Ken

MPPT Controllers
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Alexandra avatar image
Alexandra answered ·

@khave

Victron train all the dealers and sellers that are on their website. Plus there is a ton of self learning free resources from. That being said it is difficult to diagnose from a distance though.

However there is now with the second mppt not charging with the low voltage voltage from the panels is likely the issue there. The panels need to be 5v above battery which yours barely are. This would also explain the cycling as well. Put them in series not parrallel and see what happens there. (So a set up or install issue)

5A pv short circuit with 20voc suggests your panels are faulty. Since 20x5 = 100W and you say they are 200 or 300w? And you have 2....

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khave avatar image khave commented ·
Thank you Alexandra for the suggestion, I think you've got it figured out. I disconnected all 5 panels, and reconected 2 parallel pairs in series, and see roughly 44 volts. Now the controller is working normally, so I think you're right that the cycling was due to low PV voltage. So either some/all of my panels are bad or there's a bad connection between the panels and the controller. This makes sense because I see the PV voltage at the controller drop 6 or more volts even with just a few amps of PV current. Hopefully a bad connection the rooftop. Now I have to decide whether to tear into it myself, or tow the trailer 1 hr each way to the nearest dealer and wait for them to get to it as a warranty repair.

Because the controller came with my new Airstream, Victron referred me to an Airstream dealer who clearly had no Victron training much less any electrical troubleshooting experience. I looked and that dealer is not on their web site so I don't know why they referred me there.

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kevgermany answered ·

Reading this makes me wonder a little about how the extra solar capacity was added.

How many panels in total? Are they all the same model? What is the specified Voc (open circuit voltage) for each panel type.

It would help to see a screen shot of the MPPT readings from Victron connect.

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khave avatar image khave commented ·

img-1006.jpeg3 x 100W (unknown brand) panels came with the Airstream as part of a solar package, and we had the dealer add 2 x 100W Zamp panels. The Zamp specs say 25.6V open circuit and 21.9V operating. Screen shot here is all 5 panels in parallel on a cloudy day. The PV Voltage should be much closer to open circuit voltage at this low power level which makes me think that there's excess resistance in the wiring between the panels and the controller. This could cause the cycling once the PV voltage drops below 5V above battery voltage, e.g. when the sun comes out and more current is being generated.

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