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mpowell avatar image
mpowell asked

Solar MPPT 100/50 Keeps turning on and off

I have an MPPT 100/50 and it cycles on and off every few minutes. Sometimes it will charge for a few hours, other times it will run for 30 seconds, then shut off for 30-60 seconds. You can hear it clicking on, and almost a spring actuated noise when it cuts out.

I have 540AH of lithium and it is feeding a fridge and basic outlets. The appliances do NOT cycle on and off. The solar charger will cycle, feeding the batteries, then shut off. This happens at different battery levels, there does not seem to be a correlation there.

I have 800W of panels. It seems to shut off whenever it gets about 525W from the solar. It does have the bluetooth control option.

Is there a setting that limits max solar input power? Is something tripping the controller off?

I have searched the troubleshooting guide and this forum and have not seen a similar problem.

Thank you!!


MPPT Controllers
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4 Answers
ramack avatar image
ramack answered ·

What's your battery voltage and the configure charge current limits?

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mpowell avatar image
mpowell answered ·

I do have a victron shunt as well. Current battery voltage showing on the shunt is 13.2V.

The charger just showed 625W of charge. It clicked off showing a charge voltage of 13.9, spiked to 20V for less than one second when it cut charge voltage, then dropped to zero.

Charge current limits: Max charge current 50A, Absorption voltage 14.6, float voltage 13.7

Absorption duration was adjusted to 22H just to make sure there was no false limits on charging.


Current battery charge level as shown on the shunt bluetooth interface is 71%

Thank you for the quick answers! In the wilderness and need some charging...

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ramack avatar image ramack commented ·

ok, you are at the limit of the 50A charge current, but yea that should not cause trouble...

When you are using lithium batteries, I guess you have a BMS installed. What does that say? is is possible that it disconnects the battery?

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Kevin Windrem answered ·

I experienced a similar cut-out and click but tracked it down to an automatic reset circuit breaker in the connection to the PV panel. The breaker was underrated for the current provided by the panel (recently upgraded). The cycle rate depended on the amount of solar energy.

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mpowell answered ·

I bet you are right... It seems to cut out when PV spikes above 25 or 30A's. It seems to not be setup for the amount of PV it is connected to. I'll see if I can locate that breaker.

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seb71 avatar image seb71 commented ·

If that's the cause, don't replace it with a new breaker.


Replace it with fuse holders and fuses. Use a fuse on each PV wire (+ and -). Fuse type: gPV. Fuse rating: depends on your PV array.


If you have multiple strings in parallel (and that 25- 30A suggest you have), also use fuses on each string + and - (same gPV type). Especially if you have more than 2 strings in parallel.


You also need a disconnector switch for the PV array.


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