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don-binns asked

Controller oscillating power from 14 to 32 volts continuously

I’ve just installed a BMV 712 monitor and a Bluesolar 100/30 controller and I am seeing some very odd behaviour. First this is a dark, gloomy, rainy, windy day here in the Pacific Northwest. I have two hard panels wired in series and two semi flex panels wired in series, both sets wired in parallel to the charge controller. Each panel is 100 watts for a 400 watt total.

With everything connected the power and current from the charge controller oscillates from a low of 14 volts then rises to 32 volts before immediately dropping back to 14 volts. This pattern repeats every 30 seconds or so. The 14 and 32 volt thresholds might change by a volt or two on every cycle but the pattern is consistent. As the volts go up the amps go down. We’re talking 0 to .8 of an amp.

FYI the panels are one year old and worked just fine as configured with my old Epever controller. The wiring has not changed

has anyone seen or is familiar with this pattern? Any suggestions?

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don-binns avatar image don-binns commented ·

Correction. It is the power from the panels that oscillates. Prior to connecting the controller the panels would register 40 volts for the hard panels and 37 volts for the flex panels. I checked all the wiring and the panels yesterday prior to wiring in the controller last night.

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Justin Cook answered ·

@Don Binns, how are you viewing this oscillation? You say the power and current coming "from" the controller... which, if you're seeing 32v coming out of the controller, there's a very big problem indeed and you should immediately disconnect it from your battery bank. The controller should be putting out around 13-14v to your batteries (assuming 12v nominal system). If you truly are seeing these voltages from your charge controller (presumably seeing these voltages in the BMV), then you should immediately disconnect the controller and examine all your wiring methods, as there's a very good chance that something is connected incorrectly.

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don-binns avatar image don-binns commented ·

I have misspoke. It’s the power from the panels that is oscillating the power to the batteries remains fairly steady around 12.35.

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Justin Cook avatar image Justin Cook ♦♦ don-binns commented ·

Ohhh okay *whew* that's a lot better of a condition then. Now, to some extent this is to be expected, as the MPPT will apply varying loads to the PV array trying to get the most power out of it... so you'll see voltage go down, amps go up, and vice versa... but it should find a happy medium and settle down for a while.

If it's not doing that, then that's a good indication that you have a bad connection somewhere on the PV side of the controller... what you describe sounds like a bad connection or loose crimp that's heating up as the controller tries to put a load on it, increasing the resistance of the line, which causes the voltage to drop until the controller backs off.

I would go over all your wiring on the PV side and make sure that there are no loose MC4 connectors, no loose crimps, make sure the wire going into the MPPT on the PV side is making a good connection and the terminals are tightened appropriately, etc.


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spirou answered ·

Have nearly the same setup and had the same apparent issue a few weeks ago. The conclusion was that there simply wasn't enough sunlight to be much use. The PV input on MPPT could go through the entire day just fluctuating between 40 and 12V as it attempted to load the panels but they had nothing to give.


I suspect, without any proof other than my experience with 75/15 and single smaller panel, that bigger units (100/30 etc.) have a different algorithm and are programmed to put more load on the panels which don't respond as requested under low winter light, ultimatelly giving you equal or possibly less output that a smaller setup. Which in any case will be close to 0. But like I said, I have no proof and I can't compare directly. Hopefully someone on staff can either confirm or deny.

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don-binns avatar image don-binns commented ·

Thanks Spirou.

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don-binns answered ·

Here’s an update. I tested the system early this morning with just the flex panels wired in. Same problem; oscillating power curve. Granted it was still raining but seemed bright enough to me, in my experience for the panels to produce power. So I swapped out the flex panels and put the hard panels in the loop. After a couple of deep dives to 14 volts the curve settled into a range of 28 to 37 volts. Considering that is only two panels (200 watts) and it was still cloudy I’ll take it as a win. While changing the panel wiring the day got a fair bit brighter so I’m not sure if there is a panel problem or if there was insufficient light to get things running. I’ll try again on a sunny day.

my thanks for all of the advice. It was much appreciated.

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