Trevin Corkery avatar image
Trevin Corkery asked

MPPT charge controller acting weird, negative current, watts bouncing

I have a gif to show you what's happening but this just recently started happening after I turned on my inverter for a few mintutes and turned it back off, and repeated for a little bit.

But I am getting negative current when load on the charge controller is turned off, and notice how the watts just bounce around. (When I turn on the load it will stay at a stable +60w so its not my solar panels)

When this was taken the inverter was turned off completely and this also happens on the bluetooth app and my own custom application. (I thought my application was bugging up so I tested it out on VictronConnect and its doing the same thing)

**Edit** It just switched over to Float charging and now the watts are stable and everything is going smoothly so it had to do something with Absorption.

MPPT Controllers
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1 Answer
Justin Cook avatar image
Justin Cook answered ·

@Trevin Corkery, I've seen two different MPPTs doing this, and in both cases it was caused by a mixture of insufficient-gauge wiring, bad crimps, and knockoff brand components between the controller/battery and controller/PV array.

Short story: bad crimps or other loose connections will build up heat very quickly, which increases resistance, which makes the controller throttle itself so it doesn't overheat... when the current is throttled the heat and resistance dissipates, the controller starts flowing current again, and so on ad infinitum.

Check all your cables, your crimps, your lugs, and your physical connections to make sure none of them are good and tight, and make sure that all your fuses, holders, switches, breakers and etc. are brand-name (Blue Sea, Bussman, FTZ, etc.) It really does make a difference.

This is not to say that maybe you haven't already done all these things; it's certainly possible that the MPPT itself is misbehaving. In fully 90% of the cases that I deal with where an MPPT is reported as misbehaving, however, the actual fault is somewhere in the connecting components rather than the controller itself.

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Trevin Corkery avatar image Trevin Corkery commented ·

I haven't had a problem since it left Absorption. I actually drained it back down where the charger would start bulk charging and everything was fine (was charging around 98w).

This is the first time it's happened so I wouldn't think the wiring would be the problem since I've had the controller for a couple of months now and nothing really changed except I updated the firmware to v1.42. But as previously mentioned it hasn't happened before nor has it happened since earlier (I've re-entered Absorption and everything works).

TLDR, I am not sure what happened. It may have been a fluke.

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