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jeb asked

Smart Solar 75/15--Aberrant Readings

I recently replaced the Victron 75/10 charge controller in my travel trailer/caravan with an upgraded Victron 75/15 to try and eke out a few more amps during boondocking. Unfortunately, since the swap, I have been getting extremely odd readings from the Victron app and was hoping for help in diagnosing what I might have screwed up during the swap.

On the input side the app is reporting 0W and no current from the solar panel (which is 190W) but positive voltage of 31.55V. On the output side, it's showing the charge controller in float mode at 13.39V. The output side is not surprising. The batteries are fully charged because I keep the trailer plugged into 30A shore power. The input side, however, is odd. The previous charge controller showed positive watts, volts and amps even when I was plugged into shore power. I took a look at the history chart and it appears that the results I see below have been consistent since the replacement. Any specific help diagnosing the problem--if it is a problem--would be greatly appreciated. Thanks in advance.


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JohnC answered ·

Hi JEB. There's probably no issue. If your mppt is in Float mode, then it's likely targetting a lower V than your batts have already reached. And then winding W down to zero.

To test for that, turn off the other charger and put a load on the batts. Under maybe 13.2V you should see a W response from the mppt.

Depending on what charge profile you have set, you may see 'strange' behavior sometimes. The unit doesn't know that there's another charger happening, and may 'adapt' it's behavior somewhat from one day to the next.

A conclusion you might draw from this is that your shore charger is pushing harder than the mppt would prefer. Fair enough if that's what you want..

The History in the app should confirm what's been happening - time in float, etc.


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jeb avatar image jeb commented ·

Thanks, but it actually was a problem. Turns out it was a bad inline fuse on the solar panel side. I pulled the battery-side inline fuse and inspected it and it looked fine. I then pulled the solar panel inline fuse and it looked fine as well, but when I reinserted it into the holder it immediately blew. So, I pulled both fuses again and waited about 20 minutes. I then started with the battery side and it worked fine. Solar controller powered up normally. I then replaced the inline fuse with a new one on the solar panel side and it too went in normally. No popped fuse. When I checked the app, everything was back to normal. About 90W of power on a partly cloudy day and just under 3 amps delivered to the controller. The voltage was also down to a normal approx. 24V on the solar side.

Best I can tell, the solar side inline fuse was either not properly seated or had blown only part of the way, which allowed the charge controller to register aberrant voltage leaching through the fuse but the damage was enough to prevent sufficient current to pass to register amperage and therefore wattage. In any event, it appears fixed.

From this experience, it seems that battery state of charge (SOC) appears to have nothing to do with what the charge controller registers on the solar panel side. The panel side is just an input measuring what the panels are generating, not what is being passed to the batteries via the battery side. So, if there's sunlight, you ought to be reading wattage and positive amps regardless of the battery SOC if the panels are operating properly.

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JohnC avatar image JohnC ♦ jeb commented ·

Yeh ok. Your dicky fuse doesn't explain your issue away though.

Your 75/15 doesn't know about SOC, just V. If it were being controlled by SOC via another device like a GX box, it's status wouldn't show 'Float' (or 'Absorb'), but 'External Control' or 'ESS'. So it's chasing V parameters, and if they've already been met by your shore charger, then W will wind down to zero anyway.

Don't pay too much notice of panel V. Under full production Vmp will be tracked, and if the mppt is wound back Voc will be approached. In poor light both those will be reduced. Call panel V the 'camp follower' of the real action.


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