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seltsam avatar image
seltsam asked

Low voltage readings on MPPT 75/15

I was wondering why my battery was empty and checked the setup again. Turns out that the charger doesn't seem to show and handle the wattage that is actally put out by the panels:


Charger display: 16v 1.8A

Multimeter readings: 30v 3.4A (measured on the disconnected panel cables)


How is this possible? (The battery is not full, and also pluging in a laptop or something doesn't increase the reading.)


Could this have to do with a firmware update lately? If yes, how can I roll back the firmware?


Thank you

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seltsam avatar image seltsam commented ·

Here you find pictures from my meassurements vs the reading in the app. Should I refund the Charger?


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JohnC avatar image JohnC ♦ seltsam commented ·

What you appear to be doing there is measuring the open circuit V with no current flow (Voc), then the current in short circuit conditions (Isc). Your panel should have it's rated specs for those on it's label.

Meaningless unless under production conditions, which are neither of those. They become Vmp and Imp, and multiplied together become W.

You could send your mppt back if you want, but you may well have a sick panel. I'd be looking thereabouts first.

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seltsam avatar image seltsam JohnC ♦ commented ·

Hi, Thank you! How can I measure the panels to get the actual output to validate the panels are OK?

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klim8skeptic avatar image klim8skeptic ♦ seltsam commented ·

Given your previous post https://community.victronenergy.com/questions/19796/smartsolar-7515-just-died.html I suspect you have a couple of bad solar panels.

Please post a photo of your solar panels, and make/model#.

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JohnC avatar image JohnC ♦ seltsam commented ·

Perhaps try first running them through the mppt individually. Mppt's are marvellous things, they can apply a V to a panel where the max W can be achieved. Like in your pic above, 16.72V showing, and would be typical of a single '12V' panel. So I know from that you don't have a series string there, or if you do, one of the panels is contributing nothing.

But don't be impatient. It seems the Victrons will rescan for a better mpp every 10 minutes, which is fine for most applications as those rescans will suspend production for a second?? or 2. So don't go shadowing the panel(s) while you're testing, and even intermittent cloud could interfere.

Troubleshooting being the beast it is, hard to define. You may have a dicky panel with cracked cells, connectors, wiring issues, or even diode in the j-box. Just gotta hunt it down.


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Robert avatar image
Robert answered ·

Hello,

what size panels? how many? parallel? series? Do you have a screenshot of the 16V 1.8A reading? How are you getting 3.4A on disconnected panel cables? What battery setup are you using? Plugging in a laptop (where?) doesn't increase what reading?

Robert

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seltsam avatar image seltsam commented ·

Hi Robert,

please keep in Mind that the Panel-Setup worked as expected previously.

Panel Size shouldn't be an issue, since I didn't change anything on my setup.


> What size panels?
100W

> how many?

2

> parallel? / series?

Readings are off for both, tried it.

> Do you have a screenshot of the 16V 1.8A reading?

No.

> How are you getting 3.4A on disconnected panel cables?

1. Remove the panel-cables from the PV-connections on the charger

2. Put your volt-meter to the cables, plus and minux

3. Read what the volt-meter shows

> What battery setup are you using?

90Ah lead

> Plugging in a laptop (where?) doesn't increase what reading?

Connect my laptop-charger to the controller output to have a source that pulls power (to make sure its not the batteries fault).


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