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ncr1 asked

MPPT showing 0W

I hope somebody can advise? I have a 75/15 smart solar mppt hooked up to a 150w solar panel and 105ah battery on my campervan. The battery is 5 years old and been used quite a bit. It was tested and showed 26% health, but then the person also said the solar panel was faulty and quoted me to replace it. Would a poor condition battery cause this? I was going to replace it with a 120ah AGM, but before I invest I would appreciate any advice.

I presume from the readout below the solar panel is working fine (sunny today). I notice the battery state is off, but it does go on intermittently. Could the mppt be faulty? The blue light flashes every 4-5 seconds and every 15 or so times (I didn't count) all three lights flash quickly 8 times. The history shows little activity.

Please treat me gently. I'm new to this so simple terms would help. Thank you.screenshot-20230226-095200.jpgscreenshot-20230226-100541.jpg

mppt state
screenshot-20230226-100541.jpg (285.3 KiB)
screenshot-20230226-095200.jpg (349.5 KiB)
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kevgermany avatar image kevgermany ♦♦ commented ·
Suggest you also click on the why is my charger off at the bottom of the screen. This time it will tell you panel voltage too low, but in future...
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ncr1 answered ·

Sorry, just to add that I have checked the fuse in the controller and the 15a inline fuse and both are fine. I can't see any obvious wiring issues. I'll check again. The battery is less than a meter from the controller and the solar panel is about a meter from the controller.

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nickdb answered ·

PV has to get 6V above the charge voltage, in the example it isn’t even 2V above so it won’t be able to charge anything.

Your peak PV voltages are also very low, so I suggest you check your panels, cabling etc.

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ncr1 avatar image ncr1 commented ·

Thank you. What are the expected peak values from a 150w panel?

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nickdb avatar image nickdb ♦♦ ncr1 commented ·
No idea. What are your panel specs? Looks like it’s broken or you need another in series.
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ncr1 avatar image ncr1 commented ·

Unfortunately it's bonded to my camper roof. I'll do some testing. Thank you for your help.

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kevgermany avatar image kevgermany ♦♦ ncr1 commented ·
Looking at the yield and PV voltages in your screen shots, most likely the panel, as @nickdb said. Worth checking the cabling for breaks as well.
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ncr1 answered ·

Thank you. Much appreciated.

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jetlag avatar image
jetlag answered ·

Disconnect the MPPT charger and measure the OpenCircuit voltage of the panel with a multimeter.

If possible, then you could also measure the short current of the panel, sunshine on the panel would be good for this second measurement.

With this two values, or at least with the open circuit voltage we know if the panel seem ok.

Because for know it looks like the PV power is too low to get the battery charged, that's why the battery might be so low in health...

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ncr1 answered ·

Thank you all. I did measure the open circuit voltage of the panel yesterday in sun. It was 21v. Does that help?

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jetlag avatar image jetlag commented ·

Yes this is helpful, - 21V would be enough for your system, but are you also able to measure the short current?

Best case would be to measure the short current directly at the mppt charger so you could include all the PV module cabeling and a possible problems there could be excluded.

Check that there is no shade or dirt in the PV module and measure as good as possible in bright sunlight. If you have those two values, you can completely exclude the PV module and the cabeling.

Then the problem is located elsewhere...

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ncr1 avatar image ncr1 commented ·

Thank you @Jetlag. How do I measure the short current at the controller? Thank you.

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ncr1 answered ·

So, basically the same as measuring the voltage, just setting the multimeter to amps. I'll do that later. There is a bit of sun today.

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nickdb avatar image nickdb ♦♦ commented ·
Measuring the current/voltage is mostly academic if you don't have the panel specs.

How would you know what it is supposed to be?

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jetlag avatar image
jetlag answered ·

Yes, your multimeter should be able to measure the current. So please check if you maybe have to swap the connection on your multimeter and select the highest current measurement range (often 10A) the multimeter ofers you.

Then just check there is some sunlight on the PV module and measure the current.

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ncr1 answered ·

I managed to get hold of the company who supplied the solar panel, through the camper conversion company. Open circuit should be 30v, I got 21 on a cloudy day. Short circuit current is 6amps, but they said they expect this in June time in the UK. Today through the controller with sun on the panel I got 14.06v and short circuit of 3.8 amps. The company think maybe the panel is not functioning.

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klim8skeptic avatar image klim8skeptic ♦ commented ·

@NCR1 Open circuit should be 30v, I got 21 on a cloudy day

30Voc seems high, 21Voc would be normal for a 32 cell panel. Count your cells....

Today through the controller with sun on the panel I got 14.06v and short circuit of 3.8 amps.

If you short your panels, the voltage will be 0.00. If you measured Isc as 3.8a that would seem reasonable.

If 3.8a Isc is accurate at the panels, repeat the test at the mppt. Disconnect the PV wires from the mppt and do the Isc test on the PV wires. This will rule out any fault in the PV cables between the panel and mppt.

Count your cells, and dont fall off your roof.

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ncr1 avatar image ncr1 klim8skeptic ♦ commented ·

Thank you @klim8skeptic. I have 44 panels on the solar panel. I measured the 3.8a at the controller on the screw terminals for the panel. Ill do the pv wire test tomorrow when I have more sunlight. I think I did isc. Amp output at the mppt controller.

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ncr1 avatar image ncr1 ncr1 commented ·
44 cells sorry
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ncr1 answered ·

The reason is due to the battery not seemingly charging, but it has very much had it based on the voltages measured (below) screenshot-20230301-113652.jpg


screenshot-20230301-113652.jpg (354.3 KiB)
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jetlag answered ·

Hmm, - there is still something weird.

Although the 21V and 3,8A should be fine, the open circuit voltage is normally reached at only little daylight. The current is strongly dependant on the sunlight, the voltage is not. It could be the case, that the voltage of the PV panel drops rapidly when current is drawn. This would match with the results the mppt charger is showing, that the PV voltage is not really high enough as soon the charger tries to pull current out of it.

A weak battery should still reach the absorption voltage of about 14,xxV. It can only store less energy, but still reaches the voltage. So the 12,8V max an the battery shows us, that the battery is not charged.


So in the end thats no rocket science, either the mppt charger is defective or the PV panel is.

With that data I would rather guess the PV panel is causing the problem.

Can you maybe try to connect some other panel? Just to cross check the issue?

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ncr1 answered ·

Thank you @Jetlag. I will see if I can use another panel and hook it up. Or, better for me, try another controller. I have a separate mppt controller (not victron, but Epever), on a garden room set-up, but I have bolted the panel down, so harder to remove.

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christern avatar image christern commented ·

but I have bolted the panel down, so harder to remove.

Well, you don’t have to remove the panel, just connect another panel to the controller.

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