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dirkme911 avatar image
dirkme911 asked

MPPT voltage from battery to PV

Hi,

Please see picture below. screenshot-20231224-195136-vrm.jpg

I have 3 MPPTs, at the moment I have removed all the PV wires from the MPPTs, only the batteries (48V) are connected. The inverter is switched off, the batteries are on.

MPPT1 (CC1) which is a 150/100 Tr shows voltage flowing back towards PV from battery. I confirmed by using a tester to read the voltage on the PV terminals of the MPPT.

I would like to know if there is a reverse diode or something I can add to prevent voltage back to panels. That should be a cheaper option than having to replace the MPPT, as it works fine otherwise.

Also if the diode is DIN rail mountable even better :)



MPPT Controllers
screenshot-20231224-195136-vrm.jpg (195.3 KiB)
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kevgermany avatar image kevgermany ♦♦ commented ·
The CC1 MPPT is not showing battery voltage, there's a big difference. The batteries are charging slowly, but are showing over 99% charged at a lower than expected voltage. Something does not add up. You're going to have to check the readings with a meter and trace your wiring properly to identify the cause(s).


Adding a diode will cause a voltage drop, add resistance and heat. Most important is that it will not correct the underlying problem(s) and so your system will not be safe, potential fire risk/risk of further damage.
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greendovefarms avatar image
greendovefarms answered ·

The are diodes built in to the MPPT's

By chance have you connected your CC1 with the reverse polarity of the PV input as that will cause damage to the charge controller ?


I have a customer that has the same problem with a voltage display at night time on their MPPT caused by (self install) PV wiring polarity.

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dirkme911 avatar image dirkme911 commented ·
Hi, I bought the house with the CC1 MPPT doing this, so it was like that already done by the solar installer (even though it passed CoC). I want to know if there is a way to fix the issue without having to replace the MPPT. The others do not have this issue, only the first one. The MPPT works fine during the day, no issue, just this voltage at night which is not great.
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panpower avatar image
panpower answered ·

I had the same problem with the one of my smartsolar. And they replaced it under warranty

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panpower avatar image panpower commented ·

There is a 5 year warranty. Before you try to repair the diode you better check this first. It seems that a diode is short (0 Ohm).

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