Odd solar behaviour on new install

[Ting Tong]

I fitted a Victron MPPT 75/15 and 120w panel last week and it spent most of the weekend on float. However, the control panel switched the fridge off on the second night and the battery voltage was showing around 10.8v on the control panel in the morning. We’ve driven it home since but today the control panel voltage still looks low compared with the Victron and is only showing 50%, so I’d expect it to be on bulk not float? (The reason for the current is I’ve just turned the fridge on).


I wonder whether anyone has any thoughts on what might be going on. My initial suspicion is that the leisure batteries may be disconnected and so the control panel is looking at the front flat battery whereas the Victron is looking at the charged rear battery. I have checked the Victron battery and panel wiring.

 

[WelshGas]

I fitted a Victron MPPT 75/15 and 120w panel last week and it spent most of the weekend on float. However, the control panel switched the fridge off on the second night and the battery voltage was showing around 10.8v on the control panel in the morning. We’ve driven it home since but today the control panel voltage still looks low compared with the Victron and is only showing 50%, so I’d expect it to be on bulk not float? (The reason for the current is I’ve just turned the fridge on).


I wonder whether anyone has any thoughts on what might be going on. My initial suspicion is that the leisure batteries may be disconnected and so the control panel is looking at the front flat battery whereas the Victron is looking at the charged rear battery. I have checked the Victron battery and panel wiring.

View attachment 95258

View attachment 95259

Have you checked the 75amp cube fuse on the rear leisure battery?

 

[Ting Tong]

Have you checked the 75amp cube fuse on the rear leisure battery?

That's my next job but I was trying to gauge opinion before maneuvering the rear battery out again. I recall there's something on the front battery too?

 

[WelshGas]

That's my next job but I was trying to gauge opinion before maneuvering the rear battery out again. I recall there's something on the front battery too?

On the T5.1 there is a brown 80 amp fuse, not a cube fuse, for the front battery. If it blows the front battery won’t charge from the engine.
I think this is still the same on the T6.
All the Leisure power connections are to the front battery only.
From your photos the rear battery is fully charged, but not the front. If both batteries are connected then the voltage should be the same on the MPPT and the Control Panel.

 

[Ting Tong]

On the T5.1 there is a brown 80 amp fuse, not a cube fuse, for the front battery. If it blows the front battery won’t charge from the engine.
I think this is still the same on the T6.
All the Leisure power connections are to the front battery only.
From your photos the rear battery is fully charged, but not the front. If both batteries are connected then the voltage should be the same on the MPPT and the Control Panel.

Yes that’s my thinking too. If the cube fuse has blown, then presumably I need to equalise the charge of the two batteries before directly interconnecting them otherwise there will be a current surge from the rear into the front.

 

[WelshGas]

Yes that’s my thinking too. If the cube fuse has blown, then presumably I need to equalise the charge of the two batteries before directly interconnecting them otherwise there will be a current surge from the rear into the front.

Yes. Either plug into EHU to charge front battery, or connect Solar input to the red+tve lead in the rear battery compartment, not the rear leisure battery.

 

[Ting Tong]

@WelshGas yes the cube fuse had blown….I wonder what would cause that.

As suggested, I plugged in the mains for a day first to charge front battery and there wasn’t any sparking when I bridged the fuse with a screwdriver before changing it.

Hopefully the solar will work correctly now but I’ll have to wait to see until the batteries have depleted a bit.

Thanks for your input

 

[WelshGas]

@WelshGas yes the cube fuse had blown….I wonder what would cause that.

As suggested, I plugged in the mains for a day first to charge front battery and there wasn’t any sparking when I bridged the fuse with a screwdriver before changing it.

Hopefully the solar will work correctly now but I’ll have to wait to see until the batteries have depleted a bit.

Thanks for your input

It will work OK. The cube fuse is very delicate and easily broken when tightening. That's from experience.
You should always see an increased voltage on the Control Panel if Solar is working BUT only if the Solar +tve connection is between cube fuse and battery.
If connected between cube fuse and red +tve lead you will always see the increase Solar voltage even if the cube fuse blows.