Solar Panel CBs

[johnabbott893]

My Solar Panel Circuit Breaker keeps popping and I can’t work out why. I have two 12v 125w panels connected in a parallel configuration through separate 10amp CBs to a 30amp regulator. One CB keeps popping and the other doesn’t. The odd bit is it only pops when the weather quickly turns from hot and sunny to rain. Full sun all day is fine. Rain all day is fine. Full sun to rain and I get a popped CB – just the one though.

Now I need to start swapping connections to see if it’s the CB or the panel but access is predictably difficult. It may be easier to live with the issue. I just wondered if anybody has any bright ideas as to the cause.

[lw395]

Is one panel somehow putting current into the other, when only one is illuminated?
Is the breaker tripping due to reverse current?

[noelex]

My Solar Panel Circuit Breaker keeps popping and I can’t work out why. I have two 12v 125w panels connected in a parallel configuration through separate 10amp CBs to a 30amp regulator. One CB keeps popping and the other doesn’t. The odd bit is it only pops when the weather quickly turns from hot and sunny to rain. Full sun all day is fine. Rain all day is fine. Full sun to rain and I get a popped CB – just the one though.

Now I need to start swapping connections to see if it’s the CB or the panel but access is predictably difficult. It may be easier to live with the issue. I just wondered if anybody has any bright ideas as to the cause.

Solar panels produce their maximum output when cool. On a day with sunshine and rain the battery's will tend to be low. Just When the sun pops our from a cloud the panel temperate will be low and the combination of direct sunlight and diffused sunlight from the cloud often produces, for a short time, the higest power from the panels. This can sometimes exceed the panel rating. Are these the conditions when the CB is tripping?
A 10a circuit breaker is a bit low and if it's value is slightly off it will trip. The thermal breakers are a bit sensitive to instalation and without adequate clearance they get a bit hotter and trip earlier.
The wiring will carry much larger current safely so you can up the CB size without any problems. CB the panels and controller are unlikely to ever protect much anyway. CB between the battery and controller are more important.

[johnabbott893]

Solar panels produce their maximum output when cool. On a day with sunshine and rain the battery's will tend to be low. Just When the sun pops our from a cloud the panel temperate will be low and the combination of direct sunlight and diffused sunlight from the cloud often produces, for a short time, the higest power from the panels. This can sometimes exceed the panel rating. Are these the conditions when the CB is tripping?.

Its just the opposite sadly. The CB pops when the panels are hot and the sun suddenly vanishes. It could be a reverse feed through the CB from one panel to the other. That is easy enough to check when I get the conditions.

[Wunja]

Could the panel be shorting out and it is current coming back through the regulator from the battery that is causing the CB to pop?

[whiteoaks7]

I wouldn't have though this was a problem of logic. If you have all the right diodes in all the right places (which you probably have by default) then you can't get current running backwards. You're also unlikely to get 10A out of 125W panel more like 8 as max so the CB at 10A should be okay. I think maybe Occam's razor is called for - the most likely cause is the right one - a bit of equipment failure. Why have you got a CB in the line at all? Just in case something shorts somewhere?

David Berry

[lw395]

I wouldn't have though this was a problem of logic. If you have all the right diodes in all the right places (which you probably have by default) then you can't get current running backwards. You're also unlikely to get 10A out of 125W panel more like 8 as max so the CB at 10A should be okay. I think maybe Occam's razor is called for - the most likely cause is the right one - a bit of equipment failure. Why have you got a CB in the line at all? Just in case something shorts somewhere?

David Berry

Fair comment.
One panel I have seen had a diode badly installed to the factory-fitted lead, so if the lead twisted, the diode cold be shorted out. It still worked, I only noticed as I took the back off the connection box to change the cables for longer ones. It could be something like that.
It could be worth testing the diode works properly, put a resistor of a few k ohms in series and apply 12v to the dark panel, with its normal polarity. No current should flow.

Any cables connected fairly directly to the batteries need to be protected by either breakers or fuses. In general, I like fuses for the simplicity.

[noelex]

It is a puzzling problem and a potentially dangerous one. I think the bypass diodes must have failed in the effected panel. Can you check the output of both panels?

It would also be worth connecting the panel directly to the battery with a fuse and see if their is a discharge current.

[whiteoaks7]

Any cables connected fairly directly to the batteries need to be protected by either breakers or fuses. In general, I like fuses for the simplicity.

Quite right - good point. My fuse is between the regulator and battery which is what SunSaver recommend. Seems sensible since it then protects the regulator too. I think Steca (maybe others) have a fuse built in.

David Berry