Solar Combiner box breaker getting hot??

[GoneDiving]

My solar system is five, four panel, 1000w parallel strings to a 6 in 2 out combiner box then to 5000W inverters also operating in parallel. Typically, I feed all the solar to the master inverter and only turn the second slave inverter on when I need high AC draws. The battery is Lifepo4 840ah @48v.

The combiner box is rated at 63amps per inverter. However, if solar production is a constant >25 amps, then the one 63amp breaker in use gets very hot.

The beaker is 4 pole with the negative passing through once and the postive passing through the remaining three poles one after the other.

Why does the positive pass through three poles in series? Does this contribute to the over heating? Any other suggestions in what to look at?

See photos below.

Many thanks.

 

[Bmarler]

That’s kind of goofy. Only things that came to mind was phase loss detection, or load balancing, but those ideas don’t make any sense here.
Is there a schematic we could look at to see what the heck they’re doing there?

 

[GoneDiving]

That’s kind of goofy. Only things that came to mind was phase loss detection, or load balancing, but those ideas don’t make any sense here.
Is there a schematic we could look at to see what the heck they’re doing there?

Sorry, I don't have a wiring diagram and am hopeless at drawing them.

If you look at the wide shot photos above you have six fuses receiving current from the PV panels (+ve at the top, -ve at the bottom). These fuses output to a common busrail. Busrail to lightning/surge protector. Surge protector to 63a output circuit breaker. +ve passes through the three leftmost poles in series. -ve passes through the right pole only. Upper din rail is for +ve PV input and master inverter. Lower din rail is for -ve PV input and second, slave inverter.

Note:
1/. One fuse is open as I have 5 parallel PV strings not 6.
2/. Typically all PV flows through the upper breaker to the master inverter. At ~25amp, this breaker gets almost too hot to touch.
If the top breaker is turned off and the bottom turned on, the PV is sent to the slave inverter only. At ~25amp the lower breaker then gets warm but nowhere near as hot as the top one.
3/. It was explained to me that 3 poles are used for the PV +ve to enable breaking higher voltages. The combiner is rated for 1000vdc. However, my system is 90vdc max. I'm thinking that I don't need the three poles and actually this is worse for me as it introduces more internal resistance.
4/. With a few clouds, a little shading etc the system typically outputs 20 to 30 amps continuously. However, in full summer sun, full capacity is 60 amps.

Out of interest, I'll try moving the +ve PV output to only use one pole and see if that reduces the internal resistance and hence heat build up of the top breaker.

Either way, I'm highly suspect of the breakers and they will be changed out.

 

[twistedtree]

Your are correct about the series breakers being used to interrupt higher voltage/current. And I agree that the heat is from internal contact resistance. Probably time to replace that breaker. You test will help confirm.


BTW, what are the fuse ratings? The holder says 35A, but I'm wondering what the fuses themselves are.

 

[GoneDiving]

Your are correct about the series breakers being used to interrupt higher voltage/current. And I agree that the heat is from internal contact resistance. Probably time to replace that breaker. You test will help confirm.


BTW, what are the fuse ratings? The holder says 35A, but I'm wondering what the fuses themselves are.

They are 15a ceramic fuses inside 32a rated housing. I think the 35 you refer to is that the fuses are 38*10mm

These fuses do not get warm at all. The heat build up started at the most +ve pole and spreads from there.

I'm not sure if the wiring diagram below indicates that there is an internal bridge between 1&3, 5&7 that could give an internal short?? Either way something's not right with the breaker.

Cheers.

 

[Bmarler]

I can buy into the higher interrupt rating with the series connections. If you think you’ve got bad connections within the breaker contacts, (highly probable) get a volt meter and check the top contact against the bottom. Any volts shown there indicates resistance on the contact itself.
As an aside, it’s always best to cover the panels (depower them) before tripping that breaker. There’s a lot of juice flowing from that array, easy to have arc damage on the contacts.

 

[twistedtree]

They are 15a ceramic fuses inside 32a rated housing. I think the 35 you refer to is that the fuses are 38*10mm

These fuses do not get warm at all. The heat build up started at the most +ve pole and spreads from there.

I'm not sure if the wiring diagram below indicates that there is an internal bridge between 1&3, 5&7 that could give an internal short?? Either way something's not right with the breaker.

Cheers.

The jumpers appear to have been moved for this application vs what the imprinted schematic shows. You can see them in the pictures