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Circuit Breakers & Temps - TOMZN overheating

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nate_syd

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So i'm all up & running & want to do some thermals to see how its all going.

2x5kw Deye hybrids, 2x16kw 48v packs with JK BMS
Big DC Cabling is 35mm welding cable, some smaller stuff which is being upgraded.

Discharged at 8kw for an hour & did some thermals... EEPERS
BMS happy at 35-38c, inverters arent that hot (66/48 c), cabling all ok...

TOMZN 125A Circuit breakers are WAAAAY TOO HOT, no way i'm keeping them in place. Was running 85-90A through them & they were 120c!!!
This is a fire waiting to happen.

I've got Class T's on the batteries, the breakers are just used to isolate inverters as i need - never used to switch anything, but no way i'd use them in an emergency!
 

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nate_syd said:
So i'm all up & running & want to do some thermals to see how its all going.

2x5kw Deye hybrids, 2x16kw 48v packs with JK BMS
Big DC Cabling is 35mm welding cable, some smaller stuff which is being upgraded.

Discharged at 8kw for an hour & did some thermals... EEPERS
BMS happy at 35-38c, inverters arent that hot (66/48 c), cabling all ok...

TOMZN 125A Circuit breakers are WAAAAY TOO HOT, no way i'm keeping them in place. Was running 85-90A through them & they were 120c!!!
This is a fire waiting to happen.

I've got Class T's on the batteries, the breakers are just used to isolate inverters as i need - never used to switch anything, but no way i'd use them in an emergency!
Click to expand...
Agreed! Something needs to be corrected in your setup. How are the wires going on and out of those CBs?
 
Sorry - how are they going in & out?
Cables are stripped & screwed in securely - no ferrules or anything like that, just thick flexible stranded cable all squished nicely.
 
What is Vdrops between the two terminals of the breaker? It must be quite big Vdrops to produce that much heat.
So the top wire is one single large wire, and at the bottom are two wires?
DIN mounted MCB breaker, correct?
Pictures of the breaker?
Which side of the breaker on pix #1? side view?
I use this series TOB1Z-125, C125 250VDC running 80A through it for more than a year, it only gets warm.
1673924428533.png
 
Last edited:
nate_syd said:
Sorry - how are they going in & out?
Cables are stripped & screwed in securely - no ferrules or anything like that, just thick flexible stranded cable all squished nicely.
Click to expand...
Meaning the temperature of the wires.

The most common cause of overheated CBs is lose wiring. Electrical resistance increases at points of loose connection and that generates heat. This means that your overheated breaker may simply be loose. When installing a breaker, you have to give it a good push to seat it on the clip that holds it to the bus bar. If the breaker isn't seated properly, one end will protrude slightly. Push in that end until you hear the click of the breaker seating securely. If the breaker is already seated, the problem may be that the wire connected to it is loose. Pull out the breaker and tighten the lug that holds it using a screwdriver and ensure no insulation is causing the CB from making full contact with the wire. Lastly, tug on the CB to ensure it is clamped tight in the bus.
 
ahhh - yeah no issues with any of that, checked all that thoroughly during install. Everything super secure etc.
Just got some new breakers that are to local standards... $140 vs $40... they are huge & weigh a ton... so doubt i'll have issues.

Thead was also an FYI to do thermal checks & be cautious with "ratings" of components!
 
nate_syd said:
ahhh - yeah no issues with any of that, checked all that thoroughly during install. Everything super secure etc.
Just got some new breakers that are to local standards... $140 vs $40... they are huge & weigh a ton... so doubt i'll have issues.

Thead was also an FYI to do thermal checks & be cautious with "ratings" of components!
Click to expand...
Hope that solves your problems. Please post a picture of those CBs once everything proves out.

Quality of components is getting murky as so much is coming out of China these days. I did a sub-panel install for my cousin this past weekend and noticed he had quite a few slim line CBs. I recommend folks stay away from those unless no other options. They are difficult to get clipped in, they can place 40amps on the same side bus, and can pop out easier than full size. Tandem breakers are also generally not allowed in a new service box and are frowned upon and are rules regarding retrofit use. I also wonder how the smaller and tandem breakers handle current and heat.
 
I am regularly fiddling with my systems as I learn more. Every time I take some stuff apart to redo it, I find a loose connection on a clamp down to wire circuit.
And I crank the shit out of them. I am starting to understand where ferrules are required and why.
 
Quattrohead said:
I am regularly fiddling with my systems as I learn more. Every time I take some stuff apart to redo it, I find a loose connection on a clamp down to wire circuit.
And I crank the shit out of them. I am starting to understand where ferrules are required and why.
Click to expand...
Ferrules may not allow good surface area, I prefer to NOT use them unless there's a reason too. - Off Grid Garage just did a vid about these.
He used them & the lack of surface area was causing overheating.

Old vs new... old uses screws, the new one has HUUUGE ring terminals with a hex head bolt.
20230117_223947.jpg
 
Made the correct call to re-do the breakers & wires...
They were melted inside of the enclosure - so there's no way I could actually see the damage.

The copper was discolored a fair bit too!

20230117_224339.jpg
 
Its never tripped, but there's some corrosion on the contact points - concerning & probably a good source of heat.
20230117_231456.jpg


Discoloration on the main internal bar, having a close look it seemed to start at the flexible interconnection cables.
20230117_231348.jpg
 
Sorry - Pic1 was the JK BMS...

Same wires in & out - 2in, 2 out - just an issue with resolution.
Yes Din mounted 2 pole

I ran these & originally spec'd them for 70-80A, at that level mine were also just warm.
But pushing them to 100A for an hour - whole different outcome. Even after this warming event - the next day at lowe

Bud Martin said:
What is Vdrops between the two terminals of the breaker? It must be quite big Vdrops to produce that much heat.
So the top wire is one single large wire, and at the bottom are two wires?
DIN mounted MCB breaker, correct?
Pictures of the breaker?
Which side of the breaker on pix #1? side view?
I use this series TOB1Z-125, C125 250VDC running 80A through it for more than a year, it only gets warm.
Click to expand...
 
Under load what is the voltage drop across the breaker?
nate_syd said:
ahhh - yeah no issues with any of that, checked all that thoroughly during install. Everything super secure etc.
Just got some new breakers that are to local standards... $140 vs $40... they are huge & weigh a ton... so doubt i'll have issues.

Thead was also an FYI to do thermal checks & be cautious with "ratings" of components!
Click to expand...
I have found that most electrical products that are imported from Asia have ratings that are based on unrealistic assumptions. They tend to use minimum size wire, flimsy connectors and fasteners of dubious quality and metallurgy. However if you know this and avoid operating at the top end of their rating they can work fine.

Different philosophy of engineering at work over there. Here in the US most engineers calculate the minimum necessary and double and triple it for safety. Over there they calculate the minimum necessary and than try to find a cheaper way to barely reach it.
 
High amperage breakers get hot. They are typically in the 3 to 5 milliohm range for series resistance when new and get worse if you repeatedly open and close them under high current. If you have a YR1035 four-point resistance tester, check their resistance yourself.

It is the main reason to use an inverter input capacitor charging resistor to limit surge current on breaker contacts.

Reason why they have so much series resistance is they have brad wires to make flexible connections to moving latch switch and their short circuit trip mechanism has an electro-magnetic solenoid coil that has two or three turns of about #4 to #8 gauge wire which is in series with breaker current.

4 milliohms x 100 amps^2 = 40 watts of heating and 0.4 vdc of voltage drop. They need some free air circulation to help cool them.

For a 12v system that has high DC current and cannot afford the voltage drop, a fuse should be used instead, which has 0.5 to 1 milliohm of resistance.
 
Last edited:
nate_syd said:
Old vs new... old uses screws, the new one has HUUUGE ring terminals with a hex head bolt.
Click to expand...
I was pleased when I saw you were singing the praises of ZBeny breakers, as I originally purchased Tomzn but decided not to use them, and instead purchased ZBeny ones. I purchased direct from ZBeny on Alibaba, $52 each. One reason that I decided to go with ZBeny was that SolarEdge had suggested in one of their documents to use one of their products, so I figured it should be OK. Good also to hear that they are to local standards, hopefully somewhere with high standards, presumably America.
 
nate_syd said:
Made the correct call to re-do the breakers & wires...
They were melted inside of the enclosure - so there's no way I could actually see the damage.

The copper was discolored a fair bit too!

View attachment 130079
Click to expand...
strange that the insulation melted at the bents, were these wires touching the the TOMZ CB body ? It would seem that the melting should start at the strand and move back to the wiring. The thermal image clearly shows the hot spot is internal to the TOMZ breaker however, and not at the clamp down terminal. I've found that I need to go back and re-tighten the terminals after a while as the copper "yielded" a bit. How is the insulation on the 35mm welding cable ?
 
Ron-ski said:
I was pleased when I saw you were singing the praises of ZBeny breakers, as I originally purchased Tomzn but decided not to use them, and instead purchased ZBeny ones. I purchased direct from ZBeny on Alibaba, $52 each. One reason that I decided to go with ZBeny was that SolarEdge had suggested in one of their documents to use one of their products, so I figured it should be OK. Good also to hear that they are to local standards, hopefully somewhere with high standards, presumably America.
Click to expand...
The ZJBeny's conform to our local Aus/NZ standards - specifically in battery isolation installations
 
summit said:
strange that the insulation melted at the bents, were these wires touching the the TOMZ CB body ? It would seem that the melting should start at the strand and move back to the wiring. The thermal image clearly shows the hot spot is internal to the TOMZ breaker however, and not at the clamp down terminal. I've found that I need to go back and re-tighten the terminals after a while as the copper "yielded" a bit. How is the insulation on the 35mm welding cable ?
Click to expand...
Yes - they were tucked tight in there, a combination of both the internal wire & also being against the CB body.

The ZJBeny's are fully sealed! but HUGE amount of space in there, so will be interesting to see how the heat is - will check next time.
"How is the insulation" - in what way? Specs are here: https://www.electracables.com.au/flexible-welding-cable
 
Nitrile-Butadiene-PVC Copolymer, a.k.a. 'vinyl'. No respectable welder would use vinyl insulated cables.

'Excelene' welding cables, accept no substitutes. Cost a bit more but once you try them you will use nothing else for battery cables.
 
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