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Discussion Starter · #1 · (Edited)
Hi All,

I was running some tests on my inverter charger and had it pulling 10A @ 115v or about 70A at 13.6 and noticed some heat expansion-y noises as it was getting going. I decided to feel around a bit and noticed that the lug that is attaching to my busbars is hot to the touch.

I took some temps with an infrared thermometer @ 1ft.

Busbar right under lug: 224f
Busbar Lug: 131f
Cable between breaker and busbar: 68f
Breaker Lug (To busbar): 145f
Breaker lug (from inverter) 68f
(Van temp is 44f)
The setup:


Hood Electrical wiring Cable Bumper Automotive tire



Now what is odd is that on the cable coming from the inverter I ran out of the 4awg lugs I was using and used a 1awg that I crimped down hard. That one is holding up really well.

Are my lugs causing this? I'm assuming this isn't normal (and have shut everything down for now!)
 

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2018 136 HR Ont.
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Are my lugs causing this? I'm assuming this isn't normal (and have shut everything down for now!)
I use these, I put the cable connectors from the house batteries and the inverter input on the same stud so the current doesn't actually pass through the bar but straight from cable connector to cable connector. It simply eliminates the number of possible poor connections.

It looks like you could reposition you cables to connect this way. Maybe you could try that and see if the temps change.
Hand tool Tool Bicycle part Bicycle handlebar Wood


The fuse location is no problem. The cables are short, protected and clamped. It's just there in case of inverter meltdown.
 

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Discussion Starter · #3 ·
I think a poor connection is exactly what I have. These busbars are rated for 600A!

I torqued down the nut more and that helped a lot, but I think I need a bigger lug, especially if I'm planning on running 250A through this. The cables are short enough to not matter but I think lug surface area might be an issue @ 4awg.

@83Grumman Thanks for the suggestion. Given that this will be my biggest load I might move things around on my busbars to close the gap. I'd rather not add more hardware into my electrical cabinet though, things are already a bit cramped!
 

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2018 136 HR Ont.
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I'd rather not add more hardware into my electrical cabinet though, things are already a bit cramped!
I am not suggesting more hardware. I am suggesting moving the highest current carrying cable ends to the same stud so they have a direct connection. You might have to trim some of your shrink wrap and play with the angles for the best contact.
 

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4 awg seems pretty light for 100 amp continuous use even though it is within the ampacity chart ratings.

It is useful to remember that this rating number is based on the 105 C insulation use temperature being "acceptable".

I would normally use 1/0 for 100 amps or a link bar.

I know that you don't want to hear this, but it might become necessary to run dual / parallel wires and dual breakers from the bus bar to the inverter to fully support 250 amps.

The thermal breakers operate like a fuse and trip based on getting warm. There is an assumption that the wire is able to carry heat away from the breaker, not toward the breaker or it reduces the amps trip point.

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Is the bus bar a tin plated copper one, or aluminum? If it is aluminum, then it is possible that the surface has oxidized.

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Crimping is a funny thing. It is all based on the mechanical action ripping off the surface of the wire strands and welding them together into a almost sold block inside of the lug.

It takes surprisingly little for something to go wrong and not be able to use the wire at the expected capacity, which is another reason to consider over size wires.
 

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Discussion Starter · #6 ·
4 awg seems pretty light for 100 amp continuous use even though it is within the ampacity chart ratings.

It is useful to remember that this rating number is based on the 105 C insulation use temperature being "acceptable".

I would normally use 1/0 for 100 amps or a link bar.

I know that you don't want to hear this, but it might become necessary to run dual / parallel wires and dual breakers from the bus bar to the inverter to fully support 250 amps.

The thermal breakers operate like a fuse and trip based on getting warm. There is an assumption that the wire is able to carry heat away from the breaker, not toward the breaker or it reduces the amps trip point.

___

Is the bus bar a tin plated copper one, or aluminum? If it is aluminum, then it is possible that the surface has oxidized.

____

Crimping is a funny thing. It is all based on the mechanical action ripping off the surface of the wire strands and welding them together into a almost sold block inside of the lug.

It takes surprisingly little for something to go wrong and not be able to use the wire at the expected capacity, which is another reason to consider over size wires.

The busbars I'm using are these: https://www.bluesea.com/products/2107/PowerBar_600A_BusBar_-_Eight_3_8in-16_Studs__

Tin plated copper

The other issue is that 70A is the minimum continuous load. I'd like it to (and our setup should support) 250A for at least an hour or two. (We are planning on using a 2000w induction cooktop).

I'm pretty sure it is my lugs. I took some more measurements and everywhere I used the crappy 4awg lugs the temperature was spiking.

That being said, Upgrading the wire is probably not a bad idea, especially for this load. I don't think 1/0 will fit (and should be overkill, considering the entire wire distance is ~1ft) but I might try to upgrade to 2awg or run a second set of 4awg wires.
 

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You may want to look for a higher quality lug. A lug made from heavier Guage copper will have less resistance.
 

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I used #2 for all the high current wires and #4 or 6 for everything else. I also had issues with I/r drops across lugs so I filled them with solder after crimping and I torqued down the bolts to minimize the voltage drop.

I also rearranged the topology to minimize number of lugs in the inverter loop. In particular by running a separate #2 return directly between the battery and the inverter. I don't run heavy currents through a bus bar preferring to double up the lugs on a single stud.

10 minutes at 150 amps and the wires get warm, but not hot. I measured ~.5v drop @150a, or about 75 watts dissipated in the inverter loop. #2 might be a little light for 250a over an hour dissipating 120watts...
 
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