Heat build up in wire

[Yoshi]

Hi,

I have a small camper with an inverter set up. Below is my diagram.

To check for heat build up in connections and wires, I placed a cup of water in the microwave and ran it for 5 minutes under battery and inverter power.

All of the connections (including the T-Fuse) stayed cool with maybe a 2- 4F increase except for 1 (circled in yellow). The load side of my shunt raised about 40F with the 2/0 wire getting warm to the touch with about a 40F increase in temp. I used an infrared temp. gun to measure. This connection point is a 2/0 wire going to the busbar.

I checked for the obvious loose connection, but it seems tight.

Do I need to be concerned? Any suggestions ?

Thank you

 

[SeilerBird]

No wire should have warm insulation. You need a bigger wire.

 

[Utclmjmpr]

Or less load..>>>D

 

[Isaac-1]

Or it may be a loose nut or bad crimp connection that is getting hot, replace it with another good quality all copper wire and see if the problem continues.

 

[Mark_K5LXP]

What are the wire gauges at these other connections? Seems if they're all the same but only one is getting hot implies a bad connection. To isolate the issue to a part one can measure voltage drop across different points when a load is applied. So with a simple multimeter you'd touch the probes to any two points along the circuit and paths that have higher than typical resistance will be evident by higher voltage readings.

Mark B.
Albuquerque, NM

 

[Isaac-1]

Mark, the problem in this case is the shunt the wire is connected to has resistance, though in theory that is only a tiny fraction of an ohm.

 

[John From Detroit]

Is it ONLY warm at the joint or is it warm along it's length?
If "Along it's length" bigger wire
If only where it connects.. Re-do the connection making sure the wires are good and clean and the bolt is good and tight. Also clean the connection (Wire brush) treat with DE-OX-IT before brushing, after brushing and then DE-OX-IT prenetive spray (You can get that on line or from micro Center stores. Nice stuff)

 

[Yoshi]

Hi,

I did a a double check and what I thought was tight ..was not . When I put a torque wrench on it it was not to spec. (20 Nm). I torqued it and is better. It was much cooler but still a tad warm.

I am confident that the wire sizing is correct.

I plan to double check all the connections with a torque wrench and do some cleaning as @John From Detroit suggests and use the DE-OX-IT

Thank you for the suggestions..I'll report back.

 

[John From Detroit]

As I said Disassamble the joint and clean both the wire and the connector Treat with DE-OX-IT both the deoxidizer and the oxidation preventer and re-assemble... The poor connection did damage. that will (Hopefully) Fix it.

 

[SeilerBird]

I am confident that the wire sizing is correct.

Not the right size if there is any warmth at all.

 

[Mark_K5LXP]

Copper is a great conductor of heat, so a point source at a bad connection or terminal can conduct a ways up the cable and surrounding metal. Same for the shunt, it's got a bit of thermal mass at the ends. A microwave can draw upwards of 1800W if it's a big one, that's north of 150A DC to the input of an inverter. That's enough current to warm even 2/0 (140F per ampacity charts) so it would be useful to know what that current is and expect some warming to occur. An IR thermometer and a voltmeter to measure millivolt drops will reveal hot spots and connections that might be marginal.

Mark B.
Albuquerque, NM

 

[Yoshi]

Not the right size if there is any warmth at all.

Copper is a great conductor of heat, so a point source at a bad connection or terminal can conduct a ways up the cable and surrounding metal. Same for the shunt, it's got a bit of thermal mass at the ends. A microwave can draw upwards of 1800W if it's a big one, that's north of 150A DC to the input of an inverter. That's enough current to warm even 2/0 (140F per ampacity charts) so it would be useful to know what that current is and expect some warming to occur. An IR thermometer and a voltmeter to measure millivolt drops will reveal hot spots and connections that might be marginal.

Mark B.
Albuquerque, NM

Hi,
Tks for the reply. It's a 900W microwave. Well below the capacity of the inverter.

Below is the calculation I did to size wires and fuse. I confirmed both with a few other sites and it came up the same. 2/0 wire and 225 A fuse.

My plan is to first see if I can get voltage drops across wires and devices to see if anything shows up. In conjunction, I plan to check to make sure each connection is;
busbar or device>wire lug>lockwasher>washer>nut>properly torqued .

I also have a IR thermometer that I plan to check the connections.

tks for the help. I'll report back what I find.

 

[SuwanneeDave]

Not the right size if there is any warmth at all.

But why would only the negative get warm and not the positive.

 

[Gary RV_Wizard]

2/0 wire should easily handle the max possible loads in that circuit, so I'll agree with John & others who say there must be a poor quality connection. Disassemble, clean thoroughly, and coat with a conductive grease when re-assembling.

 

[SeilerBird]

But why would only the negative get warm and not the positive.

I can't read your schematic, it is too confusing. However if the wire that gets hot is terminated properly then you don't have a lot of other reasons.

 

[Yoshi]

Hi, I was able to check voltage drops. Do these numbers make sense?

This was before doing any changes or inspection of the connection points.

Top or first number was inverter on, but no load.

Second or bottom number is inverter on with microwave (900W) heating water

Circled number was voltage along the circuit with inverter on but no load.

The largest delta across the switch lines up with the wire getting warm (not hot) after 5 minutes.

I plan now to check all the connections.

Tks for your insights.

 

[boatbuilder]

Those voltage drop numbers look real good. You are under 3% which is what boat's critical circuits are sized for.
Heat in a circuit is generated by resistance. The higher the resistance the more heat. Resistance in a conductor is generally caused by wire being too small or loose or compromised connections. Since you found and remedied the cause of your heat you should be good to go.

 

[John From Detroit]

Not the right size if there is any warmth at all.

It might be the right size. as I said when the bolt was lose it caused some damage to the end of the wire (And to the clamp) and thus the clamp needs cleaning and the wire end "redressing" (Trim back a bit and cut off the damaged part) have seen burned wire ends many times. Not often mine.

 

[Isaac-1]

One other thing if the wires came from different sources make sure they are all pure copper and not CCA (Copper Clad Aluminum) which looks a lot like copper upon first glance.

 

[OldWEB]

You need to watch where you place the voltage probe for the voltage drop. EVERY connection needs the drop test done to isolate any problem, so going from the actual wire under the insulation to the crimped connector (or clamp-on connector) will measure that connection, going from the bolt/nut on the battery to the connector will measure that connection. Going from connector to connector in any length of wire will measure the first connector crimp, the wire voltage drop and the second connector crimp.

EDIT: Don't forget to have good current flow to do the voltage drop test, the more the better.