Battery Charger Cables Getting Hot

[Overlord]

The positive wire from my 100a charger to the fuse gets very hot. The other day i switched on my ac and water maker without flipping the generator switch over. I melted the battery switch that i had in line. It did not blow the 250a fuse that is after the battery switch. The connecting wire between the battery switch and fuse holder melted(only the plastic insulating on wire melted) The fuse holder itself got so hot that the bolt holding the fuse melted its plastic housing. I am not in a place to get spares so i have removed the switch and put both cables on the one remaining good stud of the fuse holder. This now gets very hot while charging.
Any idea why this is happening now. the cables i am using from charger to main Bus bar are at least 2/0 and are about 2ft long

[rtbates]

Either the cable is under sized for the current required, or there is additional resistance somewhere in the line...

A chart of wire size vs current can determine the first.

An ohm meter can determine the latter

In the meantime BE CAREFUL...You could be closer to a fire than you think..

[Wotname]

What rtbates said, especially the BE CAREFUL part.

Assuming this is a new problem, I would suspect the crimp terminals (at least one) has gone high resistance or a connection has gone high resistance - either or both due to corrosion.

[David M]

Be sure to gauge the new wire (if that's the problem) for a 2% drop and not a 10% voltage drop. Some tables show both drops.

[skipmac]

The 2/0 wire should be more than adequate, especially with only a 2' run (don't forget to consider the round trip length).

If this worked without overheating in the past and it gets hot now then the should confirm that the wiring is fine and something has changed. As mentioned, most likely high resistance at a connection, either due to corrosion or a loose fitting.

Some sort of electrical failure is possible but the other is much more likely.

[Cheechako]

Check and see if one of your batteries is also hot after charging. You may have a battery with a short. Has happened twice to me over the years.....

[djmarchand]

Are we talking about an inverter/charger? If so when you turned on the A/C and watermaker without flipping the generator switch, the inverter was supplying about 20 amps AC which should draw 200+ amps DC.

This isn't too much for 2/0 wire and it didn't trip your 250 amp fuse. 2/0 is good for 330 amps. But as others have said you probably have a bad connection which caused a voltage drop and generated enough heat to melt the plastic.

David

[mrm]

If things melted in spots, like near connectors, bolts etc. it would suggest oxidation of the mating surfaces (which increases their resistance and generates heat due to larger than usual voltage drop). Look for trouble spots at connectors and similar, near melted areas.

If isolation melted more-less equally along the whole conductor, it would suggest an overcurrent which overloaded the whole path. In this case look for trouble on circuit ends (too high load or supply).

Marius

[bloodhunter]

Would concur that most probable reason is at the connectors as this has to be a new problem.
What ever the reason, you now have two lines connected where one was before and an overheating problem that is likley to get worse. Would suggest you get or make new cables (2/0 wire should be more than enough to handle your current load) and a new switch and fuse holder before you end up with a fire which can ruin anyone's day.
I'd also suggest a label or sign with big letters near your AC switch reminding to turn on the generator. I have a numberf of those 'disaster avoidance labels on my boat.

[skipmac]

Originally Posted by Cheechako

Check and see if one of your batteries is also hot after charging. You may have a battery with a short. Has happened twice to me over the years.....

Yes. Forgot about the battery as a possibility. Definitely check that as well. If you have a hydrometer check the specific gravity of each cell.

[hellosailor]

chris, as some folks mentioned, you've come very close to a boat fire. If I may suggest, until you find out what the problem is, and until those replaced wires and parts run "cold" to the touch, you might want to make sure all power is OFF unless you are onboard and awake. You've got a "live bomb" onboard and if the troubleshooting is more than you can handle comfortable right now, keep the power OFF and call in a pro.

Fires can get out of hand very quickly.

[Overlord]

I replaced all cables fuses etc and now cold as a cucumber !

[Jbaffoh]

I'm a little concerned about a few things: (1), your 250 amp fuse is AFTER the battery switch instead of w/in 7 inches of the battery? And (2), the charger is connected to a "main" buss--how close is that buss to the house bank, and how is it connected?

[Overlord]

Pos wire from inverter/charger goes to battery switch , then fuse then house batt buss bar. 600 lithium ion phosphate bank positive connects to same bus bar

[Overlord]

positive cable from inverter /charger goes from inverter to battery switch , then to fuse and then to house battery bus bar. 600ah lithium ion phosphate positive then connects to this bus bar too.Bus bar 1ft from batteries