Camper hot wires at fuse

Submitted: Saturday, Nov 29, 2014 at 12:47
ThreadID: 110280 Views:1572 Replies:4 FollowUps:5
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Forumites,
Some advice will be appreciated.
Facts are:
1) Camper trailer with two 120AH batteries at front, in parallel
2) 40 Amp blade fuse close to batteries.
3) cable run from fuse to back of trailer, where the merit plugs service lights, fridge, etc.
4) 80 litre weaco freezer running at the back through merit plug

And, my question is, with the freezer running, the cables connected to the blade fuse gets quite hot; When putting the voltmeter between the in and out cables of the fuse, I measure 0.6V
Is this normal? seems to be a big voltage difference, which is contributing to the voltage drop to the back of the trailer

Advice appreciated, maybe upgrade to a better fuse connection?
Cheers, CJ
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Reply By: HKB Electronics - Saturday, Nov 29, 2014 at 13:16

Saturday, Nov 29, 2014 at 13:16
How much current is the fridge drawing?

If it is only around 4A the fuse should not be getting hot, have a look
at the fuse terminals and see if they have lost tension, they should
"grab" the fuse terminals.

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AnswerID: 542324

Reply By: Notso - Saturday, Nov 29, 2014 at 14:25

Saturday, Nov 29, 2014 at 14:25
A 40 amp fuse shouldn't get hot when it's only running about 4 amps. Either a high resistance between the blade grippers and the blades (as above) or a poor connection between the cables and the blade grippers. I suppose it's also possible that the fuse is faulty.
AnswerID: 542327

Reply By: The Bantam - Saturday, Nov 29, 2014 at 14:26

Saturday, Nov 29, 2014 at 14:26
When you say "quite hot" how hot is that.
warm to the touch
hot as the outside of a coffee cup
so hot you can hold it for long
so hot it burns on contact
the insulation is melting

There are a number of reason why things arround terminals and fuses get hot.
A high resistance can produce heat that travels some distance in wires, giving a false impression of where the exact cause is.

The standard of workmansip across the trailer industry is not good and far from consistent....there are a only few out there who know their business and do nice work.


Poorly cripmed lugs can produce hot spots....a properly crimped lug should be "as good as welded" and should not represent a high resistance point.
Even though passable ratchet crimpers can be had for under $20, there are many persisting with pressed tin crap.
Good quality lugs have never been as easily avaiable and as cheap...but there is still crap put there.
If a good quality lug of the correct size has been crimped on a wire with the correct cripmer it should be as good as welded and should not present any problem.

The #1 test for lugs and one that people consistently fail to do is....try to pull it off.....the wire should break before the crimped union fails.

Apply the pull test to your lugs.....if the lug pulls off the wire it needed recrimping anyway.


Blade fuses are far more reliable in an automotive setting than any of the previous options...but people push them too far.

If you have a 40 amp blade fuse it should be a maxi blade fuse.....anything above 25 amps is hard to get in a standard blade fuse, I will not use over 30 amps in standard blade fuse.
My limits are
nothing over 20 amps on a mini blade fuse
nothing over 30 amps on a standard blade fuse
and unless there is no other choice either a circuit breaker or an ANL fuse for anything 60 amps and over.

Even IF the bade fuse it self is adequate for the job the fuse holder may not be rated for the fuses fitted to it. Some standard blade fuse blocks and holders are only rated for 20 amps continuous on a single circuit and an 8 way block may have a total rating of 60 or 80 amps continuous.

Many people fail to even consider the rating of the fuse block or holder.

Failures here manifest as hot points where the fuses contact the holder terminals....the terminals may not have sufficient tension or current carrying capacity..even if they do the surrounding plastics may not have the capacity to handle the heat.
Some heat arround fuses can be quite normal under full load situations.

Light cables can be a problem.....but in automotive the voltage drop becomes a problem before the curret carrying capacity becomes an issue.....that said I have seen some very light cable used.

There may be some issues with screw terminals not being tight enough....remember no wire should be soldered before putting in a strew terminal.
There may also be issues with spade and bullet lugs lacking tension..a squeeze with pliers on the femal lug can fix this.

SO
If you have a 40 amp fuse and the cable runs the length of the trailer I would expect to install at least a maxi blade fuse if not an ANL or a circuit breaker.
I would expect to install at least 6mm2 twinn ( not 6mm automotive cable 4.6mm2) if not 10mm2.
This would mean I would not be using insulated lugs as 6mm2 wont go onto a yellow lug.
I'd be using non insulated lugs and heat shrink.
I' d expect to see some sort of sub fuse block at the rear.

so what does this all look like.

cheers





AnswerID: 542328

Follow Up By: The Bantam - Saturday, Nov 29, 2014 at 14:31

Saturday, Nov 29, 2014 at 14:31
If the problem on a 40 amp circuit is present woth only 3 to 8 amps flowing ether something has been damaged due to high current flow at a previous time or there are some very real resistance issues.

cheers
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Follow Up By: Allan B (Member, SunCoast) - Saturday, Nov 29, 2014 at 14:36

Saturday, Nov 29, 2014 at 14:36
My head hurts! lol
Cheers
Allan

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Follow Up By: The Bantam - Saturday, Nov 29, 2014 at 14:54

Saturday, Nov 29, 2014 at 14:54
best go back to bed then.

cheers
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Follow Up By: Allan B (Member, SunCoast) - Saturday, Nov 29, 2014 at 14:56

Saturday, Nov 29, 2014 at 14:56
Now that's sound advice!
Cheers
Allan

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Reply By: CSeaJay - Saturday, Nov 29, 2014 at 15:24

Saturday, Nov 29, 2014 at 15:24
Notso, Bantam and Allan

Thank you for your input.
Based on above advice I popped in at Supercheap and bough a new 40 A maxi fuse and waterproof fuse holder. Replaced the previous fuse holder and under the same circumstances
a) it is not hot anymore, and
b) there is now only 0.01V difference between before the fuse and after
This also appears to have ridden me of what I previously thought was a Voltage drop to the back of the van; this is now gone. Appears the previous fuse holder/contraption/connection/fuse grab was to blame for many sins

Thank you again
CJ
AnswerID: 542329

Follow Up By: Member - Phil G (SA) - Saturday, Nov 29, 2014 at 19:17

Saturday, Nov 29, 2014 at 19:17
CJ,
Well done - nice to solve a problem. Most common problem I see is cheap fuse holders developing corrosion after a couple of years. They go high resistance with the corrosion and the plastic in the blade fuse eventually melts.
My solution is to solder the maxi fuses into the circuit, and to use tinned wire.
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