Why would spotlights blow fuses?
Submitted: Sunday, Apr 30, 2006 at 17:02
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Ron173
G'Day All,
I'm having trouble with my spotlights blowing the fuse.
They are Hella and as far as I know 100w. Initially I did watts = volts x amps, and divided 100/12 and got 8.3amps so fitted a 10amp fuse. Which lasted a few days then blew.
I then realised my error, that as its 2 lamps should be 200/12 = 16.6 so fitted a 20amp, which again lasted a short while then blew.
I know its bad practice to just up the fuse, but thought would try 25amp considering a direct short would still blow it, just to see.
True to fashion, it blew aswell.
Now the fuse is blowing but you can sit with lights on full and spotlights and they wont blow. Its only after driving a few days that it seems to blow.
They are wired correctly with a relay and are independently earthed and it is a good tidy job with heat shrink used where needed.
I dont want to up the fuse any higher till I find out the cause of blowing.
Any pointers greatly appreciated.
Ron
Reply By: Jarrod - Sunday, Apr 30, 2006 at 21:41
Sunday, Apr 30, 2006 at 21:41
Is the fuse blown "too smithereens" i.e. vapourised in centre part that you look at or just cracked? if blown to bits, suspect intermittant short.
Also, is fuse "warmish" to touch while spotties on? - if so, poor contact/connection in the fuse holder, increasing resistance. a vicous circle, aka thermal runaway - as temperature increases, so does resistance, this causes further temp. increase, more resistance, hotter, causes more resitance, hotter, bang. blown fuse after a few hours operation.
a fuse should be same temp as all other fuses while things are operating - normal, - not even slightly warm, otherwise bang, thermal runaway.
AnswerID:
169923
Reply By: Member - Bradley- Tuesday, May 02, 2006 at 14:50
Tuesday, May 02, 2006 at 14:50
any high resistance in the circuit will cause fuses to go, usually most people use wire that is way too small for the job, and earth them to the bullbar etc.
re-wire them with at least a 10 amp wire for each light ( 15 amp preferred) and use good quality fittings, and return the earth directly to the battery. This will give you a circuit with very little voltage drop and your lights will be nice and
bright to boot.
Remember the fuse is there to protect the wiring in case of a short circuit, not the lights, they will only use as much current as they need. the wiring should always be rated higher than the fuse fitted.
AnswerID:
170225
Follow Up By: hl - Thursday, May 04, 2006 at 09:01
Thursday, May 04, 2006 at 09:01
Hmmmm
"Any high resistance will cause fuse to blow"
Are you into qantum physics or did you just make that up?
Cheers
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