Melted fuse

[michaelgreeny]

Hey guys,

Question for you all.

Just wired up my new light bar from Paul at ledlightco, and a bloody beautiful thing it is too, if you're looking for something to go at the front of your roof rack I would definitely recommend this one (37' extreme from ledlightco.com.au)! We had a tree down on our road today so decided to put the winch to good use and snatched it off a nearby tree and dragged it off the road. However after using the winch for maybe 20 or 30 seconds the new light bar cut out. Turns out the fuse had melted, not blown, melted.

As far as I can tell there's 2 options
1. It was going to do it anyway and there was too much power going through the cables
2. For some reason using the winch caused the light fuse to melt

Does anyone have any ideas?

Light bar is set up pretty simply, switch in cab goes to relay. Relay has 2 positives, 1 straight to battery, 1 straight to light. Single negative coming out of relay with is split at the battery to go to terminal and to light.
Light bar draws 25 - 28 amps. 30 amp fuse between positive battery terminal and relay.

Not sure on the diameter of the wire between relay and battery, we had 6mm wire to put in but it looked like the same stuff?

Cheers.

[mudnut]

Could be that the winch dragged too much out of the system and caused the light bar to run on a reduced voltage. Did you run the motor while winching?

[michaelgreeny]

Run the motor as in, was the car engine on? Yeh the engine was idling the whole time. That was my initial assumption but I have no knowledge/experience as to why that would actually be the case.

[mudnut]

Yes. I usually bump up the revs with the hand throttle locked at around 1900 rpm. You need to check all the connections especially the fuse holder.

[mudnut]

Here's a table that redarc use for cables. The light bar should be OK on 6mm according to this. https://www.redarc.com.au/images/upl..._worksheet.pdf

Other than that, you may need to upgrade if the wiring is longer than a couple of metres.,

[mudski]

Hey guys,

Question for you all.

Just wired up my new light bar from Paul at ledlightco, and a bloody beautiful thing it is too, if you're looking for something to go at the front of your roof rack I would definitely recommend this one (37' extreme from ledlightco.com.au)! ...

Cheers.

Yeah I wouldn't know as some bloody basterd bought their last one.

As for your issue. Got me. Hopefully @Yendor or @the evil twin or @someone will pop in and help.

[4bye4]

There are a couple of things here that have already been mentioned in a way. First if your winch drew enough to lower the voltage a small amount, electrical devices will compensate by drawing extra current. Without going into ohm's law too deep, power is a function of voltage and current. If the voltage goes down the current will go up and vice versa. The second thing is that you have a 30 amp fuse in a circuit capable of drawing 28 amps. Fuses are not the most accurate thing and 28 amps in a wire that is designed to melt at 30 amps is fairly close. The fuse operates by melting at or about the rated value. If you can imagine 29.9 amps in the circuit the fuse is going to be very hot, in fact nearly melting. It could be that at the high end of your lights rating (28 amps) the fuse could be very hot, in fact hot enough to melt the holder over 20 to 30 seconds. The answer? I would consider putting the revs up when winching as suggested above, which should bring your available voltage up to about 13 to 14 volts, thus reducing the current draw slightly. I would also run a 35 or even 40 amp fuse in a 28 amp circuit. This would mean the fuse would not heat up as much at the high end of the current draw (28amps) but would still blow if the wiring or light shorted. After all, 28amps is 93% of the rated value of a 30 amp fuse, but only 80% of a 35 amp fuse.

[michaelgreeny]

Cheers guys, love all the information on here! I'll give all that a go and see what happens.

Sorry @mudski but definitely worth the wait!!

[mudski]

All good bud. Hopefully 4bye4's explanation sorts you out. But yeah if I use my winch I always increase the revs for that little extra voltage punch.

[the evil twin]

LED lights will run at full power on a wide range of voltage, typically 9 to 30 odd.
As others have said as they voltage drops the current increases.
If supply voltage drops to say 9 volts then the Bar will pull maybe another 33% of current (extra load, heat etc) IE if it was using 30 ish before it will now draw 40 ish Amps

Sooo... your fuse melted due to extra current demanded by the voltage drop in the Vehicle caused by the winch current draw
Winches will pull waaay in excess of what an Alternator can supply so the vehicle voltage can drop to 9 or 10 volts very easily

Putting the revs up will help BUT the Alternator it will not hold anything like 13 volts with any sort of load on the winch.
Winches will pull upwards of 500 amps fully loaded IE stalled out

Purely as a hypothetical... at idle lets say a 100 amp Alternator will supply 75 amps at min 13.8 volts
Draw more than 75 amps and the voltage will fall
It is only at say 1200 RPM that the Alternator will supply the 100 amps but again if you exceed that 100 amp demand the voltage will fall and the Battery will start to load share

Rules of thumb...
Fuses at the supply end of wiring are rated to the cable size IE 25 amp cable 25 amp fuse, 50 amp cable 50 amp fuse.
Fuses at the equipment end are rated to the equipment IE 10 amp device then 10 amp (or better 15) fuse