100a Fuse

[tofts]

As an electronic Kind of guy. I Was thinking, why not a circuit breaker? So...

http://www.ebay.co.uk/itm/221271392061?_trksid=p20...

Have ordered, thought it may be of interest to some?

[gruffalo]

Is 4mm large enough cable diameter and do they do a 125Amp version as 100Amp is very close tolerance to the rated output of the alternator which is why the 100 Amp fuse fails so often heat off teh engine, being run close to capacity (especially after a hot start) and vibration.

Looks interesting, let us know how you get on.

[tofts]

100a is close yes, but on the assumption that I have reduced loading by probably 50% with all LED bulbs, I don't feel it will be a problem.

But yes, 125a ones are avaliable!

4mm OD is good for about 25mm CSA so yes, it should fit fine

[mk1fan]

I was thinking to use similar.

[aide]

Any thoughts on removing the 125a fuse altogether?

[tofts]

The likely hood of a wire touching ground in this car is slim. But if it did, and no fuse to protect it then a fire could be the outcome. So no I would not remove it completely just for safety. I would be cautious at fusing 125a as well under exceptionally high load scenarios it could overload the alternator windings. Which is a lot more expensive than a fuse.


But all of the above is why the circuit breaker is a better idea. I will just re-mount it in a more sensible position so as to be accessible!

[aide]

Thanks, good insight and much appreciated.
Aide

[ukkid35]

aide said:

Any thoughts on removing the 125a fuse altogether?

Explanation from a Toyota forum

Coolerman on ih8mud.com said:

Under NORMAL circumstances you will never have a problem with the 10 ga wire and a 140 amp alternator as long as the battery you have installed is not larger than stock AND it stays charged.

However, lets look at a situation where it's winter, at night, and the battery has becomes discharged. You jump the truck to get it started, and let it idle to get warm. You turn on the headlights and the heater fans(s). So far so good. But then the 40 amp fan kicks on, and suddenly smoke pours out from under the hood and dash and the truck dies and goes up in flames.

What happened?

You tried to charge a dead battery = 25 to 40 amps (Depending on battery size)
Headlights = 6 amps
Park lights = 3.5 amps
Heater fan = 3-5 amps
Cooling fan = 40 amps

You were trying to pull almost 90 amps through a wire rated for 40. Worse case it goes up in smoke, best case you overheat the charge wire and melt it inside the harness.

Apparently there is also a risk from one of the Alternator diodes failing and causing a runaway current.

[tofts]

ukkid35 said:

Apparently there is also a risk from one of the Alternator diodes failing and causing a runaway current.

I recently repaired a 7.5kw motor drive which, as it happens, was a failed 3 phase diode pack, it booted, but complained there was a phase open circuit. The same would apply to an alternator as its just a three phase generator running through a six pack of diodes. I have never seen a diode fail closed on high draw equipment as it just blows the diodes to pieces so I don't know this would apply. Dead right with the charging cable scenario, although the charge cable on the cerb should be good for well over 100a, believe its 16mm or 25mm CSA from recollection.

However, I did just upgrade the main battery tails to 35mm which should push a few more amps through the starter and to reduce overall resistance, seeing as its now 4.7 anything I can get would be great!