I knew the length was different when I bought it, because it was sized for the 100A alternator that could come on these trucks. I figured the new alt I was buying would use the bigger belt, especially since the pulley looked bigger. What you seem to be saying is despite the new alternator I should still use the 1255mm belt. Gotcha.

 

Have you tried installing your old belt ?

 

It's ancient. That's why I got a replacement at the same time I ordered the alt. I still have it but honestly it's not worth putting back on. I'll just get a couple new ones the same size so I have a known good belt + a spare.

 

Instal it to make sure it fits If it is to tight you could go to a 6PK1270 that is the next size up the one after is a 6PK1280 but 5mm is not going to make a difference from the 1285.

 

I've watched an alternator shop test my 130 amp junkyard 3g, single v belt driven alternator put out 150 amps, wasn't slipping, but the belt was tight and she spun the heck out of it. I believe 97-04 f150s have a charge cable with a megafuse and holder from the factory.

 

Some Mountaineers/Explorers use the Mega-Fuse holder rather than the more typical (I think?) fusible link setup as well. Don't remember what amperage rating the fuses were that I saw though.
We include a 175a fuse in our kits because so many 3g's (new or rebuilt) will put out 140-150 amps easily. I read test sheet after test sheet from the BBB factory alternator builds and very few listed max output less than 140a.
At that point, while even a 150a fuse might be fine, I felt like it would be better to include the heavier fuse for just that max output scenario. I should have paid more attention to what Ford used fuse-wise in those setups I guess. Maybe someone here knows?
Hopefully everyone the install and especially those using the higher rated fuses is using the larger gauge charge cables too. Like Ford does.

Paul

 

Fuses or circuit protection is in place to protect the wire. If the capacity of the wire is say 100A then it should be fused for 100A What ever the capacity of the wire is what is what the the fuse should be.

 

Thanks for the reminder. But do you know if a fuse will blow quickly at it's rated amperage if the alternator momentarily puts out a little more than that? Say for a few seconds or so? Or will they take a little bit before letting go?
I'm not sure how quickly this type of fuse will blow, so was curious.

And do you have any good charts around that show the capacity of wire per foot? I used to have a great one saved from RB Electronics, but that page is long gone. Wonder if I can dig it up in some internet archive?
Some of the other charts I've found seem inconsistent and I like having an easy reference.

We use about 2.5 to 3 feet of 6ga cable in our 3G charge kits, which I believe is capable of taking well more than 175a before melting down. So that fuse size seemed a reasonable choice for protecting the wire, while not under-rating it for the potential output of the alternators.
Ford used 6ga in many applications I believe, but I've seen plenty of 4ga charge cables in applications where the cable was longer, or those with heavier expected use perhaps such as trucks. I saw one van that had a VERY LONG charge cable and was still the 4ga. Don't remember if it had a Mega-Fuse or not though. Or if it did, what the rating was.

Thanks

Paul

 

Most automotive fuses are not fast blow fuses so they can handle significant over current for a short period of time. They basically use a link that melts at a fairly low temp as the link heats up it melts and breaks the circuit. If it is a dead short the link quickly heats and blows apart.
I have used this chart for wire sizing as it matches the engineering standards. If you are feeding something like a winch that needs both a pos and neg wire both are added together to calculate the acceptable wire length. Example you have run of 6 ft needing both a pos and a neg, so you'd use 12ft to calculate your required wire gauge.

 

The above chart is a good standard to go by, but there are many variables that affect the amperage capability of a wire. The amperage capabilty of any wire depends on how hot you will allow the wire to run while in service. So a wire that has better high temp insulation, can be rated at a higher amps, even though it has the same amount of copper in it. A wire that is run out by itself can handle more current, since it can dissipate the heat better. A wire that is run in conduit with a bunch of other wires has to be de-rated because of heat build up potential.

Looks like the chart above is for automotive applications, since it specifys "13.8" volts and it is running more amperage through the wiring than NEC would call for, but like I said running wiring out in the open means it can be rated to carry more current.