chen123

iTrader: (1)

What size of fuse should I use for the positive lead of the Alternator wire after I've done the Big Three upgrade...my alt is either 70amp or 75amp.

Is an 80amp fuse ok?

Creamedweasel

I didn't fuse that wire at all, but if you must do it make the fuse anywhere from 10-25% larger than your alternator output. IE if your alt puts out 105amps, use a 125amp fuse.

Starterwiz

You want to add as little resistance as possible to the wire. Use a fuse that protects the wire from the battery's output eg 200 amps or better.

silverbane

iTrader: (1)

Always fuse to wire size.

http://www.the12volt.com/info/recwirsz.asp

chen123

iTrader: (1)

Thanks for the link....but I'm not sure I understand what you mean by "fuse to wire size." I will be using 1/0 for the Alternator positive lead and for both grounds.

My amplifiers power wire seems more straight foward. RMS will be <950, each amp has a 60amp fuse ....so I'll use a 120amp ANL fuse.

However, the alternator is more confusing. What is being protected by the fuse, the wire? the battery? the alternator?

And So, who is correct? Starterwiz (200amp Fuse) or Creamedweasel (approx 100amp fuse in my case) or don't use one at all.

92zed34

iTrader: (4)

need to protect the wire at all costs www.bcae1.com

chen123

iTrader: (1)

That's a great link! I think I'll need to read over it again.

Didn't realize I had to use a fused distribution block when using 4 gauge to 2x 8 guage....thought that the amps fuses and the main fuse would be adequate.

JohnVroom

Read this post again, and think about the principle behind the post

Before you go crazy, with the wire size fusing (your wire should ALWAYS be oversized IMO) the fusing should be the correct size based on the limiting component. SO if you have 0 gauge wire and an amp that only draws 150 amps what size fuse should you use? A proper fuse would be around 175ish amps (not every fuse (AGU, ANL, Maxi, MIDI etc) is available in every amperage you might desire so you might have to settle for a 150 or a 200 amp fuse). The bottom line here is if the system draws more than it can (150a) then there is a fault and the fuse should open to limit the damage.
If your wire is undersized then you have to fuse to the wiring (say 4 gauge in a system that draws 200 amps)

chen123

iTrader: (1)

So for the alt, if it puts out 70amps than an 80amp fuse should be fine (%12.5)

I'm now more confused than ever with regard to the amps. According to that web site, 8 guage can only handle a 50 amp fuse....If I use a 60 amp fuse will the wire be unprotected? What will happen?

I bought a non fused distribution block, if that wire won't be protected once it leaves the block as 2 - 8 gauge wires (from 4gauge input) then why do companies such as PG in my case make an unfused block like this?....if the output was = to the input wire then I wouldn't need another fuse after or in the block.

thanks for everyones input

Westec

iTrader: (1)

What you are actually doing is not fusing the "alt" wire. You are protecting the wire in case of an accident. If you got in a frontal collision, you would have an unfused wire directly of the battery that will more than likely start a fire. If you fuse to the campacity of the wire, this is good. You are protecting the wire from shorting not the over drawing. This is why companies like Honda and GM use some sort of fusing, for safety. On GMs there is a "plastic white thing" roughly 6 inches from the "alt" this is a fusible link or one time only fuse. Honda's use a white wire and connect to the fuse distribution center under the hood, it does have a fuse but it is "after" the main input fuse to the distribution center.
Or use add a 150-200 amp in line, you should be fine, if you have a older GM, we will have to adjust things. Hope this helps...