The Stovebolt Site Forums The Shop Area The Electrical Bay Amp Rating for fuse box

I am fixing to start putting together my main under dash wiring harness (building it myself). Right now I have purchased 1 auxiliary fuse box with a rating of 80 amps max (plan on buying 1 other). My plans were to have one fuse box powered from the battery and one from the ignition switch. My question is this, how do you know the max amp rating the truck will put out. Can I get away with the 80 amp boxes or will they be to small.

They will be plenty. If you use an electric fan use a relay & take the hot wire directly from a junction block or selinoid term. with a circuit breaker or fuseable link. Same with the horn. Buy many spools of different size & color wire.

Rusty64,

It sounds like you are planning on lots of electrical goodies. In my estimation, even one 80 amp fuse box is huge.

A typical battery would have 500 amps available. Your charging system could deliver anywhere from 40 amps clear up to 150 amps.

I think you need to reverse engineer your thinking. Make a list of what you are going to put on the truck and the average current consumption of that item.

If the fuse box (block) is rated for 80 amps, that means it physical construction will safely handle that. If it has 10 spaces for fuses, the total combination couldn't exceed 80 amps...that's a lot of juice!

If you hit your charging system hard, the battery will supply a large amount of current, but the charging system must be able to match that or you will do into a 'discharge' condition.

The answer to this predicament is a high output alternator. This will feed the battery plus keep all your do-dads humming.

There is a number stamped on the alternator somewhere that indicates its current output. It probably is contained in the part number so it might not be obvious, but I'll bet someone will show up with proper info.

A standard, 12 SI alternator from the '70's usually came with a 37 amp output....I think! This wouldn't be anywhere hefty enough for your rig, but you can get one that puts out 150 amps if you feel you need it. This probably would be a more modern unit than a 12SI...again, more knowledgeable folks will be along soon.

I have stuck in a link to a place that will give you some idea of how much typical electrical devices use. This will help you to determine just how much charging capacity you really need.

Sorry for the long novel!

http://www.crowbarelectricalparts.com/specifications.htm

Stuart

Guys, thanks for the quick replies.
No I am not going to be adding a lot of electrical things (at least not in my mind). I do want to add a 3rd brake light, bed light, updated radio and air conditioning.
I just wanted to hear the type of response that I am hearing (don't want to do all this and find out it could fail). As you know, it's hard to get the smoke back inside the wires :-).

this next link shows all the parameters about the typical alternators any one of you's guys would use
>> http://www.extreme4wheelin.com/tech/alternators/tech.htm
&
Find out what a vehicle model had: http://www.olyonline.com/PPR%20Application.pdf
Cross Reference various alternator numbers: http://web2.wai-wetherill.com/new/crossref.cfm
How to tell a 10SI from a 12SI and more: http://www.madelectrical.com/electricaltech/delcoremy.shtml

you should run you're headlights, fog, horn and electrical fan (if so equip'd) && any higher amp/appliances off relays and NoT off the fuse panels. the relay ''trip/trigger'' wires run off the in cab switches.
http://www.madelectrical.com/electricaltech/brighter-headlights.shtml
Check out madelectrical's site.
http://www.madelectrical.com/electrical-tech.shtml
i scratch wired my 51
KEEP good notes and diagrahms and make a copy(s) to put in the truck under seat storage compartment
http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=DSC00492_0008.jpg

I would question powering a fuse box from your ignition switch. The ignition switch and supply is not good for too many amps.

Never power a fuse box from the ignition, as that is not the primary that currently feeds the box now. Keep it simple and you will be ok.

I always power part of the fuse block from the accessory side of the ignition switch. That way the heater, turn signals, & radio etc. will go off with the key.

Fuse boxes are not supposed to be powered from the ignition switch-- other way around. Boxes are -- for the most part-- powered all the time-- even when the key is off. Some of the treminals are keyswitch activated-- like ignition, fuel pumps, etc. Look at the mini-fuse panel from Centech-- PD-3 I think. Keep in mind-- your house probably doesn't have 80 amp capacity ! Most new houses have a 60 amp service.

I guess me & the auto manufactures have been doing it all wrong all these years.

Are all the items on a fuse box only powered when ther key is on?

try your headlights-- do you have to have a key on for them to work? How about your horn-- key on for it to blow? Brakelights? Manufacturers put certain circuits on a "HOT buss" ( that means powered all the time) and some on an accessory buss. Those are powered only when the key is on. Otherwise, why would you need the 8 or 10 guage wire from the battery or starter terminal direct to the fuse panel with a fusible link in it?

All, I am only planning on doing what Wrenchbender Ret. is saying. I plan on most of the power throughout the system to be from the main power. However the factory wiring has some systems fused after passing the ignition switch (radio, heater, panel lights and wipers). My intention is to keep these the same.

I'm w/ Wrenchbender Ret.
I run 6 relays to power the big amp items ... fans-lights (lo-hi)-fog-horns-etc
I have a fuse panel and when i turn off the key switch some of the appliances that are run off the ign are off. don't get confused by ign and start !!
radio works on acc. also