what size megafuse?

[Rapid Robert]

63 dart stock car. blue high performance MP voltage reg. race hei module. pertronix flame thrower race coil. std 70's square back alt. 12V battery behind dr seat. I was thinking of useing a megafuse right at the battery (on pos or neg cable?). I had seen alot of posts regarding megafuses but the amperages are all over the chart. what do you guys suggest? or another route if that would be a better way to go. Thank you for your time. RR

 

[sabre67]

Learning?

 

[273]

I don't know exactly what you need but it's got to be more than the maximum amps you will draw and small enough to protect the cable you put it on.

Here's the 1st chart I found

Power wire	Max fuse size
00 AWG	400A
0 AWG	325A
2 AWG	200A
4 AWG	125A
8 AWG	50A
10 AWG	35A
12 AWG	20A
14 AWG	15A
16 AWG	7.5A
18 AWG	5A

 

[RustyRatRod]

I think it would go in the big wire from the alternator and I believe you want it to be as much as the alternator could put out in an extreme situation. In other words, whatever the maximum amp rating for the alternator is. At least, I think. LOL

 

[Mike69cuda]

Are you wanting to fuse the starter? If so, why?

Not being critical, just curious.

 

[Scody21]

The maxi fuse in the painless (not painless to install) harness is 70 amps, this is between the battery and the fuse panel.

 

[Rapid Robert]

good info guys, yes that makes sense that there's no need to fuse the starter & I was just thinking of protecting the whole system at the battery but it ain't set in stone cuz this is new territory for me. I will see if O'reillys can full field the alt & get a amp # and I have a 12 gauge output wire from the alt.

 

[mod5v]

First off we need we need to clarify the intended purpose of the fuses in a circuit.
Fuses are there to protect the wiring in case of a short not the "components" in that circuit.
That is why you want the fuse to be close to the power source. If you put the fuse close to the component and have a long wire run between it and the power source and you have a short somewhere between the fuse and the "battery" that wire is going to fry its whole length. The fuse as stated earlier is sized for the wire it is protecting or for the max "draw" in that circuit which ever is the lesser amount.

 

[Garrett Ellison]

On the charging circuit, the fuse should be 130% above rated alternator output. i.e. If your using a 50 amp alternator, you'll want a 65 amp fuse. Multiply output amperage by 1.3 to determine charging circuit size. Or, use a fusible link wire four gauge sizes smaller than a properly sized charging wire (by alternator ampacity) on the charging circuit and use an AGC fuse block on the battery positive for the small circuits.

 

[273]

good info guys, yes that makes sense that there's no need to fuse the starter & I was just thinking of protecting the whole system at the battery but it ain't set in stone cuz this is new territory for me. I will see if O'reillys can full field the alt & get a amp # and I have a 12 gauge output wire from the alt.

If you go Ford type starter relay then only a short wire from the battery to the relay has power all the time the rest of the cable only when starting.

 

[Garrett Ellison]

An example of similar to what you’re talking about. A little hackery of a modern (2002 Dodge Durango) battery tray with a touch of overkill for connections. AGC 2 fuse box mounted to 1/4 inch lexan and connected via a copper bus bar fed by a 100 amp fuse and a separate 8 gauge loop with 100 amp fuse from a 75 amp alternator. All non factory loads connected directly to battery and auxiliary fuse box.

 

[Rapid Robert]

good comprehensive info, much appreciated. I'm gonna need some time to sort all this out. RR

 

[Rapid Robert]

Or, use a fusible link wire four gauge sizes smaller than a properly sized charging wire (by alternator ampacity) on the charging circuit and use an AGC fuse block on the battery positive for the small circuits.

For starters I could go 4 sizes smaller fusible link IF the 12 gauge output wire is the right size. I will call O'reillys & see if they can full field an alt for max capacity amperage. I am running a large cable from battery to the main of/off switch "in" terminal & the other "out" terminal with a large cable to the starter & everything else is also fed from the out terminal but I could switch the starter cable to the other side so the starter is hot all the time if this would be a good move keep everything else seperate & then I could fuse the "out" terminal that powers the rest of the system. I'm out of my league here!. RR