Topic: Higher output alternator, larger (fused) wire??

[Fowlhunter]

Attached is an interesting article I found for those of us with a higher output alternator. Enjoy!

http://www.alternatorparts.com/do_i_need_a_bigger_battery_wire.htm

[Main One]

Interesting article FH.  The electrical engineer in me would have written it a little differently, but then I suppose only the other geeks would be able to understand it.   

[Fowlhunter]

What are your thoughts?  I upgraded from a 105A to a 145A alternator for the electric fans, I also have an amp (need to finish the install) under my back seat for my stereo system, with that being said and you've read the article what are your thoughts on the cable from the alternator?  The current cable is a fusible link but I thought about removing that and the cable from the battery to the red box and going with a 4ga cable from the alternator directly to the + on the battery with an in line ANL fuse.  I've read a few articles of guys going with a 150A in line fuse but not sure.  I'm sure everbody is different depending on what is being powered?
Thanks!

[Main One]

What are your thoughts?  I upgraded from a 105A to a 145A alternator for the electric fans, I also have an amp (need to finish the install) under my back seat for my stereo system, with that being said and you've read the article what are your thoughts on the cable from the alternator?  The current cable is a fusible link but I thought about removing that and the cable from the battery to the red box and going with a 4ga cable from the alternator directly to the + on the battery with an in line ANL fuse.  I've read a few articles of guys going with a 150A in line fuse but not sure.  I'm sure everbody is different depending on what is being powered?
Thanks!

My thoughts are:

1.  Using a secondary cable as suggested (properly fused) is a probably a good idea.  The total current running out of the alternator will split between the cables.  The current will not all flow in the path of least resistance, it will flow in inverse proportion to the resistance in the two paths.  (If the resistance is equal, the current will be equal.  If one cable has 10 times the resistance of the other, it will get a tenth of the current.)  The resistance will be somewhat dependent upon the actual resistance in the cables themselves, which is largely a function of how thick the conductors are, but in practice, a lot of the total resistance will be at the terminations of the cables.  Assuming though that your secondary cable's total resistance is not greatly lower than that of the existing cable, then it should be good to go.  If however the existing cable's resistance is significantly higher than the new cable's, then the new cable and fuse will need to be sized at close to the alternator's output.  At the extreme, if due to corrosion or other reason, the resistance through the original cable were to go to infinity (no electrical connection) then of course all of your current would have to flow through the secondary cable and fuse.  Hence the importance of putting a fuse in line with the secondary cable.

2.  If your existing cable is a fusable link, then I would be fairly confident that it should be fused at an appropriate current level for the cable, and hence not worried about it being a hazard.  That said, you may want to check out the voltage drop across the cable (preferrably from mounting stud to mounting stud to capture all terminal interface losses) when you have a high load on the alternator - fans on high, lights and rear window defogger on, amp, etc.  Keep in mind that generally the alternators need to see more belt speed driving them than they see at idle in order to put out their specified output.  However, even with all of the accessories sucking power at idle, the alternator should be able to keep up, else if you idled long enough with all of the things on, you'd be running your battery down.  I'm not sure at what voltage level I'd be worried, but I'd think that it would be somewhere around a full volt of loss in the cable/connections.  Keep ohm's law in mind - if your alternator is putting out 100 amps, it only takes 0.01 ohms of resistance to get a 1 volt drop.

[Fowlhunter]

Damn brother, that is awesome but I may need to  a little before I can get all this info into my thick skull!  I'm going to have to read it again but slower!!  You are the man!!!   

[Main One]

5+ years of higher education and most people can't understand me?

What's wrong with this picture!   

[MyBigToy]

5+ years of higher education and most people can't understand me?

What's wrong with this picture!   

I understood everything you wrote. But then I started out at UMR as a EE major. 

[Enkei]

I've said it many times before.. If you are going to up grade your Alt upgrade the main power leed and the ground wire on the frame to motor.  Keep the current flowing..When I had the 250 Amp Alt from Ohio Gen I upgraded all wires to 4Ga..And never had a problem in 6 years. No Clipping or turn offs on the JL Amps Even after 8 Hr's of Full volume...

[Main One]

Hey FH, this is a follow-up to what I just PM'd you.

I wouldn't sweat much over installing an alternator with less than a 50% increase in current output.  Whatever cable losses you had before, they are not going to increase by more than 50%, which means in all likelihood they aren't going to be an issue.  If the cable fuse was sized as I noted in my PM per what the cable could support, then having a higher output alternator with the same cable isn't going to change what's needed there.  Keep an eye on the cluster voltmeter guage as you switch things on to make sure nothing, or everything together, isn't pulling your voltage reading down too far without quickly recovering from the load transients.

If you are more than doubling your alternator's output, such as Enkei mentions, since I would assume that one wouldn't do that without needing all of that capacity, then you need to upgrade your cables as Enkei mentions as would guess that most automakers would not be so generous as to put that much spare material margin where by their design it isn't required.

It's like putting on a supercharger in some respects.  Keep the power gain to under 150 hp or so, and the stock drivetrain is likely still going to hold up fairly well.  Double the output like KY_Bob has done, and things are likely to not stand up, such as his rear end.

[Fowlhunter]

I've said it many times before.. If you are going to up grade your Alt upgrade the main power leed and the ground wire on the frame to motor.  Keep the current flowing..When I had the 250 Amp Alt from Ohio Gen I upgraded all wires to 4Ga..And never had a problem in 6 years. No Clipping or turn offs on the JL Amps Even after 8 Hr's of Full volume...

When you upgraded the fusible link from the back of the stock alternator to 4ga what size in line fuse did you go with?