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I am putting a 140a alt on and planning on upsizing my alt wire to a 4ga, direct from the alt to the starter thru a circuit breaker. Do I just remove the existing wire that runs from the alt to the horn relay and just let the rest of the existing wires remain as is?
TIA
Short answer, Yes just remove the existing main charge wire and leave the rest alone.
Longer answer. I tryed running a circuit breaker down by the starter as you suggest. Problem. Circuit breakers work by popping a bimetal spring. Which of course works on heat. I found that the heat from the exhaust would get the bimetal spring inside the breaker hot without any electrical issues and would randomly pop. And there I was on the side of the road resetting it. Not fun.
I put in a strip fuse panel and run my 140 amp Alternator through a 100 amp strip fuse. Haven't had any trouble since.
And I had tryed 2 different circuit breakers.
When I did this on my car it was suggested by the people at Painless wiring to leave the factory wiring in place and add the heavy wire as a second supplemental wire.They stated reasons for this but I cant tell you what they were at the moment. I also went the way of adding an inline fuse. I do use circuit breakers for my rad fans though.
I would just run the second wire with the first. If you want to, there is a kit sold by MAD Electric. Mark over there is very knowledgeable and a good guy to talk with. http://www.madelectrical.com/catalog/alt-1.shtml
I would just run the second wire with the first. If you want to, there is a kit sold by MAD Electric. Mark over there is very knowledgeable and a good guy to talk with. http://www.madelectrical.com/catalog/alt-1.shtml
Do you run the new wire thru the horn relay or bypass it. I would assume bypass and straight to a fuse then to starter.
Even if you use a fuse/fusible link or circuit breaker(not a fan of these under the hood) it poses a over current possibility- melting factory wires and a possible fire.
Every time you drop a wire size - you need to fuse the wire for it's current capability.
Not to mention current running in parallel (see below)
If you still wanna do an upgraded wire with the existing factory wire- at the LEAST you need to fuse the smaller gauge factory wire at the alternator.
Just look at the idea behind a fusible link- the smaller wire connected to a larger higher current wire will burn if there it too much current.
Difference being is the fusible link is covered with material not to start a fire.
The 10GA wire from the factory was never designed to carry the current the your 140A alternator is capable of-
EVEN using a 100A fuse for the new Alternator- there is still a possibility of torching the factory wires
All my power wires are protected by correctly sized fuseable links or fuses. I have the wiring in diagram #2. If the heavy wire I added pops a fuse for some unforseen reason, and by some chance the factory wire has too much current being pulled through it at that same time, The fusable link should pop.
For my case, keep in mind my car had higher 63 amp vs 41 amp alternator from the factory for the AC that doesnt work ...I think I have the 80amp replacement in there now. I now run rad fans but only one 15 amp fan typically runs on and off to maintain the temp and the second rarely kicks on while sitting running for long periods on hot days. So im generally not actually drawing more current than the stock car would if the AC worked and was running. especially with my lower current/ wattage 35w led headlamps and heat/ac off 99.9 % of the time.. But I also have that battery reserve to help out if needed along with that second fused wire off the alternator if it ever did. My rad fans are powered from the starter lug connection were the heavy wire terminates
I have a digital volt meter on the dash to show me if the alternator is having any trouble keeping up with the current as the voltage would drop and have done some testing with everything on possible at once just to make sure and theres no problems even sitting at idle after a long drive hot with both fans tricked to be on im over 13.9v
Last edited by augiedoggy; Feb 24, 2022 at 04:11 PM.
I’m with the others. I ran a 6awg wire in parallel with the factory wire. I put a 10awg fusible link on the 6awg wire. No issues 10+ years later.
A couple things to remember:
For the heavier add-ons, I added a big junction block near the alternator. My electric fans and ECU tap into that. They will primarily be driven by the alternator with the battery taking up momentary new load as the alternator ramps up to the new current demand.
Generally, after you’ve started the car, your battery will only temporarily be a big load on these wires (unless significantly discharged). After that, most of the load will be temporary such as the electric fan scenario above.
Any current going back to the battery will be split across the two wires, with a proportional load going to the 6awg wire vs the 10.
I’m with the others. I ran a 6awg wire in parallel with the factory wire. I put a 10awg fusible link on the 6awg wire. No issues 10+ years later.
A couple things to remember:
For the heavier add-ons, I added a big junction block near the alternator. My electric fans and ECU tap into that. They will primarily be driven by the alternator with the battery taking up momentary new load as the alternator ramps up to the new current demand.
Generally, after you’ve started the car, your battery will only temporarily be a big load on these wires (unless significantly discharged). After that, most of the load will be temporary such as the electric fan scenario above.
Any current going back to the battery will be split across the two wires, with a proportional load going to the 6awg wire vs the 10.
I agree, Except I was told not to run anything directly off the alternator due to electrical noise and possible load damage to the alternator. It did make sense that having the load drawn from closer to the battery would help have an effect like a smoothing capacitor. Especially since the alternator is actually outputting a modified ac wave into a crude DC signal which is not as ideal as a true DC wave so ive read for some DC loads.
I agree, Except I was told not to run anything directly off the alternator due to electrical noise and possible load damage to the alternator. It did make sense that having the load drawn from closer to the battery would help have an effect like a smoothing capacitor. Especially since the alternator is actually outputting a modified ac wave into a crude DC signal which is not as ideal as a true DC wave so ive read for some DC loads.
To be clear, the junction is not driven solely by the alternator, the 6awg battery (+) is attached to this point as well. I'm sure it would be cleaner to isolate them.
I agree, Except I was told not to run anything directly off the alternator due to electrical noise and possible load damage to the alternator. It did make sense that having the load drawn from closer to the battery would help have an effect like a smoothing capacitor. Especially since the alternator is actually outputting a modified ac wave into a crude DC signal which is not as ideal as a true DC wave so ive read for some DC loads.
If rewiring your car- adding electronics- ECUs/Vintage air/ aftermarket stereo-
Here's simple way to upgrade- as electronics don't like voltage swings and AC ripple.
The big main wire from the battery to the starter has a low enough resistance that the solenoid works fine as a power feed point. Come from the solenoid to a power terminal block for new accessories including the new charge wire to the alternator.
If you use the remote voltage sensing of the alternator correctly, you can compensate for conductor voltage drop at the new power terminal block. Basically, connect a wire from the sensing terminal of the alternator to the power terminal block.
Wires run from the rear mounted battery need to be bigger to avoid voltage drop. You can't use the alternator remote voltage sensing to compensate for this voltage drop either without risking over-charging the battery.
Definitely remove the old charging wire, don't just add a new parallel wire. It does work if nothing goes wrong, but could burn the car down if there is a wiring failure.
Alternator ripple can be measured at the battery at a somewhat reduced level, so the battery doesn't filter it very well. It's really not that much to begin with. The risk to anything electronic that the small level of voltage ripple the alternator creates in car with the proper wire sizes (big enough to avoid excessive voltage drops) is greatly exaggerated. Remember, car electronics are built to work in a car where the designers know that some alternator ripple exists as well as switching noises/transients existing.
Last edited by lionelhutz; Feb 25, 2022 at 10:20 AM.
Definitely remove the old charging wire, don't just add a new parallel wire. It does work if nothing goes wrong, but could burn the car down if there is a wiring failure.
Alternator ripple can be measured at the battery at a somewhat reduced level, so the battery doesn't filter it very well. It's really not that much to begin with. The risk to anything electronic that the small level of voltage ripple the alternator creates in car with the proper wire sizes (big enough to avoid excessive voltage drops) is greatly exaggerated. Remember, car electronics are built to work in a car where the designers know that some alternator ripple exists as well as switching noises/transients existing.
These cars were built/designed way before anyone even imagined the cars would see the level of electronics being added today.
With the introduction of a "ECU" in the 80 model- GM tried to clean it up by routing the alternator charge wire directly to the battery.
These cars were built/designed way before anyone even imagined the cars would see the level of electronics being added today.
With the introduction of a "ECU" in the 80 model- GM tried to clean it up by routing the alternator charge wire directly to the battery.
Why'd they go back to using the solenoid or whatever other connection point was convenient instead of straight from the battery then? The connection point was sometimes used to connect the alternator, car power and run to the battery all together.
Upsize Alt wire
