Upsize alternator wiring?

[efnfast]

2001; aftermarket accessories are radio, intercooler pump, 2x Walbro 267 and radiator fan from TheViperStore. Canadian car so low beam headlights are always on.

On a fully charged battery when I start & idle the car and check the voltage w/ a multi-meter I get 13.9 (intercooler pump and dtrl are always on w/ key on).

If I turn on maximum headlights, hvac, radio, etc (i.e., all accessories) it's like 13.8.

If I turn off the accessories, when the low speed fan comes on it holds 13.8 indefinately.

When the high speed fan comes on, it quickly drops to 12.6. If I rev to around 1,500 rpm it immediately jumps up and holds 13.5 indefinately (as long as I keep the RPMs up, immediately drops to 12.6 when I left off the gas).

I tried replacing the alternator to see if it was just getting old but the readings didn't change.

From the service manual it looks like it goes 2ga wire from the battery to the starter, then branches off to the alternator as a 6ga wire.

Would I benefit from changing the 6ga wire to a 2ga wire (and replace the fusible link w/ a heavy duty inline 150amp circuit breaker) to try to get the voltage back up to the upper-13s? All the race cars I build I've always used 2ga wire for alternator, so I'm kinda surprised to see a 6ga wire for a car with accessories.

 

[Goggles Pizano]

Remember the voltage regulator is built into the PCM. The alternator/ generator doesn't have a regulator like other non Chrysler cars.

 

[efnfast]

If the PCM were culprit I would think it would struggle to charge with any loads on it, no? All the threads I've read on here where the PCM was the culprit (and the person installs an external voltage regulator to solve it) all had slow/constant voltage drops while driving. I'm good until the high speed fan kicks on and then fine again when it kicks off.

If I wanted to test my theory, is it okay to leave the stock 6ga wire connected to the alternator and then run a second 2ga wire from the alternator to the battery (fused with 150amp fuse/circuit breaker)? I think that would be okay since all it's doing is a secondary path for more current to flow ..... I'd rather avoid cutting into the main power harness since it looks like it's spliced all over the place and not as simple as just running some new wires to the starter, alternator and pdc

 

[Old School]

I'd just measure to voltage at the alternator when idling.

 

[Goggles Pizano]

Just making people who stumble on the thread to be aware the PCM has the voltage regulator.

There is a procedure in the SM about testing it at the output post.

 

[MoparMap]

Upper 13s isn't really all that bad for voltage. I believe the computer also monitors the battery temperature to control charging current. The systems are a fair deal more complicated than the old mechanical regulators of yore. I think it sounds like everything is pretty much running as expected on your car. The drop to 12.6V is a little iffy, but since it comes back up with a little rpm and it's only with the highest load on there, it doesn't strike me as too odd.

 

[Dan Cragin]

Your issue is the additional draw at idle from the added accessories. I found using the next size smaller alternator pulley fixes that.
You might need to downsize the belt a bit.

 

[efnfast]

Victory is mine!

I ran a 2ga wire from the alternator to a 150 amp mega fuse, then to the starter stud. Upsized the alternator ground to 2ga. I pulled the factory 6ga wire out of the harness and ran it to a junction block incase i ever want to use it again for something (I was concerned about letting out magic smoke from the wires if I hooked it up to the alternator).

Results (Before / After)

Start & idle: 13.9 / 14.4
All accessories except fan: 13.8 / 14.3
Radiator fan on low: 13.8 / 14.3
Radiator fan on high at idle: 12.5 / 13.8
Radiator fan on high w/ RPM: 13.5 / 14.4

With the battery in the rear I just don't see how a 6ga could remotely be deemed adequate. Compared to stock my biggest aftermarket draws are realistically the dual Walbros, so the only thing i can think of is stock cars are basically at the bleeding edge of what the oem wiring can handle without being impacted.

It's just surprising that after 25yrs I can't find any posts on any of the sites about needing to upsize the wiring if you do some supporting mods for a Paxton car.

 

[Dan Cragin]

Good info

 

[MoparMap]

Victory is mine!

I ran a 2ga wire from the alternator to a 150 amp mega fuse, then to the starter stud. Upsized the alternator ground to 2ga. I pulled the factory 6ga wire out of the harness and ran it to a junction block incase i ever want to use it again for something (I was concerned about letting out magic smoke from the wires if I hooked it up to the alternator).

Results (Before / After)

Start & idle: 13.9 / 14.4
All accessories except fan: 13.8 / 14.3
Radiator fan on low: 13.8 / 14.3
Radiator fan on high at idle: 12.5 / 13.8
Radiator fan on high w/ RPM: 13.5 / 14.4

With the battery in the rear I just don't see how a 6ga could remotely be deemed adequate. Compared to stock my biggest aftermarket draws are realistically the dual Walbros, so the only thing i can think of is stock cars are basically at the bleeding edge of what the oem wiring can handle without being impacted.

It's just surprising that after 25yrs I can't find any posts on any of the sites about needing to upsize the wiring if you do some supporting mods for a Paxton car.

Some of that might have to do with where the wiring connects as far as the battery being in the back. Depending on how you hook it up, not all the current from the alternator would have to go all the way back to the battery and then forward again to the engine bay. More than likely the alternator goes to a power distribution block that spreads out it where it needs to be in the engine bay and the excess is all that goes back to the battery, so the voltage drop wouldn't be as bad because you'd have less wire length than you might think. I'd have to look at the full schematics though. 6 gauge is rated for 100A for chassis wiring, though realistically you should almost never be pulling that much for long.

Does anyone know if it changed between gen 3 and 4? Radiator fans are probably going to be one of the biggest draws in any vehicle electrical system, and the gen 3 was hydraulic. If they sized the wiring based on that, but then swapped to electric fans in gen 4 and forgot about it, I could see the wire being a little undersized. Or maybe it was still "close enough", but gen 4 cars would be at the upper limit of the wire capabilities.

 

[efnfast]

I believe I have a gen 2 fan, definitely not a gen 3 and probably not a gen 4 unless that's what the ViperStore sells.

The reason I thought about upsizing the wire is because when I built my 65 cobra I originally ran a 6ga wire. That thing is as bare bones as possible, and when my radiator fans (2x 30 amp Spaal) came on I"d get similar voltage drops until I changed to 2ga.

Although I didn't find any posts about needing to upsize the factory wiring if adding supporting mods for Paxtons, I did find several threads involving gen 2 supercharged and twin turbo setups where people are complaining about voltage issues and the responses are all 'pcm or generator dying', but no follow up. So maybe the OEM gen 2 wiring is on the bleeding of what can be fully supported?

 

[MoparMap]

My bad, I forgot to check which forum this was in. Gen 2 would have been electric from the get-go, so I would hope they would have accounted for it.

I did learn that the factory 60s wiring for the puny 40-60 amp alternators is not up to the task of a modern 100+ amp alternator though, lol. Got lucky on that one and now have something like 2-4 ga wiring from the alternator to the battery on that car since I picked some up from work. I think my fans are still only ~10ga each, but I think they are only 20A rated. They will surge higher than that on initial start up, but that's not a huge concern.