Hello my buddy has a 1980 Monte with the 229ci and we are trying to figure out some voltage drop issues. We added some amps and upgraded the grounds a bit but even when the 2 air compressors turn on, the voltage dips a lot.

I was thinking of doing a big 3/big 4 and putting 1/0 everywhere. The alternator bracket grounds look like a fairly weak link as well (is there a better spot to ground the alternator?)

We added a 150a alternator but I'm guessing it's only 150a peak and does 100a or less on idle.

Here are some pics.

Any suggestions appreciated. Seriously like any suggestions on wire size would help too. Right now it's all 4awg copper and we have 1/0 to the sub amp. But I'm thinking 1/0 or 2/0 copper everywhere.

I know it looks like ****, I tried to suggest better but he never wants to do it the right way.

 

My guess is that you're way over drawing the system. You mention 1/0 to the sub amp (which alone can support a huge current draw), plus 2 compressors, and a concern with idle amperage on the alternator. It makes me think you're drawing out way more than you're putting in.

What is the actual current draw on the sub amp and compressors? Does your alternator have any kind of output chart/certification? Is it a major name brand alternator?

I've seen some off brand "HO" alternators that actually do worse than stock at the usual low / cruising RPM, so I'd be pretty suspicious of it unless they give you an output chart or you've measured it yourself. You mention its probably putting out less than 100 amps at low rpm, and I'd bet you're right but also that its WAY lower than you think.

Not saying bigger wiring wouldnt help to some extent, but I just think the most strategic approach is to figure out exactly whats going out vs whats coming in to see how hard you're leaning on the battery's reserves. Just hate to see you spend a bunch of money on 2/0 everywhere only to end up with similar symptoms.

 

The first amp was a sundown saz2500d which can handle the low voltage no problem. Just put a prv 3500 which is supposedly more efficient but it shuts off at 10-11v.

I have a ton of 2/0 and 1/0 so it's not a real issue.

he said it does 150a but I have no idea what it does idle or what rpm's it puts out 150a. Or if its even a legit 150a

looking at JS alternator. They have a huge 3320 or 350a for $300-$400

but I think my first step will be 1/0 or 2/0 for the big 3/4/5 first and get all the grounds and power wires solid first.

the stock alt is like 60a so I know it's gotta be upgraded no matter what

the ppi 900.4 has no issues so far, no voltage drop at all even full tilt. 2 channels bridged and the other 2 at 4 ohms. 70a onboard fusing so it's probably only drawing 60a max I'm assuming.

not sure on the compressors but I cant imagine they should cause any voltage drop at all in a proper electrical system. 2 viair but unsure of the models

we did use some low strand electrical wire for alt to battery (only has like 6 or 10 strands but is 4awg copper) so I'm sure some higher strand bigger wire would help.

 

The thing is though, it shouldn't HAVE to handle low voltage if the system is sized correctly. The electrical system should never be dropping that low.

Im not familiar at all with those amps - but on the PRV site it says at a minimum it needs a 60 AH battery bank + 220 amp alternator (up to 180 AH worth of batteries for long duration musical use). Thats just to support this one piece of equipment.

My point was more that this alone won't fix your problem. Youll certainly need to do it, but you need to do it in conjunction with an alt + maybe even a battery(ies).

The current alternator definitely needs to go. Even if it does do 150 amps, it doesn't even meet the requirements of the sub amp alone.

Rather than just buying a big alternator, I still think you need to take an engineering approach to it. Figure out the worst case for the electrical system- which will likely be low engine speeds. Add up your factory current draw (can be measured with an inductive clamp if you want to be most accurate, or just add the relevant fuses up and apply a usage factor to them for a ballpark) - then add up the actual current draw of your add ons. Then size your alternator / battery(ies) appropriately - at the engine speed of highest concern (knowing it'll be better than needed at all others).

Id also be very cautious about just looking at the peak rating on alternators. 350 amps of output does no good if thats only at 6k engine rpm and it only does 50 amps under 2000. The amperage roll off vs rpm is usually a pretty steep curve so you've got to be sure it makes the necessary amperage at the rpm you need it to. Many high end alt companies will offer a table or a graph to show output vs rpm and test for conformance to that minimum spec before shipping to you.

You say 'only' 60 amps, but that's still a huge amount of current - thats likely as much as the entire stock car during normal operation. Id bet the car running + this alone is enough to eat up most of the current alternators output - especially at low speed.

I wouldnt underestimate them. Even very small air bag compressors are about 10 amps each. The larger ones can easily get into the 20+ range. Plus you've got 2 of them. 30-40 amps total draw is a significant circuit for car electical.

The electrical system is clearly insufficient for what is being run, so as long as this is properly factored into your calculations for the new system, all should be fine. The big question will be - is there ever a chance these will run on top of either amp? If not, then clearly sizing the system for the amps will be more than sufficient for this. But if they will be run in parallel, then this just bumps up the necessary capacity that much more.

IMO regardless how many strands, its still barking up the wrong tree with the existing system. 4 gauge is fine for a short run even if that alt really puts out 150 amps. No doubt you could reduce resistance by a tiny % and get a little more power to the battery with a bigger cable, but its not going to be anywhere near enough to fix the problem here since the alternator just isn't capable of making what you need.

I'd overhaul the whole electrical system in one shot using real data / math to make everything matches well with each other. Thatll dictate exactly what size wires need to be run to support the new system.