Under Driven 200 Amp Alternator: A Bad Idea

Bullitt347 · Nov 11, 2017

FastDriver said:
Max speed of the 3G alternators from PA Performance, based on their website is 16k RPM.

Oooops, I have spun mine as high as 19K+ with no issues.....but it is for such a short duration that I don't think it matters much. Kind of like I am over-spinning the KB S/C by a ton with no problems.

FastDriver · Nov 11, 2017

Which alternator do you have? A stock 3G?

Rick seems to think that it matters even only doing it once, but that may just be the party line since they have to warranty these things. As for me, I'll overspin if it comes down to getting enough voltage at idle vs. overspinning, hence the spare, but I'll avoid it if I can get the exactly right pullies for the job. Low voltage is a PITA because it throws off the tune, and is hard on batteries and starters. Most likely other electronic devices as well. My Escort Radar detector said, "Low Voltage" and shut itself off the other day, which prompted all of this.

FastDriver · Nov 11, 2017

Noobz347 said:
Post them as resources with use instruction under the discussion tab.

I don't know about that. It's not my most professional work, and I'd definitely want to revise them before I'd make them public.

Bullitt347 · Nov 11, 2017

I bought mine from PA Performance. I don't know if they "heavy duty" the parts or not.

Bullitt347 · Nov 11, 2017

9.5" crank pulley with a 4" alternator pulley at 8,000 rpm = 19,000 rpm. I have gone out the back end at 8,400 rpm before. Alt still works. I think a lot of published "Max" spec's are suggested continuous max rpm, not the brief spin to the stratosphere, lol

FastDriver · Nov 11, 2017

Yeah, that's pretty extreme. Good to know. Then, if the 2" alt pulley doesn't fix it, I'll try the 1 7/8" next. That would "only" take mine to 16,800.

Mustang5L5 · Nov 11, 2017

Just for reference, the coil cover decal listing RPM ranges.

I run an oversized power wire from my alt to the solenoid. I was an electrician at the time so I snagged a lenght of #2, #1 or even 1/0 wire and crimped some solid crimps and ran that as my power wire. pretty much no voltage drop at temp

Bullitt347 · Nov 11, 2017

I had 0 gauge cable coming from my alt as well. I figured if I was demanding so much power from the system, a 200 amp alt better have enough cable to support the draw.

FastDriver · Nov 11, 2017

4# on mine. PA Performance said it was plenty.

FastDriver · Nov 15, 2017

I've been tuning as of late and reviewing a lot of datalogs where I can see that RPM does not have enough effect. 2000+ rpm push the voltage into the 12.6-12.7 range, but rarely will it go over 13V. So, I'm probably just going to throw the 130 amp on the car, and take the 200 to a parts store that can test it.

I'm also rethinking this 4# wire. I run 4# to the starter solenoid where 2/0 90C connects and runs the rest of the way back to the battery mounted in the rear.

This is what's running from my Alternator to the solenoid: http://www.paperformance.com/standard-long-9903/ and according to the description:

using this large (#4 Gauge) wire kit will add the safe carrying capacity needed for our high output alternators. In some applications you must use this cable to retain warranty coverage. All kits are provided with 200-amp Littlefuse Brand Fuse and Holder.

If this amp rating chart is to be believed, 2/0 is looking like plenty, but 4# is looking kinda weak. Am I missing something? I see diagrams from jrichker and others that seem to confirm 4# is ok, but the chart defintiely looks concerning.

Mustang5L5 · Nov 15, 2017

Are you really pulling 200 amps though?

Honestly, stock fox with standard fuel pump, average stereo and some sort of Efan might pull 90-100 amps tops.

Now if you have extra fuel pumps, electric water pump and other high draw accessories you might need more, but 130a is plenty for 90% of foxes. Even then you probably aren't maxing it out. The e fan tends to spike to 30-40a on startup but it's not continuous.

I have a dozen or so electrical meters but none will do D/C amps over 10A or I'd get some real numbers

FastDriver · Nov 15, 2017

Not sure at all. I just went overkill so I didn't have to think about it, lol. But now I'm having problems and thinking about it anyways. Twin electric fans, Weldon 2025A pump are probably the biggest draws. Not sure how much more my MSD 7531 box, HVCII Coil, Racepak dash, and BS3 draw. Maybe I'll get an amp clamp and measure it at some point.

Mustang5L5 · Nov 15, 2017

FastDriver said:
Maybe I'll get an amp clamp and measure it at some point.

Most of those only do A/C voltage though (what I have). Most of the meters I have will do up to 10A DC but require the meter hooked up in series.

I don't even know if a clamp on DC ammeter exists

General karthief · Nov 15, 2017

May be @jrichker can help with this amp dilemma you have, I sure he will jump in when he gets time.
Seems to me you could get the amp draws from you equipment like the race pac and the fans, msd and all then add it up to get a presective on what your normal running amp draw will be.
Just thinking out loud, probably more like babbling.

Mustang5L5 · Nov 15, 2017

Found a few models that will do DC amps with a clamp.

Interestingly enough I am considering buying one. I've actually come across a few situations where I wish I had a clamp on meter for dc current. I'm going to search around a bit more. Ebay has a few Chinese cheapos as well

EDIT: Found a used Extech MA220 on ebay for $40. Lets see what my car is drawing for actual real-world amps.

FastDriver · Nov 15, 2017

With 3.5 stars on amazon, do you think this is the best one for the money?

Mustang5L5 · Nov 15, 2017

Probably not. But i'm not using this meter to rewire my house. Really just satisfying curiousity and some light automotive troubleshooting.

There's also this one as well

Amazon product ASIN B0038RPP8OView: https://www.amazon.com/Extech-380950-Mini-Clamp-Meter/dp/B0038RPP8O

There's this one for $40 on Amazon that has decent reviews, although I don't know the brand well
Amazon product ASIN B0721MKXBCView: https://www.amazon.com/dp/B0721MKXBC/ref=pd_luc_rh_sspa_dk_huc_pt_sub_1?psc=1

Or you could pony up for one of these. I just don't have enough use to justify spending this much right now
Amazon product ASIN B01NBYMVYBView: https://www.amazon.com/Fluke-Capacitance-Measurements-NIST-Traceable-Calibration/dp/B01NBYMVYB

Amazon product ASIN B01NAXGZERView: https://www.amazon.com/FLUKE-1000A-Wireless-Clamp-Iflex/dp/B01NAXGZER

FastDriver · Nov 17, 2017

I've tried to do a little research on the amp draw on all of my electrical components, and here's what I came up with:
MSD 7531 (1.1amp / 1k RPM): 7.7
HVC coil (8251): 1.1a
Weldon 2025A: 17 expected at 65psi. conservative guess 20amp
Twin spal fans: 40a
Lights: 20a
Racepak: 5a
BS3: 20-30 amps. Most likely 20-25
Blower motor (dash): 10a
A/C?

All of that added up is 133.8 but it doesn't all necessarily apply at idle where the stress on the system will be highest.

What else am I missing? That's a lot of amp-draw. 200 amp alternator is apparently the correct one as it puts out 100 amps at idle.

jrichker · Nov 17, 2017

Try this:

Under no circumstances connect the two 10 gauge black/orange wires to the 3G alternator. If the fuse blows in the 4 gauge wire, the two 10 gauge wires will be overloaded to the point of catching fire and burning up the wiring harness.

The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. Any car that has a 3G alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects.

Electric fan = 3G alternator if you want long life & reliability from your car.
The electric fan saves some HP. The stock fan's parasitic drag runs from 7-12 HP depending on who you talk to. The electric fan uses about 1/2 HP of power from the electrical system.

Figure this:
Ignition system & computer = 12 amps
Fuel pump = 12 amps
Exterior lights = 15 amps
Fan (heater or A/C) = 15 amps (can run between 5-25 amps depending on setting)
Radio & instruments = 10 amps
Wipers = 10 amps
Rear window defroster = 5 amps (optional, not found on most southern fox mustangs unless the moved down with the snowbird owner…)

That's grand total of 79 amps from a 65 amp alternator. Talk about overdrawn at the bank!

FastDriver · Nov 17, 2017

The ground from the rear-mounted battery runs to the chassis about 2 ft from the terminal through a 2/0 Gauge ground wire.

The block has two grounds, it seems to me, though one is not technically connected to the block itself. One actually runs from the timing chain cover to the chassis on the driver's side and measures ~0.380" sleeved, which I think is 4 Ga, as that's the diameter of the sleeved alternator power wire that is stamped 4 Ga. The other block ground runs from the block itself to the chassis on the passenger side and measured ~0.370", again I think that's 4 Ga.

There is no ground running behind the intake on the driver's side that I could see. I do not yet know where the a/c system ground is, but that's for another time. Does it just ground to the block, too?

The figures you've mentioned are obviously stock numbers. The ones I posted were based on researching my specific components, but I didn't take into account running the rear defrost, wipers, radio, and I was guessing at the blower motor. I'll include them in my data. Looks like my base idle during daylight should be in the 85 amp range (w/o radio/lights/blower/wipers/defrost). My my... even the 3G 130 amp alternator is only supposed to put out 80 amps at idle. No wonder the stock alternator was terrible.

I have attached a picture of the power wires on the alternator. Is the left-most wire in the pic one of the black/orange wires you're talking about? There are two of them there. So, I assume that's what you're referring to. Apparently my installer didn't know about what you're referring to. What does it do? Will disconnecting it have any negative side-effects that I'll need to remedy? Should it be replaced or just disconnected? One seems to run to the starter solenoid. I lost the other into a cable bundle on the driver's fender. Maybe I'll just add in-line fuses to protect those wires.

Under Driven 200 Amp Alternator: A Bad Idea

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