Under Driven 200 Amp Alternator: A Bad Idea

[Mustang5L5]

Got that Meter in the mail.

No time to really play with it but I did a quick check on my Efan with the car off.

Startup surge was between 35-40A each time. Only lasted 1 second or so.

Continuous load was 11.5 amps. I also notice the fan motor is starting to sound a tad rough. Lovely.

I'll get more time this weekend to start the car and take more measurements. I'm interested in finding out minimum load, as well as max load on my system

 

[FastDriver]

That's not bad at all -- less amps than expected.. Let me know how you like that meter. I may not get the smoking deal you did, but I'll still buy it if it works well for you.

 

[Mustang5L5]

That's not bad at all -- less amps than expected.. Let me know how you like that meter. I may not get the smoking deal you did, but I'll still buy it if it works well for you.

I put it on AC and did some comparisons against two other meters I had in my electrical panel. It was pretty close....within 1/2 AMP of the others. I'd love an NIST certified meter, but for informational purposes, i'll take this $40 used meter instead.

This weekend i'll fire the car up and take some readings in various states of having accessories on and off and so.

 

[FastDriver]

Thanks for the recommendation, Mike. I don't know what NIST is, but if a cheap one will let me troubleshoot the basics, that's good enough for me.

 

[FastDriver]

The 2" pulley is on back order until the end of November. So, I ordered a 1 7/8" pulley from ASP. The one I got was actually 1.69" where the belt rides. This requires me to limit the motor to 6k to prevent over-spinning the alternator.

The jury is still out on whether it has corrected my problem. I just put an optima red top in the car and while it started over 13.5V, by the end of the first trip to the store and back with a lot of idling running the blower and the lights, the battery is at 12.8V.

 

[General karthief]

I've got a 2" off a stock 89 alt if you want it

 

[FastDriver]

I think it'll measure 2.17, because I have a stocker, too. It so happens that the 2.1" that LMR sells is also 2.17, because I have one of those, too... lol! Thank you for the offer, though.

 

[jrichker]

I put it on AC and did some comparisons against two other meters I had in my electrical panel. It was pretty close....within 1/2 AMP of the others. I'd love an NIST certified meter, but for informational purposes, i'll take this $40 used meter instead.

This weekend i'll fire the car up and take some readings in various states of having accessories on and off and so.

Check an see if your meter has an internal calibration potentiometer. If it does there are precision zener diodes for less than $5. Add a suitable resistor and a pair of 9 volt batteries and you have a precision voltage source to calibrate your meter. Once it is set for the 1-2 volt range, it is linear for the entire DC range of the meter


http://www.frankshospitalworkshop.com/electronics/diy-voltage_reference.html

 

[Mustang5L5]

Here's what I got for my car. Measured off the alternator power wire.

Car on, no accessories and e fan off: 7.5 amps

Car on, Efan on: 20.4amps

Car on, Efan on, all headlights on: 30amps

Everything on!: 53 amps.


Amazing the that tail and headlamps were 10amps by themselves

 

[FastDriver]

Good stuff, Mike. Any idea what the blower motor specifically was on max?

 

[FastDriver]

I slapped that 1 7/8ths pulley on, limited the car to 6k RPM and went out to the street scene last night. The pulley made a huge difference! Also got some runs in with 2 coyotes I wish I could tell you guys about. Looking forward to getting the 2", and getting the limiter back up to 7. This 1 7/8" pulley would spin me up over 18k.

 

[Mustang5L5]

I didn't think to do that one.

I set ac to max so the compressor was engaged and fan motor on high. Next time I start the car I'll do just the fan motor alone.


As for everything on, what I mean was Efan, ac max high, headlights, hazard, defrost, radio.

I could have added rolling the windows down too. I'd imagine that would put the car pretty close to 65 amps or so.

 

[FastDriver]

Haha! I just got a mental image of you there trying to get a reading while working the locks and windows, lol!

I'm curious because I notice that the blower drags the voltage down pretty decently. With the a/c, is the only power used due to the clutch engagement? If so, I wouldn't think it's really much of an electrical draw.

 

[Mustang5L5]

Windiws was easy actually. I have a door panel off so I just clamped the window motor wire.

6.5amps when rolling down and 15a when you reach end of travel.

Door locks were 2amps and 6 if you hold the button down

I think you are right about the A/C. Just engages the clutch

 

[FastDriver]

To put a bow on this thread, here are my takeaways from this experience:

Alternator pulley specs are not well represented in advertisements.
The stock "2.25-in." pulley measured 2.17".
The "2-in." Powermaster pulley measured 2.05".
The "1 7/8-in." ASP pulley measured 1.69".
These measurements were all taken on the ridges upon which the belt rides with a micrometer.

The only pulley that worked to my satisfaction on my alternator was the ASP pulley, presumably because it gets the alternator up to a ~2,400 RPM shaft speed at my ~900 idle RPM. I'm going to put it back on and take my chances with spinning that alternator nearly 19k rpm. After talking with PA Performance, and Powermaster performance, it is apparently true that at lower idle alternator shaft speeds, the 130 alternator falls off less than the 200 amp. They also say that 130-amp alternators can make upwards of 170 amps at and beyond 6,000 RPM, where they level off at their maximum output.

Both PA Performance and Powermaster told me that the ~18,600 RPM I'll spin the alternator up to is not crazy, and though it's beyond what they'd guarantee, it will probably hold together.

PA performance convinced me to keep the unused 130amp I ordered from them, because they can build it into a 200 amp for an additional $90 + shipping. If I blow up the current one, I'll play it safer and see if the 130-amp does the trick at lower idle speeds. It's nice to have a backup.