I've got the 37 amp alt and was wondering if'n I installed the 55 amp that the lights would not dim so much at idle?

Yes.. depending on your pulley sizes...

heck, if you're using a 10SI, go all out and get a 63 amp.... or, if you want something that will fit in the same space as the 10SI, get a 94 amp 12SI. all will cost about the same...
Bill

The lights dimming at idle is probably due more to low voltage than anything. This low voltage is from a few issues, misadjusted voltage regulator, current load in the car, poor grounds, battery not up to snuff, or bad alternator.

The first check would be to put a voltmeter on the alternator and check the voltage while idling and while revved to say 2000-2500 rpm.

Try it again with the battery disconnected, but shut off the engine before reconnecting the battery.

You can try connecting the alternator frame to the frame of the car and see if it makes a difference. Grounds are the most common problem in these old cars.


Now some dimming is normal. If your idle is low enough, the alternator simply isn't making that much voltage.

But these are a start. I doubt the 55 amp would help unless there is a big load (AC, big stereo, Halogen fog lamps, etc.) elsewhere.

read the voltage at the battery at idle and at 2000 rpm, a couple of relays on the headlights fixed my dim lights and will probably fix yours.

see my friends at madelectrical.com

The 10SI/12SI hook up the same? I have an external regulator with the square plug in. Thanks

the 10SI & 12SI both have internal regulators (that's what the "I"
indicates). somewhere in the archives you will find instructions from Plasticman on how to convert from an external regulator to an internal one (really rather simple...)



Bill

Meh, I just picked up the 55 amp alternator. I don't speak 'legtricity' all that gewd. I'll check the ground wires if I can remember where I put 'em.

Dave,
I changed from 37amp to 55amp (NAPA #13-4013) last June. There is no difference at idle. Mind you we are talking about only 650rpm and 550rpm in Drive (Powerglide). Those old alternators simply do not put out at those low revs.

if you want amps at an idle try the CS130 (105 to 140 amps); it is designed for output at low rpms.
Bill

I have a 135 amp with an external regulator. It's plug and play as they say.

I did put a 60amp fuse between the alt output lug and red harness line, just in case the some incredible demand was made on the alternator through the factory wiring.

High output alternators generate more power at lower revs too, so the lights don't dim.

I went with PowerMaster for the same reason. But if you go this route, don't forget to bypass the Ammeter! I made that mistake. Also, if you go this route, you'd be well advised to run a direct heavy-gauge line back to the battery, so the alternator get's a good signal when the battery is at full charge. It's no fun overcharging a battery. Difficult cleanup of frame and battery tray. Been there too! Glass beading can be messy! *LOL* A fusible link is always adviseable. - Pat

I talked to an alternator 'expert' and we came to agreement to take off the standard 2.5" pully and install the cadillac 2.25" pully. This will effectively spin the alt quicker at all rpm's and keep the lights bright at idle.

Bill

Sounds like a good plan. If you rev and start to throw belts JohnZ has recommended the Dayco Top Cog belts available at Advance Auto.

Installed the 55 amp alt last night using the 2.25" Caddilac pully instead of the 2.50" std one. Turned on all accessories (headlights also) and the lights stayed bright at an engine idle of 700 rpm. The ONLY thing I noticed was that with the old 37 amp alternator the battery gauge was always slightly on the + side of 0 at speed and would dip alot to the - side of zero at idle. Now the needle stays from center to a tick to the minus side wether at speed or idle. I am using the solid state regulator also. Think the reading is ok?

Check the voltage at the battery under those conditions. A reading above normal battery voltage (12.6 Volts) says it is charging. 13.5 to 14 Volts would be ideal.

Plasticman

Actually gates is a better belt because it`s not a top cog. Top cog doesn`t help drive small pulleys which is why the Gates internal cog closes up tighter and specifically for use with small pulleys. Its the only difference however. The statement came from the Gates field rep....

I have stocked and sold them both at one time or another.

Will do this afternoon, thank you.

I have the cogged fan belt. I checked yesterday with everything on I got 14.45 at the battery at 700 rpm. Everything off I got 12.6. That's the good news.

This morning I went to drive it to work and saw the door was ajar. This left the interior lights on, but it fired easily and was charging. The needle was about half way between being pinned and zero. About 20 minutes later the needle went back to a tick before zero and the lights dimmed some. ??? Then the needle started bouncing between zero and max and then all went black, no engine or lights. This was at freeway speeds!! Got it off the fwy at an exit ramp and pulled over. Smoke!!! Grabbed my extinguisher and raised the hood. The windings on the alt were red hot and fire was coming out of the alt. I sprayed it but it didn't go out. I hit the battery shut off switch and the windings went black and the fire went out. WTF!!! I pulled all the wires off the alt, hit the batt switch and it started and ran fine, although off the battery only. Took the alt off at work and will wait 'til daylight to drive it home on the batt. It's about 20 miles, should make it. Ideas? Brand new (rebuilt) alt with about an hours running total. Sheesh.....

Dave
this might sound like a frivolous answer, but i'd guess it was just a bad alternator; get another and try again. but this time i'd suggest converting to an alternator with an internal regulator (no particular reason other than having an internal regulator is one less thing to go bad...)
Bill