I just finished my custom dashboard including new speedo,tach,light and ignition switch. Went for a short ride about 6 miles,made a 5 min stop. Went to start it and the battery was dead. Got a jump and noticed my volt meter around 10v, made it about 1mile while keeping my rpm up volt meter showed 12v.
The car died at the next light. The local police made me get it towed since I was at a major intersection $112.25 for 5 miles (ouch). So here's my problem with a volt meter on the back of the one wire alternator to ground at idle I have 11.50 v at 4k rpm I get 12.95 v with just the electric fuel pump on. The battery is relocated to rear and there is rear shut off switch. .Is it possible for an alternator to be weak? Or is something drawing the battery down. All lights work and the the battery holds a charge.Or should I unplug everything for my dash and check the voltage again?


Thanks Dave

So here's my problem with a volt meter on the back of the one wire alternator to ground at idle I have 11.50 v at 4k rpm I get 12.95 v
Thanks Dave
Take the alternator to a shop, if it's a one wire internal reg. ? It sounds like it's dead.

That was easy. to the shop it goes. Thanks

Have you tried bypassing the regulator? If the alternator has good output when you full-field it; and crappy output otherwise--you need a regulator, not an alternator.

Full-field an internally-regulated alternator by locating the "D" shaped test hole on the back side, and slide an "L"-shaped 1/8" Allen wrench (short end) into the hole so you ground the internal tab to the case. Don't go deeper than 3/4" into the alternator case.

IF the alternator hummmmms like mad; and the lights get really bright--you've got a bad regulator.

There are six diodes inside the alternator. One or more of them could be bad causing low output from the alternator.
Squido

Schurkey
It is internally regulated.
I looked for the "D" shaped test hole with a mirror in the back
and could not find it, could you be more specific with the location.



Thanks Dave

I'll post a photo tomorrow.

Note the metal tab inside the "D" shaped hole at the 11 0'clock position. That tab is part of the integral regulator. Touch that tab and the body around the tab with a screwdriver and you ground the regulator and make the alternator put out maximum current @ RPM.

The "D" shaped hole I am referring to is the one that is about 2" above and slightly to the left of center. The "D" shaped holes around the outer circumference are for cooling purposes only.

http://www.chevelles.com/showroom/data/500/Delco_test_hole_1_small.jpg

http://www.chevelles.com/showroom/data/500/Delco_test_hole_2_small.jpg

If you have an alternator off-the-car, you could probably see the tab that you're grounding to the alternator case by looking through the D-shaped hole. I don't have a photo of the regulator outside of an alternator, but you can see the tab in this link: (it's the little bitty guy sticking out to the right.) A one-wire regulator--I think--is just like this one, but it has the two bigger terminals electrically tied together.

http://www.napaonline.com/NOLPPSE/(S(yjqhn1qwh4ctwdy3x4ksma55))/Detail.aspx?R=ECHVR178_0208875498#

With the engine at ~2K rpm (depending on pulley ratio) a full-fielded alternator should throw it's rated amperage; and 17+ volts assuming the battery is reasonably charged and in good condition. Don't full-field it for more than a couple of seconds or it'll overheat.

With the battery in the back, I'd also be interested in voltage drop between battery and starter (both + and ground) and between alternator and battery (both + and ground)

A fully-charged battery should have 12.6--12.7 open-circuit volts. 12.25 volts is half-discharged.

I brought my alternator to .a local shop (Barbin elec. in Milford CT.) The alternator checked out fine. The owner who is also a gear head is full of info. He said since I have MSD, duel elec. Fan, elec. fuel pump, under drive pulleys and an electric vacuum pump for my brakes I could be using more power than is available. Also he does not like optima batteries. The first thing he wants me to do is swap the battery for a known good battery from a daily driven vehicle and recheck the alt. output. If that doesn’t work he said I could bring the car to his shop and he would check the amp. draw of my accessories with a D.C. ammeter and offer more suggestions. Thanks for your help and the pictures. I will repost with the outcome.



Thanks again Dave

What does he not like about the Optima battery :confused:

He sold 3 and all 3 came back. Also he said if they die 100% (like if you leave your lights on overnight) you can not get them recharged. Weak will recharge dead will not. Like I said though that’s his opinion I’ve had no problems in the last 2 years with mine.

Dead will recharge if using the correct charger. I have had success on Optima's that have been drained by bringing them back up using a Battery Tender Plus I purchased to maintain the Harley battery. It takes a couple of days but works. One was rescued from the dumpster showing zero volts and brought back to life.

I just replaced my underdrive crank pulley, 5 1/2", for a regular 7" pulley tonight. Much better charging.
Might check it out. That small pulley is turning the alternator real slow.
Hope you get it figured out.