The Stovebolt Site Forums The Shop Area The Electrical Bay Another bad alternator?

I purchased a new alternator 3 months ago, last weekend it failed on me (failed test at flaps also). Thinking I would be smart, I put in a voltmeter after installing the new alternator. On this last one, I ensured it was good by having it tested prior to purchasing it. Voltmeter read between 11-13 which is low when driving. Today, I replaced the battery since it is 6 years old.. Even after replacing the battery, the voltmeter is still reading 11-12. On Monday, i am rewiring it directly to alternator and it’s own ground.

I can hear a slight squeal on acceleration. I loosened the belt for 1/2” of play. Going to adjust alternator slightly for better alignment. Hopefully that resolves the issue.

Any thoughts? Bad gauge?

Chris

1952 3100 with single wire alternator

Guessing and shotgunning parts at a problem is not the best way to resolve an electrical problem. A fully charged battery should have about 12.5 volts at the posts before starting the engine, and if the alternator is functioning properly, the voltage should be between 13 and 14.5 volts. It sounds like you've had another alternator failure, or something is wrong with the way the charging circuit is wired. Are you running a so-called "1-wire" setup? (which actually requires the use of two wires)?
Jerry

I have a one-wire 12v alternator that has been working for 21 years on a 1954 pickup.
It was cheap - from J C Whitney (around 35 amp, as I dimly recall).

Wired like this: http://powerking.co/wp-content/uploads/onewirealternator-4.jpg

I trust your advice/statements, Jerry - where is the other wire?

I was not trying to shotgun parts. We originally figured out alternator was bad, so we fixed it. After that, the Bad battery was at 11.6 volts between the posts so I replaced it. I play on starting the engine up and using my tester to go between the one wire bolt to a ground to see the actual voltage it is putting out. I plan on checking that with the gauge I am rewiring.

OK, you got me, if there is more than one wire, where does the other wire go? Is it a ground on the extra bolt on the back of the alternator?

If you're using a 10 SI alternator, it needs a "voltage monitor" wire from either the ignition switch, or it can be just a jumper wire from the big charge output lead to one of the terminals around the perimeter of the alternator. Looking at the back of the alternator, it's the blade terminal to the right side. The other blade terminal is used as a ground wire for a "no charge" light on the dash if you choose to use one. That one is not necessary, but the jumper to battery voltage must be there.

http://alternatorparts.com/images/repair_manuals/10si-15si-type-116-136/figure0004.png

Did you recharge the battery before you replaced it? If not, it was probably still good.
Jerry

My system sure worked better when I ran a dedicated ground wire, 8 gage, from the back of the alternator ground lug to the battery negative terminal. If your brackets or alternator are painted you might not be getting consistent ground to the alternator. That was my situation. It worked without the ground wire for a while but after a time it did not charge properly. Ground wire fixed it.

FIRST: Battery terminals clean. Alternator grounded well. Battery to motor, motor to chassis, chassis to body grounds all checked.

Then:
Use a separate multimeter at the battery posts. Around 12.5-12.6V motor off. 13.5-14.5V high idle and short rev. Report the results of the multimeter. NOT the voltmeter (for now). Probably best to do the tests after driving and again after truck sitting awhile to detect a battery problem.

Aftermarket alternators have been known to be junk. Hope you are getting a good brand and a good warranty. After you buy another battery and alternator you should have the FLAPS check with their handy dandy hand held machine to get a baseline reading of both. When installed and running in your truck.

I will go everything on Monday and report back my findings to you all.

Questions: where does ground come off of a single wire alternator? (No blades on back only a second bolt)

Chris

The mounting ears of the alternator itself. The case is ground.

Ground on our trucks is overlooked many times. Powder coating, paint, corrosion, rust, loose hardware..... all cause loss of ground. Everything has rubber "cushions", vibration isolators and etc. Since ground is accomplished by using all the metal (motor, frame/chassis, body, brackets, component housings and cases) we must be sure these components are tight, mounted to clean bare metal. Star washers are used in some places. If there is a bracket mounting a component, all it's bolted connections must be clean metal. To "bypass" all this rubber, the battery ground post cable is attached directly to the motor. Then from there, heavy flexible braided straps are used to maintain a ground path to the body and to the frame. There are a few dedicated ground wires here and there on some trucks.

You can see why 80% of all electrical problems are just bad ground.

If there is a doubt about ground being lost, a separate ground wire can be added.

The motor has rubber mounts. The body has rubber pads and fender welt. The gas tank has pads. There are rubber bushings and gaskets all over the place. Sometimes we can't rely on just the bolts and screws that mount this stuff. They have plating and their contact area is not enough, especially after corrosion sets in.

The local alternator/starter/generator rebuilding shop around here will sell you a one wire alternator. They make all of the modifications to make it work internally. Only wire to hook up is the big red one which goes directly to battery. It will not "turn on" until a specific RPM is reached, then stays on as long as the engine is running.
I have had 2 of them over the past 20 years in 2 different vehicles without a hitch.
Don't ask me what they do to make it work. I do not believe in electricity.
Carl

If it was that simple, why didn't GM do it at the factory? They're not really famous for making things more complicated (translation: E$$$$pensive) than necessary. Even putting the voltage monitor on as a short jumper instead of bringing the reference voltage from somewhere downstream has its critics, but I believe that's probably getting a little too picky.
Jerry

Hotrod,

So are you saying that I can or can’t hook up directly to the single wire lead since there are no blade plugs on my alternator.

Chris

Going thru a bit of this now on a 46 - 12v - one wire 10si sooooo...... A normal key off/ all accessory off draw is supposed to be 30mA or less a drain on the battery for a one wire delco. This may result in a discharged battery thru the diodes on prolonged non use- may slightly warm alt case. I measured 39mA on my one wire. A battery maintainer will offset this. But I do not like this ---- I will go with 3 wires from now on if I differ from stock. Either a 36 ohm resistor or a idiot light bulb can be used in the lug 1 exciter circuit to key on ---key off no drain thru diodes. Lug 2 sensor goes to the battery ---- 12v+. As I understand the big 3 did not use a 1 wire for this off key draw reason.Even tho there may be an off key draw for other reasons. I could be wrong.

All 10SI alternators have blade connectors- - - -look at the wiring diagram I posted above for their location:

http://alternatorparts.com/images/repair_manuals/10si-15si-type-116-136/figure0004.png

They're plainly visible in this photo:

http://www.carid.com/images/powermaster/products/7127.jpg

The bolt on the far right can be used for a dedicated ground wire if you choose to do so. It's sort of a "belt and suspenders" thing if your mounting bracket and engine block are well grounded, though.

Jerry

Mine is a regular 10SI series alternator, not 'one wire'. There is a threaded boss on the back side of the alternator to attach a heavy ground wire. Some are threaded metric, so don't be surprised by that.

BARTamos,

Engine idle was just above 12v, battery was at 12.7v. I didn’t have enough hands to test at high idle. (Not coordinated) when I drove her tonight, voltmeter on truck stayed slightly above 12v. Do I need to connect blades? (Ie right blade to positive.) will it make a difference?

Chris

today's drive:

Everything seems to be charging great. Voltmeter was sitting at 14v while I was driving today. FIX was to run a lead off of the Right tab to the positive output on the alternator.

Thanks guys!

Chris

You did it "correctly". You have hooked up the sensing wire. You need to hook up the other blade to a bulb, thru the bulb and to ignition source. This would be the alternator exiting wire. Everybody here is right about the wiring EXCEPT many "One wire" alternators sold or modified are made using a SI (System Integrated) CASE! So they look like a normal SI.

The original SI is known as a three wire alternator. There were three wires leaving the alternator in the original GM system. Then a new three wire scheme was borne, but it's really a two wire. One of them attaches the alternator to itself. That little guy is a wire from the famous "blade" terminal 2 and goes to the battery stud on the alternator (that's the sensing wire). That works OK on our old trucks with little or no accessories. So only two wires leave the alternator: The battery wire and a wire from the famous "blade" terminal no.1 to a idiot light, thru light, to ignition switch "ON" terminal, which provides necessary resistance and glows if we are not charging properly. (This is the exciter wire). If you don't care about having an "annunciator" light, just wire no.1 to ignition "ON". ACC....or to an ignition terminal not connected to anything else.

So to be technical. The only "true" one wire alternator is one you buy that is a one wire alternator. They "self excite" and "sense" internally/electronically. These one wire alternators supposedly have a different internal voltage regulator.

The reason the indicator lights is that if alternator is working it sends 12V to one side of bulb. The other side of bulb has 12V also, from ignition switch source. As voltage drops on one end due to low alt output, the bulb starts to glow/come on receiving less than 12V on one end/getting grounded. Voltage drop causes it to light. It will also light when key on (bulb check), until the dynamo spools up.

Fin

Bart,

And that is where the confusion came in! A non electrical guy trying to figure out a so called “one wire” alternator. Only destroyed 3 alternator that were under warranty! Ops! Good thing it was a free lesson!

Thanks guys for all your help, she is running so smooth that I found other little issues!

Chris

Good job Chris. Keep it up.

Interesting depictions of what is and what is not a one-wire alternator.

For about 20 years, I have been using a JC Whitney 1-wire alternator on a 1954 truck that I converted to 12v. Yes, it is "self-exciting" - at around 400-600 RPM. Thereby, it starts charging every time we start that truck - the fast-idle/throttle and choke at start-up allows the engine to briefly reach 800+ RPM.

Here is the wiring diagram I found/use - found in the early years of the public-Internet.

Interesting!