Technical Chasing Parasitic Draw Help

Trying to get a test done on my one wire alternator and having a time of it. Took it into Autozone and Advance and they need a number for a one wire to put into their testing machine and cant seem to come up with one that is currently in there. It is for a small block chevy #7127 but converted to one wire. Can anyone come up with a fitting number in their machines? Long story but its out of the car and i cant take the car in. It is a project at the end of the build and not running yet. I need to trouble shoot some bugs and need to eliminate the alt form the mix. Thanks in advance

 

It's a..."one" wire...device !

Put it back in the car, make sure that it's grounded "properly", connect ONE (10 gauge min.) wire to the "battery" post and the other end to the positive post on the battery.
Make sure that the car has a volt meter / gauge in the car, or buy one, and connect it to the electrical system (!).

Start the engine, watch the gauge needle.
If the gauge doesn't read anything, the alternator is bad. If it reads low (below about 12 volts) voltage, rev. the engine a little and see what happens. If it's still low, then the alternator is bad.
The gauge should read a high 12 to mid 13 volts to be a good alternator.
Simple, a five minute job.


That's ALL there is to it !

Mike

 

The alternator won't work until you get it spinning....and then you can put a volt meter on the wire and see if it's working.

Since it wasn't used on any production cars, it's not likely that you'll find a setting on a tester for it, eh?

 

Does your town have a Alternator Starter or Auto Electrical repair shop that doesn’t have key board staff?

 

Take it to O’Reilly and have them test it as a Wilson 90-01-3125

 

or Autozone as a Proform 66434

 

Thanks but I think you missed the part about not running yet....Takes alot of juice to get one started for the first time

 

ok the two numbers led me to other cross over numbers , we will see what happens.

 

This probably won't be any help. Back in the 80s when I lived in Columbus and worked at Battelle, there was a shop that worked on starters and alternators and the like on King Avenue about halfway between the thruway and Battelle. Probably gone by now, but if it's still there it may help...

 

Wasn't on King Avenue. Other side of Battelle is 5th Avenue. Hey it's been a while...

 

An alternator has NOTHING to do with an engine's ability to start except for having charged the battery to capacity before it was shut off last time. You do not need an alternator, generator or any charging device on an engine or even belts for that matter to fire it up for a few seconds. Meaning it "won't start because of the alternator" is total bullshit if the battery has a full charge. You need the alternator to recharge the battery after you start and or run the engine long enough to put a drain on the battery.

What you do need is a good strong battery and good cables to crank the engine to start it.

 

So now that we are on it....I am chasing a draw. Can a bad alt show as a parasitic draw on a battery during a test with a multimeter between the neg cable and neg post even if the car has never been started?

 

An alternator can have a draw inside. Have had a couple of these problems over the years even with a new one out of the box.

 

understood but my question is can it show during a draw test even though car has never been started?

 

In some cases, even a burned-out idiot light will render a G.M. alternator inoperative.

 

If you suspect the alternator is drawing power do this. Have it connected as should be for a few hours. After which time but a multi meter to the battery and record voltage. Now disconnect alternators “1 wire” then watch multimeter to see if voltage creeps every so slow up. If it does, well…

 

you can use an ammeter (or milliammeter) to find a current draw. But you might need to learn about what an ammeter does, and how to use it, so you don't create mayhem. Most digital multimeter have this function.

hint: the ammeter goes in between the alternator and the wire that connects it to the battery. You do NOT connect one side to ground! Start with the meter on the highest current setting, and work your way down until you get an indication. If you get down to the lowest setting, and no current indication, then there is no draw.

A leaking diode in the alternator can cause a draw.

 

That test means that there is some live circuit, but it doesn't tell you where or how much current you are drawing. If you have a modern radio with a memory it will show as a draw with this test. However, the draw is so slight, maybe 10 or 20 milliamps, that it would take multiple months to draw a battery down. If you have a fuse block that allows you to get to all the fuses, a better test is to check the voltage drop across each fuse. That will allow you to pinpoint the source of the draw. Set your voltmeter to millivolts, mV, and connect the meter across the fuse, red lead on one side, black lead on the other. With everything turned off in the car, you should read zero across each fuse. Fuses that give a voltmeter reading means there is current flowing in that circuit.

Here is a chart that gives you current draw based on voltage drop. Note that the voltmeter reading is in millivolts (0.001 volt). Any reading that results in a draw over 150 - 200 milliamps will cause a battery to drain. The higher the number, the quicker the drain. So if you have a 30 amp fuse and you read 1.1 millivolts across it, the current draw on that fuse is 564 milliamps. That will drain a battery in a fairly short time.

 

I am using the multimeter to measure draw and it shows none. Test is breaking between the neg cable and neg terminal. 10A setting. Battery volts are good 12.8V and its new. Starter is new. Problem when i start it i get about two revolutions and its goes to clicking and dead. Lights work fine when turned on.
Its a small block chevy in a model A truck. No radio. Only lights and three gauges. Nothing that would create a constant normal draw. Advice appreciated

 

If you suspect a draw on the electrical system, and easy way to check is to disconnect the negative battery terminal and with everything turned off in the car touch the negative terminal lead to the battery. If you see a arc of any size something is trying to draw power and you need to find out where it's happening or it will kill the battery.

 

Sounds like a dead battery. How old is the battery? If it's more than a month old, tell us it's history...

or just try another battery.

 

Sounds like a battery or cable problem. Disconnect all the cables from the battery to the frame and starter and clean them with sandpaper or emory cloth. Do this even if they look good. Make sure the grounds are clean, both cables and where they attach.

 

new battery tests at 12.8 V

 

Load test will tell more than a voltage reading will.

 

Charge the battery, unwire or remove the alternator, see if you still have a draw. Like @Mr48chev said, it doesn't need to be there to start the engine. If the draw is gone...process of elimination.

 

Unfortunately not battery had it tested twice at two different places

 

Yep did that and still current situation of two revolutions and no draw showing on multimeter

 

Ok....how about you tell us about the battery's history. And let us know when you try another battery, and it works just fine.

 

Do you have another battery? Take one out the daily.

 

Hold on a mo. You’re trying to start it with the multimeter in series with the negative cable.

Your multimeter won’t be able to cope with that sort of current. What’s it rated at 5amps max ???