Alternator test.

[flattop1]

Any of y'all ever do this test for bad diodes .
Chasing a parasitic drain .
Note: we set our meter to AC. We usually use DC when testing our car. By selecting AC, your meter will ignore the DC voltage and focus on AC. If AC is leaking out, your meter will see it. The diodes are supposed to block the AC from getting out of the alternator. If a diode goes bad it will let some of the AC get out. For the simple alternators in our classic cars, anything over 0.5 volts AC is too much. You will probably see a little AC. The diodes are not perfect, so a small amount of AC will always get out. Sensitive meter. Typically, it’s 0.010, 0.020, or 0.030 of a volt. Again, check with volt meter.

 

[KartRacingLA]

Im about to try this on one of our tractors. SOB is dead every time we go to get on it

 

[flattop1]

Ten 4 i know on my boat it's the black box / regulator . Still charges but battery goes dead . Change that and it's fine .

 

[flattop1]

I almost always look for a work around . A diode in the batt line should do the same thing ,stop the back flow .

 

[XXX#40]

Im about to try this on one of our tractors. SOB is dead every time we go to get on it

Most older tractors used the 1 wire GM alternators and an external voltage regulator, easy to check with a voltage meter.

 

[KartRacingLA]

Most older tractors used the 1 wire GM alternators and an external voltage regulator, easy to check with a voltage meter.

Ours are all fairly newer deeres

 

[DynoDon]

On the older tractors/cars if the engine kept running when removing one of the battery cables the voltage regulator was bad. If the engine quit the alternator was bad.

 

[flattop1]

Looking at parasitic loss through the alternator.
Vehicle runs when battery is unhooked . 14+volts when running .
Battery goes dead in a couple weeks .
Multiple vom meters connected to no avail.

 

[Surveyor]

Why do you assume through the alt? Could you unhook it from the battery after you shut down and see if the battery still discharges? I could be a bare wire anywhere on the battery side of the key, or wire running to the alt. I am not familiar with the test you are discussing so you are probably way past this.

 

[flattop1]

Yes I've exhausted most power drain techniques.
It seems a bare wire is a possibility. As it is somewhat intermittent.
Just never know when it would be dead .

 

[95 shaw]

Have you disconnected power wire at alt and read amps between alt and power wire?

 

[shiftyag]

Disconnecting the battery is not a good idea, voltage can surge to 25 volts + and also cause diode damage. I work in the industrial engine field and the common problems are alternator, ecu, and computer not going to sleep. Either way whether it is one these items or not, by using the amp side of your meter will show the parasitic draw. One lead on battery, one lead on cable. turn key on, do not start! Should show draw of ignition system etc. turn key off will show parasitic draw, should be less than .15 or 150 ma. If the unit is newer then it could take up to 30 minutes for the ecu, computer etc. to go to sleep. If you have more than .15 amps, start disconnecting components /circuits until you find the draw.
FYI if you use the ma side of our meter most only have a 1 amp fuse, and they are usually already blown, so that is why I stated to use the amp side.
Good luck!

 

[flattop1]

Have you disconnected power wire at alt and read amps between alt and power wire?

No I have not , Good idea .

Disconnecting the battery is not a good idea, voltage can surge to 25 volts + and also cause diode damage. I work in the industrial engine field and the common problems are alternator, ecu, and computer not going to sleep. Either way whether it is one these items or not, by using the amp side of your meter will show the parasitic draw. One lead on battery, one lead on cable. turn key on, do not start! Should show draw of ignition system etc. turn key off will show parasitic draw, should be less than .15 or 150 ma. If the unit is newer then it could take up to 30 minutes for the ecu, computer etc. to go to sleep. If you have more than .15 amps, start disconnecting components /circuits until you find the draw.
FYI if you use the ma side of our meter most only have a 1 amp fuse, and they are usually already blown, so that is why I stated to use the amp side.
Good luck!

Finding a Digital meter without auto off is tough . (I Did )
I will have too go through that procedure again with a Bit more Dillegence .

 

[JLSRacing]

I have use a 12dcv test light for checking low draws. Remove a battery cable put the test light in series. Start with key off. Don’t start, If it lights, then there is a draw. Start pulling fuses or plugs till you find it.

 

[flattop1]

Computer and anti theft seem like they are always on . Pretty much accepted, pull the batt cable if I leave it sit .