battery drain / Alternator internal short?

[krispoulin]

Is it likely that smoking an ammeter could cause an internal short in an alternator?

Basically, I accidentally started the car without alternator ground wire connected and destroyed the ammeter gauge. Bypassed gauge with 30A fuse and have been chasing & fixing shorts since (some from before I bought car, apparently). I thought I had found them all, but still am suffering from a slow battery drain. It takes about 48 hours to drain it to the point where the car won’t turn over. Also should mention that the voltage regulator clicks when I connect battery.

I put my multi-meter (measuring Amps) between battery’s negative terminal and ground cable. Measured 0.6A. Removed fuses one by one until all four were out. Still measuring 0.6A. Disconnected white wire from alternator. Measured 0 A. Same 0 A happens if I disconnect 4-wire harness from alternator.

Looking at wiring diagram, checking other things that might possibly be causing the draw. Left fuses out and disconnected radio, but the battery still drained.

Currently (no pun intended), battery is connected with white wire removed from alternator to see if it still drains. We'll see...

Any suggestions or direction would be greatly appreciated. I've found lots of good info searching the forum, but nothing that 100% confirms what I think. Then again, I'm not really sure what I'm talking about!

[garth]

Sounds like your alternator has a fault or less likely the voltage regulator.

The battery drain test is a good test.

Disconnect the white wire from the alternator and measure resistance from terminal to ground (alternator case). Make sure the ohm meter postive is on terminal. Resistance should be be at least 500kohms. Swap leads and put the negative on the alternator terminal. Resistance should be <2 ohms. If you can't get this pattern the diode bridge is faulted.

Did the ammeter fail with the engine running? Sometimes an ammeter will just act like a fuse and melt open and some times it will also open and short to ground. In the latter case you have to remove it as well as jumper it.

When running did the alternator charge? If no ammeter, battery voltage above 12.9-13.0 volts usually indicates the alternator is charging at least minimally.

Keep testing.

[redroadster]

a short detector may assist you in locating the draw .225 will draw down a group 56 batt in 36-48 hours
but yeah sounds like what Garth said

some of you may want to scope the alternator too, we did at the dealer and some of the results were wild,diodes leaking A/C voltage , some looked like you could plug in a blender to it and it would work .
a internal draw in the battery itself is common too or a cell that is not up to proper volts

[fj20spl311]

Sound like the field is activated. If it was a short, the wire would be smoking from the high current.
If its a point type voltage regulator, The points might have "welded" closed. I don't know off the top what keeps the field circuit open until the car start......I use internally regulated Alternator.

[spyder]

With the key off, check the (f)ield wire on the alternator. It should have zero volts on it. If it has more than zero, than the (ignition on) voltage is getting to the regulator. If it is zero, pull the (a) wire off the alternator (wire on stud post) and see if the current draw on the battery stops. It is possible to have a leaky diode in the alternator.

[krispoulin]

Sounds like your alternator has a fault or less likely the voltage regulator.

The battery drain test is a good test.

Disconnect the white wire from the alternator and measure resistance from terminal to ground (alternator case). Make sure the ohm meter postive is on terminal. Resistance should be be at least 500kohms. Swap leads and put the negative on the alternator terminal. Resistance should be <2 ohms. If you can't get this pattern the diode bridge is faulted.

Did the ammeter fail with the engine running? Sometimes an ammeter will just act like a fuse and melt open and some times it will also open and short to ground. In the latter case you have to remove it as well as jumper it.

When running did the alternator charge? If no ammeter, battery voltage above 12.9-13.0 volts usually indicates the alternator is charging at least minimally.

Keep testing.

Voltage regulator is a new one from Dean at Datsun Parts.
Alternator was rebuilt in April or about 250 miles ago.

After battery being connected 40 hours (but with white wire not connected to alternator), battery measures at 12.8V.

Regarding garth's suggestions & questions:
• Measured resistance from alternator terminal to ground = 23 ohms.
• Swapping leads just gets me 23 ohms again.
• Engine was running when ammeter burned up. It was the first time starting the car after a lot of jobs with the engine out. Ground wire on alternator got overlooked and wasn't connected.
• Alternator definitely charged before rebuild, but I can't confirm one way or the other if it recharged after it was rebuilt and ammeter got destroyed. I believe that it was.

With the key off, check the (f)ield wire on the alternator. It should have zero volts on it. If it has more than zero, than the (ignition on) voltage is getting to the regulator. If it is zero, pull the (a) wire off the alternator (wire on stud post) and see if the current draw on the battery stops. It is possible to have a leaky diode in the alternator.

• I checked field wire and got 0 V.
• As mentioned above, I'm at over 40 hours of having that (A) wire off the alternator and am at 12.8V. {(A) wire was reconnected for field wire test.}

Voltage regulator clicks loudly when (A) wire is connected to alternator. Or, if (A) wire is already connected, it clicks when I connect the 4-wire alternator harness.

At this point, it seems like it could be a leaky diode, based on the great info and troubleshooting tests you've provided. Could that have been caused by the event that smoked my ammeter? Or is this something that my alternator guy should have noticed when it was in for the rebuild?

Thank you to everyone for their help on this.

[Linda]

As I recall the alternator grounds thru the case, so the bottom bolt helps it ground. The ground wire though is also used.
Running with the neg battery cable undone is the bad one for the alt., not sure if you did that
You can take the alt to get it checked, perhaps at O'Reilly's or AutoZone or an alternator/starter shop.
Linda

[Toptech360]

If i read all this right, sounds like you methodically diagnosed the problem and narrowed it down to the alternator. Nice job. Sorry it means probably replacing a fairly new alternator.

[garth]

Sounds like your alternator has a fault or less likely the voltage regulator.

The battery drain test is a good test.

Disconnect the white wire from the alternator and measure resistance from terminal to ground (alternator case). Make sure the ohm meter postive is on terminal. Resistance should be be at least 500kohms. Swap leads and put the negative on the alternator terminal. Resistance should be <2 ohms. If you can't get this pattern the diode bridge is faulted.

Did the ammeter fail with the engine running? Sometimes an ammeter will just act like a fuse and melt open and some times it will also open and short to ground. In the latter case you have to remove it as well as jumper it.

When running did the alternator charge? If no ammeter, battery voltage above 12.9-13.0 volts usually indicates the alternator is charging at least minimally.

Keep testing.

Voltage regulator is a new one from Dean at Datsun Parts.
Alternator was rebuilt in April or about 250 miles ago.

After battery being connected 40 hours (but with white wire not connected to alternator), battery measures at 12.8V.

Regarding garth's suggestions & questions:
• Measured resistance from alternator terminal to ground = 23 ohms.
• Swapping leads just gets me 23 ohms again.
• Engine was running when ammeter burned up. It was the first time starting the car after a lot of jobs with the engine out. Ground wire on alternator got overlooked and wasn't connected.
• Alternator definitely charged before rebuild, but I can't confirm one way or the other if it recharged after it was rebuilt and ammeter got destroyed. I believe that it was.

With the key off, check the (f)ield wire on the alternator. It should have zero volts on it. If it has more than zero, than the (ignition on) voltage is getting to the regulator. If it is zero, pull the (a) wire off the alternator (wire on stud post) and see if the current draw on the battery stops. It is possible to have a leaky diode in the alternator.

• I checked field wire and got 0 V.
• As mentioned above, I'm at over 40 hours of having that (A) wire off the alternator and am at 12.8V. {(A) wire was reconnected for field wire test.}

Voltage regulator clicks loudly when (A) wire is connected to alternator. Or, if (A) wire is already connected, it clicks when I connect the 4-wire alternator harness.

At this point, it seems like it could be a leaky diode, based on the great info and troubleshooting tests you've provided. Could that have been caused by the event that smoked my ammeter? Or is this something that my alternator guy should have noticed when it was in for the rebuild?

Thank you to everyone for their help on this.

If the alternator was not grounded when running it is likely the diode bridge partially failed and the alternator pumped unregulated and unfused AC current into the battery until the ammeter got smokey and was shutdown. The alternator might be salvageable but a new replacement might make your electrical system more reliable.

Bright lights!

[krispoulin]

If the alternator was not grounded when running it is likely the diode bridge partially failed and the alternator pumped unregulated and unfused AC current into the battery until the ammeter got smokey and was shutdown. The alternator might be salvageable but a new replacement might make your electrical system more reliable.

Bright lights!

Thanks everyone for the info and direction.

I'll take it to a local shop to confirm this, like Linda suggested.

I have no reason to distrust the guy who rebuilt the alternator, but I was hoping maybe he should have noticed this issue when he rebuilt it and I could blame him! No such luck. Looks like it's my fault for starting the car with the ground wire disconnected.

I'm wondering if driving the car with alternator in this condition could do further damage. Just curious...

[krispoulin]

If the alternator was not grounded when running it is likely the diode bridge partially failed and the alternator pumped unregulated and unfused AC current into the battery until the ammeter got smokey and was shutdown. The alternator might be salvageable but a new replacement might make your electrical system more reliable.

Bright lights!

After reading more about alternator diodes on the web, I'm curious to try to replace mine on my own. Bad idea?

Are the diodes for this specific alternator even available?

Seems like it could be a fairly easy job, but I've never done it before.

[redroadster]

your alternator should ground thru the mounting , you have a ground to the block to start it right ?
there is a small helper ground too thats what you left unhooked
you said you checked amps on the neg side ?
that won't be charge amps /volts DC systems charge NEG TO POS only
negative means it rejects current ....positive it accepts current
so check the pos charge wire off the alt ( amp clamp easyest way )
is the rotor magnetized ? does the pulley grab a screwdriver with the ign on only ( not running )

BTW any interest in a genuine DATSUN ELECTRICAL SERVICE GUIDE from 78 ( when they sent me to training ) covers alternator , starter , trouble shooting with illustrations I could scan it I guess

[Linda]

If you take the little cover off the alt you can see if the brushes are worn or not making contact. Brushes are easy to replace by soldering in.
Did the alt get checked to verify condition?
As stated the alt mounting provides grounding too so perhaps that helped.
Check the VR for grounding and that the plug wires make good contact. I had the problem with the F Field wire.
Linda

[krispoulin]

Wrapping up this one:

Alternator shop replaced the diodes and the stator (had an "open"). All seems to be working fine now. Battery has been connected since a Saturday morning drive (48 hours ago) and is holding its charge.

[garth]

Wrapping up this one:

Alternator shop replaced the diodes and the stator (had an "open"). All seems to be working fine now. Battery has been connected since a Saturday morning drive (48 hours ago) and is holding its charge.

Good post repair info. It will help guide the next roadster troubleshooter!