Alternator Drains Battery

[WayneMo]

I have a Delco 10 SI Alternator that works fine when running but it has a drain on the battery
when it is not running that will drain the battery over time. Is the drain due to faulty diodes in
either the voltage regulator, Triode, or Rectifier? I see there are kits sold with various
combinations of these 3 parts. If I knew which was faulty, I could order the right parts and fix
it myself perhaps. Or should I just get a rebuilt alternator at the parts store? Kits run about
$15 to $20 depending on parts included in them. I don't know what a rebuilt one would cost. If I
knew which component was at fault, I could just buy it alone very cheap also. Your advice?

 

[tractorguy2]

You have the same problem with your Ford and your Farmall?

 

[Bob]

Is it connected as a standard "3-wire" alternator?

If you have a voltmeter, check the voltage at the #1 and #2 terminals after shutdown.

#1 should be @ zero Volts, #2 typically will be at battery voltage.

If there's voltage on the #1 connection, pull the plug and check voltage at the connector side and the alternator #1 terminal itself.

If there's voltage present on the harness side it's a wiring or switch issue, if on the alternator side it's a voltage regulator or diode trio issue.


Another check would be to unplug the 2-pin connector, then wait and see if the battery drains.

If it DOES, then disconnect the output wire and see if that ends the battery drain.

If that ends the battery drain, likely it's a rectifier issue.

 

[WayneMo]

Hi....No, I just put the message on both boards since you guys on both are so knowledgeable. The Alt is on my Super C but I do have a 861 Ford that uses a similar alternator and would be nice to know more about the alternators. You must be on both boards and that is good.
I went back and pulled the plastic connector and the battery cable still showed 12v between the loose cable and the battery terminal. Then I put the plastic terminal back in and removed the large wire that carries the output and the voltage between the loose battery cable and the battery terminal showed 0 volts!
I assume that 12v between the loose battery cable and the battery terminal indicates there is some current flow taking place......Is that not right?
If so, the problem lies with something connected to the large output screw on the alternator. So would that be the voltage regulator, the trio, or the rectifier?

 

[WayneMo]

Hi...Thanks for the reply, you seem to be very knowledgeable on these. Mine has a plastic terminal with 2 wires and a single output terminal and one of the wires in the plastic terminal also connects to the output terminal. I guess you call that a 3 wire connection.
I went back and pulled the plastic connector and the battery cable still showed 12v between the loose cable and the battery terminal. Then I put the plastic terminal back in and removed the large wire that carries the output and the voltage between the loose battery cable and the battery terminal showed 0 volts!
I assume that 12v between the loose battery cable and the battery terminal indicates there is some current flow taking place......Is that not right?
If so, the problem lies with something connected to the large output screw on the alternator. So would that be the voltage regulator, the trio, or the rectifier?
When you said to check voltage at the #1 and #2 terminals, did you mean with the connector removed and checked at the terminals on the alternator or the harness?
If there is current draw, it must be small since I used the tractor yesterday starting it several times and left if sitting for some time with no battery problems. I left it overnight with the cable removed. Excuse my ignorance but I always thought if there was battery voltage between a loose cable and the battery terminal, that indicated there is current flow when the cable is connected to the battery terminal.

 

[JMOR]

By your voltmeter method, all you learned is that there is a drain. On the 10SI, there is always drain on #2. It is so very small that it will take most of a year to significantly drain a good battery. Insert a test ammeter in the lead to measure drain current. Then you will KNOW the magnitude and if abnormal or not.

 

[WayneMo]

Hi...Thanks, I tried to use my cheap voltmeter to measure the current but it showed nothing
and I suspect the meter was the problem. I will try another meter. I have no idea as to what
the drain might be but it may be small like ma's.
It sounds to me like the Rectifier is the problem since the output terminal is always hot
even when ignition is off. Also the voltage regulator seems to be working viewing the volt
gage on the tractor when running. I do not know the function of the Trio.
I worked on one some time back (my memory is terrible at 80 years age) but I recall to
wire the 10 si alternator you had to run a loop from the #2 terminal to the output terminal
for some reason. Also there was a requirement to put a diode in one of the lines to prevent
the motor from running on when shut off. I need to find a wiring diagram for converting the 3
wire 10 si alternator.

 

[JMOR]

(quoted from post at 16:12:05 04/22/18) Hi...Thanks, I tried to use my cheap voltmeter to measure the current but it showed nothing
and I suspect the meter was the problem. I will try another meter. I have no idea as to what
the drain might be but it may be small like ma's.
It sounds to me like the Rectifier is the problem since the output terminal is always hot
even when ignition is off. Also the voltage regulator seems to be working viewing the volt
gage on the tractor when running. I do not know the function of the Trio.
I worked on one some time back (my memory is terrible at 80 years age) but I recall to
wire the 10 si alternator you had to run a loop from the #2 terminal to the output terminal
for some reason. Also there was a requirement to put a diode in one of the lines to prevent
the motor from running on when shut off. I need to find a wiring diagram for converting the 3
wire 10 si alternator.

ost will drain one milliampere or less.

 

[Bob]

Wayne, the large output stud will always be "hot" while the battery is connected and has charge, it's NOT a reflection on the condition of the rectifier.

The "diode trio" is a rectifier separate of the main rectifier, it's purpose is to rectify a portion of the AC output of the stator to provide current for the voltage regulator to power the rotating field/rotor with.

Here's a simplified diagram showing where a diode can be installed to prevent current backfeeding/engine run-on when the ignition is switched to "OFF".

<img src = "http://www.gondtc.com/~blweltin/Bob/AlternatorHarness3.jpg">

 

[WayneMo]

Hi...Thanks for the photo, a photo is worth a thousand words! I ordered a full repair kit and will try to fix it myself. I think I have it straight now as to the wiring! You guys are great here on this forum.

 

[WayneMo]

Still do not know which component is at fault since there is 12v between the loose battery cable and the battery terminal when the ignition switch is off, indicating a drain.
Would the likely fault be with the main rectifier or the trio or possible the voltage regulator? It works fine when running as far as voltage output, now I just pull the battery cable when it is shut down.
You seem to be very knowledgeable on these, I understand most but do not fully understand the function of the trio, but I may never understand that!

 

[JMOR]

(quoted from post at 10:05:20 04/23/18) Hi...Thanks for the photo, a photo is worth a thousand words! I ordered a full repair kit and will try to fix it myself. I think I have it straight now as to the wiring! You guys are great here on this forum.

ix it!? Has it really been established that there is a problem to fix, yet? :roll: