Delco Alternator Bench Testing

[Doc Larry]

With regard to a Delco 10SI alternator with a single wire hookup:

My primary problem is that my battery is draining off, dead in a week or so after a full charge. I have a one wire Delco alternator, and I am without question losing current through that wire with the key off, and nothing else in the wiring.

I have the alternator apart for bench testing. I expected a diode problem, but the diode trio checks okay with both a diode tester and with 12 volts and a test light. The 6 diodes in the rectifier bridge also test okay. Current one way, not the other, on all six. Tested multiple times, carefully.

Question is:

Will a problem in the voltage regulator allow current to flow back through the alternator when it"s shut off? Or, is there something else I need to look at in the alternator?


Thanks, Larry

 

[JMOR]

(quoted from post at 22:05:59 03/22/12) With regard to a Delco 10SI alternator with a single wire hookup:

My primary problem is that my battery is draining off, dead in a week or so after a full charge. I have a one wire Delco alternator, and I am without question losing current through that wire with the key off, and nothing else in the wiring.

I have the alternator apart for bench testing. I expected a diode problem, but the diode trio checks okay with both a diode tester and with 12 volts and a test light. The 6 diodes in the rectifier bridge also test okay. Current one way, not the other, on all six. Tested multiple times, carefully.

Question is:

Will a problem in the voltage regulator allow current to flow back through the alternator when it"s shut off? Or, is there something else I need to look at in the alternator?


Thanks, Larry

es, the regulators always have a sense drain..yours could be excessive. Also, when checking your diodes, how much reverse current? Zero in an invalid answer as they ALL have some.

 

[Anonymous-0]

Any possibility of a bad battery?

 

[Jon Hagen]

It depends on which "1 wire" regulator you have.

Most modern "1 wire" regulators have nothing connected to the #1 and #2 regulator blade terminals. They also do not have a stud bolt on the regulator connected by a jumper wire to the "BAT" stud on the rectifier bridge.

If your regulator has nothing connected to the #1 and #2 terminals, plus it does not have the extra stud bolt connection, connected to the Big rectifier "BAT" stud, then it has no connection to the battery and can not discharge the battery

If you DO have the regulator with something connected to the regulator blades, or has the extra regulator stud and jumper connected to the "BAT" stud on the rectifier bridge, then it MAY slowly disacharge your battery. That type is not common anymore, I have not seen one in years.

 

[Jon Hagen]

The Common "1 wire" regulator almost exclusivly used today, the one with no connection to either regulator blade terminal and no internal jumper wire from the regulator to the "BAT" stud at the rectifier bridge, do not have any connection to the battery, Its blocked by the rectifier bridge, so have no "sense drain"to discharge the battery. They only sense voltage through the diode trio when the alternator is operating.

If you blew the dust out of the alternator before doing you leakage tests, you may have blown your leak away.
I have found many rectifier bridges quit leaking when you blow the conductive brush dust out of them.
That conductive brush dust coats the insulating plastic between the heat sinks and button diodes in the rectifier bridge, causing a little current leakage. Blow that dust out with high pressure air and the leaky parts sometimes heal themselves.

 

[oldironman]

Get a battery disconect from Wal Mart for $3 and shut it off after use. That will tell yor if it is your battery or the alternator. I have them on all of my tractors so that there is no danger of fire when they are stored inside. Cheap insurance.

 

[Anonymous-0]

Reverse leakage in diodes if very hard to detect.Many testers will be fooled by a diode with low leakage.

 

[Doc Larry]

So as I understand you, I should use a milliammeter and a 12 v battery to check the current on all the diodes in the reverse direction?

 

[Doc Larry]

Thanks, I can't get back out to the shop until this afternoon, but as far as I can tell this is an older Delco that's been put on an even older (1961) tractor to replace the generator. The part number is gone off the alternator. As far as dirt and dust, and moths, well, yes, this is on a tractor.

I'll try to post what I figure out, but it may be a few days.

 

[Dave Sherburne NY]

I'm not much of an automotive electrician but take a look at this. This is how I did mine and never had a problem.
Installing a one wire alternator.

 

[old]

That is the common problem with the one wire set up and yes they will in fact drain a battery over time, due to the fact they never do turn all the way off like a 3 wire alternator does

 

[LJD]

Did you take an amp draw measurement? If it's pulling power all the time it will show. Anything over 100 milliamps can be a problem.

If it is drawing over 100, you've got reverse leakage in a diode somewhere.

 

[souNdguy]

most good voms will read in MA scale..

 

[Jon Hagen]

"That is the common problem with the one wire set up and yes they will in fact drain a battery over time, due to the fact they never do turn all the way off like a 3 wire alternator does"

Old, while your statement may have been true of the first "one wire alternators of 20-30 years ago, it is totally false today with modern "1 wire" alternators.
The modern 1 wire regulators have no sense or excite connection to the battery when the alternator is not running, they can not and do not draw down the battery,

The modern "1 wire " regulator is only connected to the diode trio which is totally isolated from battery voltage by the rectifier bridge.
They have no connection to the battery and can not discharge the battery.
I have several modern "1 wire" alternators on my seasonal use farm equipment that commonly sit unused for 9 months per year. Battery drain is no faster than the ones with stock Delco SI series 3 wire alternators.

 

[JMOR]

(quoted from post at 22:22:52 03/23/12) "That is the common problem with the one wire set up and yes they will in fact drain a battery over time, due to the fact they never do turn all the way off like a 3 wire alternator does"

Old, while your statement may have been true of the first "one wire alternators of 20-30 years ago, it is totally false today with modern "1 wire" alternators.
The modern 1 wire regulators have no sense or excite connection to the battery when the alternator is not running, they can not and do not draw down the battery,

The modern "1 wire " regulator is only connected to the diode trio which is totally isolated from battery voltage by the rectifier bridge.
They have no connection to the battery and can not discharge the battery.
I have several modern "1 wire" alternators on my seasonal use farm equipment that commonly sit unused for 9 months per year. Battery drain is no faster than the ones with stock Delco SI series 3 wire alternators.

on, given "sensing off the diode trio", then they ought to have even less of an off state draw than the original 3 wire 10-SI.

 

[old]

All I can say is BULL. I see it all the time and that is why I no long will do a 1 one set up. That and the fact a 3 wire will cost half of what a 1 wire does. By the way I have yet to find a factory made 1 wire all of the ones I have ever found are aftermarket screwed up ones

 

[Jon Hagen]

Ok old, I say DOUBLE BULL.
If you would take the time to read the GM Delco publications showing the type numbers and wiring diagrams, you would see the many FACTORY 1, 2 , and 3 wire versions of the SI series alternators that Delco has built starting in the early 70's.

Open one up and look how it is wired internally. It is rediculous to claim a part that has no electrical connection to the battery is somehow magically drawing down the battery.

The battery is isolated from internal parts of the alternator, including the "1 wire" regulator, by the exact same rectifier bridge as your 3 wire alternator. If you find one that kills the battery, it has a leaky diode in the rectifier bridge, a part that has nothing at all to do with the regulator being 1,2 or 3 wire.

With no internal connection and no external Excite or sense wires attached, where is the "one wire" regulator getting access to the battery ??

By the way, my jobber price for a Delco SI series regulator is exactly the same for a 1,2 or 3 wire regulator, so your statement that a "one wire alternator costs twice as much is BULL, the regulator is the only difference and the cost is the same.

 

[Doc Larry]

First, thanks for all the helpful comments. Here"s what I discovered. When I went to put everything back to together, I found a jumper wire that I had forgotten. Someone had been installed it on the rectifier bridge from one of the diode terminals to the heat sink. In other words, it bypassed one of the diodes on the rectifier bridge. Who knows what someone had in mind. Anyway, that is now gone, the wiring is correct, and all is well.