Leaky alternator?

Vern H

Member
Hi Green Gang, I replaced a one wire alternator on an A and in a few days the battery is flat. I think the internal regulator is not doing it s job. When I remove the ground cable, there is a very slight arc when touching the lug to the post. Has anyone run into this? It is a first for me. Thanks, VH
 
The diode-trio is the most common part that fails in the SI Delcos. Very easy to replace and is cheap. $4 at NAPA and no soldering or desoldering. Just a bolt-in part.

You can test the alternator for output by bypassing the regulator with a nail or metal pin stuck in the "regulator bypass port" in back.
a176428.jpg
 
I tend to agree with the other gents opinions, although I'm more into power distribution then electronics. A bad diode could allow reverse current flow which it would otherwise block. If you look on E Bay there are regulators and diodes out the ying yang VERY CHEAP, but if you want to try and substitute parts without any actual testing, Id first suspect the diodes.

Let us know

John T
 
This search yielded diode trios and one wire conversions and regulators and all sorts of alternator repair parts, just have your alternator model number handy and go take a look see. Of course, you can shop around for name brand merchandise, different quality and local parts houses, but these searches can give you an idea of parts and prices and brands so you're an educated shopper before you decide where to make a purchase. I'm NOT endorsing E Bay or bad mouthing it, do as you please, its just a tool to educate you and perhaps make a purchase or opt for a local supplier.

Merry Christmas

John T
One of many parts searches
 
Blue Jay,jdemaris, John T, Thank you all for sharing your wisdom. I haven t messed with the internals of an alternator but I think I ll pick up part(s) and give it a shot. It might be a day or so, but I will report back. John, how goes the banjo picking? Best holiday wishes to all, VH
 
Vern, Actually I'm worse on the banjo then I was a couple years ago grrrrrrrrrrrr When you wait this late to start and lately I haven't been to as many jams a body gets worse grrrrrrrrrrr I can go to a jam and if its straight upbeat bluegrass I CAN TAKE A DECENT BREAK AND KEEP IN TIME AND HIT MANY OF THE MELODY NOTES AND no wrong or sour notes, but I'll never be a real banjo player, I just started too darn old lol

John T
 
Check the isolation diode first. If it goes bad power reverse flows and will run the battery down, you will see the spark you describe . Sometimes the alternator will get hot just sitting there. Just remove the battery wire, remove the diode (note that one terminal is isolated ), touch the batt. wire to the terminal( the one that's not isolated ) and see if you have a spark, if not that's the problem .
 
Hi John, I m old enough to remember nickel soda pop so I guess my story is the same. My best claw hammer work is done with the one in my tools. Best regards, VH
 
Delco 10SI or 12SI does not have a dedicated isolation diode. The little diode trio that I posted info on is the "weak link" in Delco SI alternators. When partially failed, it creates a small drain on the battery and a dim glow in the charge-light if so equipped. As the name "diode trio" implies -it is a unit with three diodes built in.
 
Vern, if this is the alternator you have NO WARRANTY it may or may not be, this diagram may help.

John T
a176575.jpg
 
Good morning, Thanks for the info. I think your diagram is for a three wire and this one is a one wire. As it is fairly new and I need another one for the Massey (is this allowed?:) also, I think I ll run it to the shop. Turbo & Electric Co. in Phoenix is a most excellent outfit. Thanks, VH
 

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