Alternator charging troubles

[5Tractorguy]

Been having some charging troubles on the '61 GMC and was hoping you guys could help.

The alternator is a Delco 27SI 200amp I believe (not ID tag). I replaced everything inside except for the stator and rotor. I was able to get it to charge again when bench testing by exciting it.

Went to install it on the truck and now it will not charge even when I excite it. My battery is good along with connections.

Any thoughts? Considering buying another alternator at this point, I've become a master at disassemble/reassemble with this thing.




There is also this black Delco box that was mounted in the inner passenger fender and I'm not sure what it is. Voltage regulator of some sort? Had a hot wire running into the single stud, the other two were broken off at one time or another.

[RANDY COX]

I would definitely check the wires to be sure there getting good grounds and that little black box I believe is a horn relay, I'm thinking you should have a voltage regulator on there somewhere that might be the culprit...have you visited stovebolt.com they have some good troubleshoot and things that deal with electrical...

[RANDY COX]

I'm having charging problems with mine too, I have a new alternator and a new voltage regulator and I think the new voltage regulator is already fried cause it's not charging now. I took off the cover and one of the contacts looks burned, So when I get some cash I'm going with a one wire alternator problem solved..you just run a hot wire to it and undo the plug from the regulator and tie 2 wires together, I got this from the stovebolt.com site..did this to a 70 Burb before so it works...

[Brandons63]

Have you had the alternator checked? Local parts stores do this for free.. the first step would be to start the motor and put a multimeter lead to ground and the other lead to the Batt (output) stud on the alternator and see if it's putting out roughly 14vdc. If it does then we need to investigate further. If there is no voltage, then you need to test the voltage regulator (the bigger of the two black boxes there on the inner fender)

[Brandons63]

Also FYI the horn relay will have to be reinstalled for you to get power inside the cab and to your ignition switch if I recall...

[5Tractorguy]

Thanks for the feedback guys. I was able to get the alternator charging again today, turns out it was running at too low and RPM to charge. Still had to excite it every time though. I have the idle set around 5-600 RPM. Go any lower and it won't put out. I may look into a new or re-manned alternator, but for the time being it will keep it charged.

Sounds about right to me Randy! Being that this was a fire truck that would make sense....

I did have it checked Brandon after I installed all the new parts. Guy said it had a bad diode or stator. The middle wire out of the 3 on the stator was burnt when I first took it apart, I fixed it but who knows what else may be cooked. After that I swapped in the old rectifier again and started charging. It's been a pain in the neck up to this point but I guess I've been learning a lot!

[jtrichard]

IF the 27SI is set up for ONE wire then it will NOT start charging at a low RPM and may stop charging if rpm drops to low

[5Tractorguy]

Originally Posted by jtrichard

IF the 27SI is set up for ONE wire then it will NOT start charging at a low RPM and may stop charging if rpm drops to low

So I would assume there is no other way to change this correct? It is what it is?

[jtrichard]

yes you can put a standard regulator back inside and run 2 or 3 wire setup

[andyh1956]

Anyone contemplating modifying their charging system should read this tutorial over & over until they understand everything in it.
http://www.madelectrical.com/electri...hreewire.shtml