Does anyone know anything about 20dn alternators?
 

I have 2 different 20dn alternators. Both have the same plug on the back side our trucks use. There are 2 series of them. The 20dn series 150 # 1117765 and is off a 67 I had and the other is a 20dn series 250 #1117756. Both would inter change and look the same except for the back side. What is the difference between the series and which is better? Any information out there?

Re: Does anyone know anything about 20dn alternators?
 

Any info at all? Searched the Internet and there is no info on these at all. My one alternator is #1117767 not 1117765. My mistake.

Re: Does anyone know anything about 20dn alternators?
 

Give it some time for responses. I'll admit that I know zip point zit about these alternators.

Re: Does anyone know anything about 20dn alternators?
 

I googled them and came up with not much. They were used on larger vehicles like busses and large trucks. I think the different series were just different amperage outputs.

They are listed as obsolete on some sites.

Re: Does anyone know anything about 20dn alternators?
 

Yeah Impossable to find info. Vettevet do you have any info on the transisterized regulators like this. I am just not sure if this regulator requires to be grounded to the rad support. Also not sure it this regulator needs to be mounted with the rubber well nuts the points type needs.

Re: Does anyone know anything about 20dn alternators?
 

subscribed

Re: Does anyone know anything about 20dn alternators?
 

Call Delco Remy
1-800-372-0222

Re: Does anyone know anything about 20dn alternators?
 

There are several finned aluminum Delco-Remy regulators. I'm not sure of their application.
There are two with a flat 3 or 4 pin plug. Yours looks like it has a field relay, which is used to operate an idiot light if one is used.
If you compare the wiring with the standard mechanical, 4-pin regulator, they both need a chassis ground that is not included in the plug wiring.

I thought 63-up Corvettes had them, but an internet search shows that at least in most cases they were included if a Transistor Ignition was used and the ones I found had a round 3-pin plug.

Re: Does anyone know anything about 20dn alternators?
 

There is some information at the GM Heritage Center web site if you download a copy of the 1967 Chevy truck manual from the vehicle information kits. 1967 seems to be the only year that has any information outside of C30's. There is a section on alternators and batteries that may help you. I can tell you that those are pretty old school and we phased them out in the mid 1990's at work, due to the inability to get replacement parts. Because they are designed for commercial vehicles they came in 24 and 32 volt versions, so if you looking at buying used stuff make sure of the voltages. If you can find an old rebuild shop they may be your best bet for information. Good luck.
https://gmheritagecenter.com/gm-heri...tion-kits.html

Re: Does anyone know anything about 20dn alternators?
 

When I get the second one I'll take it into a local shop. Want to find more info on these and make sure if I wire this regulator the same as the points type I won't burn it or the alternator. If anyone has any more info on these please still post it here. This old stuff is hard to find info on.

Re: Does anyone know anything about 20dn alternators?
 

Heavy truck/bus alternators. Externally regulated (same plug connection as any non-regulated early Delco alternator), use the finned electronic regulator. As the earlier posters commented, be sure of the voltage, there were many versions of these things. They are capable of very high charging rates at low r.p.m.'s, so if you do use one be sure to adjust the voltage regulator accordingly. Any late-60's Chevy or GMC heavy duty truck manual will cover these.

Re: Does anyone know anything about 20dn alternators?
 

We used them on small tugboats and we had real problems with the 30si replacements as they will not charge below about 1100 RPM. We ended up have to machine custom pulleys for a bunch of the tugs, as the low RPM rectifiers still didn't charge low enough. Not a big of an issue on most vehicles. Although when I converted my 70 Javelin to a GM one wire alternator I discovered, that commuting in traffic, at night, with the wipers on the battery will go dead at some point.:banghead::banghead:

Re: Does anyone know anything about 20dn alternators?
 

Both of these are 12 volt 62 amp the type 150 has 1 brush holder with 2 brushes used in light and medium duty it is negative ground. the type 250 has 2 brush holders using 4 brushes. used in medium and heavy duty applications can be positive or negative ground the one pictured above is negative ground. The two numbers referenced above both used the same voltage regulator. Delco service bulletin #1G-271 for type 100 and 150 #1G-272 for type 250

Re: Does anyone know anything about 20dn alternators?
 

ok i I will try to find those. is there a benefit to having 4 brushes as to 2? I have added quite a few options to my truck that use electrical power. Being that they are both the same amperage would one be better than the other for operating more power equipment such as heated seats, power windows and a/c?

Re: Does anyone know anything about 20dn alternators?
 

the tag in the box was loose from the alternator when I got it. must have been removed when rebuilt. I have had people suggest that the series 250 is part # 1117777. cant confirm though.

Re: Does anyone know anything about 20dn alternators?
 

#1117777 is 62 amp 12 volt 250 series. The major parts in both the 250 series numbers are all the same. The 150 series uses a different rotor but the stator was the same. the output is your limiting factor on running added accessories so both should do equal.

Re: Does anyone know anything about 20dn alternators?
 

Bumping this back up to the top. I found a 67 Burban in a wrecking yard and got the 1117777 alternator and its regulator and brackets off of it, but someone had cut the wiring harness off the truck leaving all the plugs. There are two junction points on the core support near the horn that obviously were part of the factory wiring. These are the same style as the junction that is commonly found near the battery on our trucks. (Which was also present on this truck too.) So in all there were 3 junctions for 12 volt positive side. My question is does anyone have a wiring diagram for the 62 amp system? It has a heavier wire at the alternator than the 38 amp alternator system. AWG 8 I believe. Since I have a NOS regulator I found on a forgotten shelf at work I may convert to this old school system in order to put some electric heat in the back of the WMB.

Re: Does anyone know anything about 20dn alternators?
 

Mine has the 2 distribution blocks by the regulator as well and I don't believe my wiring is any thicker than the other harness I have. My question is was the regulator mounted with the rubber well nuts or straight to the rad support and did the regulator have the ground wire mounted straight to the regulator like the points style one had or no ground wire to the regulator case at all?

Re: Does anyone know anything about 20dn alternators?
 

This one was mounted on the rubber isolation mounts and there was a ground wire to the core support. I don't remember where the other end when to on the regulator, but I can dig it out and get back to you on it.

Re: Does anyone know anything about 20dn alternators?
 

Ok that would be great. I can send you a picture of my harness that I have later today as well. Was it a transistorized unit with the fins like pictured above or a unit that looks like the other common regulators? Just curious.

Re: Does anyone know anything about 20dn alternators?
 

It is one of the solid state units.

Re: Does anyone know anything about 20dn alternators?
 

Sorry it took so to get back with the photo.

Re: Does anyone know anything about 20dn alternators?
 

That is awesome. It does have a ground directly too it. I've been searching that for over 5 years! I'll get you a picture of the positive wires tomorrow and I'll check the gauge of them.

Re: Does anyone know anything about 20dn alternators?
 

Im going to add photos here of my 67 harness . Its only been 8 years . All wires are 10awg to the splice and then only 12awg to the cab with a 16 awg fuse link between the junctions on the rad support. My battery cable was missing but im pretty sure a 14awg fuse link was also present at the battery cable to that junction block. I wonder why they wouldn't have just ran a q0awg to the fuse block connection as well. I added a few accessories to my build on this truck so I may upgrade that wire all the way ro the ignition switch and get a larger size fuse link at the rad support.

Re: Does anyone know anything about 20dn alternators?
 

My theory on this is GM made the larger alternator option as easy as possible for themselves. In other words the same basic harness was used on 37 amp and 64 amp trucks. All GM had to do was add a simple additional harness and provide the terminal post on the core support. Much simpler (And probably cheaper) than having two completely different wiring harnesses and fuse blocks with the advantage that a truck could be upgraded at the dealership if the owner so desired. Owners of trucks with the larger alternators were instructed to wire their accessories to the posts on the core support not the fuse block.