The Stovebolt Site Forums The Parking Lot Big Bolts 1955 GMC 630 charging system

The model 630 I'm working on, which sat for 30 years, is a 1955 2nd series, not a 56 as was told to me (I doublechecked the serial number). I'm now looking at the electrical side of things. It is a POSITIVE ground 12 volt system. My research shows that in 1955, 12v pos ground was an option, with 6v pos ground being the standard offering. Also, this being a former firetruck, it has a Leece-Neville 100 amp alternator, with a large control box or regulator, and a large rectifier. I plan to eliminate that system. I unhooked all leads from the alternator today. Would there be any harm in trying to see if the engine will start with the alternator leads removed, but leaving all the other components and wiring in place for now?

Should be okay, but I'd also disconnect any 12v leads to the "control box or regulator". Make sure none of the disconnected wires can find ground. Don't want to let the smoke out of your new firetruck.

With no wiring connected, the alternator will simply be an idler to keep the belt tight. Most Leece-Neville alternators can be set up for either positive or negative ground polarity. Is there some overpowering reason to go to a lower capacity charging system? L-N is sort of the Cadillac of alternators.
Jerry

Thanks Bill and Jerry! I'll make sure there are no ground connections, loopbacks, etc. My main reason for disconnecting the alternator now is that it has sat so long that I don't trust it or the rest of the obsolete charging system to do the right thing if the motor fires up. Wiring or components might be damaged. However, I realize that there's a chance it might still work.

Be careful, many fire truck systems are always hot(who has the keys?)

Ed

This one should be a bolt-on swap for the older system. It can be set up for either positive or negative ground, and it has a built in regulator to replace the older remote regulator and selenuim stack rectifier item you have now.

www.ebay.com/itm/404871426034?i

Jerry

Thanks Ed and Jerry for the added pointers and leads. I would love to keep the Leece Neville system bc I like to keep things original as much as possible, but I think it has to go. I would not do well if this system failed immediately or down the road. It might even be the reason, or one of the reasons, this truck was taken out of service. If I get it running, there will be a lot to do, esp. the brake system, and I would like the electrical to be relatively straight forward and serviceable. I'll keep the large control unit and rectifier mounted on the inner fender, and hang onto the LN alternator. They are part of the truck's history for sure. I'm half preservationist and half fix them up to use them.

There's a good reason for those big fins on the selemium stack rectifier- - - -they generate a LOT of heat. More modern alternator designs use diodes instead of finned rectifiers, and they're a lot more reliable.
Jerry

Interesting! It's almost as big as the alternator itself. Jumping ahead, I'm thinking of changing to a negative ground system. There don't seem to be enough good reasons to keep it positive ground. I can change the battery cable ends, and switch the ammeter wires and the coil wires. It could possibly affect something like wiper or fan motors, but I don't think so (?)

The only motors that reverse direction with a polarity change are ones with permanent magnets in the housing instead of field coils. I believe all the motors on the truck (including the starter) will continue to turn the correct direction with either polarity at the battery cables.
Jerry

Wouldn't the wiper and heater fan motors have magnets? I have no idea about any of the fire truck motors, but I used to have one of the rooftop rotating siren lights, and its motor had permanent magnets. So I guess in that case, they'd just rotate backwards.

Most wiper and heater motors have wire wound field coils, especially multi speed types.
Jerry

Thanks for the added comments. Once I get things put together and going, I'll watch for any weirdness with any of the accessories. I've been cranking the engine w/o spark plugs a bit every other day - just to get the (new) oil splashing around and building up some pressure. Come a warmer spell next week, I'll try to fire it up. I don't see any movement on the oil pressure gauge, but if memory serves me, having worked on another 503, the gauge didn't register until it was running. I'll watch that gauge closely, if and when it fires up.

I have some electric cooling fan motors, which have field coils versus magnets. they most definitely run backwards when connected in reverse. In fact I'm counting on this because space restrictions mean I'm going to have to mount one of them in front of my radiator where there's lots of room. So that fan will push instead of pull.

Interesting for sure, how various components do or don't respond to polarity.

I have a 50 amp 12 volt generator from a late 50s White which I'm considering using on the 55 GMC 630. I found it interesting that in checking Delco generator numbers in my late 50s Motors truck manual, they listed both + and - ground generators with the same part number. For example 1106822 was offered in both polarities. What would have been the difference? Did they "pre-polarize" them, but no other differences?

Generators (not alternators) don't care which polarity they run. Just polarize the item to match the vehicle it's being installed on. Regulators can have some polarity differences- - - -generators are "dumb" items.
Jerry

Thanks, that's what I had thought, but was a bit thrown by the listings. I could more easily go with an alternator, and may end up that way. But if this gen bench tests good/only needs a little cleanup and lube, I would like to try it.

If it were mine I'd go one wire at a time and replace all the frayed cotton insulation wire with new, and go ahead and run it after checking the alternator on the bench and each diode for one direction current flow. As Jerry said, those Leece-Nevilles are the Cadillac of alternators.

I'm not entirely against that idea. My concern lies not in the original alternator, but the selenium rectifier and the massive non-standard regulator which control its output. My research shows that the rectifiers were known to fail in regular use, let alone having now sat 30-35 years.

That's true. I wonder if it would be possible, since these are just rectifiers as in huge diodes, to find the schematic and then substitute modern diodes for each of the old ones. Just wire them in the same way.. it would still be a far more efficient charging system than a generator, and 100 amp diodes aren't tough to find or expensive, as in these.. https://www.ebay.com/itm/1141628294...ustomid=8c6d3ef8865313622af658aaaa605579

Regarding the regulator, is it solid state? Even if it isn't, one big advantage of the alternator is that the regulator only has to switch field current, only a few amperes, versus output current. Since you probably aren't daily driving the rig, it will last a long time yet.

Thanks for the reply. I think the regulator would not be solid state (appears to be the orig 1955 unit). I see your point using modern diodes and I'm sure it could work. One other issue is that I'm going to a neg ground system and the L-N alternator is a pos ground unit. I don't have enough knowledge to know what could be done to modify it. My other concern is that there is quite a mass of wiring under the hood and I would prefer to take it all out (charging system) and start over. Some of it appears original - some probably added/changed over the years. I have the orig wiring schematic from GMC - but the charging system was originally designed by American Lafrance, and I can't seem to find any schematics for it.

I had a similar scenario on my dump truck when I was trying to work with the existing wire harness. My advice is Instead of pulling your hair out trying to figure out the existing wire harness with a schematic, it is simpler to just gut the whole thing and rewire from scratch. The GM wiring harness diagram does give you gauge size, so it won't take much effort to get a brand new stock wiring harness.

Besides, removing all the wire will also allow you to assess if any of it could be potentially reused - if not on its original location, then as a scrap of hookup wire in the new harness.

If you decide to upgrade to diodes instead of the selenium stack rectifier, you're going to need to know how the alternator stator is wound- - - -either "wye" or "delta" configuration. There's a different diode circuit to rectify each type of winding. Most (but not all) alternators are 3 phase AC units, and they require 6 diodes to rectify all of the phases to produce a stable DC output. That was "automotive electricity 101" back when I was in the teaching business, but it's been many years since I've gotten that deep into alternator theory and servicing!
Jerry

Is the builders plate still on the alternator? You could email Prestolite (who owns the L--N brand) with that information to see if they still have some literature on it. An email to start with is info@prestolite.com

Puffie and Jerry, I appreciate all of the pointers. I'm sure there would be a way to keep the L-N alternator in service. I will pull it in the near future to see if I can find any data plates (none visible as viewed in mounted position) but if found, will contact Prestolite. My inclination is to systematically remove all of the wiring connected with the charging system, marking it as I go, and start over. The 'starting over' may involve analyzing the diodes/rectifiers and keep the L-N system with upgrades, or move on and go with a traditional generator or modern alternator system.

Late update, just in case this would help anyone: I removed and labeled all the wiring which serviced the Leece neville alternator, the rectifier and the regulator. I left everything else as I dont want to completely rewire the truck. I ended up purchasing a 60 amp 20si alternator made by Dixie Electric (found a good NOS unit on Ebay). It suited my needs because it can be fitted with a readily available large 2-groove 7/8=1" pulley (Caterpillar spec), so that the original GMC dual belt setup can be retained. I also purchased a heavy duty longer tension arm made by Jimco. I ground out some notches in the bracket half which remained on the engine block to accommodate mounting legs of the new alternator, then slid a hardened 7/16 threaded rod through all of it to hold the alt in place at the bottom. The notches keep the alt from moving forward or back. I re-used the heavy duty 100 amp ammeter which came with the truck. It works fine, even though I know most people say to use a voltmeter with alt. I wired it just as it had been, using 8 gauge (not sure, it might be 10 gauge) directly from the alternator, then back out to one side of an emergency kill switch on the firewall, which is designed to cut power from the battery. This has worked for me, not saying there wouldn't be many more ways to do it!

Sounds like you've got it going your way. 60 amps should handle all the accessories you choose to run with some capacity left over to charge the battery. Most of those people who participate in the voltmeter/ammeter discussion don't have enough electrical knowledge to have an intelligent conversation about "why"- - - -they're just regurgitating talking points.
Jerry

There's a generator repair place in Tacoma, WA that specializes in vintage stuff. You walk in there and the shelves are full of obviously old alternators, generators, and starters. They are fluent in Leece-Neville and they did a great job with my ex girlfriend's motorhome alternator.

https://www.soundstarterandalternator.com/parts-and-services/3131678

Interesting! There are still places like that, here and there. I saved the vintage Leece Neville alternator. It is a very heavy duty unit and may be useful to me or someone else down the road.

A voltmeter is a little more intuitive to the modern driver about the overall state of the electrical system, while the ammeter will tell you what kind of load is on the battery.

I've seen both types being used with alternators, so to me it boils down to operator preference.

In my thinking, if it's there and it works, why replace it. Re: the L-N alternator, I forgot to mention earlier that I did contact L-N technical with the info on the data plate, and they said 'we don't have reference materials that go back to 1955'. Even if they do, they probably didn't want to spend time on a 'minnow in their large pond'.

Back in Salt Lake, this would be a 'Henstrom Generator' question, as the original owner Randy, had run the place since the 1950s and he'd forgotten more than current L-N staff knows about anything they made more than 10 years ago. Might be worth a Google search, they never threw anything away. They probably have one of the original diode packs on the shelf from the '50s!