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What was this DC generator for?

Posted By: poorboy

What was this DC generator for? - 05/04/10 03:31 AM

Custodian found out it was live when he leaned on the compensator handle while storing old electrical material from past projects and it growled. Called us to disconnect it.

Compensator

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It's in a high school built in 1927, load wires are cut off, AC line is still live, (fed thru the starting compensator to the AC motor that turns the DC gen)

AC motor at left, DC generator on right:

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Slate DC Switchboard with DC ammeter and voltmeter and rheostat knob

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Rheostat and control knob

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Just wondering what the load was once upon a time.
Posted By: Tesla

Re: What was this DC generator for? - 05/04/10 03:47 AM

DC power in a 1927 school?


I'd think that it supported emergency DC power for phones, alarms, bells, lights.

Rectification, today, is effortless. Back in the day this was the time-tested solution.
Posted By: frenchelectrican

Re: What was this DC generator for? - 05/04/10 04:18 AM

I am not suprised that can be either phone or alarm or DC emergcy light circuits.

But if that was either 32V or 48V DC then it will be combation emegercy system,

Merci,Marc
Posted By: HotLine1

Re: What was this DC generator for? - 05/04/10 04:25 AM

I came upon a similar type setup many yeras ago that provided DC for a projector room in what was an 'upscale' ballroom. If memory serves me correct, the arc lamps in the old projector(s).

Posted By: frenchelectrican

Re: What was this DC generator for? - 05/04/10 05:44 AM

Originally Posted by HotLine1
I came upon a similar type setup many yeras ago that provided DC for a projector room in what was an 'upscale' ballroom. If memory serves me correct, the arc lamps in the old projector(s).



If that is correct due the generator size is not very big so that possiblty is a correct answer.

I did look at the photo what the OP gave to us and I did notice that the motour generator actauly did rotated a little that why the custuation did hear the control lever growled.

Merci,Marc
Posted By: techie

Re: What was this DC generator for? - 05/04/10 10:22 AM

carbon arc projector, or DC power to the physics lab? an old elevator?
Posted By: Alan Belson

Re: What was this DC generator for? - 05/04/10 11:51 AM

The main duty was probably charging lead acid batteries or acumulators, used in many appliances and motor vehicles. Radios back then ran with both lv and hv dc, [the latter usually suplied by zinc/carbon batteries]. As Tesla says, this was the usual way of rectifying ac in small powers before WWII, the alternative Hewlitic type mercury-vacuum arc rectifier sets cost a fortune. Hope this gets preserved!
Posted By: poorboy

Re: What was this DC generator for? - 05/05/10 01:13 AM

The nameplates are as follows:

DC Generator

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Compensator

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AC Motor (need a better pic)

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Here are the gauges (custodian's real motive is he said he heard you can get $150 for these on EBay)

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School has a large stage and auditorium, never had an elevator until 20 years ago, and I don't know what they would have used batteries for in the school, unless it was common practice to charge a bunch and have them for backup emergency lights in case of power failure (which probably happened more in the 20's and 30's than it does now).

I heard there is an old original blueprint (the actual blue background with white lines for the drawings type of blueprint from which came the term, I assume). Maybe I can get my hands on it.

Here is the cut off load feeder, a 1" or 1 1/4" flex connector

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Posted By: Tesla

Re: What was this DC generator for? - 05/05/10 08:11 AM

That's an a LOT of power for DC arc lamps...

Are better pictures on the way?
Posted By: poorboy

Re: What was this DC generator for? - 05/05/10 11:39 AM

Yes, I have quite a few projects to price out and do this summer here. I will continue to post more on this piece of equipment as I can.

This was built as a Catholic High School and now is a non-denominational private high school. It is a 3 story brown brick building which is quite a remarkable "living museum" as I see it.

The starter (compensator) has oil in the base of it...I wonder if it needs testing...what do you think?

[Linked Image from img.photobucket.com]

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Posted By: HotLine1

Re: What was this DC generator for? - 05/05/10 06:44 PM

In addition to a possible projector, old 'arc' spotlights. I don't know the current requirements, but one of the members familiar with old theater equip should jump in.

Posted By: mxslick

Re: What was this DC generator for? - 05/05/10 11:18 PM

It is most likely for a followspot arc lamp...it could also have been for a pair of film projectors (not too likely in a school, but things were different back then.) I did notice the generator is rated at 72 amps so that favors a followspot instead of projectors. Can you trace where that cut-off feeder goes? You'll find clues as to what it powered at the other end.

As for the oil, because of its age I would say it is most likely mineral oil but it could be pcb contaminated, it would have to be tested to be sure. In any event don't just dump it out!!

As a rough rule, I seem to recall being told that if it's mineral oil it will smell like regular cooking oil or rank if it's gone rancid, and if it has pcb's it has a definite petroleum/chemical smell.

Finally, with a bit of cleaning and some fresh bearing oil, that M/G set will still run like new. I dare any modern motor to last 1/2 as long as this good old stuff.
Posted By: poorboy

Re: What was this DC generator for? - 05/06/10 02:02 AM

Was able to get the old blueprints and now see that it fed a unitvent panel. I am not sure why, as the panel also had (according to the print) a set of #8 feeders to it.

Cool set of prints!

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The unitvent panel was right under my nose, but has been retrofitted and I had no clue to think it was that close, The pic of the cut out flex in my earlier post aimed right at this wall panel. There was only about a foot of flex to reach the wall, as you can see here.

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Here is the re-fed and retrofitted unitvent cabinet

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Posted By: Alan Belson

Re: What was this DC generator for? - 05/06/10 02:20 PM

I do hope this wonderful piece of US history is not going to be cut up just so some jerk can sell the ammeters on ebay for a few bucks!
Posted By: Alan Belson

Re: What was this DC generator for? - 05/06/10 02:24 PM

@mxslick! Long time no see, welcome back. Hope you recovered well from your illness.
regards,
Alan
Posted By: poorboy

Re: What was this DC generator for? - 05/09/10 03:07 PM

The theater in this school has been a widely used venue for many years, so I would not have been surprised to learn that this had something to do with associated equipment.

Now that I know it was not, and was used for the purpose above, what was the reason for feeding the unit vent cabinet with DC? Possibly the fan motors in the units had DC motors at one time, I guess.

Just picking the collective brain of this site out of curiosity.

Anyone??

As far as saving the piece for a museum or such, it would require the dedicated efforts of some people willing to carefully take apart, move and reassemble it in a location that would be a bit hard to find. Sad, but true in many cases of things like this. When you actually do visit a museum, esp. of mechanical things, it is evident from seeing the restored condition of things and the displays that a LOT of volunteer effort went into the whole deal.

At any rate, I did get to see it---now I wonder more about it.
Posted By: poorboy

Re: What was this DC generator for? - 05/09/10 03:23 PM

I just spent a few minutes looking over a pretty good copy of this print that I brought home. There is no line drawn to indicate the AC feed to the compensator that I see. For that matter, the compensator itself is not drawn but was probably, just as today, not that equipment specific about the disconnects and starters that may or may not come as part of an assembled piece of equipment.

But I wonder why nothing was called out to feed the AC motor of the genset.

BTW, the 3-#8's in 1" pipe that leave the unitvent cabinet go to the other side of the building to a unitvent sup panel.

All the feeds simply go to unitvents, so must have fed DC motors.

Were AC motors less desirable for some things...speed control for instance.
Posted By: mxslick

Re: What was this DC generator for? - 05/10/10 07:24 PM

Alan, Thank you for your kind words. smile I am doing somewhat better, been quite crazy on that front. Will update my other thread.

Poorboy, to answer your question, yes in that era DC motors were much easier to control accurately since there were no AC VFD's invented yet. It is also possible that the damper motors were fed off of that same generator.

As for the compensator, it was most likely an add-on as required by the local power company back then, as the requirement varied by location.

I wish I was close enough to your location to remove that equipment for preservation.
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