DC Motor/Generator help - where to go

Folks,

I have this cunning AC-motor drives DC generator, drives DC motor arrangement on a lathe I am restoring and I think the DC generator is duff as I get no continuity on any of the terminals. Does anyone know who I can ask about such things (its a GEC generator of about 1950 vintage). Is there a good newsgroup you know of that I can try, or a bloke who specialises in repairs, brushes, rewinds, servicing etc ?

Thanks Steve Richardson

Reply to
Steve Richardson
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What make of lathe is it?

Mark

Reply to
mark

A Cromwell 3.5inch

Steve

Reply to
Steve Richardson

There`s a group dedicated to Monarch lathes,some of which used this system.You can find it at

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To sort the generator out,any decent motor rewinder should be able to help.Avoid Dowding and Mills. There will be people on this group and also the stationary engine group who will know what you need to know but you will have to give some more info.Generator type/make,self exciting,seperate exciter,how many wires etc. regards,Mark.

Reply to
mark

Worth just checking that the brushes are free in their holders before you start paying for help.

Cheers Tim

Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service

Reply to
Tim Leech

Thanks Mark,

In case anyone in this group wants specifics. Its a GEC shunt wound generator developing 6Amps and 220V at 2900RPM with 170V field excitation. It has 4 wires and unless my avo has suddenly packed up it has no continuity between any of them, although there is no obvious sign of abuse/overheating and the rotor turns freely. I haven't had the brush covers off yet, don't want to tinker and mess things up.

I thought the Monarch lathes might have used american generators, so would not be of direct help for GEC items.

Ideally I want to drop both motor and generator off with someone for a check out, but I don't know where I would find such expertise (preferably locally in Cheshire). There is an auto-electrician not far from us, maybe he will know. The insulation on the motor leads is sub-standard and they will need replacing before I will happily put large DC voltages through them, so that will have to come apart even though it seems otherwise OK.

Steve

Reply to
Steve Richardson

Steve

Where in Cheshire?

Frank Vowles in Widnes have given me good service in the past, not cheap though.

Cheers Tim

Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service

Reply to
Tim Leech

I have never used them, but I drive past a place on Bumpers Lane in Chester every day that look to do this sort of thing. Can't remember their name at the moment.

Mike Cole

Reply to
Mike cole

Thanks Tim,

I'm down near Chester, but anywhere within 50 miles is OK. Must drop in on you sometime. Vintage diesel is a special interest of mine.

When I get a choice of people who know, then I'll head for the cheap one. But right now Vowles is the first direct recommendation - though I must find out what is down Bumpers Lane in Chester (seperate post).

I took the brush covers off the DC motor and its all rather complicated with a choice of notches and a wire hook presumably to set the brush spring tension. I couldn't see the brushes (must get a better light in the shed).

I reckon a DC motor and a DC generator are almost the same thing aren't they ? Both are shunt wound - 4 wire, in fact they are a matched pair with serial numbers that suggest it. I expected the field coil and armature resistances to be similar. Maybe I'll have to strip one down and have a look, but I don't want to do it in the wrong way and damage anything delicate and irreplaceable.

So maybe its off to Vowles for a quote !

Steve

Reply to
Steve Richardson

Tim,

I didn't even need to go as deep as the brushes. I thought the 4 wires passed under a plate and into the generator, but I found that under the plate was a 4 way terminal block and two of the wires were out. I now find I have 358 ohms on one circuit and 2.3 ohms on the other - which is at least continuity. I think the higher resistance is the rotor as it seems to change as I rotate it. The other would then be the field coil resistance.

The two windings on the DC motor are 130 ohms and 5 ohms.

So maybe things are not so bad after all !! Though the rubber coated insulation on the leads still will need changing. So a strip down is still required, but it may mean an expensive rewind is no longer required.

Steve

Reply to
Steve Richardson

If it's shunt wound, the higher resistance will be the field. What you may be seeing is a false reading caused by voltages being induced in the field winding by some residual magnetism in the rotor.

regards Mark Rand RTFM

Reply to
Mark Rand

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