Alternator or dynamo

[Spark plug]

I have this very old generator on the bench I’ve been asked to have a look at and clean up. From what I can decider it has a 24v output and is good for 4893 watts.

But the concerning bit is the plate on the side witch says:

Any one got any ideas before I do something silly, I’m guessing dynamo simply because of age which I’m estimating at 1930-40’s

 

[merryman]

Dynamos produce DC current because the armature windings produce the power and it is taken away through segmented commutator brushes. Alternators are AC because they take power from the stator windings so no brushes to change it to DC, or, if they do use the armature for power, it is taken away by slip rings, so again AC output.

 

[Spark plug]

Dynamos produce DC current because the armature windings produce the power and it is taken away through segmented commutator brushes. Alternators are AC because they take power from the stator windings so no brushes to change it to DC, or, if they do use the armature for power, it is taken away by slip rings, so again AC output.

I sort of knew that much to some extent, motors are my usual thing. Normally I would just strip something down fully but the plate about re-magnetising had me a bit concerned about pulling it to bits.

 

[Red'n'Black]

Old permanent magnets (i.e before the modern rare-earth ones came along) lose their magnetism if you break the magnetic circuit. It's a similar reason old horseshoe magnets needed a 'keeper' across the poles.

Can you do what you need to without removing the rotor?

I'm a bit surprised a generator this size has a permanent magnet for the field, usually it's only the smaller ones. Any idea what it came out of?

 

[Spark plug]

It came of a steam locomotive, it has a steam turbine mounted on one end and a governor on the other to regulate the steam, to control the speed of the generator:

 

[doubleboost]

Have you got this in your possession

 

[Spark plug]

Have you got this in your possession

I do, it’s not mine, I have been tasked with getting it operational

 

[Spark plug]

Old permanent magnets (i.e before the modern rare-earth ones came along) lose their magnetism if you break the magnetic circuit. It's a similar reason old horseshoe magnets needed a 'keeper' across the poles.

Can you do what you need to without removing the rotor?

I'm a bit surprised a generator this size has a permanent magnet for the field, usually it's only the smaller ones. Any idea what it came out of?

I don’t know if I can do everything without removing the rotor, although I would like to. The resistance across the windings I’m getting from the two wires coming out the generator are a bit weirded but if they where connected to brushes on a commutator that may explain that.

Up until now I have avoided removing the end plates / bearing housings, but would I be correct in thinking as long as I don’t remove the rotor from the stator all would be ok?

But also if I did remove the rotor from the stator, what is involved in re-magnetising it and is there anyone that can still do it?

 

[addjunkie]

Have you got this in your possession

I see a video in this! An interesting one at that!

 

[doubleboost]

I do, it’s not mine, I have been tasked with getting it operational

If I can help just ask

 

[Red'n'Black]

I don’t know if I can do everything without removing the rotor, although I would like to. The resistance across the windings I’m getting from the two wires coming out the generator are a bit weirded but if they where connected to brushes on a commutator that may explain that.

Up until now I have avoided removing the end plates / bearing housings, but would I be correct in thinking as long as I don’t remove the rotor from the stator all would be ok?

But also if I did remove the rotor from the stator, what is involved in re-magnetising it and is there anyone that can still do it?

Yes you should be OK removing the end plates so long as the rotor stays in place.

To re-magnetise the stator you would need some sort of electromagnet - I know the principle but never had to do one myself.
Is there any chance somebody else has had it apart and ignored the warning on the label? If it measures OK on ohms but still no output, that could be why.

What RPM does it run at normally? Do you get any output at all if you spin it up with a drill?

 

[Spark plug]

If I can help just ask

At the present I’m cleaning 100 years of crud off and trying to find out what I can about it, but I will be in touch if I get stuck

Yes you should be OK removing the end plates so long as the rotor stays in place.

To re-magnetise the stator you would need some sort of electromagnet - I know the principle but never had to do one myself.
Is there any chance somebody else has had it apart and ignored the warning on the label? If it measures OK on ohms but still no output, that could be why.

What RPM does it run at normally? Do you get any output at all if you spin it up with a drill?

Spinning it by hand, I am confident that it will work, but theres no way to check the brushes without removing the end cap and it needs a jolly good clean.

 

[500e]

Have a good mate with a tool for remagnatising dynamos can give you his Ph No if it will help he is an old machine man as qell

 

[Robotstar5]

Would sliding in a piece of steel pipe as you pull the rotor out act as a keeper for the magnets?

 

[Red'n'Black]

Would sliding in a piece of steel pipe as you pull the rotor out act as a keeper for the magnets?

Yes if you can find some the same diameter. But getting the rotor out and the keeper in will cause a lot of swearing without some sort of jig to control the movement IME.

As soon as you release the shaft from the bearings the magnets will jam the rotor against the stator. Getting the shaft aligned with the bearings to put it back in was the hardest bit when we used to assemble our own BLDC motors, as soon as you approach the stator with the rotor it tries to suck it in at high speed. We built a fixture around an arbor press in the end.

That was for fairly small 250W motors, whole thing was only 6" diameter. For a beast like the OP's the forces involved will take your fingers off if you're not careful.

 

[Agroshield]

Is there any chance somebody else has had it apart and ignored the warning on the label?

One way to help in finding out if that is true is to clean it carefully and look at the paint around the fasteners. If it is undisturbed and uniform, it may not have been apart.

Would sliding in a piece of steel pipe as you pull the rotor out act as a keeper for the magnets?

I was under the impression that the majority of stuff (i.e. except the shaft itself) in the rotor was made of a type of steel that has specific magnetic properties or was non-magnetic (the copper windings and the varnish). A bog standard steel pipe will not have those properties, so we would need to do some more research.

 

[Brad93]

Permanent magnet DC motors you turn a piece of pipe to the same Size as the rotor.
Even those are a modern type of magnet though which shouldn't lose its strength.

Dave at the Electric repair co may know. Specialises in motors but Does love the old stuff.

 

[Spark plug]

so a bit of progress this morning, I’ve spun it up with the cordless drill at 1350rpm and with the meter connected to the output I was getting no meaningful VDC output but I did observe a steady 5VAC output.

So if my maths are correct to generate 24V it will need to run at around 6500rpm

 

[Onthespotwelding]

you often see them on the front of showman’s engines at shows they look lovely when polished up



When I got a magneto remagnetised last year it cost me £400

 

[Spark plug]

you often see them on the front of showman’s engines at shows they look lovely when polished up

View attachment 360632

When I got a magneto remagnetised last year it cost me £400

This one isn’t that big thankfully. Hopefully it will clean up nice.