Stuart Dynamo

[John Haine]

On John Haine Said:

Caution is needed applying the MPT to generators!  Imagine the electricity supply network was simplified to a single alternator capable of supplying 57GW at 230V and a single load.  The generator “impedance” would be a small fraction of an ohm.  If you “matched” that with the load a huge current would flow, the voltage on the load would be 115V, half the power would be dissipated in the load – i.e. 28.5GW – and half in the internal impedance of the generator.  Only 50% efficient!  In reality for power supply systems one aims for a very small internal impedance and minimum voltage drop on load.  In the case of the dynamo the power limit shouldn’t come from the internal resistance but the capacity of the prime mover.

Ah, but isn’t the joy of AC that impedances can be matched with transformers?

John is right except there’s no need for a big generator to match at 230V.   It can be manufactured to produce the highest voltage that doesn’t zap its internal insulation, say 20kV, and then immediately transformed up to 200kV, 500kV, or more for distribution.  The impedance of the source can be almost anything.   At the other end, the voltage can be transformed down to match the load.  230Vac 100A in my home (2.3ohms), or 1.2V 10000A in an industrial electrolyser (0.00012ohms).

Do Electrical Engineers calculate impedance?   At 50Hz I’d guess the power network can almost be considered entirely resistive.  If so, then transformers simply apply voltage ratios, and provided they don’t overheat, all is well.    Guessing though, because I’ve no idea how much capacitance and inductance are in a power system.  And there are lots of wires in the air, bundled in cables, and wound in iron-cored coils.

Radio Engineers can’t avoid calculating impedance because otherwise nothing works properly.  One thing that surprised me about Model Engineering is how little maths is needed compared with amateur radio, or horology.

Dave

 

[duncan webster 1Participant @duncanwebster1]

I didn’t mention efficiency. I’m assuming the prime mover, a Stuart steam engine, not the national grid, has enough grunt to drive the generator.

[JasonBModerator @jasonb]

Someone getting on and doing it on HMEM

[noel shelleyParticipant @noelshelley55608]

Started to read up on making small dynamos, ME V2 of 1900 P23 and running on into V3 is a long series on the matter. Quite theoretical but interesting. Getting silk covered wire may prove difficult and modern Neodymium magnet may not be suitable – I will report back in due course !

I note that looking at the Stuart Models catalogue it lists Hp for some model engines, and the Sirius engine was used in the Alco Firefly radio generator. A well made D10 or Score  might be an ideal unit for the job, or any of the bigger engines. A 10 V or H may well give little scope or leeway as far as power goes ? The Mk 814 is single acting, 1″ bore and  is good for about 20W but needs a sizeable boiler to run well. Noel.

[SillyOldDuffer]

On SillyOldDuffer Said:

On John Haine Said:

Caution is needed applying the MPT to generators!  Imagine the electricity supply network was simplified to a single alternator capable of supplying 57GW at 230V and a single load.  The generator “impedance” would be a small fraction of an ohm.  If you “matched” that with the load a huge current would flow, the voltage on the load would be 115V, half the power would be dissipated in the load – i.e. 28.5GW – and half in the internal impedance of the generator.  Only 50% efficient!  In reality for power supply systems one aims for a very small internal impedance and minimum voltage drop on load.  In the case of the dynamo the power limit shouldn’t come from the internal resistance but the capacity of th

I’d guess the power network can almost be considered entirely resistive.  If so, then transformers simply apply voltage ratios, and provided they don’t overheat, all is well.    Guessing though, because I’ve no idea how much capacitance and inductance are in a power system.  And there are lots of wires in the air, bundled in cables, and wound in iron-cored coils. ……

 

Over normal distances between substations etc line inductance and capacitance can be ignored but long distance transmission often uses DC to avoid problems. Any attempt to match the line impedance would be futile.  Also avoids problems interconnecting asynchronous AC systems.  I believe connections to offshore wind turbines also often use DC because the line capacitance is greater.

[Michael GilliganParticipant @michaelgilligan61133]

All good interesting stuff, but crikey! this topic has drifted a long way from the over-priced/under-performing STUART kit.

MichaelG.

[noel shelleyParticipant @noelshelley55608]

To return to the original topic, at least loosely, That the magnet was so poor and the even as cast finish likewise I would have returned it BUT was it old stock made many years ago ? The current catalogue, beautifully produced as have the ones from the 90s been, was printed 2009 during the Guernsey owners time makes no mention of the dynamo or lighting set ? Thought the new supplement of 2024 does ! In 1992 the dynamo,a ready built unit, looking like a small electric motor was offered as a lighting set. In 1995 what looks like the OPs dynamo was going to be introduce, with a cast iron frame and gun metal ends, though the OPs unit has a gunmetal body.

I would agree with Michael that at £250 or so for what you get it seems over priced and as supplied under performed. Noel.

[JasonBModerator @jasonb]

Like a lot of Stuart stuff you don’t get that much for your money when compare dto offerings from others. The PMR one cost £76 and is only a tiny bit smaller but does put out 12V. A fabricated one would likely be even less.

[noel shelleyParticipant @noelshelley55608]

Sat here mulling ! The casing could be piece of steel pipe threaded at both ends and 2 caps. the shape could be milled out of the caps, then bearings or bushes fitted and simple brush boxes made out of thin copper or brass. A pair of brushes for a Lucas ACR ( 16, 17 or 18 )type alternator would be small enough, and used radially. Steel tube comes in nominal bore sizes, scaffold pole is 1.5″ NB, Od 48.3mm it goes up by 1/2″ sizes. 2″NB has an Od of 60.3. 2.5″ NB is a bit big maybe, with an Od of 76mm. Magnets and an armature will be need to be sourced to suit the size you choose,magnets araldited in and the ends screwed on and locked, the base or foot would be a simple fabrication of steel sheet welded or brazed, Plan B would be to mill from solid.  Just a thought ! Noel.

[JasonBModerator @jasonb]

Just take the magnets out the can of the motor that the rotor comes from. Or just use thick wall tube and make the motor’s can a tight fit.

Depending on how “open” you want the brush arrangement to look it may need extensions on the motor shaft but close fitting ones could be Loctited on and trued afterwards.

Something with the look of those motors in the link I posted to HMEM would be quite easy to do the end caps for: just turn the profile and mill some radial slots. Arrange magnets top and bottom so two tie rods can pass through on the Horz ctr line and no need for threading. Extend those tie rods and you have somewhere to mount your brushes be they flat bronze strip or the braided copper type.

[noel shelleyParticipant @noelshelley55608]

I seem to recall small Fracmo units a bit like HMEM fellow had but I fear they would be to big at about 4.5″ OD depending on power. I agree that hiding a small permag motor inside a casing is the easy way to more or less guarantee some sort of success. The idea of the caps and tube was that they are off the shelf items in plumbing, the worst issue might be having to get one end threaded, but that’s a normal plumbing job as screwed and socket tube has one end already done. At 3.5″ od they would dwarf a Stuart 10, though might look OK on a number 1. Noel.

[JasonBModerator @jasonb]

I had a look on the net at the P M Research Dynamo and it looks like the fotor an dmagnets are about the same size as a 775 motor, I just happen to have one of those which was a bit small for something I had intended to use it for. Inside of the can is 40.5mm

So did a quick sketch based on my ideas mentioned yesterday and a bit of 63 x 12.5mm wall tube that I have

The body could just as easily be turned from 60mm solid or go upto 62.5 (2.5″) and there is scope to make the body barrel shaped. Foot just cut from flat bar and screwed to the body from below.

The same material can be used for the pully end. This would just be turned on the lathe and the slots milled. The bosses just short lengths of 6mm round bonded into shallow counterbores. Motor’s bearing can be used.

The other end can have the ring turned from the same material as the body. In fact it could all be turned from solid and milled to leave the four supports but I would most likely silver solder four “L” shaped pieces to a central Hub. Again bosses for screws and terminals JBWelded into counterbores.

The existing brushes could be used so just a couple of brass terminals to add. magnets have a spring clip that retains them so can be fitted into the new bodyM

A quick look at M-Machine and materials including some fixings and a tube of JBW would be around £36. A doner motor £10 so lets say £50 all in.

[Michael GilliganParticipant @michaelgilligan61133]

On one hand, I am very impressed with the way this discussion is progressing.

On the other, I am saddened that ‘Model Engineering’ no longer appears to include modelling [or experimenting with] the Electrical side.

A look back at some ‘Model Engineer and Amateur Electrician’ magazines will show what an interesting area this could be.

MichaelG.

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Edit: __ it looks like these are only available within the USA

https://onlinebooks.library.upenn.edu/webbin/serial?id=modelengelec

🙁

[noel shelleyParticipant @noelshelley55608]

Before dismantling stick it on a meter and see if the idea has merit eg suitable output, or better mount on a base and run with the intended engine. Jason that motor would seem perfect to use with a bit of scaffold tube, ID 41.5mm or so The casing and magnets will fit inside give or take a bit of fitting, tube OD 48mm ish. The brush plate will fit inside the cast cap after machining as will the bearings, a pair of through bolts and the job would seem done ? as a commutator is being used the output will be a lumpy DC, voltage will be determined by the rotational speed.

My  reading of ME V2 last night did talk of the need for correct positioning of the brushes to avoid arcing and heating losses though not sure it matters in this case. Great thank you. Noel.

Michael, as you may have noticed in my earlier post, ME V2 of 1899, ABC of dynamo design, covers this matter in some detail and YES I agree that the magazine could well revert to it’s old name,with more electrical content, my fear would be that H S would require more disclaimers than content of any value. N

In the 1970s these old early ME editions were re printed in book form and are available at very reasonable cost secondhand, I got mine from engineers emporium/LA services. N

[Robert Atkinson 2Participant @robertatkinson2]

I like Jasons idea of a DC motor. However for a lighting rig AC is OK. so you could replace the commutator with a pair if slip rings and wire brushes. This is slightly lower loss and would look a little more vintage. If DC is requred a rectifier can be fitted in the base.

Robert.

[JasonBModerator @jasonb]

Noel, when you have finished with the reading there are plenty of images to base something on, just a few that I have stored and what I had bought that motor for but it is a bit small although I have found something larger.

Looking at an old Stevens Model Dockyard catalogue they use dto do the cast vertical columns with the half round cut outs and various other bits for those that wanted to “wind their own”

Just had the Little Clarkson up to 2500rpm but I expect it will be too weak for the 775 motor.

[noel shelleyParticipant @noelshelley55608]

Robert how would you connect 5 poles to 2 slip rings without running the risk of destroying the windings. I can’t see an easy way ? There is no spare wire or length to reach both rings. Noel.

[Michael GilliganParticipant @michaelgilligan61133]

For ease of manufacture, and great style … I rather like this:

https://www.shutterstock.com/image-illustration/electricity-machine-dynamo-electric-pacinotti-1860-2351715471

MichaelG.

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Ref.

https://ethw.org/Milestones:First_Studies_on_Ring_Armature_for_Direct-Current_Dynamos,_1860-1863

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Edit: __ My Google Fu is strong today !

Multi-Lingual scan available here in various formats:

https://archive.org/details/descrizionediun00pacigoog

[Robert Atkinson 2Participant @robertatkinson2]

Noel, I missed your post.
You might have to extend the wires or possibly take a turn of each winding to provide “slack”. Or 1/2 a turn and put the slip rings on the other end.
It will vary from motor to motor.

Robert.

[Michael GilliganParticipant @michaelgilligan61133]

https://www.gettyimages.co.uk/detail/news-photo/dynamo-electromagnetic-machine-by-antonio-pacinotti-the-news-photo/930047160?adppopup=tru

 

[noel shelleyParticipant @noelshelley55608]

Thanks to the OP Steve for starting this thread. Having read “The ABC of dynamo design” from V2 and V3 of ME 1899 and 1900, normally in bed and late I realise that A, the maths is very complexed and B, getting the materials in this day and age would be not easy !

So, my thoughts now are that using 1.5″ ( OD 48mm )nominal bore steel tube ( scaffold tube, STEEL ) and a pair of cast iron caps along with the 775 motor suggested by Jason would be a good basis for experiment. If it works as made that would be good, if not one has all the bits that matter and rewinding would not be difficult. I have 2 motors here, 1 made by Mabuchi, 36mm od, this spins easily the other by Johnson at 38mm od, this is very notchy due to the magnets strength both 12v The 755 casing with magnets will with a little work fit inside the steel outer tube. The brush assembly can again with a little work be reused. The end caps can be milled/filed/machined to look like what Jason drew up. The 48mm tube can be machined true on both ends, and the caps a register on the inside to take the tube to keep all true. 2 through bolts will hold it all together ? To support the armature shaft either extended ends can be made and loctited on, or brass/ bronze bearing supports brought in from the end caps.

A simple test bed can be made by attaching a jubilee clip of the right size to a mounting plate by screw, weld or braze to hold the motor/generator so it can be powered by the chosen engine  before a lot of trouble is gone to.

The 36mm motor could be fitted into 1.25″ (41mm od ) nom bore pipe and fittings and there is always 1″ ( 34 mm od ) for smaller units. All 3 sizes have a wall of 3.25mm.

Noel.

[Michael GilliganParticipant @michaelgilligan61133]

Just found this little gem:

http://silverbiplanes.com/SPECIFICATION_PDFS/British_DTD/DTD_5092_1959.pdf

Specification for “Soft Iron”

MichaelG.

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Ref. __ parent page:

http://www.silverbiplanes.com/tablet/british-dtd.html

[JasonBModerator @jasonb]

Keep us posted of progress Noel. I’ve a couple of other projects on the go so unlikely to do anything until the new year.

[Michael GilliganParticipant @michaelgilligan61133]

My find of the evening:

Lectures on the Electromagnet [1891]
https://archive.org/details/lecturesonelectr00thomrich

 

MichaelG.

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[Michael GilliganParticipant @michaelgilligan61133]

Recommended Sunday viewing:

2,607 views 25 Jul 2024
Although a bit of a basket case, this rare 19th century electric bipolar motor/dynamo is going to get an overhaul and will run a small knob and tube display in the lineshaft shop.

https://youtu.be/jyRkhfAS198?feature=shared

MichaelG.

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