Stuart Dynamo

[Steve RowbothamParticipant @steverowbotham77083]

I’ve only just twigged there is a page 2, didn’t realise the thread still running!

 

Dave the bulb is 6v / 60mA, so 360mW. I didn’t build this for power but because it looked interesting to construct (it has been!) and looks authentic as part of steam plant model, I just intend to power a few LED Victorian style streetlights.

Malcom your diagram of the configuration is correct, I have today bought a couple of Neodymium 10mm dia. rod magnets to connect end to end rather than cubes  – if anyone else goes down this path don’t buy a rectangular magnet as they are magnetised through the depth rather than end to end.

 

Thank to all for making this such an interesting thread – I nearly didn’t post it but am now very glad I did!

 

 

 

[noel shelleyParticipant @noelshelley55608]

Hi Steve when did you buy the castings ? Is it old stock ? I had a serious issue with Stuart but as it was bought from the original Stuart makers  the Guernsey boys were not inclined to help ! Late 1990s.  If it was from the current owners, that’s not good. Are you going to the Midland show ? Stuart will be there.

Hi Jason, yes I did look at it, may be that was a better one with true poles and a good magnet ? Noel.

[Steve RowbothamParticipant @steverowbotham77083]

Noel the kit was bought just a few months back, and yes I am going to MMEX – in fact I bought a 504 boiler kit from Stuart at last year’s show.

[duncan webster 1Participant @duncanwebster1]

Many moons ago TDWalshaw (Tubal Cain) did a series in ME on how to make a Gramme dynamo. After several episodes there was a convincing machine, but even he couldn’t get much output. Might be better with modern neodinium

https://en.m.wikipedia.org/wiki/Gramme_machine#:~:text=Permanent%20magnets%20magnetize%20the%20soft,picked%20off%20by%20the%20brushes.

I’d go for something like Jason’s suggestion, but with a rotating magnet (no slip rings) and real coils on the stator. The laminations from a big old transformer would provide material for poles

[duncan webster 1Participant @duncanwebster1]

By the way, the idea of dismantling a stepper motor and rebuilding it to look old might be more problematic than it first appears. I once had some steppers that got wet and seized due to rust in the air gap. The importers advised that if I dismantled them to clean them up the magnets would lose at least some of their magnetism and the motors would never be the same again.

[Robert Atkinson 2Participant @robertatkinson2]

A stepper is not a good generator.
As I mentioned before a BLDC motor makes a very good generator and an Ourunner type can be made to look suitably vintage.
Mounting an out-runner type with the shaft vertical would resemble the generators used on hydro electic power plants.
A old computer fan would also yeild the required parts.

Robert.

[Michael GilliganParticipant @michaelgilligan61133]

Inspired by Robert’s comments … I found this useful little Instructable:

https://www.instructables.com/Make-a-Powerful-Generator-From-a-Dead-BLDC-Motor/

It may not be elegant, but it’s an excellent demonstration of a cheapskate approach.

MichaelG.

.

Note: __ His 3-phase rectifier is electrically functional but mechanically scruffy

… more clearly described here, if you need to know:

https://m.youtube.com/watch?v=-XUsu08Farw

 

 

[noel shelley]

On noel shelley Said:

 

Hi Jason, yes I did look at it, may be that was a better one with true poles and a good magnet ? Noel.

Look again, he was getting almost nothing out of it, replaced the magnet with a new one and then got the 3V. OP says his magnet seems very weak just like the guy in the thread.

[JasonBModerator @jasonb]

I think this guy ha sstopped making the casting sets now but quite a nice small project. Not too hard to fabricate something similar, you could get a reasonable amount of detail from this thread

A bit larger but castings for this one can still be had, neodiniums if you don’t want to wind your own field windings

[John HaineParticipant @johnhaine32865]

<pedant alert>

Neodymium please. Thanks for the video Michael,  just to point out his confusion between armature and stator.

</pedant alert>

[Michael Gilligan]

On Michael Gilligan Said:

Inspired by Robert’s comments … I found this useful little Instructable:

https://www.instructables.com/Make-a-Powerful-Generator-From-a-Dead-BLDC-Motor/

It may not be elegant, but it’s an excellent demonstration of a cheapskate approach.

MichaelG.

.

Note: __ His 3-phase rectifier is electrically functional but mechanically scruffy

… more clearly described here, if you need to know:

https://m.youtube.com/watch?v=-XUsu08Farw

 

 

Yes, that’s what I was thinking of. Apart from the faked (no rotor but lamp lit) cover image for the youtube video the instructable shows the idea quite well The motor shown looks like it is off a airconditioning fan or similar. Clearly you could turn what is meant as the stator into a rotor with 3 slip rings. The bottom of the rotor “cup” could be cu out and it mounted into a frame and you have somthing very similar to the one stage of the triple set model Jason shows.
If you really want to scratch build, disecting a couple of BLDC’s (most DC computer fans and dik drives use them) will give you an idea of what is required. The biggest hurdle with scratch building would be sourcing and cutting the silicon steel or nickel-iron sheet for the lamination stack.

Robert.

[JasonB]

On JasonB Said:

…

 

Nice model.  I hope the figure is a tribute to Fred Dibnah.  Anyone know?

On the subject of early generators, the first power stations where a public nuisance.  Had to be located close to their customers and driven at high-speed by reciprocating steam engines.  Unfortunately ordinary engines caused a severe thumping vibration bad enough to rattle shelved crockery a few hundred yards away.   As early electricity was only sold in rich areas, this led to neighbours taking well-funded legal action against the supplier.  And they set up a parliamentary lobby that got the law changed.

In the long run the answer was turbines and AC technology allowing power stations to be moved out of town.     But there was an interesting phase before turbines when generators were driven by steam engines specially designed for high RPM, high-efficiency and reduced vibration.    Extra tall steeple engines like the Willans:

Steeple engines have a long general-purpose and marine heritage. I’ve seen several model steeples exhibited, but I don’t think any of them were specifically of the high rpm for electricity type.  Has it been done?

Many model engines are stand-alone, which is great, but I add extra brownie points if the model shows them driving something.   Mill engine powering a model loom,  winding engine lifting a cage in a model colliery, marine engine turning a propeller,  traction engines spinning illuminated fairground rides etc.   I guess the main reason it’s rarely done is space – a mill engine would be tucked away in the corner of a model cotton mill, itself a large factory packed full of other machines:

Dave

[noel shelleyParticipant @noelshelley55608]

A Stuart Flywheel about 3 ” dia with pockets scolloped out in the rim for Neodymium magnets might make a good rotor for a small alternator, bit like the 3 gang set shown. Noel.

[JasonBModerator @jasonb]

The German model engineers seem to be quite keen on making electricity and generally having their models do soemthing. These couple of videos from a recent show give an idea of what they run, not sure about the rabits!

Steeple engine near the start of this one, nice and slow but a good pulley ratio to get the speed up for the small dynamo that is lighting two lamps.

 

 

[duncan webster 1Participant @duncanwebster1]

Good write up on outrunner motors here

https://www.magneticinnovations.com/faq/outrunner-motor/

 

[VolansParticipant @volans]

I know that this doesn’t help resolve the problem here, but I have been considering building a dynamo to run off of a stationary model, I have located a new bike dynamo (Chinese) which I think will be too big, a short motor/ generator and a 3phase generator also not too long. I may go for the 3 phase & put a board on top for the circuitry to convert to DC ( hopefully it will resemble the showman dynamos) – takes me back  to my youth when we powered a set of gallopers with my boss’s Lord Lascelles showman. Hopefully I’ll run some lights.

[SillyOldDufferModerator @sillyoldduffer]

I mentioned the need to match the load to the generator earlier, because a 4V 6W generator will struggle put to life into a 240V 60W light bulb.  This is an electrical match.

There’s also a need to match the generator mechanically to the motor.   Stuart’s will have designed their generator to match the power output, RPM and torque of their steam engine.   Probably conservatively so that engine won’t stall if the generator is asked by the user to provide full-on output during a start.

An important match parameter is the power of the magnet.   To avoid stalling a Stuart steam engine, a replacement magnet should be of similar flux to Stuart’s original, not massively more powerful   I mention it because modern super-magnets are in a different league to older permanent magnets.  In this century it would be rather easy to to install a magnet so powerful that a Stuart engine couldn’t turn the souped-up generator!

Dave

 

 

 

[Volans]

On Volans Said:

I know that this doesn’t help resolve the problem here, but I have been considering building a dynamo to run off of a stationary model, I have located a new bike dynamo (Chinese) which I think will be too big, a short motor/ generator and a 3phase generator also not too long. I may go for the 3 phase & put a board on top for the circuitry to convert to DC ( hopefully it will resemble the showman dynamos) – takes me back  to my youth when we powered a set of gallopers with my boss’s Lord Lascelles showman. Hopefully I’ll run some lights.

If you can, do the maths!

• Calculate the load in Watts of the lights. (Say 10W)
• Confirm the generator can output that many watts.
• Assume that the generator is 50% efficient, so confirm the motor driving can output about 20W.

If the lights are LEDs, then a DC supply is wanted.   Easier to rectify single-phase than 3-phase, so I wouldn’t go for 3-phase on a model without good reason.   Such as having a 3-phase generator of just the right size to hand!

Otherwise, set the motor and generator running, and gradually increase the electrical load until it’s judged “too much”.   Balancing the prime-mover and generator and the circuitry to get acceptable volts and amps on the load might require a lot of experimentation.  Or could come together without fuss.  Depends on how compatible the components happen to be.

A brightly lit Galloper with steam and the smell of coal smoke is truly wonderful!

Dave

 

[Robert Atkinson 2Participant @robertatkinson2]

It’s not that straight forward.
The input power (torque & RPM) is totally independent of the magnet type or strength. It is proportional to the electrical load plus losses (friction, windage etc). If you change the magnet the output voltage is will change. if you kept the same lamps there might be an issue, but if your prime mover will turn the original design with a (say) 1 W electrical load at a given speed then if you change to a stronger magnet it will turn it with a 1 W load at the same speed.
However the voltage output is proportional to the magnetic field and rotational speed. So if you double the magnetic field you will double the voltage. If the load resistance remains the same the power will have quadrupled. Then the prime mover may struggle. So you need to change the load resistance to suit the higher voltage and maintain the same load power.
Alternatively you could halve the speed, but then the torque required will double. How this affects the prime mover depends on it’s charateristics.
As Dave says you should match the generator speed and torque to the prime mover but increasing the magnet strength does not change the required power input to the generator. If you want the same output voltage (assuming you don’t change the windings) the speed / torque relationship will change. This may or may not put the prime mover on a “better” point on it’s power and efficency curves.

Robert.

[duncan webster 1]

On duncan webster 1 Said:

Good write up on outrunner motors here

https://www.magneticinnovations.com/faq/outrunner-motor/

 

The motors shown are actually ‘Torque’ motors and not really intended for continuous rotation like our conventional idea of what a motor does. The term ‘outrunner’ came into usage from the model aero fraternity when brushless motors with electronic speed controllers ‘ESC’ became available. As it happens, torque motors might be ideal for generating electricity but their high cost would rule them out.

Ian P

[Robert Atkinson 2Participant @robertatkinson2]

Been busy with the day job so late reply. Strangely enough I’ve just spent 3 days here:
https://www.nottingham.ac.uk/research/groups/pemc/home.aspx
Can’t go into details but BLDC motors were discussed ;-).
Before I went I did get around to taking a 75mm 5V fan of the type used in computers apart. Unsoldered the drive PCB and soldered on 6 diodes as a full wave bridge. Off-load it gave about 5V when flicked by hand. So I connected a 6V 60mA MES bulb (0.36W). Flicking the fan caused that to light up.

Probably not the bulb for the motor but it was handy.

The observent amongst you will have noticed that the stator of this particular motor has four poles. So it isn’t the expected 3 phase design. It does have 3 connections. These appear to to be a common and 2 phases. So my 3 phase rectifier is not optimal. I’ll have to do some more work.  This will include AC to the bulb, 2 diode full wave rectifier and a different fan or two.. I only choose this one because it was to hand and the frame was broken. I assume it’s a 2 phase motor because it saves a power transistor…

[Michael GilliganParticipant @michaelgilligan61133]

Well-played. Robert

… it would be nice to think that the guys at Stuart were following this topic, but I guess they have their heads in the [casting] sand.

🙂

MichaelG.

[John HaineParticipant @johnhaine32865]

A rather odd concept of a torque motor – very difficult to discern any difference between what they describe and a conventional synchronous BLDC motor.  They say you drive the stator with 3 phase, but unless it is rotating at the right speed, or the 3 phase is commutated by the rotor, they won’t generate any torque!

In my understanding, torque motors are designed to generate maximum torque at minimum or zero speed for applications such as tensioning.  On better reel-to-reel tape machines for example there’d be one on each reel, driving forwards on take up and backwards on the feed reel, to keep the tape tight, whilst its speed was fixed by a capstan drive. For fast forward or rewind the capstan is disengaged and the appropriate motor applies much more torque to wind the tape quickly. On some computer tape machines I believe they dispensed with the capstan and just controlled the motor torques to run the tape at the right speed.

The classic torque motor is an induction type with a high resistance rotor so it has max torque at zero speed.  I once had a tape deck with two of those – the feed spool motor was actually driven backwards by the tape. Torque was controlled by putting resistors in series with the motors – the motors and the resistors got pretty hot!

I believe DC universal types were also used, possibly in tape drives, as they are more controllable.

[duncan webster 1Participant @duncanwebster1]

A distant memory says that to get max power output the load impedance should equal the source impedance. It would be an interesting faff to measure the source impedance. As it’s generating AC, I suppose inductsnce of the windings could come into it, but I’m getting well out of my depth now. In short, if it produces 5v with no load, you probably need a somewhat lower voltage bulb to get the best out of it.

[John HaineParticipant @johnhaine32865]

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.

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