Stuart Dynamo

[duncan webster 1Participant @duncanwebster1]

I wouldn’t be surprised if they are cast iron, no need for fancy low magnetic hysteresis material

[Michael GilliganParticipant @michaelgilligan61133]

John,

Looking at the short video I posted earlier … it appears that those are only pole-pieces [if that’s the right term] and there is a separate bar magnet coupling them.

Happy to be corrected !

MichaelG.

.

Edit:__ if only the instructions didn’t cost £20 … we might know !

[Michael GilliganParticipant @michaelgilligan61133]

For general reference, the photos in this ebay listing may be of interest:

https://www.ebay.co.uk/itm/196498627511

MichaelG.

[JasonBModerator @jasonb]

John/Duncan. The “Pole Pieces” are cast in and are just steel or soft iron. These form the two ( ) pieces either side.

There is a SEPARATE bar magnet that fits into the bottom after milling the lower edge of the pole pieces for it to sit against. This completed the”U”

Suggest you have a look at the photos again as both features can be seen.

Read recently of someone using neodymium magnets in a larger Dynamo to good effect.

[Robert Atkinson 2Participant @robertatkinson2]

Only the pole pieces were cast in-situ. The magnet is separate and is located in the base after machining

[Michael Gilligan]

On Michael Gilligan Said:

[…] Happy to be corrected !

Even happier to have had corroboration from Jason and Robert

🙂

MichaelG.

 

[JasonBModerator @jasonb]

I remembered discussing these dynamos before, a change of magnet makes a lot of difference as this thread on MEM shows, you need to register to see some of the images which have been posted as attachments.

[noel shelleyParticipant @noelshelley55608]

How many Stuart Models are built to be worked ? How many just sit on a shelf ? How many are chosen for there power output ?

In the case of the dynamo the design is far more about the looks, not it’s ability to produce power. The out of true pole pieces and machined faces to transfer the magnetic flux from a weak magnet to the poles are never going to work well ? IF one wanted to use your live steam model to show it producing electricity then a small permag motor (or a stepper motor) would be far better, hide it in a nice period casing if looks matter. Or dismantle the motor and use the components in a casing that suits or looks better. Plan B, Get a pair of arc (curved) ceramic magnets of suitable size and design your own ?

May be before putting pen to drawing board one should consider the power one has available, even pound/inches of torque may be a bit ambitious, Watts might be better ? Or some SI units ?

Looking at old Stuart Models catalogues there appear to have been several versions of the dynamo and the model the OP has seems to be early, 80s may be. The one offered in 1992 looks more like a small motor and by 1995 it talks of a cast iron body and GM end plates – the lighting set that went with the dynamo had a grain of wheat bulb – needing milliamps ! The Sirius was claimed to produce 300W at 2800 though when used in the Alco Firefly generator of WW2 it gave 8V at 3A (24W) and this with a sizeable boiler. The later Mk 814 cold war unit was good for less than 20W and needed a good boiler to keep that up.

One of the Stuart or other makes of engine of about 3/4″ bore or greater would work OK but a Mamod or even a Wilesco would struggle to make more than a few ma s. May be there is a reason for the poor magnetic circuit ? Noel.

 

[JasonBModerator @jasonb]

Did you see the thread I linked to Noel, 2.76V off the same dynamo when running at less than the stated 3000rpm for 3V so I would say it works as Stuarts say so no need for a redesign.

Same thread has a similar PMR dyno being used to charge a phone off a small PMR engine and boiler. Note pulley ratio so engine is not reving it’s nuts off. Most who build these are happy to have them light a single lamp often on a lamp post or several LEDs. If you want something to do real work then there are other kits available that will produce a lot more but do need a larger steam engine or hit & miss to drive them

As with model engines sometimes it is the building of it that people like so may not want to just hide a bought in motor in  a casing.

[John HaineParticipant @johnhaine32865]

Maybe someone should design a proper little alternator for home construction to run off steam & stirling engines?  Static coils, rotating magnet to eliminate brushes, “period” appearance if that matters.  Personally I don’t see the point when a small PM DC motor does the job just fine (though while a stepper can generate I don’t think it would be very efficient).

[Robert Atkinson 2Participant @robertatkinson2]

Sorry I duplicated the posts about the pole pieces. I missed the tiny blue 2 at the bottom of hte page that indicates there is another page of posts.
Even if it is intended as a “toy” dynamo there is no excuse for the state of the castings the OP received.

Robert.

[JasonBModerator @jasonb]

This one is on the “drawing board”

Options to just clamp a motor into it an paint the 3D printed parts so it looks real. Or cast it and use the commuter out of a larger motor and wind your own filed coils. Half way option is to have dummy outer field coil and a stack of Neodinium magnets in their place. rearrange the wiring a bit and you have an old bi-polar motor.

Or just dig out that old copy of ME

[Robert Atkinson 2Participant @robertatkinson2]

To reply to John’s comment on a modern design (post camr in while I was composing my last) If go in that I’d start with a modern Brushless DC (BLDC) “out-runner” motor of the type used in UAVs. These make excellent AC generators with 3 phase output. They are available from a few Watts to several kW. You can use filament lamps in sets of 3 or a six diode bridge wil give decent quality DC.
Like all permanent magnet generators you can only control the voltage by varying the speed. With modern switch-mode regulators it’s seay to convert a variable generator output to a fixed voltage if required.
The parts of the outrunner could be housed or mounted in a contemporary looking housing.
I’ve used out an out-runner as a proper generator but it was a work project so can’t say more.

Robert.

Edit: Jason has similar ideas…

[JasonBModerator @jasonb]

Jason has too many ideas 😟, just some here it is hard to decide which one to replicate. Probably an amalgamation of features I like from several different ones.

[SillyOldDufferModerator @sillyoldduffer]

Good to see Steve has got a 6V bulb to glimmer.   But how many amps or watts is the bulb?  It’s important to match the load to the generator.

A push-bike rear filament bulb is 6V @ 40mA (or 0.24W), whereas a 6V motorbike headlamp will be 25W, requiring 4A for full brilliance.   0.24W is a light load, and should work.  Not full brilliance because this is nominally a 4V generator.   A 25W bulb is a heavy load, and if Steve got light out of one, then the generator is OK.   What’s the current or watt rating of your test bulb Steve?

I don’t think Stuart’s blurb says what the dynamo’s output power is, naughty them, because it’s not obvious what the test load should be.    Stuart only mention it being able to light up a few 4V filament bulbs.  Probably made sense in ye olde days because I believe 4V bulbs were common on push bikes and torches before WW2, but after then bulbs seem to be either 3V or 6V.    Small 4V bulbs appear to be almost unobtainium today!  My initial guess is the generator is good for 1W out, roughly 250mA at 4V.  Unlikely to manage anything like 10W out, which is 2.5A at 4V.

Steve’s basic multimeter may be misleading him:

• As a load, the meter isn’t not matched to the generator.
• The lowest AC scale is max 200V, not ideal for measuring a device outputting 4V or less.
• The meter is probably only designed to measure AC accurately between 50 or 60Hz.  Depending on what’s inside, it may  misreport voltages at both higher and lower frequencies.

However, if the generator is making a 6V bulb glimmer, then it’s certainly capable of brightly lighting 4 to 6 LEDs, maybe more.  Rule of thumb I assume 20mA for an ordinary junk-box LED, but 2mA LEDs are cheap enough, so maybe 40 of them.  Won’t do of course if Steve wants power rather than pretty lights!

Question for boffins:  if a Model Engineer doesn’t have 4V bulbs of the type recommended by Stuart’s before WW1, or a decent meter/oscilloscope with a selection of load resistors, what’s the easiest way of testing the generator?  Kitchen table method needed!

Dave

 

 

 

[JasonBModerator @jasonb]

4V lamps easy enough to get Dave, this is 1.2W rather than the stuart stated 1W but should be OK as it says the Dynamo will gight four at 3000rpm

Blurb says the wattage of the lamps it will light at various rpm so easy to work out the wattage it is putting out.

Dig the old pre LED set of christmas lights out the loft, many of those used 4V lamps if you want to do a quick test

[John HaineParticipant @johnhaine32865]

Question for boffins:….

Obviously by making a galvanometer from scratch…..

[JasonB]

On JasonB Said:

4V lamps easy enough to get Dave, this is 1.2W rather than the stuart stated 1W but should be OK as it says the Dynamo will gight four at 3000rpm

I stand by what I said: 4V bulbs used to be common and are now difficult to find.  RS only carry 4, all too many watts, and Sparks just the 1, which happens to be about right.

Blurb says the wattage of the lamps it will light at various rpm so easy to work out the wattage it is putting out.

Dunno how I missed it in the ad but pleased to see my guess the generator is between 1 and 10W was correct. Up to 8W at 5000rpm.

 

Dig the old pre LED set of christmas lights out the loft, many of those used 4V lamps if you want to do a quick test

Good idea – I wonder what mine are!

Dave

[John Haine]

On John Haine Said:

Question for boffins:….

Obviously by making a galvanometer from scratch…..

Now that takes me back to school.   Didn’t have to make the galvanometer, but were given a compass about 150mm diameter, which sat inside a coil, rather like this:

Not too difficult to make.   Didn’t go well at school.   I messed up the calculation.

Another back to basics approach might be to measure the volume of Hydrogen evolved by electrolysing water with the generator running at a fixed speed for a fixed time.

Dave

 

[MacolmParticipant @macolm]

If the configuration is as in this sketch, with a flat interface with the pole pieces (green), I would be tempted to buy some cube shaped rare earth magnets (red) and make a couple of flux couplers (blue) from iron or mild steel. Air gaps need to be minimal, but will be much less than running clearance, and magnets should be as big as can be fitted in. Magnets in series will “add”, and should all attract each other in the correct layout. Avoid parallel magnets which repel each other if “added”. Should work, but no guarantee!

 

[Ian PParticipant @ianp]

+1 to Malcolm’s suggestion

Ian P

[Grindstone CowboyParticipant @grindstonecowboy]

I thought the old torches etc were 4.5 volt, running on those flat (shaped!) batteries with the two unequal length brass strips? What combination of what type of cells would give 4 volts? Three zinc-carbon would be about 4.5 volts. Maybe the 4 volt bulbs were meant to be over-driven a bit for added brightness? Sorry, wandered off-topic a bit there 🙂

Rob

[Robert Atkinson 2Participant @robertatkinson2]

Filament lamps tend towards constant current, the hotter they are the higher the resistance. This allows a bit of over-running. The battery voltage is at low load. Using a lower than nominal bulb maintains brightness as the cells deplete. Cycle lmps tended to be two large cells on the front (some with one contact on the middle of the side). Nominally 3V and with 2.5 or 2.8 V bulbs. Rears often used smaller, flat 3-cell (4.5V)  top strip contact batteries with 4V bulbs. These were also used in small flat torches.
Little known fact, some old Soviet equipment like radiation detectors used unobtainum odd size single cells. These are the same size as tha cells in the flat 4.5V torch batteries so breaning one up and a bit of tape makes 3 soviet cells. I don’t remember (and can’t be bothered looking up) the designations of the batteries and cells.

Robert.

[Robert Atkinson 2]

On Robert Atkinson 2 Said:…

I don’t remember (and can’t be bothered looking up) the designations of the batteries and cells.

Robert.

3R12 apparently.  I remember the battery well, though not by that number, because they were the power source recommended in my Ladybird Book of Electricity.   Aged 8 or so I was deeply impressed by the idea of connecting to the battery with wire wrapped around paper-clips.   This was long before McGyver!

And I still think of D-cells as U2.

Dave

[Steve RowbothamParticipant @steverowbotham77083]

Thank for the suggestion to eliminate a rectifier Duncan, I’ve ordered some Neodymium magnets to play with today, so will soon know where I end up peak voltage wise and whether the extra diodes will be required.

Noel, I did indeed question the castings with the supplier before machining, and yes the pick-ups could well be improved!

John the magnet fits in a recess machined in the bottom of the casting where it sits across the ends of the 2 pole pieces which are cast-in situ.

I do wonder how many of these get built, I don’t think writing my construction notes up as ‘Building a Stuart Dynamo from Castings’ constructors guide would get snapped up by Tee Publishing!

 

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