Double Dynohub: 2 Sturmey Archer generators in one - to be steam driven

[Steamchick]

The idea: Make a Genset from some bicycle generators - as bicycle wheels don't go round so fast - like old model steam engines.
So I acquired a few old and almost scrap gensets for "not a lot" on eBah Gum.
After cleaning up the bits of 3 gensets I had 2 workable units, so mounted in a Nylon carrier, on steel shaft, ball bearings, etc. here is the "work-in-progress".
With help and advice from HMEM contributors, I have set the 2 independent AC outputs - via rectifier bridges - in-parallel - into a Buck-controller, for 6V ~12V output. - Well, I experimented and although I had initially thought I would need 2 Buck-controllers, and then combine the 2 outputs afterwards, it seems that combining the 2 outputs after rectification and before the single Buck-controller does the job without anything frying so far.
I have 3 Steam engines, and am considering which is the best fit and most suitable power/torque/speed for the genset.
Using my "fridge compressor" - as a limited air supply, I checked the free-wheel of the engines:
Single 1/2" bore DA x 3/4" stroke (TBC) = 220rpm.
Twin ST Sun engine: 5/8" bore SA x 3/4" stroke (TBC). = 450rpm.
Twin oscillator: 9/16" bore SA x 5/8" stroke. = 850rpm. - so this looks favourite at the moment? - It is also the easiest to mount and check with a belt-drive, although finally I prefer direct shaft drive, if the speed ratio 1:1 will work.
I have a re-designed and built old boat boiler and blow-lamp style burner to finish for the steam plant, so all in all I expect to take about 17 years to complete this as I keep mis-placing the "round-tuit".
Here are a few pictures of the genset.

.

 

[BaronJ]

Hi Steamchick,

Please don't take this post as a criticism of your work, simply an observation ! It looks good and should do what you want.

Two things that occur to me here, since you have two similar dynamo's and you are rectifying the outputs and then paralleling them. The phases are unlikely to be synchronised, so you will get an uneven AC ripple on the dc output, simply due to the lack of phasing.

I would be inclined to deliberately phase them 90 degrees apart. This will have the effect of doubling the ripple frequency enabling you to reduce the smoothing capacitor value to half of what you would normally need. It won't make any difference to the output voltage.

The second is as long as the input voltage is above the minimum value for the voltage regulator you will have a stable output voltage.

Once the input voltage drops below the minimum the output voltage will be entirely dependent on the load, and the ability of the driver to keep the generator turning

 

[Steamchick]

Thanks Baron. Really useful. I have deliberately phased the 2 gens at 90 degrees (magnet) offset. Just for the same reasons you explained. But it is good when an expert takes the time to confirm my "amateur" ideas. Makes me happy that I got the right answer (like a tick from Teacher).
Do tell me anything else. All feedback is welcome, if polite.
1 + 1 = more than 2, when it comes to sharing ideas and knowledge.
Thanks,
K

 

[Steamchick]

How about this? (If I have managed to attach a graph I prepared earlier...?):

I made the mounting so the aluminium centre bosses hold the bearings for the rotor-shaft, and are fixed with the stators. They can be rotated within the brass mounting clamps (Inherited from a kn@ckerd job) to change the phase angle relationship between the 2 generators, the Magnets (rotors) being glued in place and cannot be relatively phase shifted.
I set the stator on one side in-line with the magnet poles, and the opposite side stator in-line with the magnet pole gaps. The idea being a 90degree out-of-phase on the 2 AC outputs. That then gives 20 half-cycles of rectified DC per generator revolution, times 2 generators = 40 x rpm. This is then smoothed by a capacitor before feeding the buck controller.

For the technically minded...
Generator "red" = 25V AC OC, 5,5 V loaded. (max 0.5A).
Generator "blue" = 30V AC OC, 7.5V loaded (max 0.5A)
At the moment, I have determined my preferred LED bulb array wants 12V 0.4A DC. So I have reset the Buck Controller to give 12V. With a battery (instead of generator) input the bulb is bright. I am hoping that the generators - at >200rpm? (Maybe 800rpm? - subject to engine!) - can generate the 4.8W at 12V. They are both rated as 6V AC rms and 3W. (0.5A). So I want to stay within the current rating, but see no problem collecting the power generated at a higher voltage (>13V to power the buck for 12V output) as long as I don't exceed the 0.5A limit? - Q: Is this logical?
I guess the current from generators may be "shared" proportionately to 1/R per generator - less back EMF? But I'm not really sure how to work this out or what will really happen. - Any expert advice?

Thanks for your interest.
K

 

[Steamchick]

Graph didn't attach...

 

[Steamchick]

And the schematic circuitry.

 

[BaronJ]

Hi Steamchick,

If each generator can supply 3 watts of power, then you have 6 watts to play with. Even if you can increase the voltage you still only have 6 watts. Even If you used a transformer to change the AC voltage output you still only have 6 watts.

It may be that the generator can produce more power, but that will be dependent on its speed and efficiency. After that you then have to provide enough power from the source driving the generator, because as you load the generator it will require more energy to keep it turning and producing power.

In other words, "you can't win and there is a penalty for trying !"

Sorry, I couldn't resist not leaving that quote out.

 

[lennardhme]

Hi Steamchick,
A bicycle wheel may turn relatively slowly. but you are looking at a large perimeter driving a small gen wheel at quite a fast speed. Not sure a steam engine will drive the gen fast enough unless geared up considerably. [assuming I understand your plan correctly.] I have a couple of bike gens as well & planned to do something similar but have'nt had the time to date, so look forward to your results.
Cheers,
Lennard

 

[Steamchick]

Thanks Baron, I appreciate the comments.
Some of things I understand are the equations involved - but I like the diagram you included! However, when I was quoting the rating of the generator, I think this is a single point on a variable curve of power/speed/voltage - which defines the current limitation for which the generator has been wired. A Rating of 6V 3W defines the current as 0.5A. - and impedance of 12 Ohms. However I guess this is not just the resistance of the windings (6 Ohms), but the resistance + impedance of the coil and core at the frequency generated by the shaft speed and number of poles + resistance of load..?
But I have experience of dynamos, on old motorcycles where there was "adequate" input power, and I converted from 6V to 12V by re0-wiring the controller to keep the field managed by switched 6V supply, and the armature fed a 12V battery and the lights, ignition, etc. - In that case, the limiting factors were the current in the armature and field coils - too much and they would simply overheat/burn-out. But the increased voltage across the armature didn't seem to affect it. (I did thousands of miles and had good 12V lighting!).
In the case of your comments about power, yes, you are right, but that is a different problem for me in increasing the power input, as I am changing from a couple of legs (for the Bicycle-driven generator) to a steam engine powered toy. (I have a 60psi boiler with a lot of steam generating capacity for this application, just need to build the engine to the generator and see what steam pressure is needed for an adequate speed to generate..). However, I am worried that the generators are designed for 6V AC across the internal resistance of 6 Ohms, and I'm not sure if that suggests I'll burn-out the generator by allowing it to generate at 12V, as surely that will double the generator internal current? - Unless I limit the current with an appropriate external resistance? - Which constrained me to running the buck controller at 6V. output... on a load "not exceeding" 6W for the pair of generators.
What will happen to the generators if I allow the Buck controller to output at 12V? I have an idea that the generator will need to be protected by not exceeding 6W total load? - This will drop the current demand to 0.5A - so should I be OK? - With the Dynamo case that I used on 4 motor-bikes, the double voltage allowed nearly twice the external load wattage - as the current did not exceed the original designed limits. (10A. in that case). But it was limited and controlled by switching the field from the regulator. The Bicycle generators have no field control, so will running the generators faster with a 12V setting on the buck cause them to run too much current and burn-out?
I also have some experience of a few motorcycles with PM rotors and outer stator coils, and where originally designed for 6V, I converted them to 12V. I used the standard method at the time of setting the output across a proprietary Zener diode and re-fitting the bike with 12V parts and battery, and got 90W instead of 60W. I think this was due to the configuration of coils, and current limitations, but never quite understood it! Sometimes expertise isn't enough, you need the education and brains to use it correctly.
Thanks for your help,
K

 

[Steamchick]

Thanks Baron, I appreciate the comments.
Some of things I understand are the equations involved - but I like the diagram you included! However, when I was quoting the rating of the generator, I think this is a single point on a variable curve of power/speed/voltage - which defines the current limitation for which the generator has been wired. A Rating of 6V 3W defines the current as 0.5A. - and impedance of 12 Ohms. However I guess this is not just the resistance of the windings (6 Ohms), but the resistance + impedance of the coil and core at the frequency generated by the shaft speed and number of poles + resistance of load..?
But I have experience of dynamos, on old motorcycles where there was "adequate" input power, and I converted from 6V to 12V by re0-wiring the controller to keep the field managed by switched 6V supply, and the armature fed a 12V battery and the lights, ignition, etc. - In that case, the limiting factors were the current in the armature and field coils - too much and they would simply overheat/burn-out. But the increased voltage across the armature didn't seem to affect it. (I did thousands of miles and had good 12V lighting!).
In the case of your comments about power, yes, you are right, but that is a different problem for me in increasing the power input, as I am changing from a couple of legs (for the Bicycle-driven generator) to a steam engine powered toy. (I have a 60psi boiler with a lot of steam generating capacity for this application, just need to build the engine to the generator and see what steam pressure is needed for an adequate speed to generate..). However, I am worried that the generators are designed for 6V AC across the internal resistance of 6 Ohms, and I'm not sure if that suggests I'll burn-out the generator by allowing it to generate at 12V, as surely that will double the generator internal current? - Unless I limit the current with an appropriate external resistance? - Which constrained me to running the buck controller at 6V. output... on a load "not exceeding" 6W for the pair of generators.
What will happen to the generators if I allow the Buck controller to output at 12V? I have an idea that the generator will need to be protected by not exceeding 6W total load? - This will drop the current demand to 0.5A - so should I be OK? - With the Dynamo case that I used on 4 motor-bikes, the double voltage allowed nearly twice the external load wattage - as the current did not exceed the original designed limits. (10A. in that case). But it was limited and controlled by switching the field from the regulator. The Bicycle generators have no field control, so will running the generators faster with a 12V setting on the buck cause them to run too much current and burn-out?
I also have some experience of a few motorcycles with PM rotors and Stator windings, with "switched" loading and rectifier but no control. These were rated 6V and 60W but easily converted to 12V and between 90 and 110W - depending on when-made / what-design for wiring. (Simply jon 2 of 3 wires together, and then feed the rectifier bridge). This 12V version used a Zener Diode to regulate system voltage and dump surplus electrical power to heat... - But I never managed to understand exactly what the joining of 2 wires really did? I thought they were 3 wires from a delta wound stator, but shorting 1 phase shouldn't be the most efficient way to get more volts/more power should it?
On bicycles... the wheel speed is of the order of 200rpm at 15MPH I think? - so these hub generators were designed for that sort od speed - which is not a difficult speed for model stationary engines. I have 3 possible engines, that run at ~200, 450. and 850 rpm when coupled to my usual Fridge compressor air supply. Therefore with steam at higher pressure, and selecting the most suitable engine from those 3, I think I can make the generator work nicely.
Attached is another engine and a bicycle "bottle dynamo" that lights the bulb easily on the same fridge compressor. Although this bulb is only 0.5W or less.
Keep writing,
K

 

[Steamchick]

Hi Leonard, I selected the Dynohub as being a low speed device, running at the wheel hub. I think bicycles easily do 100 rpm at the wheels?
As set-up, I get full output from 200rpm to 900rpm. Possibly a wider range of speeds, but that's just how my drill works. Whether my steam engines will develop adequate torque, I don't know, but my "favoured" engine is a twin oscillator, single acting, that will run at 800rpm with just my fridge compressor, so will do a lot more on steam - and develop more torque. I'm happy if the gen gets power at 200rpm... or 800rpm.
Doing the sums... wheel dia 18" = 4.7 ft. circumference. 1 mph = 5280/3600 = 1.47 ft/sec.. or = 88.2 ft/min. which means the wheel does 18.7rpm per MPH. I reckon most people cycle at least above 3MPH or fall off. so at least 56rpm - and maybe well over 200rpm? I don't know when pedalling, at what speed the lights became bright, but I remember my sister had one on her bike that was easier to use at night than my "little bottle" generator dragging on the side of the tyre. ( I have one of those driven by a belt from a flywheel on a small single cylinder DA steam engine.).

Thanks,
K

 

[BaronJ]

Hi Steamchick, although "K" is easier to write.

It very highly unlikely you could do any damage to the dynohub generators even if you could spin them fast enough to get much more than the 25 or so volts out of them that you have measured no load.

As far a power output is concerned, the manufacturer designed them to light a low voltage low wattage bulb without burning the bulb out at a high road speed. I forget the exact voltage of the bulb and its wattage. You've mentioned 6 volts and 3 watts which certainly is in the right ball park.

The power limit becomes a function of rotational speed and internal impedance, which then becomes frequency dependent. So as the speed goes up it gets to a point where the voltage output starts to drop, limiting what the generator can produce.

One way of getting useful data is to go ahead and couple the generator up, put a volt meter across the DC output and measure the voltage at whatever speed you choose with known load resistances across the output. Start with 100 ohms. That will give you an immediate reference figure. Knowing the rotational speed will also be of value. So you can relate output voltage to generator speed at known loads.

 

[fcheslop]

The old GH-6 only gave 1.5 watts at 6v or that is what they claimed .
The Prince of Darkness aka Lucas was slightly better but only just
I seem to remember some playing with old stepper motors but have no idea what they got out of them
Lucas used to make a nice sized 30 watt dynamo in the 1930s-50s for model work . I have one fitted to my old royal oilfield but dont use it often in the dark a bit like a *** in a jam jar once the battery gets low
Interesting project good luck
https://www.cyclingabout.com/best-dynamo-hub-bicycle-touring-bikepacking/

 

[Sprocket]

I know we are separated by a common language, but what does "a *** in a jam jar" mean?
Doug

 

[Steamchick]

*** = cigarette, probably hand-rolled with very little tobacco, so just about the smallest red glowing thing you can have....
Jam-jar? - Glass container for Jam, so you need to know what that is! Often about a half-pint size, or thereabouts.
Jam is a Fruit Jelly, fruit preserve using its natural gelatin or setting agents, like LOTS of sugar!
Maybe your Grandma made it? - My Mother did - Lots!

 

[Steamchick]

Oh, another one: "old royal oilfield" = More than 20 years old, Royal Enfield Motorcycle, renowned for their inability to retain all the oil inside the engine... - the space where they were parked often resembled an Oil-field" - a large black patch on the ground. Hence the play-on-words.
Old Gits like me understand such inane jargon...
Git is someone you wish would "git ouda here!" (Git = slang verb for Go away).

Enjoy!
Language is the lubricant of society.... - sometimes things squeak a bit!

 

[Steamchick]

Thanks Baron, I was planning some more testing today - but was nervous of toasting windings with the buck controller set at 12V... and I plan to use a 5W 12V bulb as the load.... - but first I'll try a sub-1W, and 3W bulbs I think? I'm using my battery drill as a motivator, so limited on speeds and control. (I need 3 hands!).
I'll post results later.
K

 

[Steamchick]

Oh, Sprocket? Maybe you don't appreciate the reference to "prince of darkness" and Lucas?
Lucas and Wipac were 2 "great" British manufacturers of electrical kit used on cars and motorbikes for the 20th century.
Except, that the older gear wasn't always very reliable - usually at night, just when you want some light to see the road. So when it failed - and usually on a dark rainy British night miles from assistance - you "Blessed" the "prince of darkness" that made your electrical system - I.E. Lucas!
However, the only problems I had (and those were many) were basically because I was using old, worn-out, 7th-hand bikes, that had generally had no servicing of the electrics, and wires that were out of warranty... hard, cracked insulation and wires broken next to the soldered ends.... with insufficient length to be bodged into a get-home connection. - Buts that's another story.

 

[Steamchick]

fcheslop : do you have a picture of your Enfield? - or the 30W generator you mention?
K

 

[fcheslop]

Not at the moment its just a model G circa 1944 put back into civvy trim by Enfield in 1949
The Dynamo is the early mag/dyno set up .The dynamo is similar to the later one just a wee bit shorter maybe a bit of a lump for youre needs
We used to use a 3phase alternator from a French car the make I cannot remember may well have been the 2CV. This alternator would fit in the space of the dynamo on the Bonny or T110 pre unit with a little bit of machining. Im pretty sure it was crank mounted like the BMW R series bikes upto the 1980s but smaller
Lucas also made a very small alternator that was built into conveyor rollers the reason I cannot remember all this was pre ttl cmos technology. A simple prox switch would now be used I guess
I will take a few pics next time Im in the playroom. I have a safety valve to finish then my new marine boiler should be a goer
keep well
kind regards
frazer