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Discussion Starter #1
I have just tested my Heilmann after the winters break.... I can only say that I am as unhappy with it as I was in the autumn. I would like some thoughts and suggestions as to doing a rebuild.

This is where I am at the moment.

A: Increase the number of cylinders from 4 to 6 and reconfigure either as a 60 degree Vee 6 or dual inline 3.
B: Step down the steam motor shaft speed to 50% by gearing down 2:1.
C: Replace the Gramme Ring Dynamo with an Poly Phase Alternator (maybe using a s/h stepper motor?)
D: Install water tubes into the Porcupine Boiler -or increase the number of quills.
E: Install water pump and feed heater to increase duration of boiler.

Thoughts and comments greatfully received!!!

Yes, I know it has taken the better part of 18 months to get to the point where I can race snails -but  feel that I have proved the point that a model Heilmann can be built and that it will work (but with vile output!!!) Now is the time I think to progress the model to something that is normally usable.

The reason, (I believe), that the model has such a poor output are down to the fact that, as a model, the dynamo can only have a low radius of rotation -thus the number of lines of force cut per second per radial centimetre (AKA "rho" ) is low. The efficiency of the dynamo is better at higher speeds -which requires vast amounts of steam -but the torque required varies as the SQUARE of the rotation. I opted for a rotational speed of 1,900 to 2,400 RPM and worked out "rho" for this. I have been pretty succesful and my home made 1910 design dynamo is very nearly 40% efficient. I have got amps by the bucket load -but I cannot get the very high voltages (12+) that I feel I need to really get this moving.

regards

ralph
 

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Hey Ralph, you should be very proud of your achievment!!! While some of us are glueing bits of plastic and wire together to creat the illusion of an era bygone, you have been designing and building working machines and when all put together, IT WORKS!
I am not qualified to make reasonable criticism of your work, but since you ask!!!
It sounds like the boiler is a bit small, which as I recall has happened to many of the cheif engineers of the bygone glorious days of steam.
Also you need a few more volts from the generator. It may not be practical to increase its speed. I don't know what the rotor is like, but generally, my experience with industrial equipment tells me that speed increases are usually bad news. ( even tho it is done in industry all the time as a cheap fix).
I don't remeber what the generator looked like now, but if the stator was bigger in diameter, you could get some more windings in there.
Seems to me that making and adding a gearbox would be about as time consuming as re-working the generator.
Ralph, we stand (sit) in awe at your achievements and I do hope that I have not insulted you by my comments. Please continue to keep us posted as this is such an interesting project.
 

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You can get lots of current, but not much volts? I think before I tried anything drastic, I'd look at regearing your traction motors. It seems like you have something like an impedance mismatch between your input - engine and generator, and your output - motors and gearing.
 

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Discussion Starter #4
The boiler steaming may be too low -I have wondered about that... I have not done a qualitative boiler test on it, but it boils 0.5 litres of water to steam at 3 Bar for ten minutes -then I have to refill it!!! If I go to 6 cylinders this will definately put it under load. I am resigned to a complete re-build, so at this time I am looking for any suggestions to put into the redesign draughts. The gearing is 1:30 and the required amperage of all 4 motors is just under 6 Amperes under no load conditions. The point about the miss match is quite a good one each motor has a 6 Ohm resistence, and I have never tested what the operating resistence of the dynamo is....

regards

ralph
 

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Ralph, I think Torby nailed it down for you. You have mismatch in your system. You boiler can raise 0.5l to 3bar in 10 minutes? That is a serious evaporation capacity!!! And your dynamo can output ooads of amps but not enough volts? That only means that your motor do not match your I/V rating. You need motors that can use those amps at those voltages.

IIRC you tested your dynamo driven by a lathe or drill. Well this can be done, but it says nothing about input power or efficiency. So you have no real idea about efficiency unless you have measured at the same time a torque/rpm curve. You are exploring a part of model engineering that is rather untrodden! Common knowledge about steam engines does not apply without adaptation or tought.

Now I have been thinking along the same lines as you know. From what others at our club have done (stirling driven locs) you do not need more than 2-5W at the axles in order to pull a decent train. Start from there. Go for a steam engine of about 200-600rpm, that should be plenty. Then fix your voltage you want to use: 6-9-12V are good starting points. Then work for a load of 10W to determine your wire gauge, field strenght etc. And figure in some spare.

It is really of no use if your dynamo can deliver 25A in short circuit because it will never run that way. And motors using 6A at 12V for a gauge 1 engine... You are overdesigning too much.
 

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Discussion Starter #6
I tested the dynamo in the chuck of my pillar drill and worked out the amount of power going in versus the amount comming out at the 5 speeds that it could produce. I did do "drop test" to find the peak amperage from it at these rotations. I did get a pretty good curve from it!!! The motors are "free" and I have quite a few of them... My normal motor is either the SME 1902 or Johnson 545 -the former high voltage / low amperage and the other low voltage / high amperage. I opted to go with the Johnson because I knew I could not generate very high (>10) volts and it will run quite happily on 3 Volts. At the moment I am getting 5 Volts at 10 Amps out of it. The Heilmann has had to be turned into a Gauge 3 loco -simply because of its size!!!

regards

ralph
 

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Hmm. You haven't tested the dynamo output with the steam engine? A drill motor has lots of watts.

I still think your motors are spinning too fast. Lower your gear ratios so they pull harder and make better use of what your dynamo is producing.
 

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Ralph, if you get 5V and 10A out of it it should run like a scalded cat! Seriously, if you have 50W at your disposal and it "doesn't run" then there is something else wrong. The stirling loc at the club pulls 10 waggons and has about 2W calculated power.

You say you can't get high voltages out of it, but IIRC than you used 1mm wire when winding the dynamo. If you go 0.5mm and double the amount of windings it shouldn't be a problem to get more voltage. I admit it is a pain to rewind the dynamo.

Have you tried running the loc on a transfo? This might help finding a better voltage/amp ratio. Would also be interesting to work out the gear ratio that way. Maybe you need a little more volt and a bit less amp but that way you could find what to aim for. Just hook up a long wire and put a volt and amp meter on it. See what you need to pull the train you want to hook after it.
 

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Discussion Starter #9
There does appear to be a miss match between the generation side and the motor side ... The dynamo presents a high impedence source to the low inpedence of the motors!!! I have sat with my little book and looked at possible re-wire configurations for the rotor and stator that I have. None of them are really that much different to what I already have. The 1910 design is very specific and details rotors from 1 inch to 6 inches in diameter or from 4,000 rpm to 1,750 rpm.

Possible re-winds give the following:
5 volt 8 ampere
10 volt 4 ampere
20 volts 2 ampere

This is for 1,400 to 2,000 rpm. If it take it up to 2,000 to 2,500 rpm then I will get the voltage I require....

So, the first thing I think I will do is to increase the boiler output ie D and E

regards

ralph
 

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Not quite what I meant.

Your dynamo produces a fairly low voltage. At that voltage, your motors turn slowly, but they don't draw near as much current as your dynamo can produce. So you want to trade some torque for some RPM, or put a heavier torque load on your motors so they draw more current, but drive the wheels faster.
 

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Discussion Starter #11
I am limited to the size of motors and gears etc that I can cram between the wheels. The only other gear ratio I have is 16:1 -but I cannot "pin" this size to the axle -but I would have to rely on friction between the gear bore and the axle -once that goes... I will next re-wire my dynamo rotor for 10 volts 4 amperes, (currently! I use 5 volts 8 amperes) -thus giving the increase in voltage that is required and (possibly) an easier load to the steam motor. The output from the dynamo should thus be a theoretical maximum 10 volts 12 amperes (3 sets of windings) at the same rotation.

I have been using the steam from the boiler for testing another project and I think that the combination of porcupine quills and water tubes will form a good half way house for the next boiler that I have to build to power it -even though it will not have any pistons....

regards

ralph
 

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That sounds like a plan.

I figured out what I'd do.

Get a handful of low value power resistors, like 5 or 10 ohms.

Disconnect the traction motors.

Start up the engine, put one of the resistors for a load and measure the voltage.

Add a resistor and measure the voltage.

Add a resistor and measure the voltage.

And so on, until I'm bogging the steam engine to the point of not running.

Now calculate Amps and Watts at each number of resistors.

You'll find a point where the Watts peak as the Amps increase and the Volts decrease.

Design the drive to go a pleasant speed at that volts.

Of course, you're keeping the drive the same and designing the dynamo for the volts and amps you want to your drive.
 
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