Author Topic: model D.C. generator build.  (Read 5641 times)

Offline airmodel

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model D.C. generator build.
« on: November 16, 2015, 04:08:02 AM »
Hi everyone.

I have started a new project, a model D.C. generator for my model steam engine.

Small D.C. motors are very easy to buy or salvage from other devices. 12 volt motors are the most commonly available.

The motor I used for this project was from the heater/air conditioning fan in a car. There are two reasons why I selected this motor, 1. Size, I like to work on something that is not to small. The smallest tap I own is a 3mm tap, any smaller I tend to break them. So the 3mm tap will be used to tap four holes, so the two end covers can be held on by using four screws.  2. The laws of physics cannot be scaled, the smaller a generator is it needs spin faster to reach the same voltage as a larger generator.

The physical size of my model generator is a good compromise between speed and output. I have experimented with 48 volt motors, they can output a sizable voltage at a very low speed but can be very hard to find in a size that suits model engines. Another problem is matching the speed of my model motor to the speed that the generator needs to run at. Nearly all model motors have not the speed capabilities to direct drive a generator, so most people run a belt of a flywheel on the model engine to a very small pulley on the generator to get the speed they need. The other alternative is to design and build a small generator suited to be direct driven of their model engine. Very few have gone down this path because it takes specialistís skills to achieve this. So where does this leave us to if we want a model generator, We can buy a model generator kit or take the path I have taken, build a custom frame from an existing motor. Have a look at my video machining the frame.  https://youtu.be/qstZkKsxB5M  If you are interested in foundry work have look my video showing how the mold was made.  http://www.modelenginemaker.com/index.php?topic=5497.new#new


Offline airmodel

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Re: model D.C. generator build.
« Reply #1 on: December 13, 2015, 11:41:58 PM »
Hi everyone

I am progressing well with the model D.C. generator.

The end covers have been cast in iron and have been  machined with all the bores and mating spigots. I will be using countersunk screws to hold the end covers on and drilled matching countersunk holes for them.

One thing to watch with thin castings like these is not to tighten the chuck jaws too tight as it will distort the casting and after the machining  has been done the casting will spring back after loosening the chuck jaws. So your carefully machined circle will end up not a true circle. Another hazard of not tightening the chuck jaws enough is you have to take very light cuts, if you donít the casting will come out or will start to run out of true. This can be really bad news if it is the finishing cut, resetting the casting can be next to impossible.

Have a look at the video of machining the end covers.

The last video will be about painting, assembling  and testing the model D.C. generator.

Offline Don1966

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Re: model D.C. generator build.
« Reply #2 on: December 14, 2015, 12:24:38 AM »
Seems like a lot of work Airmodel but the results look great. Thanks for sharing I really enjoyed it so far.

Don

Offline airmodel

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Re: model D.C. generator build.
« Reply #3 on: December 15, 2015, 11:33:26 PM »
Don

 thank you for watching the videos.

 In my workshop I can pour iron castings so the idea is to make the generator housing look like the ones I have seen in museums. I don't think there are generator kits in iron available so that is why I do it.

Offline Don1966

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Re: model D.C. generator build.
« Reply #4 on: December 15, 2015, 11:56:41 PM »
I have a set of casting I bought at CF two years ago. It's the Proteus Dynamo and I will post some photos for you. One is the casting and the others is it complete.

Don
« Last Edit: December 16, 2015, 12:02:27 AM by Don1966 »

Offline b.lindsey

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Re: model D.C. generator build.
« Reply #5 on: December 16, 2015, 12:46:30 AM »
Nice looking castings Don. Is that your finished version too or not? Given the 6" scale, its a good sized model too!!

Bill

Offline Don1966

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Re: model D.C. generator build.
« Reply #6 on: December 16, 2015, 01:15:19 AM »
Nice looking castings Don. Is that your finished version too or not? Given the 6" scale, its a good sized model too!!

Bill
No Bill, that's not my finished model. I plan on building mind this coming year. All the material have been acquired so there will be no reason not to complete it.

Don

Offline PStechPaul

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Re: model D.C. generator build.
« Reply #7 on: December 16, 2015, 02:33:10 AM »
That's a pretty nice project. I do wonder, however, how well a dynamo with cast iron magnetic components will work. It appears that the stator is magnetized with a DC current, probably with six poles alternating N-S. The voltage would be produced by the windings in the rotor and transferred to the output by means of slip rings. In that case, I think it would be AC output, but perhaps it could be converted to DC mechanically by using a segmented commutator. But my concern is the behavior of cast iron versus steel laminations for the components that see an alternating magnetic field and voltage, because of eddy currents.
 
I searched for "cast iron dynamo", and found the following kit:
https://www.ministeam.com/acatalog/Dynamo-Kit-12-Volts-PMDYN_1.html
 
The kit seems to have an armature pre-wound, possibly on a laminated core. This model is rated at 10V and 10 watts, 12 V nominal, at 5300 RPM. That would take a fairly large ratio for model air/steam engines. When I demonstrated my wobbler with a generator at Cabin Fever last April, I was able to get about 12V at 600 RPM, with (IIRC) about 5:1 ratio, so about 3000 RPM.
 
<a href="http://www.youtube.com/watch?v=8naEh12f4IE" target="_blank">http://www.youtube.com/watch?v=8naEh12f4IE</a>
 
The motor I used is a 24V 2100 RPM model (2A stall current) that I purchased from Surplus Shed for less than $1. I bought perhaps 20 more when they had a 1/2 price sale. They still have them in stock for $0.75 each:
http://www.surplusshed.com/detail.cfm?ID=M3226
 

 
I can bring some to Cabin Fever if anyone is interested.

Offline Ian S C

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Re: model D.C. generator build.
« Reply #8 on: December 16, 2015, 11:22:07 AM »
I built an alternator from a small shaded pole motor, I made a permanent magnet armature, and cut the pole shading rings, although I don't think it actually made much difference, here it is with the end cover off.  The second pic is the completed alternator, it's designed for one of my hot air engines, it produces about 18V no load, 12V under load, and I can us a wide range of ratios, the motor seems to have a fairly flat power output over a wide rev range.
Ian S C
« Last Edit: December 16, 2015, 11:33:30 AM by Ian S C »

Offline Don1966

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Re: model D.C. generator build.
« Reply #9 on: December 16, 2015, 01:55:45 PM »
That's a pretty nice project. I do wonder, however, how well a dynamo with cast iron magnetic components will work. It appears that the stator is magnetized with a DC current, probably with six poles alternating N-S. The voltage would be produced by the windings in the rotor and transferred to the output by means of slip rings. In that case, I think it would be AC output, but perhaps it could be converted to DC mechanically by using a segmented commutator. But my concern is the behavior of cast iron versus steel laminations for the components that see an alternating magnetic field and voltage, because of eddy currents.
 
I searched for "cast iron dynamo", and found the following kit:
https://www.ministeam.com/acatalog/Dynamo-Kit-12-Volts-PMDYN_1.html
 
I think your missing the point Paul. You have to remember that they didn't have silicone steel back then and eddy currents were unknown. This Dynamo was designed to be built as a replicate. This will be a DC Generator by the way as AC was not till later.

Don
« Last Edit: December 16, 2015, 01:59:05 PM by Don1966 »

Offline PStechPaul

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Re: model D.C. generator build.
« Reply #10 on: December 16, 2015, 11:56:53 PM »
I'm not sure when laminated magnetic components were introduced and used for dynamos (DC) and generators (AC). That's why I searched for cast iron dynamo, and didn't get any definitive information. I tried "old dynamo construction materials", and found the following:

http://www.edisontechcenter.org/generators.html

http://www.electrical4u.com/construction-of-dc-generator-yoke-pole-armature-brushes-of-dc-generator/

In the following 1916 patent it was stated that the advantages of thin steel laminations were "well known":
http://www.google.com/patents/US1353658

This 1911 article discusses the need for laminated iron in the armature:
https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Dynamo

So, I'm not disputing the value of a historical model, and perhaps some very early designs were all cast iron, but it seems that the principles of eddy currents were well known by at least the early 1900s. Eddy currents were first discovered by Lťon Foucault in 1855:
https://en.wikipedia.org/wiki/Eddy_current

Apparently laminated cores were first used in the 1870s:
http://gluedideas.com/Encyclopedia-Britannica-Volume-8-Part-1-Edward-Extract/Electric-Generator.html

Offline Don1966

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Re: model D.C. generator build.
« Reply #11 on: December 17, 2015, 12:17:46 AM »
Paul your still missing the point here. Please read the article I posted with the photos? This was built from an article published in 1902 in Model Engineer and Amatuer Electrician magazine.

Don

Offline PStechPaul

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Re: model D.C. generator build.
« Reply #12 on: December 17, 2015, 02:08:00 AM »
OK, I read the article more carefully and noticed that he mentioned the possibility of greater efficiency with a laminated field. But AFAIK the field is the stator and is fed with DC to produce the fixed magnetic field, and laminations would not necessarily improve performance. It seems that the power is extracted from the rotating armature and mechanically rectified by means of the commutator. The commutator design is unusual in that it appears to be a flat planar piece with radial sectors upon which the brushes ride. A more common design uses a cylinder with multiple segments and brushes with a concave mating surface.
 
Don, I think we may be hijacking this thread from the OP, who has a different design. I seem to remember that you may have started a separate thread on your project, and I hope your results are as good as those reported in the article. 80 watts is rather impressive for such a dynamo. I suppose my engineering instincts kicked in and I look for ways to improve upon a design  :zap: , rather than consider the historical aspects. Sorry about that.  :shrug:

Offline airmodel

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Re: model D.C. generator build.
« Reply #13 on: December 17, 2015, 03:15:53 AM »
Don

All I can say is wow, wow and more wow! That is a lot better looking than mine. I did not think that it was possible to buy kits like that. There is nothing like that in Australia where I live.

My armature has laminations and the reason for that is that it generates A.C. and then the commentator rectifies A.C. to D.C. If the armature  was a solid block it would tend to get hot from eddy currents.

Offline Don1966

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Re: model D.C. generator build.
« Reply #14 on: December 17, 2015, 03:31:21 AM »
Don

My armature has laminations and the reason for that is that it generates A.C. and then the commentator rectifies A.C. to D.C. If the armature  was a solid block it would tend to get hot from eddy currents.
And you are correct the DC Generator has AC generated in the armature. The commutator serves as a rectifier. Isn't it odd that when they designed the DC motor and generator that they didn't fully see what they had? This same AC also allows the DC motor to work properly by generate a CEMF that opposes the current flow that turns it. The fast it turns the greater the CEMF.
CEMF is ( counter electrical moving force for those who don't know the meaning, it opposes the working current and is generated by the armature turning in the magnetic field)

Paul I am glad you understand now. And yes the engineering has a tendency to kick in instead of seeing the overall picture.

Don