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deeferdog

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This may seem a strange title for a thread, let me explain. A lot of us here spend a good portion of our time making small engines, steam, internal combustion or whatever, and on completion would like to see the thing do a bit of work after all the effort of construction. It also provides a riposte to the inevitable “....yes, but what does it do?” question from those around us.
The most obvious solution to putting a small engine to work is to have it generate electricity, generally low voltage DC and watch the wonder in small eyes as lamps flicker and glow into life. The problem is finding suitable small DC generators that can fulfil the need and yet still look to be part of model making.

One solution is to use small series universal motors that power most plug in power tools. These are readily found used and are cheap. I had an old 240 volt AC Ryobi trimmer router that had broken it’s plastic guide plate and was hence useless (no spare parts) but the motor was still in good shape. I stripped it down, retrieved the armature, field carcass and brush holders and, because this was going to be driven by a model of a Victorian era steam engine, rebuilt it so that it looked as antique as I could make it. Now, here is the really good thing about series universal motors, they will generate low voltage DC, which is safe, if the field coils are arranged to be wired in parallel with the armature rather than series. This is now termed a Shunt wound generator. (I will post the circuit diagrams later if there is enough interest.) I separately excite the fields with low voltage DC as this allows me to control the output very precisely, however they can be made to self excite. Interestingly they will also run happily as a DC shunt wound motor and as can be seen in the video. At 32VDC the motor spins to around 2000 rpm which I think is pretty impressive. Perhaps I’m easily impressed but I thought this was worth sharing. Cheers, Peter.

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cwelkie

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Yes please Peter - carry on with your description and wiring diagrams for this approach to making a generator from reclaimed bits. I’m sure many would appreciate your insights and ideas.

Although not a “scale model” the project in the photographs looks vey nice.
 

ianjkirby

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Yes please, I'd like to see more progress on this. It looks like an ideal display load for miniature engines.
Great work.

Ian K.
 

Richard Hed

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This may seem a strange title for a thread, let me explain. A lot of us here spend a good portion of our time making small engines, steam, internal combustion or whatever, and on completion would like to see the thing do a bit of work after all the effort of construction. It also provides a riposte to the inevitable “....yes, but what does it do?” question from those around us.
The most obvious solution to putting a small engine to work is to have it generate electricity, generally low voltage DC and watch the wonder in small eyes as lamps flicker and glow into life. The problem is finding suitable small DC generators that can fulfil the need and yet still look to be part of model making.

One solution is to use small series universal motors that power most plug in power tools. These are readily found used and are cheap. I had an old 240 volt AC Ryobi trimmer router that had broken it’s plastic guide plate and was hence useless (no spare parts) but the motor was still in good shape. I stripped it down, retrieved the armature, field carcass and brush holders and, because this was going to be driven by a model of a Victorian era steam engine, rebuilt it so that it looked as antique as I could make it. Now, here is the really good thing about series universal motors, they will generate low voltage DC, which is safe, if the field coils are arranged to be wired in parallel with the armature rather than series. This is now termed a Shunt wound generator. (I will post the circuit diagrams later if there is enough interest.) I separately excite the fields with low voltage DC as this allows me to control the output very precisely, however they can be made to self excite. Interestingly they will also run happily as a DC shunt wound motor and as can be seen in the video. At 32VDC the motor spins to around 2000 rpm which I think is pretty impressive. Perhaps I’m easily impressed but I thought this was worth sharing. Cheers, Peter.

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I'm always interested in generators/alternators. And I am one of those peeps who say "but what does it power?" To me, model making may be fun, but it has to power something useful, no matter how small that is.
 

skyline1

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Another yes please from me

"Universal" motors are basically series wound D.C. machines that can be run on A.C. as the field polarity reverses with the armature polarity so the magnetic effect is the same.

In their "normal" use they do suffer from a couple of drawbacks (as any owner of an elderly electric drill will know)

1. High brush wear and sparking.
2. They generate high levels of Radio Frequency Interference (RFI) and need to be well suppressed for this reason. Get an old electric drill close to a portable radio and you can hear it.

However running at a modest few hundred RPM instead of their usual 20,000 to 30.000 RPM "scream" generating low voltage D.C. both of these effects are almost eliminated.

I would be fascinated to hear how your experiments go.

Best Regards Mark
 

deeferdog

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OK, here we go. Firstly, recognize the fact that I am not an electrical engineer and feel free to jump in and correct any mistakes that I make and secondly, electricity is inherently dangerous. Low voltage DC may not normally cause electrocution but when it comes to starting fires it's up there with the best of them. Be sensible.
If you decide to fiddle around with one of these motors you will see that they basically consist of the armature, the spinning bit, and the stator which is made of iron and has two internal faces. Each face has a wire winding, called a field, attached to it. When electricity flows through these windings a magnetic pole is produced in each internal face of the iron stator, north pole on one side and south pole on the other. Invisible lines of magnetic flux cross from one pole to the other. The strength of each magnetic pole depends on the amount, or current, measured in amps, running through the coils. The wire has resistance to this flow of electricity and this resistance causes losses which results in heat. Voltage is the pressure forcing the current through the wire, raise the voltage and the current will increase, as will the strength of the magnetic poles. Unfortunately, so will the heat as the losses accumulate until at some point the coil will produce alarming amounts of smoke, pungent aromas of burning varnish, intemperate language on your part and frosty opprobrium from your wife because the place will stink for weeks. Try and be sensible.
The armature, or spinning bit, has a number of wire coils arranged around it’s shaft. Each coil has each of it’s ends terminated in a copper segment of a commutator, thus if there are 20 copper segments then there are ten coils.
Electricity will flow through these coils through carbon brushes which bear on the commutator when the armature is placed through the stator and arranged with bearings etc. such as to allow it to spin becoming a motor. The reason this is so is due to the magnetic interaction between the armature coils and the magnetic flux of the stator, those requiring a more detailed explanation should arrange a consultation with Professor Google.
If the electricity flows from the battery, through one brush, then the armature coil, out the other brush then through one coil and then the second one and back to the battery, everything is in series and it is called a SERIES wound motor. (Fancy that!).
On the other hand, if the electricity, on arriving at the brush from the battery, can flow through the coils and the armature due to a forked connection then this is called a SHUNT wound motor.
From now on we are only going to consider the shunt configuration.
That’s enough for this post, already I can see the eyes glazing over. A few pics and a couple of what I laughingly call circuit diagrams, both coils are drawn as one for clarity.
We’re off for a week in our little camper to a place called Warwick in the Darling Downs of Queensland, I’ll post from there. Cheers, Peter.
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skyline1

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Yes building a miniature Dyno is quite feasible I have considered doing this myself. In fact their full sized cousins (older ones anyway) do use large D.C. motors mounted in a frame which allows the whole machine to rotate a few degrees on it's axis.

An arm is attached to the dyno with a weight on it ( or by another means like a spring balance) the weight or it's distance is adjusted until the dyno balances between it's stops like an old weighing scale. By multiplying the distance of the weight from the dyno axis by the size of the weight the torque of the machine under test can be calculated. The speed in our day was usually measured with a mechanical tachometer and Speed x Torque = Power

They are called not unsurprisingly Swing Frame Dynomometers

Nowadays the speed would be measured optically and the torque probably by a load cell or similar device. With modern devices like Arduino controllers
the project would be cheap and simple enough for hobbyists. I would be surprised in fact if someone hasn't done it already.

Best Regards Mark
 

modeng2000

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Deeferdog, thanks for a really interesting project. I expect there will be a lot more generators following your lead.

John
 

NickP

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... at some point the coil will produce alarming amounts of smoke, pungent aromas of burning varnish, intemperate language on your part and frosty opprobrium from your wife because the place will stink for weeks.
We’re off for a week in our little camper to a place called Warwick in the Darling Downs of Queensland, I’ll post from there. Cheers, Peter.
Thanks for the explanation on the motor internals Deerferdog, I look forward to your next instalment - two things sprung to mind - 1) appreciate the warning about (yet) another way to cause friction and grief with SHMBO / your significant other! There are sooo many ways 😂. 2) enjoy your week at Warwick!
Thanks again, Nick
 

74Sprint

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I'll start by saying that I'm an electrician (AAR railroad) and a electronics technologist, but I'm not going to get into how and why.

Deerferdog your correct in saying that electricity can be dangerous, especially with an open ended generator. with an open ended (no output load) generator the voltage can rise very rapidly and the potential current can kill you, electrocute you. Oh I hate when people say they got electrocuted because one can only get electrocuted once otherwise they got a shock. The risk for fire is low when the output has a proper load.

The big difference between a series wound and a shunt wound (parallel) is how the device is to be used. Also it is a lot easier to change direction of rotation on a series wound motor than a shunt wound. It also depends if the motor is to be used with AC or DC current which, changes the design of the motor, mostly the armature. A shunt motor can also be used as a generator. On the old locomotives they used a DC generator that could be used as a motor connected to the batteries to start the diesel and then switched back to a DC generator.

skyline1; a Swing Frame Dynomometer, now that's that's old technology and only uses constant speed. Today people use either a water brake, eddy current, or a loaded generator. Each has it's pro's and con's. Since I had worked for CP Rail I prefer the loaded generator. Water brakes can be finicky and eddy current which feeds back into itself get hot quick and need cooling time. Almost all the locomotives in CP Rail's inventory use Dynamic braking to slow the train down to low speed. But the dynamic brake resistant grids and cooling fans are in series and can be used to calculate Hp also when standing still. The nice thing about this setup is that through generator excitation one can instantly vary the generator output. I have killed a 3,000 Hp diesel so fast at full throttle (918 rpm) that I don't think it did more than 5 revs after applying full excitation. The locomotive actually rocked over I bet 3 feet, a true "WHOA" moment. I don't think I bent the crank or rods.

Next summer I plan to make a mini dyno for small motors, my RC motors, from 0.049" to 30cc. I have a small frame alternator from a car with external excitation terminals and the heating elements from a scraped stove/oven for resistance/load coils 4Kw total. And yes I plan to use an Arduino for computer control of excitation. To start with I will need to find out the power needed to just turn the armature, angular momentum stuff. Part of this will be using an electric motor to turn the armature and then measure the voltage, current, and rpm to find the Hp and include that in the calculations (parasitic). Like an inertia dyno. I have seen some DIY setups so there are some examples out there. I will be posting my progress, results, and share my design on this forum so others can duplicate or improve it. The horsepower of this setup is only limited to the alternator output and the heating elements.

Ray
 

Cogsy

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Oh I hate when people say they got electrocuted because one can only get electrocuted once otherwise they got a shock.
I've heard this before so I had to look it up. It seems in industry they use 'electrocute' to mean death but Websters Dictionary defines it as "to kill or severely injure by electric shock ". I don't know how severe the injury has to be but you don't have to die. Another one of those terms that have a different meaning to the experts - I get triggered when people incorrectly use the term 'theory'.
 

skyline1

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Yes indeed Swing Frame Dynos are very old tech. This was some thirty years ago and the Dynos themselves were about Thirty years old then !

As you say they are used in constant speed mode which makes some forms of testing difficult if not impossible. As these were used for testing Electrical Machines rather than I.C. or Steam Engines they were fine for carrying out the tests we required. and by measuring in a purely mechanical way we did not have to make allowance for the power needed to turn the armature.

Sometimes we used them in loaded generator mode as the parasitic power had been calculated and known. It all depended on the job in hand.

I like your idea of using a Car alternator it sounds like quite an effective solution. and no danger of accidentally producing high O.C. voltages as it is likely to reach magnetic saturation (by design) well before the output became dangerously high.

Stalling that Diesel sounds like a day you never forget. I had a somewhat similar incident using a 2MVA diesel genset to test a 25KW machine but that's a story for another day (and thread).

Best Regards Mark
 
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74Sprint

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I've heard this before so I had to look it up. It seems in industry they use 'electrocute' to mean death but Websters Dictionary defines it as "to kill or severely injure by electric shock ". I don't know how severe the injury has to be but you don't have to die. Another one of those terms that have a different meaning to the experts - I get triggered when people incorrectly use the term 'theory'.
At work we use to say that one got a poke. One thing about electricians is that we are curel buggers and laugh when someone gets a poke. But and this is a big but, is we also are very concerned when someone gets a severe shock such as a burn usually from a flash arc. I have had friends and a few colleges that got severe shocks and burns luckly they did not get electrocuted. "Electrocuted", I say patato you say potato, tamato, tomato. I guess it is semantics.

Ray
 

awake

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I've heard this before so I had to look it up. It seems in industry they use 'electrocute' to mean death but Websters Dictionary defines it as "to kill or severely injure by electric shock ". I don't know how severe the injury has to be but you don't have to die. Another one of those terms that have a different meaning to the experts - I get triggered when people incorrectly use the term 'theory'.
Al, "in theory" the meaning of any term is solely determined by how it is used within a given community - at least, according to the consensus of modern linguistics.

That still doesn't keep me from grinding my teeth when people say things such as, "I literally died when she did that"!
 

Cogsy

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Al, "in theory" the meaning of any term is solely determined by how it is used within a given community - at least, according to the consensus of modern linguistics.
I didn't phrase it very well - I mean when someone (generally online) pipes up with a crackpot idea and claims it as a 'theory'. They'll then claim this 'theory' deserves as much credence as other theories (like evolution, special relativity, etc.). The colloquial use of the word is fine but using the formal form incorrectly literally makes my head explode.
 

awake

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I didn't phrase it very well - I mean when someone (generally online) pipes up with a crackpot idea and claims it as a 'theory'. They'll then claim this 'theory' deserves as much credence as other theories (like evolution, special relativity, etc.). The colloquial use of the word is fine but using the formal form incorrectly literally makes my head explode.
I'm with you 110%!
 

awake

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I didn't phrase it very well - I mean when someone (generally online) pipes up with a crackpot idea and claims it as a 'theory'. They'll then claim this 'theory' deserves as much credence as other theories (like evolution, special relativity, etc.). The colloquial use of the word is fine but using the formal form incorrectly literally makes my head explode.
To expound a bit further on this topic - whenever students start to ask a question with "Is it possible ..." I jump in and say, "Stop right there. Without even hearing the rest of the question, I can tell you the answer: yes, it is possible. Here's the real question: Is it probable?"

Note that I teach in the area of religious studies, so the "possible" in this case has to do with piecing together history and the interpretation of texts. Since we don't have a videotape of what happened 2000 years ago (the era of history with which I am generally concerned), and we don't have access to the mind or intentions of long-dead authors, it is generally difficult-to-impossible to rule anything in or out with certainty. Could Paul have meant such-and-so in his letter to the Corinthians? Could Jesus have secretly been married? Could ... (fill in the blank). Sure, nearly anything is possible ... but is it probable? How well does it fit with the other (however much or little) evidence we have?

The logical error that so many people tend to make is, if it can't be ruled out, then it must be true - right? This is the foundation for conspiracy "theories." One can nearly always come up with some way of explaining contrary evidence - it's a conspiracy to hide the truth from us, so of course "they" have manufactured that contrary evidence! And if it is possible that there is a vast conspiracy at work, if you can't disprove it, and it all hangs together, then surely it must be true!

I actually find it helpful to affirm the possibility when talking to someone who is oriented this way. Simply pushing back - "That's ridiculous!" - results in the person digging in. But saying, "Sure, that's possible. But let's think for a minute - what else is possible?" can - at least sometimes - open up a fruitful discussion.

Sorry - way more discussion of this than anybody wanted ... what was the original topic of this thread??
 
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