Edison dynamo

[bobcjohn]

Dave:
I'm sorry to hear your having trouble. I too had a hard time to get my dynamo running. I also experienced high current when running the dynamo as a motor. However after I gave it a helping spin, off she went and after a time the current came down. I think 4 amps is probably reasonable.

I don't know anything about magnetic theory, but I wound both of my coils in the same direction. It's like they are connected S/N to S/N, sort of in series. I look at the Bi-Pole arrangement like a horseshoe magnet.

I wonder, what is the purpose of neodymium magnets??

Wish I could be of more help.
Bob

 

[peterl95124]

I too have built an Edison Bipolar Dynamo, based on google images, and fun facts of electromagnetism from my college physics text. Its not quite as detailed as the awesome work displayed in this project, but you can see some photos at http://www.baemclub.com/crkcallarchive/jan20nl.pdf

The armature was a replacement part for an electric drill from eBay, everything else is from bar-stock. I designed the field coils for 12 volts at 1200 RPM, and hit the mark pretty well, I got about 11.7, not too shabby.
The dynamo built around a 1.5" diam armature is a good looking match for the 1.5" bore Stuart-9 I'm powering it with.

If there's interest I will write up the equations for the field coil and have it added to the baemclub newsletter as a "tech topic".

Peter A Lawrence, San Jose, CA.

 

[skyline1]

Dave:

You probably don't need to do a complete rewind just reverse one pole with respect to the other and have another go. This would happen quite often in full size practice and when you are dealing with a four pole split compound machine with interpoles and compensating windings it can get pretty complicated. You can end up with different windings "fighting" each other and often at different parts of the RPM range.

We had the occasional "runaway" through these sorts of effects. Quite scary on a large machine, you need to be "quick on the breakers" to stop it damaging itself.

The neodymium magnets are probably to retain some residual magnetism as I mentioned previously. It might be worthwhile inverting one or both of these also to see what effect it has

Best Regards Mark

 

[bluejets]

Dave I have this image saved and will be winding mine as per the lefthand illustration, windings in opposite direction.

The left and right diagrams are correct.
The centre diagram is incorrect.
Reason being one must have a north and a south pole.

Where the confusion came with the centre top illustration is, it is common to connect start of one winding to the finish of the next to reverse the poles.
This only applies where the winding was all done in the same direction.
It can clearly be seen this is not the case here.
Centre diagram has 2 north ( or 2 south )poles, depending on which way the current flows.
A tip for generators and motors is the right or left hand rule respectively.

 

[peterl95124]

I too have build an Edison Bipolar Dynamo so I can appreciate your work. I'll add that I recommend going to the trouble of removing those ball-bearings from the armature so you can make some more Edison-period looking bearings. FYI, I once had to use a slitting abrasive disk on a dremel to do that as sometimes they're a press fit.

To design mine I dusted off my college physics text book and did the math so that it puts out 12-volts at 1200 RPM. anyone that wants to see how to do it just say so and I'll post the formulas here.

I've set mine up on a board with a Stuart No 9, the 1-1/2" bore is a good match for a 1-1/2" armature at least looks wise, and a cabinet with meters on the front and a light bulb in a socket on top.

 

[William May]

JB.
I'll try my 'artificial canvas' first and if not successful, I might try you r suggestion.
Have you watched this video

Bob
The lever on the bridge piece is the on/off switch. The other (larger) one adjusts the phase (I think) but to be honest I don't have a clue!
Come up and see it at Doncaster in May.

Dave
The Emerald Isle

I think you are right about the phase adjustment. If you watch old movies of German U-Boats, the electric motor guys have handles that they move that seem to slide around the periphery of the electric motors, and I assume they are shifting the brushes from one setting to another. (Trading higher speed for lower torque perhaps, as the U-boat speeds up?) All I really know about electricity is what I learned putting a 9 volt battery on my tongue. The rest of it is a mystery to me.

 

[Steamchick]

Love it! - But don't put anything larger than 9V. on your tongue- or anywhere else for that matter. Electricity burns nerves and flesh - so can leave long lasting pain and disability (As people who sat in Electric chairs found out!). Remember, I think it was that "wonderful guy Eddison" who killed Elephants to demonstrate how "powerfully" electricity can kill - and to try and discredit that really clever guy Nicolai Tesla who promoted Alternating voltage and current. And didn't Eddison sell the Electric chair to the US government? - And it used "Tesla's AC", not his own DC.... I think?
What do you use for control of the field current to control the voltage? 40 years ago I converted a few motorcycle dynamos from 6V to 12V by the addition of a few coils to the voltage contacter of the Regulator, and a resistance in the field-coil circuit. Interesting simple devices. But modern electronics come "off-the shelf" at such cheap prices, that you don't seethe old electro-mechanical regulators any more. I think on WW2 ships and submarines it was all done by Manual-switching of the field - depending on load -to keep the voltage in the right range. (My grandfather was on the dynamos when "4th" on White Star ships during the first world war (- wish I could ask him....!). But post WW2 I'm sure voltage control went automatic.
Anyway: Perhaps like you, I would like to see something to explain DC motors and generators and how to determine the "lag" or "Lead" required for brushes? I have been thinking of replacing the Armature in my Unimat - SL 90W motor - that burnt-out when I ran it for more than the book allowance of 10 minutes. Anyone with clever ideas will be a help.
Biggest I worked on was the Dinorwig Power station - But I was on the design team for Busbars for the Starting circuits... so didn't ever get involved in Motor or Generator design. (And there are only brushes for the Excitation coils in the Dinorwig Motor-Generators as far as I understand).

 

[skyline1]

Yes indeed Edison wasn't entirely the "great guy" he seemed to be, in fact a bit of a commercial "shark" . He was willing to try to discredit the technically superior and much more efficient Tesla system by any means possible, including executing an elephant. He wanted to "prove" for commercial advantage that Tesla's A.C. was dangerous as it used much higher transmission voltages. In fact Edison's own D.C. system used voltages that were also lethal, any high power distribution system is going to be dangerous due to the sheer amount of energy in it.

Tesla's polyphase A.C. system had many advantages and because transformers could be used to step voltages up and current down power could be transmitted over long distances with low losses (I²R). Edisons's system however, although limited by transmission distance could provide large amounts of torque at low RPM
(theoretically zero) ideal for traction use.

As a result of these "dirty tricks" Edison became very wealthy and Tesla died in total poverty a broken man.

Today, High voltage A.C. transmission is almost universally used. and until fairly recently D.C. was used for high torque applications (like locomotives for example)

Many of Tesla's more exotic ideas that Edison (and others) thought fanciful or even impossible have actually become very useful today.

Wireless Phone chargers and Switch Mode Power Supplies (which seem to be in everything nowadays) actually use Tesla's high frequency induction technique, as do induction cooking hobs.

Early "spark gap" radio transmitters so beloved of the likes of Marconi were nothing more than Tesla's famous induction coils with a large antenna attached

Steamchick you have probably guessed that I too am a great Tesla fan and could go on for hours about the man, but I will stop here before I bore the whole forum to death.

Best Regards Mark

 

[Steamchick]

Thanks Mark. I like your response - some new information form there. Here's another snippet - if my memory is correct from over 40 years ago... Dinorwig Power station Motor-generators were designed for an A.C. spec something like: 0.3Hz to 50 Hz. (3 Phase). 18Kv. nominal voltage: I think they are 135Mw per set - or something.... so LOADS of current for the torque to start pumping water UPHILL. There were a few operating modes: e.g. Starting from zero to full speed in 3 minutes "in Air" (Blown-down water turbines) - or maybe this was in water, much quicker in air ... , but also starting with WATER in the turbines: They had starting (variable frequency) via a power supply, or by using another turbine generator from rest to synchro-speed connected to a pump, already wet, that was similarly run-up from Zero to Sychro-speed, when it was switched to pumping water up to the Top reservoir. I think this was the preferred way to start the pumps wet, only using the "electronic" variable frequency starter on the last of the 6 pumps after it had been used as the generator to start the first 5? The Electronic variable frequency starter was used mostly (I think?) to spin-up Generators "in-air" ready to supply electric demand at peak times - such as the half-time whistle in a football match of "coronation street" when everyone switches on their electric kettles for tea... When demand was needed all they did was open the water valves simultaneously and let the water generate... then turn off when demand dropped 2 minutes later! I would enjoy anyone else's experiences of how these things were operated. Much more interactive than keeping a big compound steam engine pushing a large ship across oceans for days at a time, I would think? Sorry, I have prattled on too long...

 

[deverett]

When I wound the coils on my dynamo, I Thought I had them wound like a horseshoe magnet as shown in Bluejets fig 1.
There is only one layer of copper wire in the coils and the neo. magnets were to try and make up for the lack of coil layers. The magnets were placed in the bridge N down on one side and N up on the other. One possibility is that I put the magnets in the wrong way up/down! Without stripping the dynamo down, I can't say now which side is up. The cores and bridge are made from mild steel.
Other projects at the moment have put this on the back burner for now.

Dave
The Emerald Isle

 

[Steamchick]

Hi, a relatively quick check is with a compass needle. Check each item in turn. E.g.

1. Without magnets, 1 coil at a time (half the voltage you would use for the whole field). Be sure you apply the voltage the correct way per coil.
2. The combined coils at your normal voltage.
3. 1 magnet at a time, without any current in the field coils,
4. With it all assembled, no current in the coils.
5. Fully assembled and with the current applied to the coils.

The compass positioned in place of the armature should follow the field in the same direction for all conditions.
I think you'll pick-up any assembly glitch immediately by following this procedure.
Thanks, I am enjoying this thread.

 

[Shopgeezer]

If I could borrow a time machine I would head back to Tesla’s era and whisper in his ear 1 cent, 1 cent. George Westinghouse offered Tesla a fairly high license fee for each kw sent down the lines from Niagara Falls. The partners in the company complained about this and Westinghouse had to go back to Tesla several times to get the fee reduced. Finally in the greatest mistake of his life Tesla just gave the license to Westinghouse. No further payment. If he had just kept 1 cent per kw he would have been a rich man instead of living in poverty for the rest of his life.

 

[Steamchick]

Must remember that one.... A bit like the song "seven and a half cents" from the Pyjama Game? The most useful lessons come from everyday life....

 

[ytrose2]

I have been thinking of replacing the Armature in my Unimat - SL 90W motor - that burnt-out when I ran it for more than the book allowance of 10 minutes. Anyone with clever ideas will be a help.

[/QUOTE]
Last year I had a similar problem with my Unimat motor. After looking around, I finally made use of a sewing machine motor. However, I had to modify the wiring to make it rotate in the opposite direction, and machine the motor bracket to get the pulley in line, with new mounting holes. Good luck.

 

[Steamchick]

Thanks for that. I'll look further for something suitable. I am currently using a old lawn mower motor, an open type with fan cooling - about twice the size of the correct SL motor. (I have t use a speed controller to get is slow enough for the SL! - and it sounds like it is "mis-firing" or stuttering most of the time at slower speeds.). But like you, it was wired to wrong way. It is VERY noisy, so I want to change it for something more user friendly.
This thread interested me, because the motor I am now using did not have the brushes "at 90 degrees" to the alignment of the pole pieces. I suspect that the way it was wired was the opposite to the manufacturer's original - and I think I am now replicating the original - but I suspect there is some "phase angle" built-in to the armature, so when the brushes were originally swapped it didn't run very well. (It had been used on a small home-made bench grinder that I don't need). Therefore the person who made the small grinder rotated the brush holder to the optimum - which (I guess) is twice the phase angle (built-in to the armature) away from the original brush position.
The Edison motor/generator seems to have some way of using a lever to rotate the brush holder around the axis of the commutator - like a manual "advance-******" for the timing of the armature as it passes the pole pieces. I am interested to know (from anyone who knows DC Motors and generators, if there is a "lead" required to get the optimum magnetic field from the armature when armature aligns with the field in the poles. Would this "lead" be the same for a motor and generator? Or would it be a "lead" for the motor, and "lag" for the generator? Or does it swing a full 180 degrees to be used asa a reversing device? I think I can work it out, but don't want to write my own "Text-book", when someone has already done that.
Thanks for the posts. Most interesting!

 

[Steamchick]

I too have build an Edison Bipolar Dynamo so I can appreciate your work. I'll add that I recommend going to the trouble of removing those ball-bearings from the armature so you can make some more Edison-period looking bearings. FYI, I once had to use a slitting abrasive disk on a dremel to do that as sometimes they're a press fit.

To design mine I dusted off my college physics text book and did the math so that it puts out 12-volts at 1200 RPM. anyone that wants to see how to do it just say so and I'll post the formulas here.

I've set mine up on a board with a Stuart No 9, the 1-1/2" bore is a good match for a 1-1/2" armature at least looks wise, and a cabinet with meters on the front and a light bulb in a socket on top.

View attachment 115533

Hi - I love what you have done here. It is in the right style for demonstrating the period of DC generation. Please can you explain the brush holder? - as I am "guessing" from what I can see in the photo?
I assume the brush holder rotates around the axis of the armature, so is set such that when the current flows into a segment of the commutator, the poles of the armature are passing from the axis of the poles, towards where the "generating" segment of the armature leaves the poles? I'E. for a particular pair of armature poles, they enter the magnetic field of the poles, and "reluctantly" build up an EMF as the rotation cuts the lines of flux until they reach a maximum EMF - at which point the brushes align and "discharge" the magnetic flux by drawing out the electric current and "de-magnetising" to segments of the armature?
If the poles do rotate around the axis of the generator, have you rotated the brush holder to a "maximum" point where the generator is matched to the speed at which you run the generator? I have figured-out that this angle of "lag" may need to vary to get the optimum for any particular speed? - But my reasoning may be completely ****-eyed! I would like to hear more about this from your experience.
It strikes me that if the brush holder is at the wrong phase angle for the speed and "phasing of the armature windings", then the generator will be "poor" (low current, even if the voltage is OK). - This could be the problem with poor generation after the resolution of any "field and winding issues.
But thinking a bit further: Generator problems may be as simple as "not enough speed" - to develop the voltage. The current will then depend on the ability to maintain that speed and voltage against the load by an adequate current in the field coils - up the the safe limit (which is usually the temperature inside the windings, which, if too hot, causes catastrophic breakdown of insulation, shorting and burn-out of the windings). The "rating" of the insulated wire is "in free air" - not when buried inside a hot coil - so PLEASE watch the field coil temperature. Too "Hot to the touch" is over about 55 degrees and the current needs to be turned-down. (Windings inside th coils will be hotter than on the outside!). If there is insufficient field for the generator at a "comfortable warm" then you simply need lots more windings to get more magnetic field into the generator. - And possibly more neodymium magnets to get it started? The design problem of too many Neodymium magnets is that you can't regulate the generator "down" as low as may be necessary. The remanent magnetism is a "minimum" - which needs to be high enough to start the generation, but low enough the generator isn't doing too much at low load. - The consequence is that the voltage will be too high, so you need to slow the generator. The current in the field coils is simply increasing the field from the "neodymium" minimum to the max that you can get at the field-coil current limit. Check the WWW as I am sure there will be a text book to explain it better than I can( - as a total amateur!).
Another comment: If there is no "initial remanence" of magnetic field in the Pole arrangement, then the generator cannot generate. (A car alternator is initially excited by a small current from the controller until it "kicks-in" - Years ago this was the main purpose of the "warning light" circuit!). I think the neodymium magnets are built-in to the pole assembly to achieve an initial remanent magnetic field for the generator to start. When running, the field needs to be controlled to keep the generator at the correct voltage for the speed and load.

 

[peterl95124]

Steamchick, lots of good questions, lets see if I can answer any of them, starting with the most interesting.

if you replaced the armature's commutator with a series of rings arranged axially, with each separate winding in the armature connected to its own ring(s), and then placed separate brushes one for each ring, so in the end instead of having two brushes you had say 20 brushes, and then if you had a 20-input oscilloscope you would see 20 AC sine-waves, each one at a different phase. But an Edison Dynamo puts out DC ?. Aha, that's the right question. What the commutator does is select the one winding that is at its peak AC voltage, and as the armature turns and that winding's voltage is going down the brushes switch over to the next winding whose voltage is about to peak. etc. etc. etc. The brushes are adjustable because you have to find that peak by trial and error. The peak occurs when the winding is passing through the maximum magnetic field flux, which is typically at the center of the pole pieces, but you don't know which commutator pieces the winding that's nearest to the pole centers is connected to. As you can see in the photo the commutator in my armature is connected such that the brushes are vertical while the poles are horizontal, that's 90-degrees away from how the commutators were wired in Edison's time, but I can't do anything about that, so mine looks a little weird if you know what to look for. Notice that the word "lag" doesn't appear in this description, only "peak", which by the way is independent of both speed and load, IE there are no analogies with IC engines.

My dynamo has no magnets, I first run it as a motor from a battery or DC power supply and (if I don't disassemble it) there's enough residual magnetism in the steel to get it started (self excited) as a dynamo after that. The nice thing about not having magnets is you find out if its wired correctly when you try to run it as a motor. If the field coils are wired backwards they cancel each other's magnetism and you end up with effectively no field, and if you connect the brushes to the field backwards, again the field is reversed compared to what the armature requires. These are the two ways in which the wiring can be incorrect, which can be difficult to diagnose, and made worse if you're using magnets in addition to coils. That and the fact that magnetic alloys didn't exist in Edison's time mean to be period faithful you shouldn't use magnets if you're designing from scratch.

The output voltage of generators with magnets is linearly proportional to speed, but with field coils is quadratic with speed, IE with magnets double the speed and that doubles the voltage but with field coils double the speed and that quadruples the voltage. This is because with magnets the field flux is constant, but with coils the field strength keeps going up with speed, and the voltage is proportional to the product of speed times field strength ("Faraday's law of induction"). Hence voltage regulators are required in automobile generators and alternators and what they control is the current in the field.

The current in the field coils (if they are producing the field flux alone without magnets) is limited by their resistance, and is typically an order of magnitude or more higher than the armature resistance as the field coils are usually made with hundreds to thousands of turns while the armature has tens of turns. This is done because current in the field coils is lost power so they are intentionally made with as many turns and as much resistance as possible to reduce lost power. This also means the armature will burn up way before the field coils do if you let too much current through them (load resistance is too low).

well, I think that's enough for one post, hope that helps, additional questions welcome,
Pete.

 

[skyline1]

peteri95124

Wonderful, simple explanation of what is quite a complex subject if you go into it in any detail, well done.

I have worked on large rotating machines both A.C. and D.C. mostly military stuff but also traction motors. But this was a very long time ago and it is nice to have one's memory refreshed by someone who knows what he's talking about.

Best Regards Mark

 

[Steamchick]

I plan to convert a bicycle wheel-hub generator into a generator for a model steam engine. (an old - but working - Sturmey Archer 6v 1A unit). Has anyone done this - and made plans - before I attempt to re-invent the "

 

[skyline1]

I think it is possible to do it but IIRC these are actually small brushless permag alternators, the old "rub on the tyre" type certainly were. You could use some electronics to turn it into D.C. though. I have designed a regulator for doing this sort of thing for use on my steam turbines. It would simply need a small bridge rectifier in front of it I'll PM you the circuit and PCB layout if you are interested it uses very common and easily available components.

The regulator unit itself forms the basis of a miniature switch board with real working little knife switches, working rheostats and indicator lights.

despite being solid state internally it looks very period and using the knife switches and regulators to control the loads is great fun.

Best Regards Mark