Bicycle Dynamo powered by model I.C. engine

[Brian Rupnow]

The bulb holder is just a bit tricky. It has to contact the outer shell of the bulb, but not the center contact. Since I don't have any Corian, I will fall back on the "hillbilly" insulator and turn one from a piece of hardwood. The insulator will epoxy into the end opposite to the bulb and have a 3/32" hole through the center for the contactor wire which gets the electricity from the dynamo up to the end of the bulb.

[Brian Rupnow]

The engine has a throttle on it so I can run it at a reasonably low rpm. The bulb I have is out of a flashlight with two D cells in it, so is basically a 3 volt bulb. The dynamo probably puts out 6 volts at peak rpm. Now in a perfect world, I would be able to get a 6 volt bulb with the same diameter base as the 3 volt bulb, but the world is seldom perfect. There is a blizzard going on outside at the moment, but I think perhaps I will mush my Huskies down to Ideal Supply and see what sizes (if any) their 6 volt bulbs are before I go any farther.---Brian

[Brian Rupnow]

Well I'll be----Sometimes ya just get lucky. The hardware store had 6 volt bulbs with the same sized base as the 3 volt flashlight bulb I based my bulb holder on. I must have done something right in a previous life----I have absolutely no idea why the package says 6 volt lanterns at the top of the package and 4.8 volts at the bottom of the package.

[Roger B]

I would guess that these are for the  hand lanterns that take the big square 6V battery with the springs on top. Although the voltage is nominally 6 it will drop under load hence the 4.8V to give good brightness even as the battery ages.

[Brian Rupnow]

So---If I just had a handle to disengage the sprag when I want to loosen the belt, I think I would almost be done.  I have spent the day playing and have grandchildren coming to visit overnight, so I won't get back to this today. I also got a "good news" phone call from a customer who wants me to design a packaging machine for one of his products, so I will be gainfully employed for a week or so.

[philjoe5]

Brian,

This is all very much interesting to me as I'm fascinated by generators.

I'm interested in what the "guts" of the sprag look like.  Any chance you'll be posting drawings for them?


Cheers,
Phil

[Brian Rupnow]

Philjoe--I can do that. The sprag isn't very exciting--It's just a piece of 1/4" square steel bar with a 1/8" pivot hole thru one end and a taper on the other end. It is the sprag that engages with the teeth on the rack to hold the belt tight. --Is that what you meant?

[philjoe5]

Brian,
I get the steel bar engaging the rack but what puts tension on the belt?  Is it just a matter of moving the lever to tighten the belt, then engaging the bar in a tooth on the rack?

Cheers,
Phil

[Ian S C]

With my hot air engines I started off using 3V bulbs on the generator, when the motor became freer, and I'd burned out all the 3v bulbs, I went to 6V, then to 12V, and although the 12V ones don't quite get to full brilliance, they at least last a little longer.  With your bike dynamo you should exceed 6 V, the thing is to get a low wattage bulb, then the motor won't have to work so hard,  you could use a number of bulbs with switching so you can load the motor.  Using amps, and volts, and rpm you have some idea of the power out put as the generator is working in place of a Prony Brake.  The generator will only be about 50% efficient, so if you get 50 Watts, the motor is nearer 100 Watts.
                                           Ian S C

[Brian Rupnow]

Brian,
I get the steel bar engaging the rack but what puts tension on the belt?  Is it just a matter of moving the lever to tighten the belt, then engaging the bar in a tooth on the rack?

Cheers,
Phil

You are correct Philjoe. I put tension on the belt by pulling back on the handle to rotate the mount holding the generator. The belt gets tight and gravity pulls the sprag down to engage with a tooth on the rack, holding the belt tight. I still have to make a release handle to disengage the sprag for when I loosen the belt.

[Brian Rupnow]

Yes!!! We have a sprag release handle. Nothing too scientific here--just something to disengage the sprag from the rack so I can loosen the belt off when I want to.

[Brian Rupnow]

So, here we have a view from the rear, with everything wired up. I just tested it on the mill spindle, and it seems to work the way I intended it to (the bulb does indeed light up). One of the things you see from this side is the tapped #5-40 hole in the side of the socket which holds the bulb in place. It has a set screw in there with a very light pressure against the base of the bulb, just to ensure that I have a good path for the electricity to flow.  What you don't see is the wooden insulator that sets inside the bulb socket to keep the electricity from shorting out and finding a path to ground through the aluminum holder. The bulb holder is press fitted into the 1" x 3/16" flatbar which bolts to the top of the dynamo bracket. At this point all that is left to do is make a video of the engine driving the dynamo and lighting the light.

[Brian Rupnow]

And away we go!! Everything went very well on this project, except for one surprise. If the dynamo turns one direction, it runs fine and freely. If it turns in the opposite direction, it tightens up inside and becomes very stiff to turn. My original plan was to have the engine setting on the left hand side of the engine with the pulley facing out. The result was that the dynamo would tighten up to the point where it stalled the engine. So---I turned the dynamo 180 degrees and put it on the right side of the engine. That reversed the rotation and fixed the problem, and it works like a charm. The bulb I have in there is only rated at 2.9 volts, so I bought two "back-up" bulbs for a 6 volt light in case I need them.
<a href="https://www.youtube.com/watch?v=xP1bOhvse8Q" target="_blank">http://www.youtube.com/watch?v=xP1bOhvse8Q</a>

[b.lindsey]

Nicely done Brian!!  Its nice when things work just as you expect them to

Bill

[Brian Rupnow]

I may have learned something here about the Chuck Fellows carburetor which I built and installed on this engine. The carb works great, and I recommend it to anyone looking for a simple, easy to build carburetor with a "throttle" on it. The carb I built is from one of Chuck's early designs, with a #8-32 screw acting as the throttle. By turning the screw in, it closes off the 1/8" diameter main air passage, and by unscrewing it, the air passage is opened, thus letting more air (and venturi induced fuel flow) into the engine. I took matters a step farther, and made up a little handle to clamp on the head of the #8-32 socket head cap screw, so that with an arc of about 180 degrees swing I can go from idle speed up to a much higher engine speed.---And that works fine, as long as there is NO LOAD on the engine. However, when the engine is under a load, it doesn't want to rev very high. I thought about this for a while, and come up with the following theory---An 8-32 thread only advances (or retracts) 1/32" for a full 360 degrees of turn. The 180 degrees of arc I am limited to with my "throttle handle" only advances (or retracts) the screw 1/64". Now on an engine running under "no load" conditions, that 1/64" is enough to go from idle to quite a respectable "high" rpm. However, in an engine running under a load, that 1/64" simply isn't enough to feed the fuel and air the engine requires to overcome the "load" and rev higher. The main air passage on the carburetor I built is 1/8" diameter. To really feed the engine the fuel and air it needs to rev higher under a load would require that the screw be unwound possibly a full turn or even 2 or 3 turns. This is all just theory at the moment, but tomorrow I will do a practical test and remove my "throttle handle" and see what happens when the engine is running under the load of the generator and I unwind the screw more than the 1/2 turn I am currently limited to. In the video I posted, the engine is running with the throttle "wide open" within the limits imposed by the swing of my throttle handle.