Possible generator for hybrid rack/pusher

[loquin]

I need to take a nap now. That's so much to absorb.
Imagine someone actually figuring this all out.

This was the first time I'd actually thought about switching power supplies in a loooong time. When I first got out of college, oh, these many moons ago, one of the first things I worked on (with a senior engineer) was writing up a failure analysis and repair procedure for hi amperage switching power supplies (5V @ 150A)

These things just used diodes to charge up a pair of big honkin' capacitors (2000 uf, near soda can sized) directly from the AC line. One was charged to plus 170 volts, the other to minus 170 volts.

a pair of high voltage field effect transistors (FET) switched first one, then the other of these two caps through a transformer to ground. (at 40 kilohertz.) Because the frequency was so high, the main power transformer would fit in the bottom of a coffee cup. (and, about 3/4 of an inch thick)

Now, the primary failure mode for these power supplies was, when, at or near full load, one power FET to still be on when the other FET came on... This meant that, for a brief instant (about a microsecond) a 2000 microfarad capacitor charged to + 170 volts would be directly shorted to another 2000 microfarad capacitor charged to - 170 volts. That's a 340 volt differential.

Let me tell you, that makes a bang. It literally sounds like a pistol being fired. This is because all the printed circuit track is completely vaporized between those two capacitors! In just a few microseconds, it is nothing but copper & solder gas. In some cases, the copper stakes in the thru-holes in the PC boards where the power transistors were soldered were also gone.

(LOL, when I first started that project, I didn't understand why the technicians INSISTED that everyone in the immediate area be wearing their safety glasses. After the very first failure, I knew!)

 

[cooltoy]

Funny thind about this topic, I always thought I had thought of it first. Today I found another site talking about the same thing. They were asking about using a sewing machine foot speed control.
Loquin, it took me about 12 hours of reading to get my FTA sat. going and to be honest you lose me when you start talking about rewinding motors and voltage field effect transisters. I still don't understand why we could not just grab a motor like Large phil showed us and hook up to 120 out on generater with the speed control foot peddle from a sewing machine.
Don't take this the wrong way though, your knowing all about this is why I am happy to see you join this topic. How long would it take you to build this your way and how much would it cost? Just wondering//

 

[loquin]

How long would it take you to build this your way and how much would it cost? Just wondering

It would take a while. There would be a lot of design/breadboarding/testing involved in producing a pulse width modulation peed control. Once the development is done, it would probably be the most cost effective approach, though, especially in production volumes. A switching regulator is small, light, and very efficient. And, essentially what you're looking at is a 1 KW variable voltage switching regulator. Those 150 amp power supplies only weighed about 5 pounds. If they were transformer based, they would be on the order of a hundred pounds!

Back to the sewing machine pedal...

Just slowing down an AC motor won't cut it, unless the motor is ridiculously over-sized to begin with. You might need a 5 horsepower AC motor to provide a half horsepower if it is to be run for any length of time at a reduced voltage... A sewing machine motor is pretty small, and it isn't run heavily loaded, and it is designed to be run at lower speeds.

However, ... IF you get an open frame motor, wrap it with a shroud, and use a blower to force air through it at all times, you could possibly run it at reduced voltage. It would need to be tested under load, while monitoring motor temperature, to see. The extra blower would add inefficiency to the system though.

 

[Email]

I am contemplating...

... getting a Burley Piccolo so that I can take my 4.5yr old daughter around town with me. It almost sounds like a good pusher for this kind of project as well. I live in a backwards state that does not allow assist motors on a bicycle - I wonder if the same laws would apply putting it on a removable trailer bike. Additionally I wonder if it would be legal for states that have 750W motor limitations if you had one 750W for the bike and one 750W for the trailer.

Pros:
- Holds up to 85-lbs
- You can connect & disconnect quickly
- Provides the push to your wheels vs to your seat
- You can take a child around with you
- Weights 17.7 lbs / 4130 CroMoly Steel
- 20-IN wheel (lower speed, but better torque for hills, if adding an electric hub)

Cons:
- Does not support a rider >85-lbs
- Bearing mount "might" introduce wobble

 

[Bigwheel]

After messing around with motors on bikes I set up a staton gearbox/4 cycle on a kid's trail a bike to see what the effects would be. It worked ok but top speed was limited due to the smaller wheel size and the Staton setup hanging off to one side compromised the handling too much. It would start to get pretty interesting in any turn sharper than about 20 degrees and I got used to it but for mass consumption it would not work. The trail a bike uses a seat post hook up btw. I thought that was part of the problem until I saw this vid: http://www.youtube.com/watch?v=xp5xRazHd7g No problems with handling there in a tight turn that I can see and he has another vid of that setup going up that hill in the background effortlessly also.

Since I did that I have been intrigued by the idea of a generator running an electric hub motor but lack the necessary knowledge to set it up correctly. I have learned more from this post though thanks to Loquins explanations than I did up to now, but the biggest thing I learned from his posts were that I know nothing about electronics! Also the other post with ibdennyyaks setup is very cool and the best thing is that it addresses the issue of remote starting the motor.

 

[Email]

Dynamo

Perhaps instead of finding a small generator, you could make your own. I ran across this book online, perhaps it'd be a good read - check local library or buy it: The Homebuilt Dynamo

You could probably construct one using strong neodymium magnets, and lightweight durable materials (maybe Delrin from McMaster).

From there you pick your thickness of wire for max amps & find out how many turns you need for your amps (based on your magnetic flux), apply an engine and find how many RPMs you need for your voltage... and an engine of course to turn the dynamo. I think I got all that correct - but might want to check my assumptions. Oh and here's a good link.

 

[arceeguy]

I own one of those little generators, it is a Chinese clone of a Yamaha ET950 2 stroke generator. Trust me, you don't want on on your bicycle! It weighs about 50 pounds. Add the batteries, controller and electric motor for your hybrid system and you've got one heckuva heavy bike. (on the plus side, it does have a cast iron cylinder for long life!)

IMHO - the essence of motorized bikes would be a spindle drive with a small 2 stroke engine. Simple, simple, simple. A gas/electric hybrid, while an interesting concept, is the opposit of the "KISS" philosophy.

 

[Skyliner70cc]

arceeguy,
you beat me to it. I also have this generator and use it for camping. Mine is 45 lbs empty and 51 lbs with full tank of fuel. it is heavy! Its much too big for bike.
My 12 volt output is rated for 10 amps but is lucky to put out 6 amps at steady load.

 

[bgoates]

Kiss

I'm a simple guy and thinking of the following system on a trailer:

1) this generator http://www.canadiantire.ca/AST/brow...07P/GENmate%2B2-stroke%2B800W%2BGenerator.jsp

2) connected and charging a lifepo4 battery using the regular 5 amp charger that came with the battery

3) Using a 2nd battery to power my Wildnerness Energy hub motor while the other is charging and then swapping when battery runs low with the freshly charged battery from the generator

I estimate the two batteries and generator to weigh 65 lbs and will put the whole system on a trailer.

I guess my unknown is whether the generator can charge one battery as fast as I discharge the other ?

Also, can I plug the charger into the same battery that I am discharging ?

Any advice is welcomed....thanks

 

[rbodell]

Ran across this 1000 W generator (2 HP, 2 stroke engine) that might be a possibility for the generator in a hybrid system.

It looks like it has about a 1 gallon tank, which they advertise as running for 8 hours.

It has a 12V trickle charger, a 12 volt outlet (180 W,) as well as a 120 VAC outlet. Neither of the two 12 volt outlets would be sufficient to keep an electric system charged while it is operational - you would probably need your standard charger hooked up to the 120 VAC outlet for this.

Come off the 120VAC to the primary of a microwave oven transformer (because it is easy to rewind). Rewind the secondry with 12 or 24 turns (1 turn per volt) then get a bunch of those radio shack 6 amp 50V diodes http://www.radioshack.com/product/index.jsp?productId=2062591 to make DC to charge the battery or run the motor.

I have built several AC arc welders with microwave oven transformers. They are easy to remove the secondary and rewind for lower voltage.

A 1000 watt generator should get about 8 amps (v X A = W) when you half the voltage you double the amperage so dropping 120V to 13V should give you a factor of something like 9 so 8A X 9 = +-72A. You will loose something in the transformer but you should be able to get the potential of something like 40 amps easily. Since a e bike motor only uses full wattage on startup, you should have no problem keeping the battery charged, even with two motors.