Power Generation - Time to Get Serious

[210061741]

Well now this is a very interesting concept.
Working on a Jackshaft kit design lately.
I'll have to see if we can incorporate this without loosing too much HP.
Hope you guys post some more great suggestions for the Jackshaft.

 

[professor]

I just went downstairs to the laboratory (garage), clamped a 12volt cooling fan motor (from the Mustang inventory), spun it with my drill (2250 rpm) with a spare headlamp for the Mustang.
At full speed, the light was vary bright (forgot to check voltage output) - so much so that the camera blacked out everything but the light. Here is a pic at 1/2 speed or so:

This bulb was a hi/low one. There really wasn't much resistance to my hand holding the drill from torque reactiononce I got it to speed.
Your challenge would be to detirimine what rpm (oh, I forgot, aren't you the guy who made a speedometer into a tach?) to gear the motor to at the rpm you use for normal use- because the bulb will blow out if you give it too much juice (rpm).
Forget using it for starting. The cool thing is that you would not need a battery at all.

 

[machiasmort]

Professor,

That appears to be a cooling fan motor, (goes infront of radiator), please correct me if I'm wrong? Believe me, we appreciate your bench test!

A blower motor that heats the cab of a vehicle is smaller (lighter) and would be even more efficient (lower rpm)... A cooling fan motor would generate more power, I guess it depends on what you need?

I believe, but am not sure, you can simply put a resister on the hot line to only allow a limited amount of volt through the line (eliminating spikes), caused by varried rpms.

 

[professor]

Back downstairs to learn voltage-
9.8 while running the headlamp, 12 something with it off (same speed). Adding a tail light dropped voltage to 9.6 or so with the big lamp still on.
Therefore, the more load you apply- the less voltage you get.
More rpm needed?
Set that properly and you have a winner.

 

[machiasmort]

Bulbs add resistance like a resister! LOL! Took me years to understand! I still don't understand motor phasing and how to wire the coils within. Once I do, I'll be able to make a dummies guide for making your own generator. Bridge rectifiers to make the voltage dc are also confusing to me.

All said, I'm not sure that more rpms would be the answer on that motor as per our bikes? If you listen to a cooling fan run, they really whiz compared to a blower motor. This leads me to be strongly suspicious that the blower motor will produce higher V's at lower RPM's.

The thing we have going for us is that lights are forgiving of voltage!!!

 

[loquin]

A permanent magnet DC motor can be treated as a voltage source in series with a resistor. The smaller the wire used in the motor, the higher the resistance of the wire, and the greater the resistance of that 'series' resistor.

When you draw current from the generator, the greater the current, the greater the voltage loss across the internal series resistance. Adding the tail light increases the current drawn from the generator, and when it did, the the voltage across the internal resistance increased as well. That, in turn reduces the available voltage to the load.

You can calculate the internal resistance with three simple measurements. First, at a fixed generator RPM, measure the voltage output from the generator, with no bulb or headlight connected. Then, connect the headlight, and take the same voltage measurement, across the headlight terminals. Finally, at the same RPM, measure the DC current through the headlamp. To calculate the internal resistance of the motor-generator, in ohms, take the the difference between the two voltages, and divide that by the lamp current in amps.

A 55W headlight SHOULD pull about 4.5 amps. If we assume that that was the actual measured current with your test, (and with the voltages you mention, above) the internal resistance would be

(12V-9.8V) / 4.5A = 0.489 Ohm

The power loss would be

4.5A * (12-9.8) = 9.9 W

The headlight power would be

9.8V * 4.5A = 44.1 W

The power lost divided by the total is 9.9 / 55, or 18%

You could increase the RPMs of the motor, so that it produces about 20% more voltage, unloaded, to compensate for the power lost to heat with the series resistance of the wire. You can also increase the RPM to compensate for increased current load. But, there comes a point where the internal power loss due to heat will slag the motor/generator, or the increased voltage would short out windings in the motor.

 

[professor]

Very good explaination Lou (I want to think about it some more when it isn't bed time).
Mort- I think the bigger motor woul be more forgiving of wrecking it.
I remember messing with a blower motor and it seemed to spin about the same rate as the cooling fan when they both were run on 12v
Actually, what you guys need (I never ride at night) is just to upscale and refine the drive of one of those tiny DC generators that rub on the tire- the only thing is that unless you run a battery, when you slow down or stop- the lights go out.

 

[professor]

One other thing- when I spun the motor at 2250. I got 12 something volts. Does this mean that, used as a motor, the thing would spin at a little more than that? What would it spin @ 14.5 volts (alternator output setting)?

Car systems run off the alternator (in my experience, once running, the alternator supplies ALL the electrical energy to run everything on the car- it will burn out if the load becomes too great -( Go real small on that winch for your 4x4!).

 

[210061741]

Good work here.
This info will be invaluble.
Test on and report results.

 

[machiasmort]

Actually, what you guys need (I never ride at night) is just to upscale and refine the drive of one of those tiny DC generators that rub on the tire- the only thing is that unless you run a battery, when you slow down or stop- the lights go out.

You just took my idea!!! You said it and didn't realize it!

Mount that motor under the belly of a rear bike rack, friction drive it off of the tire and charge a battery.

How would I construct a diode to keep the current flowing one way? When you'd stop, the motor would want to run w/o something there to stop the current from the battery you were charging (on top of the rack)!