Generator questions..any Tech guy's around.?

[metaltrades01]

Hi there,
I'd like to use a Steam engine to drive an electric motor to generate power.

Ideally I'd like 13/14v (to charge a battery) and 6 to 8 amps @ about 400 rpm.

What I have learnt online, a permanent magnet electric motor is the way to go.


What size motor should I be looking for? one that has a bit higher amp output than this?

Is a 24 v motor too high?

and what about the motor rpm, what should I look for?

I'd happily rewind the armature if need be.

Any advise or a link to a website would be appreciated,

Thanks in advance,

Martin

 

[albertorc19]

Regarding your question about the 13/14 volts needed I think that 24V is not too high. The generator ouput should be alternating current power (VAC) therefore a diode in line will cut the peak voltage by a half but this is not very efficient since you'd be wasting half the power produced by the generator. You can turn this VAC into VDC using the proper circuitry which can include a 12VDC regulator, it is not 100% efficient but is far better than using a diode. In both cases you must be sure that the components can handle the required current.
The rpm is not big deal,if you can borrow an instrument to measure the frecuency of the VAC generated, some voltmeters have the "Hz" function. Once you know this you can do the math to calculate the values of the components for the battery charging circuit. Please work safely, batteries have acids and other substances that can be harmful if overheating or other accident occurs.
This may be useful for you: http://www.leaverindustries.com.au/Little_Black_Book.pdf

 

[MachineTom]

What you want to do is generate about 100 watts. A brush type motor with permanent magnets for the field will generate DC not AC voltage. You would need a cutout relay in the circuit, this relay would be set above battery voltage, and energized by the generator, when the output of the generator exceeded the setting of the relay, the relay would close and allow power to flow to the battery, if the voltage falls below the hold in voltage the relay opens there by disconnecting the battery from the circuit. This is to prevent the generator from becoming a motor and driving the steam engine. Diodes can be used to preform the function as well.

For sizing a motor of 300+ watts should be capable of generating 100 watts.

 

[metaltrades01]

..... it is not 100% efficient but is far better than using a diode. In both cases you must be sure that the components can handle the required current.
The rpm is not big deal,if you can borrow an instrument to measure the frecuency of the VAC generated, some voltmeters have the "Hz" function. Once you know this you can do the math to calculate the values of the components for the battery charging circuit. http://www.leaverindustries.com.au/Little_Black_Book.pdf

Thanks Albertorc19.. I'm a fitter/machinist & I don't know a lot about electricity..if you don't mind..a couple of questions...

From what your saying...do you have any idea how efficient it would be?

If the rpm of the motor is say 3000rpm, would it generate full current at 400rpm? or do I need to find a slow revving motor?..or what would be the ideal motor to find for what I want to do?

Is there somewhere on the net I can find the calc's?

Thanks for the tip about the lead acid battery's and link.

Thanks martin

...in due coarse, I'll post a thread on the steam engine and generator.

 

[Dan Rowe]

Martin,
Some of the best places to look for information about DC motors as generators is on wind power sites. I kept an eye on ebay for a while until I found a cheep permanent magnet DC motor which was a tread mill take out.

Here is a link to a Baldor motor pdf that might help. It gives the calculations I think you are looking for.
http://www3.zetatalk.com/docs/Motor...As_Generators_In_Micro-Hydro_Systems_2000.pdf

Dan

 

[kf2qd]

You want a motor with the lowest possible RPM at the rated voltage. What I mean - if you get a 24V 3000RPM motor it will put out 12V at approx 1500RPM depending on the load. It might actually put out a lower voltage. The faster the motor is rated , the faster it will have to run to put out any current. Your generator will need to run faster than engine RPM to produce useful current.

I have built some RC Brushless motors, in that field they use the term KV for thousands of RPM per volt. a high KV motor (high speed) will have to be run faster to generate and currnet, a lower KV motor will have to be driven at a slower speed to generate a usable current.

 

[metaltrades01]

What you want to do is generate about 100 watts. A brush type motor with permanent magnets for the field will generate DC not AC voltage. You would need a cutout relay in the circuit, this relay would be set above battery voltage, and energized by the generator, when the output of the generator exceeded the setting of the relay, the relay would close and allow power to flow to the battery, if the voltage falls below the hold in voltage the relay opens there by disconnecting the battery from the circuit. This is to prevent the generator from becoming a motor and driving the steam engine. Diodes can be used to preform the function as well.

For sizing a motor of 300+ watts should be capable of generating 100 watts.

I'm low getting back to you Machine Tom... I might be wrong, are talking about a voltage regulator?

 

[metaltrades01]

Thanks for the advise above... I don't know anything when it comes to power generation.

To clarify a few things, the motor needs to be..
- rated at 3 times the power (watt's) I would like to generate.
- a permanent magnet motor is best.
- turned at the same "powered motor rpm" to get the same voltage.

and which is more efficient?
1/ brush or brush less? ...which is probably a DC (brush motor) and AC (brush less motor)
2/Diodes or a voltage regulator?

Martin

 

[albertorc19]

I think that a DC motor is best suited for power generation in a small scale. I've seen great advice in this thread, the addition of a relay seems like a very wise thing to do. The relationship between rpm and voltage output makes perfect sense to me, it's Faraday's law in practice . A voltage regulator is better for VDC. Once you set up the steam engine at fixed rpm's the voltage should be a few volts higher than the desired voltage, this is the "in" voltage for the regulator, the voltage at the regulator output is the specified for it. A voltage regulator will compensate the variations of the supply to deliver a constant voltage.
VAC is more efficient than VDC for power transmission but this applies with really large amounts of electric power that must by carried long distances, that's why the electric grid is VAC. There was a huge argument when Mr. Edison said that VDC was the way to go and Mr. Tesla said that VAC was far better than VDC. Time, economics and sound science proved Mr. Tesla right.
I think I'll make my own small experiment these days with a small brushed DC motor, I'll turn it manually in order to see what can be seen in the oscilloscope and report my findings here.

 

[Ed T]

You might also want to take a look at a small alternator like those found on small tractors. I have a KUBOTA lawn tractor and it has 10AMP 12v alternator that is about the size of a large tuna fish can. I don't know if the regulator and rectifier is internal or not, but it's a cute package. Alternators work better than generators at low RPM. WRT efficiency, the overall efficiency of your steam power plant will be lucky to get out of the single digits. Also, assuming you're not planning on high pressure steam, you're going to need a pretty big engine and boiler. Using the three to one ratio suggested above, it will need to be a 1.5 ish hp engine which is bigger than you might guess. Cut lots of sticks for the boiler. It will eat them fast.

 

[metaltrades01]

I think that a DC motor is best suited for power generation in a small scale. I've seen great advice in this thread, the addition of a relay seems like a very wise thing to do. The relationship between rpm and voltage output makes perfect sense to me, it's Faraday's law in practice . A voltage regulator is better for VDC. Once you set up the steam engine at fixed rpm's the voltage should be a few volts higher than the desired voltage, this is the "in" voltage for the regulator, the voltage at the regulator output is the specified for it. A voltage regulator will compensate the variations of the supply to deliver a constant voltage.

I think I'll make my own small experiment these days with a small brushed DC motor, I'll turn it manually in order to see what can be seen in the oscilloscope and report my findings here.

Thanks for the advise Albertorc19, I don't know a lot about electricity generation. I'll go with the regulator.
I'd be keen to see the results that you get.

Martin

 

[MachineTom]

MT, What I was describing is a cutout relay, it only cuts the generator in and out of the circuit, The next step up from that is a regulator, which in the case of a permenent mag genertor dumps the overvoltage to a resistor.

A brushless type DC motor would work but you need some fancy electronics to make that happen, as well as an external power source. Unless it was a purpose built brushless generator, then its big$$$.

Have you figured out the HP of the steam engine, is it enough to run a 100W generator, about 1/2hp or so would be needed.

 

[metaltrades01]

You might also want to take a look at a small alternator like those found on small tractors. I have a KUBOTA lawn tractor and it has 10AMP 12v alternator that is about the size of a large tuna fish can. I don't know if the regulator and rectifier is internal or not, but it's a cute package. Alternators work better than generators at low RPM. WRT efficiency, the overall efficiency of your steam power plant will be lucky to get out of the single digits. Also, assuming you're not planning on high pressure steam, you're going to need a pretty big engine and boiler. Using the three to one ratio suggested above, it will need to be a 1.5 ish hp engine which is bigger than you might guess. Cut lots of sticks for the boiler. It will eat them fast.

Hi Ed,
I looked at what is labelled as a Suzuki Seira here in Oz (small 4WD) and it had a 20 amp alternator which was about 4" dia x 4" long and could be disguised with a dummy cover to look like a generator.
What put me off was the 20amp output-too high, and it would have to be geared up + drive belt efficiency loss's.
I planned on building a 1 1/2 x 1 1/2" single to drive it and the steam pressure was going to be around 175/200psi + condensing.

Martin

 

[metaltrades01]

MT, What I was describing is a cutout relay, it only cuts the generator in and out of the circuit, The next step up from that is a regulator, which in the case of a permenent mag genertor dumps the overvoltage to a resistor.

A brushless type DC motor would work but you need some fancy electronics to make that happen, as well as an external power source. Unless it was a purpose built brushless generator, then its big$$$.

Have you figured out the HP of the steam engine, is it enough to run a 100W generator, about 1/2hp or so would be needed.

Hi Tom,
After what I have learnt here...I'm thinking I'd use a standard car regulator, and a brushed DC motor.

I wasn't expecting to need 1/2 HP for 100 watt's, I was hoping for 3/8 to 1/4 HP or less?

my calc's are as follow's (correct me if I'm wrong)...
(1 1/2" x 1/1/2" single cylinder, boiler pressure 175psi + vacuum. guessing 100psi in the steam chest (thinking I can better this), but not sure how much to allow for "valve cut off")

P x L x A x N = 100psi x 0.125 x (.75squ x Pi) x 500rpm = 8283
___________ ______________________________ _____
..........................................all over 33,000

= 0.25 Indicated HP

Martin

 

[Ed T]

I sent this back through the website e-mail, but it didn't find its way to this thread. Don't know why.
Since it sounds like you're well set up to study electrical stuff, it would be pretty simple to set up your generating device hooked up to an electric drive motor preferably variable speed of some kind. Perhaps you could run it off your lathe. Anyhow, in the simplest embodiment it's some kind of variable speed electric drive connected to the generator. It would then be a simple matter to read the volts and amps into the drive and compare that to the volts and amps out of the generator. I think for this to work properly you will have to load the generator side with something. Say a car head light so it has something to "work" against. Load bank if you have one. From that info you could work backwards from Watts to HP and see where you end up. I'm pretty sure that, in any case, with a separate generator you will need to gear the speed of the generator up from the engine especially if it's a low speed engine. As I recall, chain is the most efficient, but it has some other problems, noise, lube, stretch.

 

[Maryak]

I calculate it at 0.33hp (top line = 11044.66)

If it's double acting your result is 2x i.e.0.66hp. Cut off won't significantly effect the result as the steam should continue to do work whilst it expands for the rest of the stroke.

Best Regards
Bob

 

[metaltrades01]

That's a good idea Ed, no point in making the engine and its not big enough- could always turn it into a twin or compound I guess.

Btw, I have searched for Kubota alternators and the smallest I can come up with is 14amp, which is a V belt drive (might be able to mount a coupling on the front) & I'm guessing it needs to be turned at 3000+rpm.

Do you at what rpm alternators start to develop a reasonable amount of power? ....I only need 6 to 8 amps
--------------------------------------------------------------------------

I calculate it at 0.33hp (top line = 11044.66)

If it's double acting your result is 2x i.e.0.66hp. Cut off won't significantly effect the result as the steam should continue to do work whilst it expands for the rest of the stroke.

Best Regards
Bob

Hi Bob I should have double checked the calc's, yes its double acting .66 is far better than .25...it had me concerned.

 

[Ed T]

This site has a lot of info on generators vs. alternators. First one on a google search. http://www.venselenterprises.com/techtipsfromdick_files/alternators.pdf. Looks like 2400 RPM is the sweet spot. I don't know if different alternators have different curves, but the point is made in the article that alternators have the advantage of making current at low RPM. If you decide to go with the brushed DC permanent magnet motor for your source, you can gain some advantage by messing with the "timing" of the motor. Basically you rotate the location of the brushes relative to the axis of rotation of the motor. In the simplest case of a round motor housing with a round end cap to which the brush assembly is attached, you can rotate the end cap with little modification and, using your instrumentation, find the optimum timing for max output at the RPM you want to work with. Be sure you keep track of the rotation direction because it becomes a directional device and will not work well at all if turned the other way. What kind of batteries are you charging? I'm not much of an electrical guy, but I'm not sure I understand the concern about too much current. If properly regulated, the system will charge the battery 'til it's "full" and then stop charging. Higher current will take less time to fill it up. We're not talking about putting a million amps into a motorcycle battery, but modern automobile alternators are capable of 90 amps or more and they probably dump that into a severely discharged battery until it's full. The same battery can be charged with a 10 amp charger, it just take a lot longer. A 300 AMP hour battery is going to take 3 hours at 100 amps and 30 hours at ten amps (well not actually, but that's the general idea).

 

[Noitoen]

You should look for the amateur wind generators sites. Usually the build all kinds of alternators/generators to work on slow rpm's.

 

[old-and-broken]

Alternators in todays cars and other equipment charge the battery even with wide variations in the engine RPM.

The 'regulator' also controls the voltage applied to the magnets in the alternator and increases or deceases the field strength to maintain the needed voltage level for battery charging. Higher RPMs allow higher current flows into the battery of course.

all this meaning - you will probably need to use the corresponding regulator for whichever alternator brand (chevy,Kubota, etc.) for it to operate in this fashion. It would solve most of your problem with needing 3500 rpms for a DC motor used as a generator.

just some advice from an overly talkative stranger, Good luck with this project.