Whats the most effiecient motor to use as generator?
Whats the most effiecient motor to use as generator?
(OP)
I have been working on a project recently where I want to turn a stepper motor via an air turbine to generate power. It works pretty well I have 160vdc @ .14 amps on one of my steppers and this is more than enough power for the circuit it needs to run. My question is this, is the stepper the best (most efficient) way to generate power or would some of you use another method perhaps brushless DC or induction motor?
My power needs are somewhat small 20-30 watts but I would like to generate it in the most efficient way possible any RPM is possible but I would like to stay below 2k if possible just for bearing life, balance issues etc.
Input appreciated.
My power needs are somewhat small 20-30 watts but I would like to generate it in the most efficient way possible any RPM is possible but I would like to stay below 2k if possible just for bearing life, balance issues etc.
Input appreciated.





RE: Whats the most effiecient motor to use as generator?
First question is size. Got any size constraints?
How many volts do you want, to get you that 30W?
RE: Whats the most effiecient motor to use as generator?
RE: Whats the most effiecient motor to use as generator?
Size is a concern the motor I am using now is approx 2" x 2"
with a .25" Shaft. I would like to stay this size or smaller if possible.
I am going to make the turbines voltage self regulating via a proportional valve that will close off air to the turbine as voltage goes to high. I can have a float of 5-10v on the load without issue.
This is not going to be a single unit, I hope to make many of these so I want to do it right. I was considering a brushless DC motor with Nd-Fe-B Magnets would be a nice small package, but I am unaware of how it would act as a generator compared to a stepper motor.
I can use any voltage between 12-300vdc to get my 20-30 watts
I plan to reduce the voltage to the air valve supplying the turbine via a resistor voltage divider. The load can run on any DC voltage from 24-400vdc (solenoid) I just need 20 watts or so. The coil for the regulating valve has a very small load of .67 watt at 24vdc.
I can get this done now with the stepper I have or any like it, I would just like to know if it is the most practical or efficient way to do it.
RE: Whats the most effiecient motor to use as generator?
Any motor will have very similar performance as a generator. There are a few points to note however (not an exhaustive list, I'm sure there are other points):
1. an induction motor cannot generate without a supply for its magnetizing current.
2. a commutator motor has higher losses due to brush friction and volt drop.
3. machines with wound rotor and wound stator suffer from two lots of copper loss.
The best power density results from running the machine as fast as possible; up to the point where bearing+windage losses become significant, the power output from a particular machine will be proportional to speed.
A typical 3-phase brushless PM machine will give a near sinusoidal output that can be simply rectified; if you want variable voltage you can use mosfets with controlled switching, the losses are lower than for a resistive divider.
RE: Whats the most effiecient motor to use as generator?
Barry1961
RE: Whats the most effiecient motor to use as generator?
You can get small permanent magnet DC motors and give them a try.
RE: Whats the most effiecient motor to use as generator?
Stepper while never intended to produce power work pretty well, I have done it and many wind power people use steppers for the same reason. They make good usable power at low RP M's.
The DC tach Idea is fine but I would need the brushless type and they are not cost effective.
I thing I am going to go with a brushless PM machine with rare earth magnets (SmCo or NdFeB) as UK Pete suggested as this is where my research has led me as well. Problem is I have to really spin these buggers to get power out of them.
I may change my design and utilize a Tesla turbine as they work well in high RP M's and actually gain efficiency over 30k RPM I'd just need some high quality bearings. Another option would be to gear the turbine to the motor/generator but I want to keep this simple.
I have many CNC machines at my disposal so making a turbine is possible and they are decently efficient as well.
I'm not going to quit on this until I am satisfied it is as close to perfect as possible.
RE: Whats the most effiecient motor to use as generator?
RE: Whats the most effiecient motor to use as generator?
If you are right I will move in that direction if needed. I only need to energize my load for approx .25 seconds every second or so.
Thanks
RE: Whats the most effiecient motor to use as generator?
If what you want is to charge a 24 volt battery and run an inverter you can get alternators that are designed for this application. These are used in buses and airplanes. You can get them in just about any power output you could want.
RE: Whats the most effiecient motor to use as generator?
You could even use a centrifugal pump running backwards which is often done with cooling tower water when it comes back down from the roof of a skyscraper in order to recover some of the mechanical energy the is in the water. This way, equipment on lower floors does not have to withstand the full head of water. The same thing is also done when pumping cooling tower water from a tower that is on an intermediate floor to an AC unit that is on an upper floor. This keeps the water coming back down from turning its mechanical energy into excessive heat.
RE: Whats the most effiecient motor to use as generator?
RE: Whats the most effiecient motor to use as generator?
RPM Current Watts
4400 6.9A 42
It's a very durable external rotor rare earth brushless
motor.
I have one on the way to test I hope it works spent a lot of time finding this one
27.7mm (1-3/32") diameter, 30mm (1-3/16") from back to front. The hardened 3.17mm (1/8") shaft is supported by 2 ballbearings for a long service life.
87% efficiency watts shown are with efficiency losses. 60 bucks with high quality bearings not bad.
RE: Whats the most effiecient motor to use as generator?
RE: Whats the most effiecient motor to use as generator?
And this time no, "I simply used some HTML" answer!!
:)
RE: Whats the most effiecient motor to use as generator?
RE: Whats the most effiecient motor to use as generator?
RE: Whats the most effiecient motor to use as generator?
You must have the imagine on the WEB accessible by anyone.
Then to include an image in your post do this;
In this case the image is at:
http://www.hobby-lobby.com/images/pm2212.jpg
So you enter:
"img http://www.hobby-lobby.com/images/pm2212.jpg"
Inside [..]these brackets.
And WA-LAW!
RE: Whats the most effiecient motor to use as generator?
RE: Whats the most effiecient motor to use as generator?
RE: Whats the most effiecient motor to use as generator?
Opera you took a turn off the road back there... bigmark has always been talking air turbine-proportional valve controlling the air. I would not take this to mean a windmill.! :)
RE: Whats the most effiecient motor to use as generator?
3.8:1 Planetary Gearbox
You guys are on to me, this lil bugger would bring the rpm's down nicely.
No, it's not for a windmill, it is to be used in an industrial product I am developing and hope to market.
RE: Whats the most effiecient motor to use as generator?
It's on it's way I'll keep this thread updated.
RE: Whats the most effiecient motor to use as generator?
RE: Whats the most effiecient motor to use as generator?