Induction motor generator capacitor

Click For Summary

Discussion Overview

The discussion revolves around the use of a single-phase induction motor as a generator, specifically focusing on the calculations for the appropriate capacitors needed for operation. Participants explore the feasibility, challenges, and methods involved in generating power from this type of motor, including considerations for voltage output and reactive power requirements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant seeks assistance with calculations for capacitors to use with a 1-1/2 hp single-phase induction motor intended for generating 110V output.
  • Another participant suggests that the UF:500 indicates a need for a 500μF capacitor for starting, questioning the purpose of the capacitors required.
  • Some participants clarify that the capacitors needed are for providing reactive power in a continuous generator regime, with differing values suggested for 110V and 230V outputs.
  • Concerns are raised about the complexity of using a single-phase induction motor as a generator compared to a three-phase motor, which is noted to be more straightforward.
  • Several participants discuss the challenges of achieving resonance with capacitors in a single-phase setup and the potential for high voltages involved.
  • One participant shares a personal plan to connect two motor shafts to experiment with self-excitation using capacitors.
  • There are suggestions to consider alternatives, such as using an old car alternator, which may be more practical and cost-effective for generating power.
  • Participants express skepticism about the efficiency of using a 1 kW motor to power a 90W LED load, noting potential losses.
  • Discussions also touch on the need for appropriate voltage and frequency for LED lighting and the possibility of using a buck converter.
  • One participant mentions the potential availability of a free 10 hp three-phase motor, but others caution about the challenges of using such a motor without adequate reactive power support.

Areas of Agreement / Disagreement

Participants generally agree that using a three-phase motor may be more effective than a single-phase motor for generating power. However, there is no consensus on the best approach or the feasibility of using the specific single-phase motor discussed. Multiple competing views on the practicality and efficiency of various solutions remain unresolved.

Contextual Notes

Participants express uncertainty regarding the exact capacitor values needed and the implications of using different motor types. There are also unresolved questions about the compatibility of the generated power with the LED lighting requirements.

H012
Messages
153
Reaction score
7
Hope I can get some help here. I have a 1-1/2 hp. 115/230 volt single phase induction motor I want to use as a small generator. currently it's wired for 115 volt I need help with the math to
calculate the proper capacitor/s to use. Running no load amps as a motor draws 18 amps.
Name plate states:
110/230 volt single phase
UF: 500
Rpm 1720
1.1 kv.
duty cycle 100%
Amps 18/9
4 pole
I want to use this for 110 volt output. This motor is commercial grade. I understand slip so the rpm needs to run at around 1875. Please any help would be grateful.
 
Engineering news on Phys.org
gif.latex?C%3D\frac{Q_{c}}{2\pi%20f\cdot%20V^{2}}\approx%20\frac{P}{2\pi%20f\cdot%20V^{2}}.gif


P = 1100 W
V = 110 V
f = 60 Hz
 
Capacitors for what ? Starting or power-factor? In your data I believe the UF:500 means it needs a 500uF Cap for starting. Also if the Gen is dedicated to this motor - switch both to the HV ( 230V ) taps. It will start easier. NEMA motor name plates have a specific requirement - so a picture may actually tell a little more.
 
As far as I understand, he wants to use the motor in an async generator regime. So this isn't a "start-up" cap but cap that provides necessary reactive power in a continious regime for wanted generator output. Value of the cap isn't critical (can be somewhat higher or smaller than given by formula), but there is quite a big diference regarding voltage output: for 230 V it is cca 55 μF and for 110 V it is 240 μF(!). Low voltage costs more money :D
 
I have never seen an easy way to run a single phase induction motor as an AC generator. There is no question that it can be done with a symmetrical three phase motor.

With a 3ph motor the inductance of the phase windings can be measured by reading the inductive current flowing while the motor is stalled, rotor locked. Given the frequency required to be generated, a delta of capacitors can be connected to the motor that will be LC resonant with that motor's inductance. The motor must be spinning at a rate slightly faster than the self resonant frequency before it will self excite and begin to generate power at the resonant frequency. Overloading the motor/generator will destroy the self excitation and so self protect the generating motor.

A single phase motor has two different phase windings in an “L” arrangement that can be arranged as an asymmetrical three phase topology, so I guess it should also be possible. Getting three different capacitor values that resonate at a similar frequency might pose quite a challenge.
 
Ohh - re-read and I agree, Induction motor as generator is more trouble than it is worth... esp as a one off project
 
I would experiment by connecting two motor shafts, powering one and placing AC capacitors on the other until it self excited. Initially I would do it with 3ph motors. If you really must do this then be careful of the high voltages involved. Procede carefully as follows.
Physically lock the rotor so it cannot move.
Connect the motor to the AC supply. Note the supply frequency, 60 Hz ?
Apply power for a very short period, read the motor voltage, Vm, and the motor current, Im.
Compute the inductive reactance XL = Vm / Im.
Resonance occurs when XL = – Xc. So you can avoid computation of the actual inductance.
Knowing that Xc = –1 / ( 2 * Pi * Hz * C )
Solve for the required C = 1 / ( 2 * Pi * Hz * XL )
 
Baluncore said:
I would experiment by connecting two motor shafts, powering one and placing AC capacitors on the other until it self excited. Initially I would do it with 3ph motors. If you really must do this then be careful of the high voltages involved. Procede carefully as follows.
Physically lock the rotor so it cannot move.
Connect the motor to the AC supply. Note the supply frequency, 60 Hz ?
Apply power for a very short period, read the motor voltage, Vm, and the motor current, Im.
Compute the inductive reactance XL = Vm / Im.
Resonance occurs when XL = – Xc. So you can avoid computation of the actual inductance.
Knowing that Xc = –1 / ( 2 * Pi * Hz * C )
Solve for the required C = 1 / ( 2 * Pi * Hz * XL )
I agree this motor would be better if was a 3 phase. I just want this to generate auxiliary power for the LED lighting
in my house. My house is totally LED lighting with a total wattage 90 watts. I have my main generator for my freezers
and other "have to" utilities. Great input thanks to everytone.
 
Why not acquire an old motor car alternator? They are more plentiful than induction motors and easy to replace. Moreover - they were designed to do the job you want.
 
  • #10
H012 said:
I agree this motor would be better if was a 3 phase. I just want this to generate auxiliary power for the LED lighting in my house. My house is totally LED lighting with a total wattage 90 watts. I have my main generator for my freezers
and other "have to" utilities. Great input thanks to everytone.
So you want to power 90 watts load with 1 kW+ rated rotating electrical machine? Most likely the losses in generator will be as large as total wattage of your LED load. It can work, but you're not very economic :D
 
  • #11
H012 said:
I agree this motor would be better if was a 3 phase. I just want this to generate auxiliary power for the LED lighting
in my house. My house is totally LED lighting with a total wattage 90 watts. I have my main generator for my freezers
and other "have to" utilities. Great input thanks to everytone.

So i guess you have separate wiring for the LED lights ?
Hmmm...
Read the nameplate data of your LED lights carefully.
What range of supply volts and frequency is acceptable to them? Modern switching supplies are surprisingly broad-minded about input power.
Sophie's car alternator might well be an economical solution.
 
  • #12
Here in new jersey any alternator with a sufficient wattage for my needs are outrageous in price. Even used.
I think I will do some looking for a 3 phase to experiment with. Seems from my reads that 3 phase is the chose of DIY'ers
Thanks again for all the input.
 
  • #13
H012 said:
think I will do some looking for a 3 phase to experiment with. Seems from my reads that 3 phase is the chose of DIY'ers
Looking for a 3 phase what?
 
  • #14
The LED lights are a different voltage than the "main generator" ? What do the LEDs need?
 
  • #15
Windadct said:
The LED lights are a different voltage than the "main generator" ? What do the LEDs need?
Buck converter electronics you get with them?
 
  • #16
Yeas - some type of DC supply is what I was thinking - need the OP to update us...
 
  • #17
Windadct said:
Yeas - some type of DC supply is what I was thinking - need the OP to update us...
Really no need for that. The simplest driver circuit topology which rectify has been integrated in LED bulbs since early days of commercial LED technology (looks like this) . And today you'll find more advanced topologies integrated. Hopefully OP is not looking for 100W 3-phase induction motor to power his LEDs. He will have a hard time finding such.
 
  • #18
Windadct said:
Yeas - some type of DC supply is what I was thinking - need the OP to update us...
Believe it or not a buddy of mine who works for a water company told me last night that pumping stations change out motors
as part of maintenance that some of the motors are good it;s just they are changed after so many hours. He said I could probably
get a 10 hp 3 phase motor for free if I pick it up. As cost is a consideration. I'm not looking to spend more than it would cost just to buy a generator. I would look foolish. Getting the voltage and wave to be stable is something I can do especially with info. from guys with your knowledge. Don't know when I will update you guys depends when I get a motor. As I work a 3- 11pm shift hampers my motor shopping.
 
  • #19
Are you serious?
In order to use a 10 hp 3 phase induction motor as a generator, you'll need a very large cap bank, or 2-3 Hp sync generator to supply it with reactive power. Not worth trying & money knowing your load is some 0.1 kW LED lightning
 
  • #20
I remember a project in the 70's where a guy used a simple single phase induction motor to kick power back into the grid. Back then, people put all manner of bad power factor on the grid, so I don't think a capacitor was even used.
But, you did need the grid to sync into. Otherwise, the motor spun, but wasn't generating.

A couple of interesting alternatives are the motors used in tread mills and old brush-less-DC motors from air conditioners.

With the 13 SEER mandate, I'd be surprised if there are any air handlers sold without one. The electrical drives are more likely to pop than the motor, so if you have a buddy that's an AC repairman, these are great. Just pull off the control and you'll have a 3 phase motor. Get a couple of full-bridge rectifiers, and you can cobble a three phase rectifier cheaper than buying one.
Careful though. These parts were intended to reach peak speeds at around 300 volts p-p (ouch!). Running the shaft slower gives less voltage and less power, so a 3/4 hp, 900 RPM type should be good for about 90 watts at about 48 volts and 90 RPM. The limiting factor is the wiring, which is only intended to take so much current.

Note that you can also use three 220 V transformers arranged in either a delta or wye to take better advantage of it's capability. Even though it's frequency decreases with speed, so does it's voltage, so the transformers remain happy. Also, rectifying three phase gives a fairly smooth current to your system.
 
  • #21
I just picked up a three phase 150 volt 750 va induction appliance motor at a thrift store for six bucks.
i think it came out of a modern clothes dryer or washing machine. Presumably the computer board in the appliance had quit because the motor is pristine.
You might check your local metal recycle yard, and keep an eye on streetside trash piles.
 
  • #22
Finding 3-phase sync motor, several hundreds watts, would be even better. Then, no need for big caps. But such are no easy find.
 
  • #23
Mike_In_Plano said:
I remember a project in the 70's where a guy used a simple single phase induction motor to kick power back into the grid. Back then, people put all manner of bad power factor on the grid, so I don't think a capacitor was even used.
But, you did need the grid to sync into. Otherwise, the motor spun, but wasn't generating.

A couple of interesting alternatives are the motors used in tread mills and old brush-less-DC motors from air conditioners.

With the 13 SEER mandate, I'd be surprised if there are any air handlers sold without one. The electrical drives are more likely to pop than the motor, so if you have a buddy that's an AC repairman, these are great. Just pull off the control and you'll have a 3 phase motor. Get a couple of full-bridge rectifiers, and you can cobble a three phase rectifier cheaper than buying one.
Careful though. These parts were intended to reach peak speeds at around 300 volts p-p (ouch!). Running the shaft slower gives less voltage and less power, so a 3/4 hp, 900 RPM type should be good for about 90 watts at about 48 volts and 90 RPM. The limiting factor is the wiring, which is only intended to take so much current.

Note that you can also use three 220 V transformers arranged in either a delta or wye to take better advantage of it's capability. Even though it's frequency decreases with speed, so does it's voltage, so the transformers remain happy. Also, rectifying three phase gives a fairly smooth current to your system.
Thanks, Yeah I looked up the new mandated motors for AC units it's call an ac permanent split capacitor motor { PSC ] I'll study up on it.
 
  • #24
H012 said:
Thanks, Yeah I looked up the new mandated motors for AC units it's call an ac permanent split capacitor motor { PSC ] I'll study up on it.
I stand to be corrected: After doing some more research I found that currently AC units are using An ECM Dc motors
 
  • #25
What has happened with motor from first post?
 
  • #26
zoki85 said:
What has happened with motor from first post?
After reading the posts from you guys that obviously know more than I, It would not be an efficient build. I'm still looking into the 3 phase motor build But these Ecm motors also are an option although rummaging around to find one that has a bad control unit as this is the most common problem with ECM motors not the motor head itself might be hard.
 
  • #27
H012 said:
It would not be an efficient build...
So what? You said before "I just want this to generate auxiliary power for the LED lighting in my house". If you lose say 100 w , in order to power
100 W lights, you shouldn't be worried about it. And what kind of machine will provide mechanical power for your stand-alone generator?
 
  • #28
I still do not understand really what you are looking to do -- you have a generator for large appliances but you want to make a small one for 100W of LED lighting? Is the LED lighting custom or standard household bulbs? Why are you not using the larger generator?
 
  • #29
Windadct said:
I still do not understand really what you are looking to do -- you have a generator for large appliances but you want to make a small one for 100W of LED lighting? Is the LED lighting custom or standard household bulbs? Why are you not using the larger generator?
This is custom emergency lighting for the house. I have a 10KV main generator. If the power goes out I'm pushing this generator at 85%. I can't afford another generator, Just got back to work. I was just trying to build something with components that can acquire free. I started out this whole thing about using a induction motor from you tube and other sites. Claims were that for every 1 hp 600 watts could be achieved. I am a machinist by trade I have no background at your level. I just want to build a
small generator that's it. Here in the NE I'm not allowed to have batteries for power in my basement. So building small generator
to charge batteries is out of the question. The reason I started this thread was to get real professional opinions and ideas
because I understand a person can't believe every DIY idea that's out there. I'm grateful for the continued posts. on this.
Hope this thread isn't becoming too boring, if it is let me know
Thanks HR
 
  • #30
OK - this is a lot closer to what I thought than how I read your posts...no offence. By NE you mean Nebraska?

1) 100W of load is very "light" - no pun intended.
2) Your main Gen is 10KW (watts -- I am sure not 10KV)- and 85% loaded... when all of the appliances are running - 100W is only 1%... 85 vs 86%... IMO - a non-issue to add the lights ( however I understand that as a backup - you may not want this gen running 100% of the time).
3) The no batteries in the basement rule - can probably be re-read, or challenged - the issue is when charging LEAD ACID batteries give off Hydrogen (so an understandable regulation) - but the basic battery back up sump pump I am sure violates this "rule" - does the local home depot sell these... perhaps ask them how the "kit" is allowed since these are installed in basements. Next - the "rule" has merit- you really do not want to be generating hydrogen in your basement - with no proper ventilation - with a little thinking I am sure you can find a way to ventilation. .
4) How long do you want the lights to last - etc...

OK .. getting long winded...sorry wet an rainy here in the N.E. Northeast... Really the question - what is a good and minimal cost way to supply 100W of load in a backup situation.

If you do not want to run the gen 100% of the time - find somewhere to add a Lead Acid battery and automotive inverter - 200W.

3rd to Last point -- LED lighting is efficient, at the end of the day this means it gives off little heat - if you have hot summer days, with the AC running all of the waste heat you pay for - you pay for again to remove from your house. Personally I would look to utilize the LED lighting as much as possible, even if you have a Battery charger, then inverter - then the LED lights - less heat than incandescent bulbs - so when you look at utilizing the LEDs for more than just back up - they are more valuable and perhaps worth a little more expense than "free".

2nd to last point - this is not boring, it is valuable to everyone to see the challenges faced, and how important it is to drill down to the real "problem" - I recently came across a good quote " A question well asked is already half answered"

Last - This is not professional advice... ahem...
 

Similar threads

Self excited induction generators and grid connected solar inverters?
  • · Replies 9 ·
Replies
9
Views
2K
How does a Permanent capacitor motor actually work?
  • · Replies 7 ·
Replies
7
Views
2K
Self Excited AC Single Phase Generator
  • · Replies 12 ·
Replies
12
Views
6K
Why can't a 2 pole ac induction motor run a 6 pole induction generator
  • · Replies 4 ·
Replies
4
Views
2K
Investigating Why a Century AC Motor's Label Shows 1625 RPM
  • · Replies 7 ·
Replies
7
Views
2K
Sizing the start capacitor for an induction motor
  • · Replies 2 ·
Replies
2
Views
5K
Series motors, switched to parallel
  • · Replies 15 ·
Replies
15
Views
2K
What is the best DC motor for spinning a vortex impeller at 3000 rpm?
  • · Replies 2 ·
Replies
2
Views
2K
Permanent Magnet Motors & Koenigsegg’s ‘Dark Matter’ Electric Motor
  • · Replies 0 ·
Replies
0
Views
2K
How to calculate the inductance of a stator winding
  • · Replies 5 ·
Replies
5
Views
9K