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MOTOR OR GENERATOR??
2

MOTOR OR GENERATOR??

MOTOR OR GENERATOR??

(OP)
A customer brought in a motor for repair. It is a 3 phase motor 2 pole 400 volts off a refrigeration unit of a lorry. The customer says it is a generator.The motor has a rotor and is connected star on the terminal block.When i power the motor it runs at the rated speed.So why does the customer say that it is a generator which is run by an engine???

RE: MOTOR OR GENERATOR??

Not to get in the middle of this but it might be an induction generator.

RE: MOTOR OR GENERATOR??

(OP)
THANKS dougMSOE.
Induction generator? coustomer says it powers two fan units.
I am still puzzled...

RE: MOTOR OR GENERATOR??

An induction motor can be used as an induction generator.  Go review your college textbooks.

RE: MOTOR OR GENERATOR??

When you say that it is 'off a refrigeration unit', it sounds like you mean that it powers a refrigeration unit. If can certainly be an induction generator, but it would require a prime mover.

RE: MOTOR OR GENERATOR??

...and excitation from somewhere. Induction generators are not self-exciting. I wonder where he gets it from on a truck (sorry, I mean lorry)? An inverter powered by the DC system?

Quando Omni Flunkus Moritati

RE: MOTOR OR GENERATOR??

Typically, you can start an induction generator as a motor and then use the prime mover to increase the speed above synchronous to produce power. The excitation comes from the system power you started it with.

RE: MOTOR OR GENERATOR??

Right DanDel. That is assuming that you started with a given power source (i.e. utility) to begin with, and you are connecting back to the same source as a generator as you said. In his case, the prime mover seems to be the lorry which could conceivably start and run the motor/generator from a stop to begin with. If so, there is no excitation to begin with.

Actually, as I review the original post he never says. Sorry, not enough info to go any further with this really.

Quando Omni Flunkus Moritati

RE: MOTOR OR GENERATOR??

You're right there, jraef. Same as a lot of posts; the analysis keep coming (ad infinitum), but the original posters stop responding. I guess it's time to...

Carpe Cubile

RE: MOTOR OR GENERATOR??

Suggestion: Some people think that the vehicles have generators. They do not know much about generators and motors to tell them apart.

RE: MOTOR OR GENERATOR??

Hi Hunjan

My dumb question.
If it is a motor,where do you find the 400 volts to power it in a Lorry (truck).Go with the Induction generator idea,makes a lot more sense.  

GusD

RE: MOTOR OR GENERATOR??

Refrigerated trucks usually derive the power from a separate small gasoline engine.
Power is supplied by mechanical or hydraulic power take-off.
When the refrigeration system uses electric motors, such as in this case, the electric power is derived from a generator coupled to the auxiliary engine.

RE: MOTOR OR GENERATOR??

It would be a 'messy' way to do it, BU:-

If the AC motor is electricaly connected to an AC invertor fed from the truck 24 battery system, and mechanically coupled to the truck engine or transmission in some way. Then the fridge compressors could be driven by DC Motors.

As the AC motor is 'overhauled by the truck engine, it's DC bus would rise and charge the battery, or load sharte with it.

Setting the frequency to voltage output of the invertor would be interesting, but stranger things have been done to drive air conditioners on railway rolling stock.

Also I have used AC Invertors coupled to Paper Unwinders to supply energy to a DC bus supplying an AC motor Rewinding the same paper sheet.  The Unwind acts as a brake to tension the paper and provides the majority of the energy the Rewind needs to tow the papewr of the Unwind.  The rest being supplied by the mains via the common DC Bus. This saves heat lost by disc brakes used to act as a drag on the Unwind thus saving energy. Same principle different application.

RE: MOTOR OR GENERATOR??

HUNJAN:
Any induciton motor can be converted to a generator without any mechanical changes.
There are two or more methods:

One you drive a motor above its rated RPM plus the Slip  % of it, then you apply power to one/three phase(s).
The motor will produce the energy into the biasing power.
So this case needs to an electric energy source to produce power.

The second method is simpler and is the use of biasing capacitors across the windings.

Again mechanical power is applied at RPM p;us the slip % of the motor.

The motor metal has a remnant magnetism that the capacitor in parallel with the inductance of the winding starts to resonate at the operating Frequency and grows fast until a full power voltage level is obtained.

There is a need of a ELC ( Electronic Level Controller) which is a voltage detector that inserts/remove resistive loads to maintain the desired output voltage.

There is an industry of small Hydro electric power plants that use induction motor as generators for a few KWs of energy at low cost.

I have used, Ceiling Fans as generators and induction motors for 40 watts to 15 KW hydro-electric plants.

Other methods are a bit more complicated, no comment at this time.

Regards

Nando

RE: MOTOR OR GENERATOR??

It is possible that the subject generator/motor is a synchronous machine.  Having a prime mover and the truck’s 24 VDC for excitation, it will be possible to generate 400 VAC.

Thanks,

RE: MOTOR OR GENERATOR??

Guess you have already thought of this, but in UK truck refrigeration systems it it normal to have the 'fridge plant run by a small diesel engine, with an induction motor available to keep the 'fridge plant running when the truck is in a warehouse at night, as this is more economical than unloading and reloading the truck. The engine is decoupled through an automatic clutch, so it spins the motor but the motor doesn't spin the engine. Easy way to check - see if the vehicle has a connector to bring external power onto the vehicle.

RE: MOTOR OR GENERATOR??

ScottyUK, I'm just guessing here, but it sounds like you might be on to something.  The setup you describe would look a whole lot like a generator, too, and one might even try to build what you're describing by modifying a generator.

RE: MOTOR OR GENERATOR??

Suggestion to HUNJAN (Electrical)    Mar 13, 2003 marked ///\\\
A customer brought in a motor for repair. It is a 3 phase motor 2 pole 400 volts off a refrigeration unit of a lorry. The customer says it is a generator.
///What does a nameplate say or read?\\\
The motor has a rotor and is connected star on the terminal block.When i power the motor it runs at the rated speed.So why does the customer say that it is a generator which is run by an engine???
///Please, would you post the nameplate data?\\\

RE: MOTOR OR GENERATOR??

Hunan:

Most all induction motors may be operated as generators.

The alternative Energy industry ( small hidro electric plants ) mayuse the indution motors as generator.
For a single phase you drive the motor above its rpm+slip and connect running capacitors to the phase winidng, the power available is about 80 % of the rated power as a motor.
For the 3 phase you may use it as a 3 phase power out or one phase out.
In both cases you connect capacitors to two of the phases with the ratio of C and 2C.

The value of the capacitance depends on the HP and the input voltage.

Also you may apply AC voltae to one winding and if you app;y RPM+Slip the motor is converted into a generator and feeds power into the grid, way to couple several sources of power to a single grid system.

I hope this helped

Nando


RE: MOTOR OR GENERATOR??

Here in the states I have worked on ThermoKing refrigeration units that used an engine running a generatorand a compressor to power the refrigeration unit on a truck during the day.  At night the truck was plugged into AC power, and the refrigerator compressor and the fans in the evaporator were run off AC line power.  There was a centrifugal clutch on the engine shaft that allowed this.  The fans in the evaporator were 3 phase...

Just my $0.02..

Anyone know the procedure for flashing the field of a single phase generator....??

damengr

RE: MOTOR OR GENERATOR??

hello Damngr

Last time I flashed the fields in a generator I used a 12 volt battery.Actually I had the wrong polarity,it was backwards ,so we reversed the leads and did it again.Eureka,we had power.
It was a few years ago and I don't really remember the
small detail, but for all its worth,if you use a battery
and just touch the field it should work.
Check your field resistance top make sure you don't have excess fire works.This is a momentary contact with the field leads.Somebody might have a more formalized procedure and thatwould be best.Probably wouldn't differ much from what I mention,but just to be sure.

Good luck

GusD

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