# Generator types

1. May 9, 2015

### crash_ndie

hi all am doing a project to generate 240v 2.2kwh at 10 amps out put volts can be 28/48/24/12. i can't figure out what type of generator to use ac/dc, 3phase, permanent magnets, induction, or axion flux. I need one with low friction low torque under load an low rpm as the source to spin it up is low flow rate. I've tested a DC motor and was surprised to get 188v at 800rpm not under load, connect a bulb and it stops spinning totally... what's the best generator for the job ... help

2. May 9, 2015

### phinds

(1) First you say you are going to be generating 240V and then you say it's ok if the output is 28/48/24/12. Do you understand that 240 is different than 28/48/24/12 ?

(2) You say you are "generating" but they you talk about using a motor. Do you understand that motors and generators are not the same thing? Do you understand the difference?

(3) Do you understand the dangers of messing with 220V ?

(4) What level of knowledge are you at? What grade in school

(5) Have you done any research on your own to distinguish among the types you listed (especially in terms of your list of desired characteristics) ?

3. May 9, 2015

### Hesch

Well, you must have input power (ω*T) > output power ( V*I*cos φ ). Otherwise the efficiency would be greater than 100%. You will achieve the greatets efficiency with a PM synchronous ac-generator/motor ( ≈92% ). (A dc-generator will yield about 75%?). Low rpm is achieved by using a generator with many polepairs, e.g. an ac-generator with 7 polepairs must turn 514.3 rpm at an output frequency = 60Hz. Use an autotransformer to get 28/48/24/12 V.

An induction motor cannot be used as a "stand alone" generator, as it consumes reactive power. Thus it only works when connected to some grid. A load as a resistor cannot produce reactive power, and cannot produce a reference frequency for the asynchronous generator.

4. May 9, 2015

### jim hardy

As Hesch pointed out , your two criteria are mutually exclusive.
Energy is conserved.
power = torque X rpm X some constant , constant depends on your choice of units.

5. May 9, 2015

### crash_ndie

thank you for your replies it looks like I will be using ac generator and will have to do some gearing to get the torque required ... hi phinds 1) yes I do know differences between voltage, the voltages i listed are optional for a inverter input to produce 240v 2) yes I do know the difference between motors and generators, i used the motor I had in the shed as a guide for the set up, not the final product I don't have the cash to buy 3 different generators hense me asking here. 3) yes i work on 3 phase 415v appliance's at work 4) A level at school, i am a control engineer, HVAC engineer, gas engineer, dea, and renewables engineer. I don't claim to know everything but I do try to understand 5) yes I have and didnt understand the difference or the best one for my project, so i here because I know you guys could help.... thanks again lads

Last edited by a moderator: May 12, 2015