How to Select a DC Motor

Hi Singh,

it looks like you are trying to make an inverter. The approach is very inefficient both in terms of howmuch you will spend on the project and how much energy you will use from your battery to power the 2kVA alternator.

modern solid state inverters are about 90% efficient over most of their load band but a motor /gen set is much less efficient. I think you will be lucky to get 50% efficiency, especially if you are using it at low powers.

regards

Chas

Thanks for your suggestion i feel iam luck to get a friend like you in my project definatly i am get a 50% efficiency is conform means is there any idea to get more means pls suggest me thanks. like this type if you seen before means let me know about the technical information about the motor. because i need a 12v motor to do this project how to couple with alternator is there any torque converter are nessesary pls suggest to me iam waiting for your precisious reply

Regards

singh

Hi Singh,

12 VDC motors of sufficient power to drive an 2kVA alternator are uncommon, mainly because there is not a large market for them. Winch motors (as used on trucks) are a possibility. Starter motors (for cars and light trucks) are too small, and not designed for continuous use. The motors used for fork trucks, golf carts, etc are designed for at least 36 volts.

The 4.8 hp rating of the winch motor (from the link above) is probably not continuous. I'd guess that a continuous rating might be half of that figure: about 2.4 hp, (1.79kVA). If you used a motor like this to power the alternator, you could get full output (from the alternator) for some short length of time before the motor overheats. (You'd need to get the full specs of the motor to know how long you could run at full output.) If the motor is 70% efficient and the alternator is 75% efficient, then the input to the 12V motor would need to be 2000 W/.75/.7 or 3800 kVA. That would be about 317 amps, requiring an expensive contactor for control, and a fairly large battery for supply.

Ideally, you would want to drive directly, but a chain drive can be about 97-98% efficient, if you need to get a particular frequency of AC output that is not supported by direct drive.

If you can use 36 or 48 volts, then the number of motors available would increase greatly. (You could easily find a used or new fork lift truck motor.) Of course, an inverter would be far more efficient -- and less expensive, if you need to buy the motor and controls new.

If you have not worked with motors of this size, be careful -- talk with someone who has experience -- there are many hazards: sparks, burns, exploding batteries, heavy motors spinning off a workbench and onto a foot, etc.

Dear Singh,

asyou seem determined to make a rotary converter against all advice. you will need a motor of about 2.5 to 3kW but you still need to keep the motor speed at 1500 or 3000rpm in order to get the 50Hz I suppose you will want. A torque converter will not be neccesary.

It seems to me that the way to do this is to take a frequency detector circuit and have that drive an preadjusted width "space" pulse generator so that as the frequency rises then the time the drive voltage is connected is reduced .

best of kuck with your project

Chas

In addition it is a single phase power output.

Also remember you are landing up in 2 rotating components (alternator and Motor) with their associated maintenance problems and additionally DC Motor (more headache)

The controls for the motor et al.

As mentioned by C you will be lucky to get even 50% efficiency.

For only a 2KVA power output requirement - presumably for a small house, go for an inverter with the same rating. This may be cheaper than the motor you are trying to buy with its controls.

Like the others said already - go n get a solid state DC-AC converter that's more efficient, no mechanical wear nd tear, no noise, hardly any stand by power consumption, reliable and so on.

They're also available in several KW range therefore, all you need is a reliable high current DC power supply to match your power requirement.