Generator start-up torque

[royalbas001]

TL;DR Summary

Torque calculation of СГ-18-1С

Hi
I want to design a test rig for starter generator ( СГ-18-1С ). The output of the starter generator is 28V, 18KW @ rpm 3600 - 6200. The output will be regulated through excitation winding current.

I want to choose a motor to run the stater generator. Please tell me, How to calculate the torque of the starter generator.

I calculated as Torque = Power x 60 / 2 x Pi x rpm, results a ~48Nm torque at 4000 rpm. Is it correct or need to consider the excitation winding current? Please suggest. I want to choose the motor using V- belt pully drive with step up.

Thank you

 

[Tom.G]

1 HP = 746 Watts
18KW / 746

18 000/746 = 24.13 HP

HP x 5252 /rpm = Torque (Ft.Lbs.)
24.13 x 5252 / 4000 = 31.68 FtLbs

1FtLb = 1.356 Nm
31.68 x 1.356≅ 43Nm

That assumes 100% efficiency in the starter and the belts, which of course will not happen.

Cheers,
Tom

 

[Baluncore]

Welcome to PF.

The SG-18-1S starter/generator is a Russian built direct current machine of mixed excitation, with air cooling by a built-in fan, designed for starting of diesel engines, supplying electric energy, and recharging batteries.

Specified as 18 kW.
Generator maximum current: 800 amp continuous. ( Vmax of 22.5 volt ).
Maximum applied shaft torque = 125 N∙m.
Maximum speed 7000 RPM.

To generate the maximum output will require an engine rating of 18 kW.
18 kW is equivalent to 24 HP.

4000 RPM * 0.10472 = 418.9 radian/sec.
18 kW / 418.9 = 43.0 N∙m.
My numbers agree with Tom.G

For 18 kW output, shaft torque will be;
@ 3600 RPM, 48. N∙m
@ 4000 RPM, 43. N∙m
@ 4400 RPM, 39. N∙m
@ 5200 RPM, 33. N∙m
@ 6000 RPM, 29. N∙m