What size should an electric generator have if I have 35 engines 1 HP each?

Question

What size should an electric generator have if I have 35 engines 1 HP each?

Answer 1

While the nameplate of each motor might be 1 HP, the load can be far different.  Most motors are only loaded to a fraction of their nameplate rating.

The starting inrush of a 1 HP motor might be 5-7 times the running load.  As long as the motors are not started simultaneously, you can probably use the following calculations:

1)  Assume the motors are loaded to nameplate.

2)  1 HP = 0.746 kW

3)  Assume the load for each motor is 0.746 kW

4)  35 motors x 0.746 kW per motor = 26 kW

5)  Factor in the inrush requirements of the last motor being started by adding another 6 x 0.746 kW = 4.4 kW

6)  26 kW + 4.4 kW = 30.4 kW

Look for a 30 kW generator and you're good to go.

Answer 2

Your 35 engines will draw about 26.25KW. at full load,

but you haven't given us :

loading, power factor, and starting protocall.

a 30 KVA. unit should serve unless you intend to start those motors

in groups instead of one at a time.

(Rule of Thumb is 80% P.F. and allow

200% F.L.R.C. for largest motor or group

started simultaneously.)

Answer 3

You must also consider the start up amperage requirements.  I have generally used 7X running amperage as a rule of thumb.  Since 1 hp = 746 watts, You should anticipate something on the order of a 5kw generator to start that motor.

If you try to connect and run 35 motors at one time, you're going to have all kinds of problems unless you have one really big generator.

Answer 4

1hp = 745.7 Watts but there are losses to consider.

It looks like the portable generator builders use 1hp=500watts.

If you have 1 generator connected to 35 engines, your losses will be greater.