Tue 13 Aug, 2013 12:02 pm
Hi everyone, great site. I've got a sawmill which will be running a baldor 5hp 220v motor. I've heard different things from people as to how much of a generator i will need to get this motor started and then running under load. Because we are off grid i'm thinking of getting a 15kw pto generator.
Baldor have said this 5hp motor takes 23amp to run and 5-7 times that to start. This means buying a pretty big generator.
Seeing as the mill will not start under load, do you think i can get away with a 12-15kw generator to run this?
Not sure where baldor gets their numbers but for a 5hp motor the total power needed to run under normal conditions would be 3730 Watts ( 746 watts/hP) which would than mean 16 amps (P/E). The inrush current would be up to 350% higher than normal current BUT this doesn't mean you need to go by a generator capable of producing 70Amps. You just need to make sure the fuse you are using in the generator is of time delay type.
I suggest you talk to the manufacture of the generator you plan to purchase. The manufactures specifications will sometimes specify the max motor size they are rated to start. Sometimes the generator can be sized smaller than you think while the spec will allow for motor starting. Because you are off the grid there are other considerations in selecting a generator. Also since you mention a sawmill, it makes me wonder about the elevation of your location. Small stand-by generators for residential use do not have an alternator or charging circuit for the generator battery because the battery is charged by the normal power when the generator is not in use. You can purchase a solar panel for charging the battery as an option. Also these smaller residential units are not built for continuous or long term use. You may want too look at a small commercial generator as they should be rated for heaver duty and also have an alternator that charges the battery. In addition you should check the rating of the generator with respect to the fuel type (propane, gas, diesel) and elevation as these all effect the KW rating.
thanks for all the help, i went with a 16kw generator after speaking with baldor. Maybe it's overkill but wanted to be sure