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Car Hoist Project - Do I Have Enough Power?

J. McNugget

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My next project: I am hoping to install a used Rotary 10,000 lb two-post vehicle hoist in my shop this coming summer. As some of you know, my shop is not on the grid, and I depend on an assortment of generators to provide the power I need.

The hoist I will buy has a 240 volt, 20 amp on-each-side requirement, and my 12.0 DJC 3CR will provide that. But I am uncertain if I will have enough starting current on a normal 60 degree day, or on a colder 15 degree day? I figure I can lighten the oil one grade set to help with the cold, but I don't want to install it, and then find out 12 kW isn't enough power to start the load. [Getting the DJC started on a 15 degree day (0 degrees is more likely the case) is another story, but propane will be involved :) ]

The generator is located in a shed 60 feet away, and the shop is fed by #2 aluminum wire. The shop isn't large - 28' x 20', so the wire runs in the shop are relatively short.

I can reduce the other loads on the generator to use just 1 kW for lights while the hoist is operating. I can shut off the compressor, heaters, furnace, etc. Do you think I'll have enough power?

The last part of the question is this - if I changed to a 10 kW diesel in the future, will it do the job?

Thanks, and regards at this holiday season.



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might be easier to unload when the motor starts.
a hydraulic bypass, or clutch, or a gear ratio with greater advantage.
you don't have to start under load

cat d9

I cleaned my glasses and now I see you have no utility to the shop, seems like your gen will do the job unless you have a big compressor and then you can always shed the load but those motors aren't that hard starting


I ran my 9 ton hydraulic with a 10KW 3phase when I switched the gen head to a single phase it wouldnt even think about spinning up the motor. So if your unit is 3PH you'll be fine.


Staff member
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Beavisz, That makes no sense at all. Power is Power, wheather it is 3 Phase,
Single Phase, or DC. You have something else going on, not just the
difference in the way the Power is delivered.

Bruce in alaska :crazy: :crazy: :crazy:


True power is power, but you will find almost always a single phase generator is rated at 1 PF, and a 3 phase (because it is usually used for motor power) is rated at .8 PF. The extra apparent power is provided by 20 % more generator and therefore a 3 phase generator will produce more current than the same KW rated single phase unit. An induction motor is a peculiar animal. It draws around 6 times normal current starting, but the power factor is around .25. If you look at a speed /torque/current curve you will see that there is a hump around 80% speed. If the available current required at that point is not available, the torque will fall rapidly and if the required torque is greater than that available at the existing voltage, the motor will remain at that point still drawing near 400% current until the motor fries or with a generator it falls on its butt. The engine will not act overloaded because the actual power needed is less than full rated. Hence one must be carefull around motors powered with generators. New generators at least good ones list their starting KVA capacity as a function of voltage dip. 35% is the lowest dip allowable because below that starters and relays began to drop out and chatter which is a nasty situation for a generator. A generator must be sized with ample power and current capacity at the worst possible condition because it will happen sooner than later. Automatically started motors will start together as soon as they see a generator. A good rule of thumb is 1KW gen capacity for 1/2 HP of motor (both unloaded) A PMG machine will do a little more but generally a generator will produce around 300% current for a few seconds before field collapse occurs. The problem is that it doesn't fall low enough to protect itself. Time-under voltage and over-current are essential for generator protection. A circuit breaker will not protect a generator. A field circuit breaker properly applied will provide adequate protection.

J. McNugget

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Thank you for the replies. If I understand Raymond's final point, I need not worry too much about shutting off other loads (within reason) before using a 2 hp hydraulic hoist motor. The field breaker on the DJC should protect both the load and the generator/AVR.

I also gleened that my Lincoln Ranger 8 welder (with 8 kW available power supply) should also be up to the task. I'm not sure of the type of excitation system it has as there is no obvious AVR or field breaker to snoop around.

I'm going shopping for a used Rotary hoist.