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  1. #1
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    1998 JD 4400

    Default Another PTO generator Q

    So I know there are numerous threads on pto generators and generators in general but I didn't want to hijack anyones thread.

    Like some I am considering a pto generator and am pushing to get one to power the house. I have a 40 hp tractor with a 35 hp pto.. Based on the info on the other threads I would max out the tractor with a 17kw. The one I was looking at was 15kw (rural king) and am concerned if it was enough to power the heat pump and air handler. On the tag on my heat pump it says minimum 21 amps. Also I want to run the hot water heater (20 amps) and a microwave and minimal lights.

    I've got an electrician coming out in a couple weeks to look things over but I'd like to be able to talk intelligently with him and make the best decision. When I talked on the phone with him he said depending on the total amps I may not have enough to power up with the 15kw generator.

    Any help would be appreciated.

    Lee

  2. #2
    Super Star Member kennyd's Avatar
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    Default Re: Another PTO generator Q

    A 15kw genset will be right on the hairy edge for a heat pump-It may run it but will have trouble with the starting surge. And you would not be able to run much else at the same time either.
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  3. #3
    Elite Member BobRip's Avatar
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    Powhatan Va.
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    2000 Power Trac 422

    Default Re: Another PTO generator Q

    I would try to get another form of heat. The startup currents may be as much as six times the running current. I doubt that the 15 KW genset will put that out. Can you heat with wood during power outages or get a gas log? Talking to the genset manufacturer to get you best answer. Lights, TV, radio, and refrigerator are small compared to the heat pump. You well will also pull a lot during start depending upon its rating and the well depth. 15KW will be enough though if the heat pump is not running
    Bob Rip
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  4. #4
    Elite Member RonMar's Avatar
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    May 2005
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    Port Angeles WA
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    Jinma 284 delivered 06/28/05

    Default Re: Another PTO generator Q

    "P" = "I" X "E" That is Power in watts(P) = Current(I) X Voltage(E). If you know any two, you can solve for the third(P divided by E = I, and P divided by I = E). This formula also only applys to electrical loads without a power factor, such as the hot water heater which is a purely resistive load. Inductive loads such as electric motors will use more power because of their power factor. So for an inductive load it would be current X Voltage X power factor = load in watts. 21 amps x 240 volts, with a reasonable power factor(1.1-1.2?) is probably in the neighborhood of 6KW of electrical load.

    15 thousand(K) watts divided by 240V = 62.5A of electric load current that the generator can carry/sustain. When the electrician comes out, have him measure the actual current that the heat pump draws both at startup, and while running using a clamp-on amp meter. The startup current load of an induction motor can, as mentioned be several times the running load. One reason your heat pump may have such a high current rateing is that perhaps it has supplemental electric heating elements in the air handler, that are counted as part of that 21A load. Purely resistive loads like heating elements don't have startup surge loads, and just go right to their rated value. Your hot water heater is probably 4500W, which works out to 18.75A @ 240V. If your heatpump has supplemental heating elements, you may find that the startup load of the heat pump compressor is not all that great, and well within your 15KW limit with water heater and other electrics factored in. One indicator of this situation is the size of the circuit breaker that the heat pump is attached to. How much larger is it than that 21A placard current?
    Ron

  5. #5
    Silver Member
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    1998 JD 4400

    Default Re: Another PTO generator Q

    I have breakers labels for the outside unit that are 40 amp breakers, then I have 2 other sets labeled furnace / ac. one is 60 amp and the other 30 amps. I think the heat pump is as you described with the heat strips. I'm guessing the 60 amp breakers are for the electric furnace and the 30 is for the air handler.... I'm guessing here.

  6. #6
    Elite Member SnowRidge's Avatar
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    East Tennessee
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    Power Trac PT-425 / Branson 3520

    Default Re: Another PTO generator Q

    My heat pump has a separate breaker for the heat strips. Most, if not all heat pumps can be wired that way. If yours is on a single breaker, you could have an electrician rewire it for dual breakers.

    You also may have one or more disconnect switches located near each unit. The heat strips may be on a separate disconnect switch. If they aren't, it would be relatively inexpensive to add the second disconnect.

    With the heat strips on a second breaker and/or disconnect, you can, and probably should, turn them off when you are on generator power.

    Edit: The 60 amp breaker is probably for the heat strips alone, which should be confirmed.
    Last edited by SnowRidge; 10-31-2008 at 08:43 AM.

  7. #7
    Gold Member
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    Nov 2006
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    South Central Georgia
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    Kubota L4400

    Default Re: Another PTO generator Q

    Most heat pumps will have elect strip heat in the air handler to carry you through the defrost cycle in the heat pump. A 3 ton unit will have approx 10 to 15 kw of strip heat which would use up all your gen output leaving none for the outside unit to defrost. With that said you can disconnect the strip heat and just live with a cool blast of air during the defrost cycle. this is not the best but in an emergency it will work OK and be much better than nothing. I have found the best way to size a gen is to contact the manuf. od all your loads, heat pump ,well pump , waterheater, etc. they will give you specs and recomedations on gen size and starting and running currents of their units.
    Jack

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  8. #8
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    JD2010, Kubota3450,2550, Mahindra 7520 w FEL w Skid Steer QC w/Tilt Tatch, & BH, BX1500

    Default Re: Another PTO generator Q

    Quote Originally Posted by L_Nicholson View Post
    I have a 40 hp tractor with a 35 hp pto.. Based on the info on the other threads I would max out the tractor with a 17kw. The one I was looking at was 15kw (rural king) and am concerned if it was enough to power the heat pump and air handler. On the tag on my heat pump it says minimum 21 amps. Also I want to run the hot water heater (20 amps) and a microwave and minimal lights.

    I've got an electrician coming out in a couple weeks to look things over but I'd like to be able to talk intelligently with him and make the best decision. When I talked on the phone with him he said depending on the total amps I may not have enough to power up with the 15kw generator.

    Any help would be appreciated.
    Lee
    I run a 12kW/13kW[surge] with an L2550 27HPpto. It starts a heat pump fine. It starts the compressor fine. It will run them both and start either concurrent with all incidental house and barn loads. It may even start them together, but I would have to contrive it --the chances of a simultaneous start are low. Locked rotor starting currents are hi, as mentioned prior, but they subside as soon as the motor starts to turn, and in most applications the motor will start its load even if the voltage sags a bit during start. If I were using the welder I would surely do some sequence planning. The 15kW [continuous??] will do you fine. At the very worst you will have to do some planning with water heater use-I doubt it tho.
    larry
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