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Can, theoretically, a 120V/208V generator be rewired for 120V/240V?

Can, theoretically, a 120V/208V generator be rewired for 120V/240V?

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  #1  
Old 12-14-12, 12:44 PM
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Can, theoretically, a 120V/208V generator be rewired for 120V/240V?

I've seen a very nice generator on Craigslist, Winco 30kW, propane, currently mounted on a trailer, about three grand. It's listed as 120V/208V though, not 120V/240V like my house uses.

I found the attached picture on the Internet for how 208V and 120V can be derived.

It looks like, to my not-well-enough-trained eye, like one could move the 208's neutral wire to either of phases A or C, or could move the neutral to A and the B to C, and have 240V.

Is this right? Would a generator capable of outputting 208V also have the necessary circuitry or whatever in order to do this rewiring?
 
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  #2  
Old 12-14-12, 01:02 PM
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Looks like 3-Phase. You can run single phase from that, but then you'll be worrying about load-balancing. You'd also end up with less generator efficiency.

I know they sell converters to run three phase equipment from single phase outlets, so I assume there is something that does the opposite.
 
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Old 12-14-12, 01:10 PM
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I suppose I should reiterate that I don't know if this is the only way to derive 208V, or how this particular generator comes up with it.
 
  #4  
Old 12-14-12, 01:28 PM
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Not an electrician, but you can get 240 from that gen. a,b,neutral.

Your issue will be the gen will be unbalanced and pulling from one winding. Will get bad vibration.

I do not think this is what you want.
 
  #5  
Old 12-14-12, 01:35 PM
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Well, if I bought this thing, it would be to do as much of a whole-house application as possible, could I make two separate 240V circuits and a pair of 120V circuits? I'd be putting a heatpump on one that draws 22kW at start, 5.6kW while running, a couple of hot water heaters on, and the air handler... I could balance so that each phase gets a proportional load...
 
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Old 12-14-12, 01:52 PM
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You have to do a ZIG Zag configuration. You will lose the gen rating and will only produce 20kw.

Re-wiring a three phase generator | AnOldMan.com

Are you sure the heat pump takes 22 kw to start? Seams like a lot.
 
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Old 12-14-12, 01:59 PM
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Sounds like a bad idea. The load would have to be balanced constantly or you'd burn up the transformer and/or any single phase equipment hooked up to it because of over/under current.
 
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Old 12-14-12, 02:06 PM
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You have to do a ZIG Zag configuration. You will lose the gen rating and will only produce 20kw.

Re-wiring a three phase generator | AnOldMan.com

Are you sure the heat pump takes 22 kw to start? Seams like a lot.
That's actually the small 3 ton unit's claim on the manufacturer's sticker on the side of the outside housing. The 5 ton unit, which I'm currently leaving off, takes almost 34kW to start according to the sticker.

What I am curious about is if the unit can handle instant demand loads in excess of its long term load, and what that would be.

Sounds like a bad idea. The load would have to be balanced constantly or you'd burn up the transformer and/or any single phase equipment hooked up to it because of over/under current.
How do standard 240V, single phase with 120V split-phase-center-tapped generators do it then? I'm not asking to be snarky, I'm curious.
 
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Old 12-14-12, 02:18 PM
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How do standard 240V, single phase with 120V split-phase-center-tapped generators do it then? I'm not asking to be snarky, I'm curious.
Both windings are 180 degrees in a regular gen. The power is drawn even from both windings in a 240v application.

The center tap is not off the center of the winding like on a 3 phase gen.


 
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Old 12-14-12, 02:43 PM
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Makes me wonder if a rotary phase converter to go from three-phase to single-phase would be a good idea if I want to keep the available wattage up. I know that there are single-to-three phase setups out there, I would hope that there are reverse as well...
 
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Old 12-14-12, 03:00 PM
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You would need to use a transformer. The cost involved would be high. Just go out a but a 20kw gen, single phase.

Generac Guardian 5887 Standby Generator - 20kW Aluminum Home Standby Generator

Plus the unit you describe has a 3.0 l engine. Do you realize the fuel this will consume? LP right?

You may want to rethink what you want to power....
 
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Old 12-14-12, 07:29 PM
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Originally Posted by lawrosa
Are you sure the heat pump takes 22 kw to start? Seams like a lot.
That's actually the small 3 ton unit's claim on the manufacturer's sticker on the side of the outside housing. The 5 ton unit, which I'm currently leaving off, takes almost 34kW to start according to the sticker.
What is the make and model number of your units? Or, can you post pictures of the data stickers?

I have a 200A service, which is the largest standard service available. That means I have 48kW available, max, for all loads combined. My service would not handle both of those loads at once. In fact, it would have difficulty handling the 5 ton unit by itself.

Do you have a larger service?
 
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Old 12-14-12, 08:55 PM
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If the generator you are looking at is a 120/208 three phase generator it is likely a Wye or star configuration. With a Wye you have 208v between ungrounded conductors (hots), and 120v between each hot and neutral.

The diagram you posted is for a Delta configuration. In a Delta you have 240v between hots, and 120 between A and C phase and neutral. (however in this cases it is not neutral as it is not the same voltage between each phase.) Voltage between phase B and neutral is 208v and is called the high or wild leg. You only use phase B for hot to hot or three phase loads.

There is likely nothing wrong with using a Wye generator, but the 208v mill cause your 240v equipment to draw more current. Most 240v stuff will run fine on 208v.
 
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Old 12-15-12, 01:22 AM
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The drawing shown in the original post is of a generator (or transformer) that has a delta winding with the C-A phase center tapped to provide 120 volt single phase power in limited amounts. Unless specially wound the limited amount of power available from a center tapped coil is around 5% of the total power of the generator or transformer. Drawing more than that for a significant time WILL burn up that coil.

No, that generator may not be rewound for single phase service because the slots in the stator are wrong. Nor may it successfully be reconnected to 240/120 single phase service for many reasons.

Using a rotary converter is possible but not smart. A rotary converter is essentially a motor-generator set although some are wound on a single shaft with two sets of stator coils and assembled as one machine. I seriously doubt that you could find a 240 volt three-phase inlet with a 240/120 volt single phase output as there are so many less expensive ways of obtaining single phase service. At the very least you would be running TWO pieces of rotating machinery with all the attendant noise and mechanical maintenance they require. The overall efficiency of such an arrangement would be fairly low when compared to the proper generator.

No, the generator in question is NOT a bargain, even if it is free, if the intended use is for residential standby service.
 
  #15  
Old 12-15-12, 06:02 AM
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Military generators (the larger ones anyway) are designed to be easily converted between delta and wye configurations. But what you have is not the way to go. You might look into picking up a surplus 30KW MEP series generator at a DRMO sale. But even that isn't ideal - they run on diesel fuel and are pretty noisy. What you really need is a purpose-built standby unit.
 
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Old 12-15-12, 07:45 AM
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I think I found the generator in question on CL in AZ. That is a 3 phase generator, likely wired in a Wye configuration since it is 120/208. (206? in the posting) You could use it, but as others mentioned, it would likely be easier to find another one designed for your home for the same or less money.
 
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Old 12-15-12, 08:38 AM
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I think I found the generator in question on CL in AZ. That is a 3 phase generator, likely wired in a Wye configuration since it is 120/208. (206? in the posting) You could use it, but as others mentioned, it would likely be easier to find another one designed for your home for the same or less money.
If you did in fact find the generator and it is in fact a 120/208 volt Wye configuration, the diagram in the OP's first post doesn't match that configuration. The diagram in the first post is a 120/240 volt Wye with a wild leg. I agree, it would be easier to find a single phase generator.
 
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Old 12-15-12, 09:18 AM
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Actually the diagram is a delta with a high/wild leg.

I think many posters were a little confused by the diagram and the OP's post. He found the picture on the Internet and was trying to figure out how it could be 208v, not knowing that 208v is a common voltage of a 3 phase Wye configuration.

I found the attached picture on the Internet for how 208V and 120V can be derived.
 
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Old 12-15-12, 11:17 AM
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Yeah, I'm no expert.

I've uploaded pictures of the labels. Two heatpumps, the air handlers for them, and the sticker on the water heater (of which I have two with the same characteristics).

I do see that they can run on 208, now that I look at the pictures again.
 
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Old 12-15-12, 11:20 AM
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Yes, most 240 volt equipment will run fine on 208v. Some HVAC equipment you may have to change a tap on the control transformer.
 
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Old 12-15-12, 04:25 PM
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That's actually the small 3 ton unit's claim on the manufacturer's sticker on the side of the outside housing. The 5 ton unit, which I'm currently leaving off, takes almost 34kW to start according to the sticker.
Startup load, or LRA, isn't what you need to consider in sizing the circuit, the breaker or the load on your generator.

I'm not able to determine the actual demand for your HVAC equipment from the pictures you posted, because the label in the second picture wasn't filled out by the installer - or his/her marks have faded off. Maybe an HVAC pro can.

I do note that every piece of equipment you've shown is made to work with 208V power. That's a common standard these days, so that the manufacturer can make and sell the same unit for either commercial or residential use. If the generator you've found is a 208Y/120V unit, as Tolyn thinks it is, you may be good to go.

What are the actual specs on the generator?
 
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Old 12-15-12, 05:04 PM
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All the info you need is on the labels:

Picture #1 MCA 22.5 MOCD 35
Picture #2 6.1 FLA
Picture #3 MCA 31.9 MOCD 50
Picture #4 4.3 FLA
Picture #5 is a water heater: 4500/3380 watts @ 240/208v

Info from the CL ad:

*Volts 120/206
*Hertz 60
*RPM 1800
*AMPS 104.0
*KW 30
*Fuel Propane/LP
*Model B350S-4R/DLP
*(Very Low Hours) 0233.3
 
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Old 12-15-12, 05:25 PM
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All the info you need is on the labels:

Picture #1 MCA 22.5 MOCD 35
Picture #2 6.1 FLA
Picture #3 MCA 31.9 MOCD 50
Picture #4 4.3 FLA
Picture #5 is a water heater: 4500/3380 watts @ 240/208v
OK, got it - wasn't thinking with all the burners on, I guess. Thanks.

Just over 81 amps for everything put together.
 
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Old 12-15-12, 06:34 PM
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Sorry, I forgot to mention, no heatstrips or other accessories in the air handlers. Just the fan.

A revised ad for that generator actually said 208V. My guess is that 206V was a misprint.

The first picture I posted was something I found on the Internet. As I stated, I do not know how 208V is generated, that picture seemed to make sense, but I wasn't sure if there were other methods of achieving 208V. Additionally since the generator model number and derivatives of that model number do not come up in Internet searches and therefore does not tell me anything about the generator.

Suggestions about what size unit would actually work would be appreciated. My in-laws only lost power from the hurricane for an hour, but a friend's mom lost power for eight days. I know that it's unrealistic to power my whole house and up to the 200A service my house has, but powering a heatpump and air handler, a hot water heater, and a handful of 15A and 20A circuits would be nice.
 
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Old 12-15-12, 06:52 PM
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Actually the diagram is a delta with a high/wild leg.
Wow!! Sorry about that, you are right. Don't know what I was thinking other than I needed more coffee. :bad poster:
 
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Old 12-15-12, 07:18 PM
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I dont know about that particular generator, but many generators of that size come with 12 leads out of the generator end and those 12 leads can be connected in a variety of 3 phase and one phase voltages. It might be worth a call to winco to find out if that particular generator model can be reconfigured to a one phase 120/240 output.
 
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Old 12-15-12, 09:43 PM
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It might be worth a call to winco to find out if that particular generator model can be reconfigured to a one phase 120/240 output.
Given that all of the OP's single-phase appliances are labeled as accepting 208V, that's what I'd feed them. Starting to modify the generator can run its status as a bargain down in a hurry, not to mention changing its UL listing.

T-W-X, you use any two hot legs off a 208Y/120V service as if they were the two hot legs of a 240V single-phase service. That's it. Ignore the third leg. Your appliances should be just as happy on either one. You can double-check that with the manufacturers to be sure.
 
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Old 12-16-12, 06:45 AM
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The first picture I posted was something I found on the Internet. As I stated, I do not know how 208V is generated, that picture seemed to make sense, but I wasn't sure if there were other methods of achieving 208V.
Here is how:
Name:  wye.jpg
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Rewiring the generator would likely not be cost effective and may not work. IF you really needed 240 volts for something, installing a buck/boost transformer would be the better option.

I still believe the generator is not a good fit. You still would be better off just getting a whole house stand alone generator and transfer switch. I would think you could get an entire setup for the $3300 they want for this one.
 
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Old 12-16-12, 10:26 AM
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I think then, I'll just keep out on the lookout for a more appropriate generator. This one appealed, in part, because it uses a Chrysler Slant Six as the prime mover, which is both darned-near indestructible and an engine that my friends and I are innately familiar with as we're Mopar enthusiasts.

Anyone have any suggestions as to what I should look for, in kW output? Here's a basically complete list of my house's electrical circuits/appliances:
  • 240V 5 ton heatpump and air handler on house for bedrooms
  • 240V 3 ton heatpump and air handler on house for living spaces
  • 240V Hot water heater for bathrooms
  • 240V Hot water heater for kitchen and workshop
  • 240V cooktop
  • 240V oven
  • 240V clothes dryer
  • Eight 120V 15A circuits
  • Eight 120V 20A circuits

And the shop:
  • 240V 4 ton heatpump and air handler
  • 240V air compressor
  • Four 120V 20A circuits

I would want one air conditioner (preferably the 5 ton) and one hot water heater (for the bathrooms) a handful of 120V circuits for the fridge, lower power kitchen appliances like the convection toaster oven, some lights, and the sewage lift pump in the basement, but we could probably do without the oven, cooktop, one heatpump, one hot water heater, and if the outage is under a week, the clothes dryer and washer.

The workshop is unimportant other than the fridge out there, but it's one of those Whirlpool Gladiator units with the huge wheels, so I could wheel it out of the workshop and into the attached garage. I also have a 120V portable air compressor so even if I needed compressed air for some odd reason I still have it, and anything temperature sensitive, like batteries for power tools could just be brought into the house.

Obviously I'm not opposed to being able to power the whole house at once though... *grin*

Suggestions at to what to look for are much appreciated. Propane is probably the best choice for fuel since even my wife can handle propane cylinders, albeit small ones...
 
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Old 12-16-12, 10:41 AM
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Suggestions at to what to look for are much appreciated. Propane is probably the best choice for fuel since even my wife can handle propane cylinders, albeit small ones...
I think you will need to do the math....

How long do you think that slant 6 gen will run on a #20 gas grill tank?


I believe you will need to re think what you want to power. Is propane all you have available?


 
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Old 12-16-12, 10:46 AM
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Do you have gas to the house or is everything electric? Most standby generators you can just run a gas line off your NG meter, or house propane tank, and you would not have to mess with any tanks.

Find the watts of each item you will want to run at the same time. (volts x amps = watts) then you can shop around for a generator that meets that KW.
 
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Old 12-16-12, 10:54 AM
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Anything big enough to let you keep living as normal in the house will require a BA gennie permanently installed and with a permanent fuel source like NG or a large propane tank. I may have missed if you have NG available.

You have an electric home....that can make it tough.

If you prioritize what you want or need...then maybe you could get away with something else.

Just my non-pro opinion. $5K for a NG gennie and all the other stuff and yer done.


I do have to ask....do you guys down south really lose power that often? Longest I've gone is about 4 hrs.
 
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Old 12-16-12, 11:58 AM
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IMO if you really want to run and start those items I believe you would need at least a 45 kw.

Kohler 48RCL-120/240 1PH Standby Generator - 48RCL - 48 kW Emergency Standby Power Generator

Then at 5 gallons of propane per hour you would need at least a 500 gal tank IMO. Holds 400 gallons.

400/5 = 80 hours run time at 1/2 load.

LPG Propane Tanks - 500 Gallon - San Antonio and Bandera


AZ propane price is probably $3 bucks a gallon.

So $1200 bucks and you can run for 4 days or so. Then you will need to call and get the tank refilled for another $1200 to run another 4 days or so.

Thats just my quick calculation anyway....
 
  #34  
Old 12-16-12, 02:13 PM
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Obviously I'm not opposed to being able to power the whole house at once though... *grin*
A generator that backs up the full service, that starts automatically and transfers the power automatically, and that performs a self-test once a month is always my first, second and third choice.

Given the loads you've listed as the ones you want to back up, it shouldn't take much more to do that. You can plug your data into a tool such as the Free Electric Load Calculator to get started.

if you really want to run and start those items I believe you would need at least a 45 kw.
I'm guessing about half that. Maybe 25kW. Remember that the startup load doesn't need to be included. The calculation for all of your HVAC plus one water heater only came up to about 19kW. Yes, you still need to add your cooking appliances in, but, since you don't need both heating and cooling at the same time, you might even see a lower value once you choose one of those. Choose whichever one gives you the higher demand, BTW.

Suggestions at to what to look for are much appreciated. Propane is probably the best choice for fuel since even my wife can handle propane cylinders, albeit small ones...
Personally, I'm not fond of swapping out propane cylinders every few hours around the clock, plus being in the dark while I was making the swap. A couple of big cylinders with an automatic cut-over, maybe. As lawrosa asked earlier,
How long do you think that slant 6 gen will run on a #20 gas grill tank?
Do you have NG available anywhere you? If not, I'd look into getting an LPG tank. With either of those fuels, I'd also look into replacing the heat pumps with gas packs.
 
  #35  
Old 12-16-12, 03:10 PM
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No natural gas, all electric. I've been meaning to contact the gas company to see there's any service available, but I doubt it. They tend to do whole developments or not at all around here.

The bulk of my cooking could be on the barbecue grille, provided that the weather is not so horrible as to make it impossible to cook outdoors. That's why I'm not too worried about the cooktop or the oven; we use the cooktop frequently but the grille has a side burner, and the countertop toaster oven has essentially replaced the conventional oven.

As to why, we don't lose power very often, but neither did my friend's mom in Greenwich, CT either, and those were some pretty awful days even though it hadn't yet gotten too cold. Here it's a matter of the ambient heat, especially in the summer months when so many air conditioners running means that there have been blackouts at times.

I can see why propane could be a headache if I'll be going through 20lb cylinders, though there are some bigger cylinders with the same fittings. I just don't know about the fuel, I don't have anything that currently runs on diesel (though I'm considering the cummins swap on my '82 dodge) so it's not like I could use up the fuel when it gets old if I don't end up having to run the generator often. I also only have 5 gallon jerry cans for refilling a generator tank, so refilling ten or twenty gallons at a time could make for a slow process...
 
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Old 12-16-12, 04:31 PM
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LPG, filled by the company? Use it for the heat source in your combo units, your indoor cooktop, your water heaters, your clothes dryer, your outdoor grille and... oh, yes, your generator.
 

Last edited by Nashkat1; 12-17-12 at 08:22 PM. Reason: typo
  #37  
Old 12-16-12, 04:34 PM
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It took 34 years of my life before I experienced an extended power outage. I recently picked up a small generator. It'll be enough for the refrigerator, boiler, and electronics for communication. Depending on weather, the gen won't need to run 24/7, making fuel supplies last longer. Keep in mind that making your own electricity costs a lot of money vs. buying from the electric company. So keeping your generator as small as possible will help extend run times and your wallet.
 
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Old 12-17-12, 06:48 PM
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I don't know what propane is in AZ but here (MN) i it is $1.69/gal.
 
  #39  
Old 05-15-13, 06:06 PM
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Read the generator DATA PLATE

If it says it's a 4 lead stator, you're screwed. If it says it's reconnectable for 120/240 1PH you're good. Keep in mind if you leave it as it is and try running 240V 1PH equipment on 208 your amp load will increase. There should be a reconnection diagram on the inside cover of the generator panel where the leads come off the stator.
 
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Old 05-15-13, 06:16 PM
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Equine, this discussion ended last December. I'm sure the OP has resolved the issue by now.
 
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