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Old 10-26-2020, 03:32 PM   #1
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110v to 220v transformer question

We are getting a 3kw inverter generator. 3500w peak. If I get a transformer, I lose half the wattage in exchange for 2x voltage right?

Here is what I'm kicking around, we're looking at the Predator 3500w set from harbor freight. It doesn't have 220v, but is mainly for the trailer and any small remote stuff. We are also planning on a unit for the house (Firman tri-fuel from Costco), lower priority, but nevertheless... We have natural gas heat, but the hvac runs on 220v. I am estimating the fan and electronics for heat only (not AC) probably don't surpass 800w...if that. If I really wanted to, could I use a 220v transformer on the 30amp outlet to power the furnace, and maybe a few LED house lights from the 110v? Or is my thought process off here?
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Old 10-26-2020, 04:04 PM   #2
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When you double the voltage, the amperage is reduced by half, not the wattage. Watts equals voltage times amperage. Example a 1200 watt heater made for a 120 volt circuit draws 10 amps. A 1200 watt heater made for a 240 volt circuit draws 5 amps. Hopefully this helps with your calculations... stay safe!
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Old 10-26-2020, 04:06 PM   #3
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The bigger question is why would you need such a transformer, almost all RV loads are 120V
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Old 10-26-2020, 05:12 PM   #4
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The bigger question is why would you need such a transformer, almost all RV loads are 120V
For his house.
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Old 10-26-2020, 05:22 PM   #5
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For his house.
i was wondering... he can get a lowes clunker that has 220 in it for emergency power, since in a emerg, noise doesnt mater.. well maybe..

I have one , got on clearance years back 249.... works in a pinch,, ran my welder on it in the back field a few times to fix tractor..

The cost of a trans.. may be a bunch for a good one, cheapies are $150ish...for 3000 watt 110 to 220..
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Old 10-27-2020, 09:48 AM   #6
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Thanks. Yes, 220v for the house, we don't have common power issues here, but this scenario just crossed my mind. The most urgent thing we would need in the winter is heat, which doesn't take much power, its just 220v. In the summer the most urgent would be fridge and freezer. AC would be nice, but not practical without a larger unit.

For the house, that tri-fuel Firman from Costco would meet our AC, lights and fridge needs. It's more pricey, but I really like the fact it comes with the fuel kit installed. Just plan to hook it up to our CNG line so it can run as long as it needs to without having to re-fuel.

So from the sounds of it, if I wanted to, that transformer would work in this specific situation in regards to getting to 220v just to run the furnace fan and electronics? I'm not an electrician, but can figure anything out, just want to be sure I understood the transformer properly.
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Old 10-27-2020, 10:39 AM   #7
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Thanks. Yes, 220v for the house, we don't have common power issues here, but this scenario just crossed my mind. The most urgent thing we would need in the winter is heat, which doesn't take much power, its just 220v.
A 220 volt house heating system would probably be rather high amperage, particularly if it's a single forced air electric furnace. That's one of the huge advantages of having a gas or oil forced air furnace--lots of heat with only maybe 600 watts of power.

I don't really see a generator being a good source of electrical resistance heating beyond just buying a space heater to be used when you had other low demand on the generator. Otherwise you would need too large of a generator and too much fuel (assuming you're not on natural gas in which case you'd not likely have resistance heating). If you had baseboard heat the transfer switch issues would also be significant.

If you have a lot of power outages in very cold weather situations I'd look for some other heat source, such as maybe a pellet stove. Very little power, lots of heat.
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Old 10-27-2020, 10:45 AM   #8
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A 220 volt house heating system would probably be rather high amperage, particularly if it's a single forced air electric furnace. That's one of the huge advantages of having a gas or oil forced air furnace--lots of heat with only maybe 600 watts of power.

I don't really see a generator being a good source of electrical resistance heating beyond just buying a space heater to be used when you had other low demand on the generator. Otherwise you would need too large of a generator and too much fuel (assuming you're not on natural gas in which case you'd not likely have resistance heating). If you had baseboard heat the transfer switch issues would also be significant.

If you have a lot of power outages in very cold weather situations I'd look for some other heat source, such as maybe a pellet stove. Very little power, lots of heat.
Thanks. That's why I was thinking this might be a good fit for us in the short term. It's a gas furnace, so no large power draw. Just need to be able to get the voltage up to 220 to run it. Come to think of it... if we lost power in August... we could just stay in the trailer, with AC lol. This conversation may have saved me from a 2nd generator purchase!
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Old 10-27-2020, 11:03 AM   #9
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Are you sure your gas furnace is 220V? Unless it's part of a heat pump system I'd think the blower is only 120v.
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Old 10-27-2020, 11:06 AM   #10
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Thanks. That's why I was thinking this might be a good fit for us in the short term. It's a gas furnace, so no large power draw. Just need to be able to get the voltage up to 220 to run it.
It would be very unusual for a gas furnace to be 240 volt. I'd double check the breakers in your house--I bet it's only 120 (one breaker, not two).

BTW, it's best to get a transfer switch, not only for safety, but that also allows you to limit your demand on smaller generators by only turning on certain circuits.
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Old 10-27-2020, 11:23 AM   #11
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Are you sure your gas furnace is 220V? Unless it's part of a heat pump system I'd think the blower is only 120v.
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It would be very unusual for a gas furnace to be 240 volt. I'd double check the breakers in your house--I bet it's only 120 (one breaker, not two).

BTW, it's best to get a transfer switch, not only for safety, but that also allows you to limit your demand on smaller generators by only turning on certain circuits.
Fair question, wondered myself. I just assumed since the HVAC label in the breaker is a dedicated 220, the whole unit ran on 220 (Whole unit being the compressor, fans, electronics, etc). Ill take a closer look and see what I can find out. Are you thinking there might be a separate breaker for the fans?

Yes, ill be installing a manual transfer switch. Not sure yet if I want to wire loads separately, or if I want to wire the panel, and just kill all the loads I dont want... maybe with a smaller genny better to wire separately...
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Old 10-27-2020, 11:26 AM   #12
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Fair question, wondered myself. I just assumed since the HVAC label in the breaker is a dedicated 220, the whole unit ran on 220 (Whole unit being the compressor, fans, electronics, etc). Ill take a closer look and see what I can find out. Are you thinking there might be a separate breaker for the fans?

Yes, ill be installing a manual transfer switch. Not sure yet if I want to wire loads separately, or if I want to wire the panel, and just kill all the loads I dont want... maybe with a smaller genny better to wire separately...
You probably had a gas furnace with either a heat pump or A/C attached. I think it's likely there's a separate breaker for the furnace, or maybe a sub-panel at the furnace. Even if not I think an electrician could figure out a way to wire the transfer switch so that the furnace would get the 120 it needs.

BTW, since you apparently have natural gas it would be worth considering a tri-fuel generator or conversion. That way you won't have to worry about getting fuel, and if you only use it with NG you won't need to worry about the fuel getting old.
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Old 10-27-2020, 11:29 AM   #13
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You probably had a gas furnace with either a heat pump or A/C attached. I think it's likely there's a separate breaker for the furnace, or maybe a sub-panel at the furnace. Even if not I think an electrician could figure out a way to wire the transfer switch so that the furnace would get the 120 it needs.
Gochya, Ill go check it out today. It's a gas furnace, with AC.
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Old 10-27-2020, 01:22 PM   #14
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Thanks for the info everyone, I appreciate it! Indeed looks like the furnace portion is on 120. I had to start flipping unlabeled breakers to find it.
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