portable generator question (wattage)

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I have a decent sized "costso" gift certificate for Christmas, which I want to apply towards a portable generator.... I have 2 basic choices in the store.
Coleman Powermate 5500 Watt ~ $550 Nikota 3500 Watt ~ $279
My basic questions are;
1. What does 3500 vs. 5500 Watts get me? (generally speaking) 2. If 3500 is enough, is Nikota a brand I should buy? I never heard of them
If it matters,
- This is a backup emergency generator only. No special uses. - I have 2 refridgerators, but I could condense it down to 1 if I had to. - My stove and oven are gas, so I won't need this for those.
Thanks
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I cant vouch for the brand names, but basically, watts are watts. If all you need is 3500 watts, then thats all you need to buy. I personally have a 5550 watt unit for a fridge and freezer. I also run my furnace with the generator, but I dont know where you are located and if you need a furnace. Remember, the wiring should be done with a proper transfer switch, or by using extension cords from each appliance to the generator. DO NOT try and backfeed the power into the house with a male to male extension, or a dryer outlet back-feed situation.
Bill wrote:

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Get the coleman it has a chance of lasting. For 279, you cant get much, a motor you are lucky to get 250 hs out of and voltage that will vary from probably 135-90v or worse, good motors are 250 good gen heads more than 250, and the frame and tank cost.
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If you need 220volt check the 3500 unit. I know the Coleman will give you 220v I think the 3500 unit is 110 only. 220 is needed if you are hooking it up to your service panel.

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want
them
I can't comment on the brand names , but the more watts the beter. The 3500 may not start a well pump if you have one, probably will not run an electric water heater.
One thing to look at is to get one with a large gas tank. Friend of mine had a gen with a small tank and had to check on it about every hour or two during the run time during one winter ice storm outage.
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Years ago, during an emergency, I bought what I could find, and ended up with a 5,000 watt generator (2 phase, about 20 amps per phase). I wired a generator panel with an isolation switch so I can give power to the kitchen, furnace, and sump pump. It has a 5 gallon tank, and uses about 1 gallon per hour. I have used it a few times. I mention this because:
1) If you put 5 gallons in the tank, and the power comes back on after 1 hour, you have 4 gallons left in the tank. Gasoline does not keep, so you have to use it or drain it out.
2) I saw a comment a long time ago that someone had a 2,500 watt generator, and could run it all day on 1 gallon. Probably hyperbole, but you waste a lot of gas if you don't use all the power.
3) You need to balance the load on your generator. 3500 watts is still 15 amps per phase. As long as you don't start both refridgerators at the same time, you should be ok (start-up current is large, but generators do have the ability to exceed the rated output for a short period of time for just such a purpose).
4) Some time spent wiring on a nice day sure beats running cords all over the place on a lousy day when the power fails. It is so convenient, even my wife can hook it up in an emergency (just kidding about the wife part). I ran a 30 amp circuit for the generator into the Garage, where it can sit protected from the elements when running (garage door open). Hardwire is the only way you can supply generator power to the furnace.
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Tokai writes:

That's not 2-phase, but single phase with two legs of opposite polarity.
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Richard J Kinch wrote:

True but if one is going to nitpick then one can *really* nitpick and say that from the point of view of the neutral it *is* two phases that are 180 apart. Phase doesn't have to mean 120 apart.
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Steve Kraus writes:

It's not a nitpick. 2-phase means something, but not what you said.
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On Thu, 29 Dec 2005 00:46:56 -0600, Richard J Kinch

Does the "2-phase" system you're referring to have the 2 phases 90 degrees apart? I seem to have heard of some motors using that.
Both of these (the usual system in homes where the phases are 180 degrees apart, and that other 2-phase system) fit the definition of "phase". Saying one is not 2-phase would be like saying that "AB" is 2 letters but "BD" is not.
For the system with the phases 180 deg. apart, I also hear "Edison System".
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Mark Lloyd writes:

No, it does not fit the definition. Reversing the polarity does not create another phase. (Except perhaps in your imagination.)
A transformer reversing polarity does not create multiphase from single phase.
Multiphase requires a non-zero vector dot product. That's how you get motors to turn.
You might as well say two legs 0 degrees apart are multiphase, because there are two of them.
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Richard J Kinch wrote:

180 degrees out of phase is a different phase, mathematically.
And there's no such thing as the "polarity" of a sine wave.
But you're right in saying that what power distribution folks mean by multi-phase is not the 180 degree case.
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CJT writes:

No. The mathematical definition of phase with regard to electric power involves a non-zero dot product. Simply scaling a phase yields the same phase, even if the scalar happens to be -1.
You might want to have a look at:
http://en.wikipedia.org/wiki/Split_phase
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Richard J Kinch wrote:

I stand by what I said, particularly in the context of what you snipped.
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CJT writes:

In the context of "phase" in electric power, you are in error. That mathematics has a different sense of "phase" is irrelevant.
"A polyphase system must provide a defined direction of phase rotation, so mirror image voltages do not count towards the phase order. A 3-wire system with two phase conductors 180 degrees apart is still only single phase."
-- http://en.wikipedia.org/wiki/Polyphase_system
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Richard J Kinch wrote:

BTW:
http://en.wikipedia.org/wiki/Phase_%28waves%29
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Not really. However, there is instantaneous polarity. At any particular time, the 2 phases will have opposite polarity (disregarding the extremely short zero-crossing intervals). On a 3-phase system, adjacent phases would have opposite polarity 2/3 of the time.
BTW, in radio people often incorrectly say "polarity" for "polarization".

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On Thu, 29 Dec 2005 20:51:54 -0600, Richard J Kinch

It is the opposite polarity (instantaneous polarity). It's also 180 degrees out of phase (the second phase carries the same signal, but starting 1/2 cycle later).

That has to do with the location of the reference point. The reference point is normally ground, such as what's connected to the center tap of the transformer secondary.

I think I understand that. It depends on some definition of "phase" different from the ordinary one.

I never said that. I described 2 or more legs at DIFFERENT angles. How are you equating 0 and 180?
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Mark Lloyd writes:

No, there is only one definition of "phase" in the context of electric power. The various mathematical notions of "phase" are not relevant. You commit the fallacy of "definitional retreat".
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On Fri, 30 Dec 2005 14:13:07 -0600, Richard J Kinch

Unlikely. The word "phase" has meaning, which applies to a lot of things, including mathematics and electric power. What seems to be happening here, is a specialized redefinition that I wasn't using. Sort of the opposite of "definitional retreat".
BTW, how would you respond to the question "True of false: the currents in each leg of a three-phase motor (wye connected) are equal". That question was actually on a test I had once in a NEC class. Some would say TRUE, others know it's FALSE.
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