Help with generator selection--7000 Watts OK?

jeanie_bethSeptember 14, 2008

I just got my power back on after Ike knocked it out in SE TX. I would like to buy an inexpensive generator without paying tons of money.

I found a wholesaler that sells wholesale generators. He has a 7000 Watt gasoline generator for $550. It comes with electric start (I supply battery) and pull start.

It has 110V receptacles and one 220 receptacle.

My question is, how much power is "7000 Watts"?? I just want to power a couple of refrigerators to keep my food safe and a few light bulbs and fans for when power is out--at most 24 hours.

What I am saying is that I don't really know how to figure up my wattage needs vs. the output of the 7000 W generator.

I know I can't power a central air system with this, but I do have a 12x22' portable building with a 110V 5000 BTU window unit AC in it and a bed. I could live in this little building if I had to.

My question, is 7000 Watts "OK" for my needs--again, I don't want to power the whole house, just refrigs and a few lights & maybe the portable building.

Is $550 for a 7000 Watt generator OK?

Do any of you know of other forums for "generators" as I would like to learn more about genning my own power now after Ike passed thru.

Thank you!

Jeanie Beth

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If you really can limit your loads to "a few"(lets say "a few" is 4) lights and fans plus 2 refrigerators, a rough estimate of your load would be about 3300 running watts and 5800 if all the loads started at once. Your AC unit would add about 1200w running and maybe 2400w on startup.

A well made 7000 watt generator would probably run that just fine. On the other hand, a cheaply made unit would do well to last a few hours. (See the "generac generators" thread) Remember, you usually get what you pay for-- the price you mention won't buy much of a generator anywhere that I know of. The link below is one of many power calculators on the web.

Here is a link that might be useful: Kohler calculator

    Bookmark   September 14, 2008 at 4:32PM
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As Wayne said, you can actually run quite a bit with a 7000 watt generator.
You need to buy quality or you may find yourself without power when you want it most.
You might want to consider a power inlet and interlock kit on your main panel.
This gives you the convenience of having all circuits available for use as long as you manage the load.
I'm betting that the $550 generator is some kind of generic Chinese junk.
Don't waste your money on these. If you want portable, look at Briggs and Stratton, Honda, Coleman, etc., not Chung King or E Fu Young.

    Bookmark   September 14, 2008 at 5:18PM
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I agree with the others on both points:
- 7k watts is plenty for what you want to do.
- $550 is WAY too cheap for a 7k watt generator.

    Bookmark   September 14, 2008 at 5:40PM
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Having a commercial 6500w unit with a 13HP Honda, and friends with cheapo units, I have never had a problem, get nearly twice the operation time on a gal of gas and never lost an appliance. Can't say the same for freinds that saved money on the gen but ended up buying anouther one shortly after and lost some equipment they were powering besides.

    Bookmark   September 14, 2008 at 6:06PM
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There are about 760 watts to a horsepower at 100% efficiency.

Any time the numbers do not come out correctly someone is puling a fat one.

Most of the time the actual efficiency is less than 50%.

    Bookmark   September 14, 2008 at 9:53PM
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I agree with some of the other posters that $US 550 for a 7000 KW generator seems a little too cheap. I think what you need is a petrol based portable generator as opposed to the larger propane fueled stationary units.

Before getting my generator two years ago, the petrol one I considered was the Honda EU6500ISA. Back then it was just over $US 2000, I see now it it more in the $US 3,500 range. Almost as much as some of the Generac propane powered ones if not more.

The things I like about the unit are:
1) It is on wheels -- generators are heavy
2) Electric start (with remote if needed) and also hand start
3) Low noise
4) Inverter technology -- this is significant in that it give you lower fuel consumption, lower noise and cleaner power for computers.
5) Nicely enclosed unit, hence OK in some rain and some wind

Remember to buy a big lock and chain. In a power outage people tend to steal them.

Best, Mike.

Here is a link that might be useful: Honda Generator

    Bookmark   September 15, 2008 at 6:58AM
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>>a cheaply made unit would do well to last a few hours.

What is most likely to fail in this size Chinese unit, the engine or electrical? How many hours are the sleeve bearings in the alternator good for? The referenced threads are mostly about bigger units.

They certainly do play with the numbers. I have a Coleman "6875 surge/5500 average" with 13 HP Honda. I was told if the governor is set no load for 62.5 Hz, 3750 RPM it puts out 125 V, which is the max I would want to allow. Then at full load it would run 57.5 Hz, or 3450 RPM, and 115V minus the wire resistance drop. They didn't say whether "full load" was 5500 or 6875 watts, so I'm expecting the lesser.

At 3450 RPM the engine is actually only 10.8 HP. That translates to 8050 watts at 100% efficiency. To get 6875 watts would need 85% efficiency, which strains credibility. I suspect 6875 is what it can put out for a fraction of a second while the flywheel is slowing down from 3750 to 3450 RPM. For even a few seconds it probably won't do much over its continuous rating of 5500 watts.

And 5500 watts would be about 67% efficiency, which might be possible but is better than I really expect. The cooling capacity of the unit might be strained at that continuous load.

In the end, I wouldn't plan to load it up to more than 4 KW. I got mine to run the refrigerator and furnace blower every few hours if we are out of power in an ice storm.

Also, consider the fuel requirements if you are trying to run such a machine at capacity continuously. Your lawn mower gas can won't cut it.

    Bookmark   September 15, 2008 at 9:57AM
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"There are about 760 watts to a horsepower at 100% efficiency"

That doesnt jive on my MultiQuip contractor generator.
6.5KW/13 HP Honda

Perhaps that's why mine never sounds loaded and is probably 60% the db of any similar rated gen.

I can also run 15 hours, full load with 6 gallons

    Bookmark   September 15, 2008 at 11:45AM
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At 100% efficiency, 1 HP = 745.7 watts.

    Bookmark   September 15, 2008 at 12:34PM
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ZL700, that is not what Brick meant. He meant electrically there is 746 watts per motor HP.

He was not making a generator engine HP to output watts comparison.

    Bookmark   September 15, 2008 at 5:07PM
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A typical properly specified small gen-set will have 2 engine hp /KW. The Honda example is right in the ballpark.

In reference to "... What is most likely to fail in this size Chinese unit..." the answer is whatever part is the most difficult to repair or replace at the time.

Ironically, I just returned from an errand to check on a Honda powered "5850 watt" generator, which was placed in service at about 5 am today. The owner had fuel on site and assured me that it had only run out of gas. I arrived to find the set silent, still half full of fuel, with the ignition in the "on" position. It restarted on the first pull, but to run how long?. Fortunately commercial power was available, so I didn't have to diagnose the issue.

I have had good luck with my rule to buy sets based on weight and engine HP rather than decal numbers. When you see labels that have words like surge, peak, starting watts, and so on, you can safely bet that marketing had more say in the decal numbers than engineering.

    Bookmark   September 15, 2008 at 6:41PM
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Thanks for all the input I am even more confused than I was before with all the talk of surge, strains, flywheels, etc. :)

Anyway, I looked at the generators that the supplier has for sale in the box. I copied the website down.

The supplier has the TG7000 & the TG8250. TG7000 is $550 wholesale.

When I go to the website of the manufacturer:

In the picture they show the TG7000 on the website, it is not the same as the TG7000 I looked at in the box. The one on the website says TG7000 but the picture shows TG6700. The one pictured is not on wheels on the website. The TG7000 I looked at in the box is exactly the same as the TG8250 I looked at in the box except it is rated a little higher.

What I am saying is that the TG7000 is identical to the TG8250 except for the output--they are both on wheels, same looks, the 8250 is slightly bigger in size. Why they are showing a TG6700 not on wheels in the picture on the website as the TG7000, I don't know. I guess they have "upgraded" the TG6700 to a TG7000 and just haven't updated the picture.

Anyway, yes the generators are indeed made in China. Company supplier is ETQ Eastern Tools out of Ontario. The supplier here in Texas is getting more in a couple of days.

I just don't know whether I should or should not buy one now.

Honda & Coleman are all sold out within 100's of miles of Ike's path.

The supplier of these generators has sold 100's of these in last few days for wholesale customers to resale and is getting 18 wheeler loads in Thursday. I'm not wanting to resale them, I just want to buy ONE for my house and since I can buy it wholesale, thought it might be OK for my limited use...

I'm still confused...

Thank you!

Jeanie Beth

When you're hot, humid, hungry, and gonna be out of power for at least a few more weeks, I guess you get desperate and buy anything.

    Bookmark   September 15, 2008 at 8:29PM
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time like this you take what you can get and pray it lasts thru the outage. if it does, then you will have got your money's worth out of it!

i say get the genset, but plan on replacing it with a much better unit later.

    Bookmark   September 15, 2008 at 9:14PM
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If you choose to follow D&K's advice and get what you can out of an inexpensive gennie (and I'm not criticizing that option, BTW), please, please take care in figuring out how you'll use the generator.

The best long-term backup solution involves some non-trivial wiring issues to operate safely and conveniently. Namely, if you want to hook the generator directly to one or more of your house or outbuilding circuits, you'd need to have a transfer switch installed to guarantee isolation of generator power from grid power.

THIS IS IMPORTANT. Among other potential hazzards, your generator could feed power back to the power company's transformer and zap a lineman working to restore power.

A short-term alternative is to run the generator as a stand-alone unit and feed selected appliances with extension cords. In your case, that'd mean fairly heavy duty extension cords to the two refrigerators and a couple of others for a few lamps and maybe the small air conditioner.

It may be inelegant--even ugly--but it'd probably work and it's safer than connecting the generator to house circuits without proper planning and preparation.

As for figuring out the loads, you can play around with them by incrementally adding and subtracting things. For example, get the genset running and plug in one refrigerator and then the other (so they don't start up simultaneously). Then add a few lamps and, lastly, the air conditioner.

In a pinch, you may find that you'll need to alternate loads. For example, unplug the refrigerators and let the air conditioner run just long enough to establish a bearable room temperature. Then swap back.

If all this sounds "Rube Goldberg", well, it is. But any port in a storm, right?

    Bookmark   September 15, 2008 at 10:12PM
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Thanks again guys, I understand now what you mean about load startup.

As for safety stuff, I do have a "generator manual transfer switch" that was purchased at Lowes hooked to the electric main switch box inside of my laundry room. It has a big socket to plug a generator into. It has never been used as I've never had a generator before. Ex hubby had that put in a few years ago.

This box came with a big thick 20' or so cord to go to a generator.

The only thing I don't understand now is how to get the big plug/cord from the box to the OUTSIDE of house to yard to the socket on the generator.

I know it could just be run out the door of laundry room to the generator in yard, but then I couldn't close the door as the cord is so big.

I went to Lowes and asked the young girl there in electrical dept. and she said she didn't know of any kind of "box" or contraption to run/hook a cord thru a wall and I would probably just have to cut a hole in house and plug it with something removable such a piece of capped off PVC pipe.

Surely they make some kind of electrical plug or box to join this cord from generator to transfer box don't they?

If so, what is it called and what do I need to ask for at Lowe's or Home Depot? I realize the girl in the electrical department knew about as much about this as I did and it was the blind leading the blind.

I sure hope they make something prettier than a hole in wall stuffed with a PVC pipe and caps.

If not, I guess I'll have to get a local handyman just cut a hole thru wall to outside and plug it up with something as there are no windows in this laundry room where the main box is.

Thank you again guys,

Jeanie Beth

    Bookmark   September 15, 2008 at 11:27PM
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Do you have a dryer in your laundry room? You are not going to have enough power to run your dryer anyway, you might move it out and run the cord out the vent hole as a (very) temporary solution.

    Bookmark   September 16, 2008 at 6:49AM
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if you are going to get a handyman to cut a hole anyway, why not just get an electrician to wire you a plug OUTSIDE that runs back to the transfer switch. or if the transfer switch cannot be rewired for that get him to run a plug out side and one inside, then use a short jumper from teh inside plug to teh switch.

keep in mind that running a genset right up close to teh house is a no-no, espcially if it is under a porch/carport/garage. people die in every big storm due to carbon monoxide poisoning from putting a genset somewhere that allows exhaust to enter the house. i keep my generator under the back porch, but when i use it i move it out in the yard. even then i have had a whiff of exhaust in the house a few times!

    Bookmark   September 16, 2008 at 10:23AM
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