Cheap, True Sinewave inverter from Xantrex(battery backup power)

[mark d fellows]

As we have covered this subject many times, I don't want to go back and forth. However, I have found a much cheaper alternative to Harman's Surefire 512H backup inverter.

It is called the Xantrex Prowatt SW. SW I would guess stands for Sine Wave. It is a True Sine Wave inverter for a fraction of the cost of other models. The unit I bought was 540 watts nominal with 1200 surge watts. These are important stats as Pellet stoves have AC electric motors in them that consume much more power on startup. Once the motor starts it uses the normal power, but until the motor spins creating a magnetic field and EMF you can almost have a short for split seconds. Regardless motors use more power on start-up as many on this forum know. I put those facts in for the Newbies.

I bought the True Sine Wave inverter from Manventure outpost for 134.00 plus 15 dollars expedited picking and packing and 2 day UPS. Great company by the way. Good service, and fast shipping.

http://www.manventureoutpost.com

Go to search feature and type in Xantrex Prowatt Sw and it will pull up a list of them. For some reason, I can't link directly to the product, but the link below works for a list of them.

http://www.manventureoutpost.com/search.php?search_query=xantrex+prowatt&x=0&y=0

The 600 SW is perfect for my stove, the Harman Accentra-2, which lists a max wattage of 440 watts of power typically, a of 255 after start-up sequence using the igniter, if run in auto mode which I did to test capabilities. If I ever need to do this for real, I will start the stove in manual mode using ignitor gel and then switch it to auto later.

I hooked the Xantrex Prowatt to my Duracell 600HDD power pack to check it out the new inverter and turned my stove on from a cold start. It worked perfectly, however, as expected, it drained the 28AH battery pretty quickly.

As many will know, I True Sinewave inverter is usually VERY expensive. At least 300.00. I don't have an O-scope at home to look at the wave form. I am going by the listed manufacturer specs. This is a True Sinewave not a "Pure Sinewave, which is just a modified square wave without noise spikes, which won't work, or at least not well)

The stove started up and ran perfectly with full auto control. No hiccups.

Just for lack of argument purposes.

1. Yes I know a gas generator is the best option. I have a Champion 3500 watt generator. This puts out a real sine wave like what comes out of the wall with Low THD.

2. The fun of doing this the battery way, is as I intend in the future to have bigger batteries and about 400 watts of solar panels(now I have only 60 watts, and one 28AH battery pack and two 19AH battery packs.

3. I found a Sealed AGM deep cycle battery of 79AH for 150 bucks on line, and intend to buy one or four of that size in the future.

I just wanted to share my findings for those who really want to go the battery route. A generator is more practical but battery powered is cleaner and uses less fuel. If you can get enough solar panels, and a large battery your set.

Yes it is expensive. However, I think of this as a security issue as there is a recent history of natural disasters where people are without power for a week or two. No gas stations near me have a back up generator so once I ran out of gas, I don't know how I would get it to power my gas powered portable generator.

FYI, this is way better than an UPS, unless you have an UPS with a True Sinewave and not the standard "modified Sinwave" or in reality a Modified Square wave.

Hope this is helpful!

Mark

 

[imacman]

......I hooked the Xantrex Prowatt to my Duracell 600HDD power pack to check it out the new inverter and turned my stove on from a cold start. It worked perfectly, however, as expected, it drained the 28AH battery pretty quickly.

1. Yes I know a gas generator is the best option. I have a Champion 3500 watt generator. This puts out a real sine wave like what comes out of the wall with Low THD.

3. I found a Sealed AGM deep cycle battery of 79AH for 150 bucks on line, and intend to buy one or four of that size in the future.

A generator is more practical but battery powered is cleaner and uses less fuel. If you can get enough solar panels, and a large battery your set.

Yes it is expensive. However, I think of this as a security issue as there is a recent history of natural disasters where people are without power for a week or two. No gas stations near me have a back up generator so once I ran out of gas, I don't know how I would get it to power my gas powered portable generator.....

Nice review, Mark. Sounds like a nice unit.

As for the generator, I still feel that's the way to go. With all the $$ you admit you'll have to spend on batteries, solar cells, etc, you could buy enough 5 Gal gas cans and keep them filled to run for many weeks, (or a 55 gal drum). Proven reserve power, you already have the generator, and it will run more than just the stove.....can the batteries do that?

You never know when you might need it.

Just my 5 cents.

 

[mark d fellows]

......I hooked the Xantrex Prowatt to my Duracell 600HDD power pack to check it out the new inverter and turned my stove on from a cold start. It worked perfectly, however, as expected, it drained the 28AH battery pretty quickly.

1. Yes I know a gas generator is the best option. I have a Champion 3500 watt generator. This puts out a real sine wave like what comes out of the wall with Low THD.

3. I found a Sealed AGM deep cycle battery of 79AH for 150 bucks on line, and intend to buy one or four of that size in the future.

A generator is more practical but battery powered is cleaner and uses less fuel. If you can get enough solar panels, and a large battery your set.

Yes it is expensive. However, I think of this as a security issue as there is a recent history of natural disasters where people are without power for a week or two. No gas stations near me have a back up generator so once I ran out of gas, I don't know how I would get it to power my gas powered portable generator.....

Nice review, Mark. Sounds like a nice unit.

As for the generator, I still feel that's the way to go. With all the $$ you admit you'll have to spend on batteries, solar cells, etc, you could buy enough 5 Gal gas cans and keep them filled to run for many weeks, (or a 55 gal drum). Proven reserve power, you already have the generator, and it will run more than just the stove.....can the batteries do that?

You never know when you might need it.

Everything you say is true. However, gas goes bad within a year. Sta-Bil which I use, says it will keep gas fresh for 2 but I haven't proved that. That much gas in storage is more dangerous I think.

Plus, you would have to cycle it through. I'm not running old gas through my car and risk damaging the Catalytic Converter, or O2 sensors. I don't mow grass enough or have enough land to run it in the mower within two years.

I have a small house in a housing community. I don't have a lot of space. I can store sealed AGM batteries in my house, but I'm not going to store a 55 gallon barrel of gas in my home.

Sure the batteries can run more than the stove. Not now, but when I get enough storage capacity. Eventually, I plan to buy about 1200 watts of solar panels with enough batteries to store enough energy to power a new energy efficient fridge, the stove and all our lights, plus internet modem.

This is way more expensive than just having a generator and you will have to change out batteries every 3 to 10 years depending on what you buy. However, prices on solar and solar supplies will be coming down in the future and already are.

During Ike and Catrina, a lot of gas generators were stolen. They are noisy and they tell all the thieves trolling the neighborhood right were they are. "Hey, Hey, Hey, I'm behind this house, can you hear me? Come steal me!"

You are 100% correct about the generator being the most cost effective long term solution now. That is why I already have a good one, that I bought at a good price. Not the best, but sufficient.

However, in the future things will be changing. I think I will change with the times.

When I grew up, we had a 265 gallon tank of gas on hand. Now I live in a small house in a suburban community. Gas prices will continue to climb and it i will take quite a while, if even it ever gets as costly as a battery.

However, in a solar setup that can easily run the stove indefinitely in an emergency, the only wearable items are the batteries and inverter in the short term. The inverter has a Two year warranty and good AGM batteries are listed as having a life cycle of 4 to 15 or more years. The solar panels have a 25 year warranty.

Gas is used up quickly, were as batteries, solar panels, and a good inverter get used up at a much slower rate.

Also, if all people in the house are sick with the flu(just as an example), it is tough to go out and get gas. Solar minds itself once it is installed properly.

Just thinking ahead.

Mark

 

[imacman]

Everything you say is true. However, gas goes bad within a year. Sta-Bil which I use, says it will keep gas fresh for 2 but I haven't proved that......prices on solar and solar supplies will be coming down in the future and already are.

Sta-Bil DOES work...I use it in my tractor in the winter, and my sno-blower in the summer. Both start up immediately on gas that has sat w/ Sta-bil in it anywhere from 4-8 months.

And yes, I have (6) 5 gal gas containers in the garage. I rotate them by dumping the oldest one into the car about every month, and then filling it up.....never an issue, and the car has 168,000+ miles, original catalytic converter, and just changed the upstream oxy sensor only because I just thought I should.....car ran fine before and after change. 4300lb SUV and it still gets 23 MPG on the highway.

But given your situation, I guess the batteries are the way to go. As for the prices on solar cells coming down to reasonable level, don't count on that anytime soon.....not enough demand yet.

But, hey, you have a plan....stick with it, and let us all know how it works out. Good luck!

 

[imacman]

......Also, if all people in the house are sick with the flu(just as an example), it is tough to go out and get gas. (Well, I think the chance of that happening is pretty slim....I'm sure someone could drag themselves out for 20 minutes to get gas)

Solar minds itself once it is installed properly. (just hope it's not real dark & stormy for too long) :lol:

 

[mark d fellows]

......Also, if all people in the house are sick with the flu(just as an example), it is tough to go out and get gas. (Well, I think the chance of that happening is pretty slim....I'm sure someone could drag themselves out for 20 minutes to get gas)

Solar minds itself once it is installed properly. (just hope it's not real dark & stormy for too long) :lol:

As far as dark and stormy for too long that is an issue. However, you can use the Gas powered generator to charge the batteries and provide power short term. That way it burns less gas. As far as people getting the flu, that is way more likely than you think.

We have had a lot of scares lately that haven't come to mean much in the end. Watch out for Bird Flu! Watch out for Anthrax!, etc. However, this swine flu is probably the most credible threat we have faced in recent history.

Time has projected 40% of America will be infected this year. That doesn't mean each business will have 40 percent of their employees call in sick. It means this business can be shut down, while that one has a few workers working.

I have read some examples about people going to shelters during the hurricane that just passed through Texas and the shelters ran out of food and water within 24 hours. We all know about Katrina.

Up in the north, a million customers were without electrical power for 2 weeks.

Better to plan for the worst and not need it, than to think something is silly, paranoid and foolish only to discover later that one was just being ignorant and hard headed when a resource is needed but can't be obtained.

If you had severe flu, how would you feel about going to the store to get gas? How would the clerk feel about you spreading your flu virus around while paying for the gas if you didn't have a credit card to use?

 

[jamesdjs]

Thanks for the review. I've been looking for a good inverter.
I want to tye into a couple of solar panels also. I thinks its the thrill of being able to provide your own power with out a gas generator.
Yes I do own a gas generator also.

 

[Vermont-XXV]

Markas123,
Thank you for providing an alternative to the $500 + solution to power loss. We lose power for a week about once every 8 years here. We've gone without power before and the only problem is being cold. We can deal with the rest of it. I am not rotating gasoline for 8 years to solve this problem. I keep 5 gal on hand for the various power machines I have - but I don't want another machine to maintain, store, tune up and worry about. I'll look into this. I can afford to keep $140 tied up in a converter. Can always recharge the batteries nearby, maybe at work. thanks again.

clifford

 

[hossthehermit]

In my neck of the woods, the typical power outage starts at 2:17 a.m. when it's 4 degrees F, snowing, and a northeast wind at about 36 mph. Price is the only thing that's kept me away from the inverter, budget may fit around this one. Already got a deep cycle for my trolling motor, and a smartcharger for it. If I could stay in bed and be warm until daylight instead of going outside to start the generator, sure would be a swell thing. Gotta talk to the treasury dept.

 

[peakbagger]

Heads up for folks shopping for Prowatts, this model used to be a modified sine wave. While doing a quick search,some of the older units popped up. Make sure you get a pure sine wave as they are superior to a modified sine wave.

 

[hossthehermit]

Heads up for folks shopping for Prowatts, this model used to be a modified sine wave. While doing a quick search,some of the older units popped up. Make sure you get a pure sine wave as they are superior to a modified sine wave.

Aye, there's the rub, then. If you buy the advertised model, and get a mod. sine wave, fry the motors, what are your options. Is there a way to try the inverter to tell, upon getting it, whether it is pure or not? I ask, because I had a wife once, who said she was pure as the driven snow, but, alas, it was not so. It causes one to ponder.

 

[mark d fellows]

Heads up for folks shopping for Prowatts, this model used to be a modified sine wave. While doing a quick search,some of the older units popped up. Make sure you get a pure sine wave as they are superior to a modified sine wave.

Aye, there's the rub, then. If you buy the advertised model, and get a mod. sine wave, fry the motors, what are your options. Is there a way to try the inverter to tell, upon getting it, whether it is pure or not? I ask, because I had a wife once, who said she was pure as the driven snow, but, alas, it was not so. It causes one to ponder.

I don't know if that's the rub or not. I did see the modified sinwave models. they look differently, and are much cheaper. The vendors have these in stock also. This model, with this casing is different.

I wouldn't doubt that at that price, it is a cheaper True Sinewave, but it clearly says True Sinwave inverter on the box, and in the manual, and on the vendors website. It also says it won't harm variable speed motors and such.

As I may or may not have indicated, I don't currently have a home use O-Scope although I plan to get one to try it out and see. However, I did try my stove in full auto mode and it worked perfectly.

If someone tries this and it isn't a True Sinewave, then Xantrex will be giving me my money back.

They just came out with this model.

Mark

 

[mark d fellows]

Also, this is the Prowatt SW, not just the Prowatt. They are two different models.

Mark

 

[hossthehermit]

Also, this is the Prowatt SW, not just the Prowatt. They are two different models.

Mark

Yes, I understand that. My point being, that, as I have been told by people that do this stuff for a living, a modified sine wave will run an electric motor. For a while. How long? Well, that's the question. It's like any wager, or insurance policy, I guess. If ya never use it, it's wasted money, anyway. If ya need it, and it works for a little while, then the motor dies, what is your recourse? Can you prove cause and effect? This topic has been beat to death here, I don't think there is a definitive answer. All depends on your situation, I guess. Personally, at this point, I'm leaning toward getting one.

 

[mark d fellows]

Also, this is the Prowatt SW, not just the Prowatt. They are two different models.

Mark

Yes, I understand that. My point being, that, as I have been told by people that do this stuff for a living, a modified sine wave will run an electric motor. For a while. How long? Well, that's the question. It's like any wager, or insurance policy, I guess. If ya never use it, it's wasted money, anyway. If ya need it, and it works for a little while, then the motor dies, what is your recourse? Can you prove cause and effect? This topic has been beat to death here, I don't think there is a definitive answer. All depends on your situation, I guess. Personally, at this point, I'm leaning toward getting one.

This model is not a modified sinewave. It is a True Sinewave. The industry knows what a True Sinewave is, so Xantrex would be unwise to start calling a modified Sinewave a true sinewave.

It is more than the motor that has problems with a modified sinewave or more accurately, a modified sqaure wave. It is the Triacs(variable speed control for AC motors)

Triacs work on the rise of the ac wave above or below zero. You connect a resistor onto a gate and as the waveform comes up, it turns on the device until the waveform goes back down toward zero and the same happens in the negative region.

With a modified square wave on a Triac controlled motor, it would probably slam the motor on and off and the motor and the Triac would get very hot. The motor would surge a lot more current and the triac might be damaged.

I only know that the box says True Sinewave inverter, and the owners manual specs say the same. They also say it is safe for variable speed(triac controlled) motors.

I don't know for a fact that it is a True Sinewave. I only know what the box and manual specs say.

Since I don't have an O-Scope at home, I can't really be sure.

If someone does have one at home and you buy this, please let us know what the output waveform looks like. If it isn't a True Sinewave then Xantrex will be hearing from me loud and clear.

Mark

 

[kbjelka]

......I hooked the Xantrex Prowatt to my Duracell 600HDD power pack to check it out the new inverter and turned my stove on from a cold start. It worked perfectly, however, as expected, it drained the 28AH battery pretty quickly.

1. Yes I know a gas generator is the best option. I have a Champion 3500 watt generator. This puts out a real sine wave like what comes out of the wall with Low THD.

3. I found a Sealed AGM deep cycle battery of 79AH for 150 bucks on line, and intend to buy one or four of that size in the future.

A generator is more practical but battery powered is cleaner and uses less fuel. If you can get enough solar panels, and a large battery your set.

Yes it is expensive. However, I think of this as a security issue as there is a recent history of natural disasters where people are without power for a week or two. No gas stations near me have a back up generator so once I ran out of gas, I don't know how I would get it to power my gas powered portable generator.....

Nice review, Mark. Sounds like a nice unit.

As for the generator, I still feel that's the way to go. With all the $$ you admit you'll have to spend on batteries, solar cells, etc, you could buy enough 5 Gal gas cans and keep them filled to run for many weeks, (or a 55 gal drum). Proven reserve power, you already have the generator, and it will run more than just the stove.....can the batteries do that?

You never know when you might need it.

Just my 5 cents.

In my quest to keep up with the macman I bought a generator this week. Not the standby type macman has, but a Honda EU2000i portable. Borrowed a buddies last week during a wet snow outage here and with two extension cords we were running the stove and watching TV as the generator quietly purred outside the garage below my two sleeping toddlers. My wife was sold which gave me the green light to spend the $$$. Bought a six gallon extended run tank which is good for about 72 hours at full draw. I keep 4 five gallon gerry cans filled all the time so I'm not too worried about weathering a long outage. The whole solar - battery - inverter combo seems like a lot of complexity for a backup solution. I was going for simple turn key solution but to each his own.

 

[mark d fellows]

......I hooked the Xantrex Prowatt to my Duracell 600HDD power pack to check it out the new inverter and turned my stove on from a cold start. It worked perfectly, however, as expected, it drained the 28AH battery pretty quickly.

1. Yes I know a gas generator is the best option. I have a Champion 3500 watt generator. This puts out a real sine wave like what comes out of the wall with Low THD.

3. I found a Sealed AGM deep cycle battery of 79AH for 150 bucks on line, and intend to buy one or four of that size in the future.

A generator is more practical but battery powered is cleaner and uses less fuel. If you can get enough solar panels, and a large battery your set.

Yes it is expensive. However, I think of this as a security issue as there is a recent history of natural disasters where people are without power for a week or two. No gas stations near me have a back up generator so once I ran out of gas, I don't know how I would get it to power my gas powered portable generator.....

Nice review, Mark. Sounds like a nice unit.

As for the generator, I still feel that's the way to go. With all the $$ you admit you'll have to spend on batteries, solar cells, etc, you could buy enough 5 Gal gas cans and keep them filled to run for many weeks, (or a 55 gal drum). Proven reserve power, you already have the generator, and it will run more than just the stove.....can the batteries do that?

You never know when you might need it.

Just my 5 cents.

In my quest to keep up with the macman I bought a generator this week. Not the standby type macman has, but a Honda EU2000i portable. Borrowed a buddies last week during a wet snow outage here and with two extension cords we were running the stove and watching TV as the generator quietly purred outside the garage below my two sleeping toddlers. My wife was sold which gave me the green light to spend the $$$. Bought a six gallon extended run tank which is good for about 72 hours at full draw. I keep 4 five gallon gerry cans filled all the time so I'm not too worried about weathering a long outage. The whole solar - battery - inverter combo seems like a lot of complexity for a backup solution. I was going for simple turn key solution but to each his own.

Solar+Backup battery is complex at first, until it is setup and then it takes care of itself. I like to tinker.

If you are looking for a fuel that has the highest shelf life, look into getting Coleman fuel. Goes by other names. Naptha, and white gas, I think.

I know from experience a can NOT taken care of and left in the porch exposed to direct sunlight and extreme cold will last 10-15 years without going bad. You can run it in your gas generators but you need to add a certain amount of marvels mystery oil or two stroke oil to it if the engine is a four stroke.

If you have a two stroke engine in your generator, you don't need to add anything to the Coleman fuel, but just mix the fuel at the manufacterers directions.

Using Coleman Fuel is outrageously expensive but it practically never goes bad where as you have to cycle through gas, every two years if it has Sta-Bil and quicker if not.

For those of us in parts of the country that have steady wind, you can use a wind powered generator that is inexpensive and powerful.

About a dollar a watt. You still need a charge controller, battery, and True Sinewave inverter though. The wind still blows on rainy days.

Mark

Cool setup!

 

[Bigb62]

I find it interesting that there is a 'shelf life' on gasoline. A few years back, when gas was skyrocketing towards $2.00/gal ! I bought 150 gallons from a town shop that was left over from at least 5 years in an underground tank for $1.00/gal. I figured that was a heck of a deal. Wife wasn't impressed when I stored it in 55 gallon drums in the garage (next to a running oil furnace). But she liked not having to go to the gas station. Her car, my truck, the lawn mower and even the chainsaw ran just fine on that 'old' gas. Just my $.02

 

[kbjelka]

I find it interesting that there is a 'shelf life' on gasoline. A few years back, when gas was skyrocketing towards $2.00/gal ! I bought 150 gallons from a town shop that was left over from at least 5 years in an underground tank for $1.00/gal. I figured that was a heck of a deal. Wife wasn't impressed when I stored it in 55 gallon drums in the garage (next to a running oil furnace). But she liked not having to go to the gas station. Her car, my truck, the lawn mower and even the chainsaw ran just fine on that 'old' gas. Just my $.02

Google "ethanol gas phase separation" and you will find that ethanol blends have a shorter shelf life due to water absorbtion and phase separation. Like everything else they don't make gas like they use to. You must have got 150 gallons of the good stuff. I still think you can get a year in a sealed can but some say three months max.

 

[Bigb62]

Luckily, I can still get offroad premium gas (no sqeezins) locally, my prefered fuel for small engines other than my mower. that should still have a pretty good shelf life, no? A tad more $, but less hassle.

 

[imacman]

In my quest to keep up with the macman I bought a generator this week.......

Don't do it GroundHog....you'll end-up in the poorhouse, like me. LOL

BTW, I put a post in the other thread where you discussed this genny set-up.

 

[jtakeman]

Luckily, I can still get offroad premium gas (no sqeezins) locally, my prefered fuel for small engines other than my mower. that should still have a pretty good shelf life, no? A tad more $, but less hassle.

In CT. All our fuel blends have the extenders in them "Ethanol". My 4 stroke motors are OK with it, But the 2 stroke outboard hates it. I've had to rebuild the carb every season. When the fuel dries out it leaves a white colored residue behind, Almost chalk like, Next year I am going to add a smaller micron inline filter to see if it helps remove the crap.

 

[hossthehermit]

Luckily, I can still get offroad premium gas (no sqeezins) locally, my prefered fuel for small engines other than my mower. that should still have a pretty good shelf life, no? A tad more $, but less hassle.

In CT. All our fuel blends have the extenders in them "Ethanol". My 4 stroke motors are OK with it, But the 2 stroke outboard hates it. I've had to rebuild the carb every season. When the fuel dries out it leaves a white colored residue behind, Almost chalk like, Next year I am going to add a smaller micron inline filter to see if it helps remove the crap.

Have you tried a marina or an airport? Sometimes you can buy from them. Some won't let ya.

 

[jajackson]

Mark Fellows: I am very interested in your comments about the Xantrex Prowatt SW backup unit. I have a Harmon DVC500 Coal burner. I really need the backup unit when the electric goes out. The Surefire 512H backup unit is pricey but will power up for 8 - 9 hours. You mentioned the Xantrex Prowatt SW backup unit drains very quickly . Can you tell me how many hours the Xantrex Prowatt SW will last?

 

[mark d fellows]

Mark Fellows: I am very interested in your comments about the Xantrex Prowatt SW backup unit. I have a Harmon DVC500 Coal burner. I really need the backup unit when the electric goes out. The Surefire 512H backup unit is pricey but will power up for 8 - 9 hours. You mentioned the Xantrex Prowatt SW backup unit drains very quickly . Can you tell me how many hours the Xantrex Prowatt SW will last?

It all depends on the battery, not the inverter. The Xantrex is listed as 90% efficient which is pretty good. You need to know how many average watts you will use and how many max watts you will use.

To determine battery time. Take the average watts listed that your stove uses and convert that to amps.

for example, if your average power useage is 250 watts. you can do the following formula.

250/120=2.08 amps.

Now that is at the inverter output. My inverter is 90% efficient so devide 2.08 by .9 or 2.08/.9=2.31

so you know that you use 2.31amps at the inverter output(120 side) for 250 watts.

Now you have to determin what is used on the intake side of the xantrex inverter(the supply side from the battery)

to get the 120 volt output, the 12 volt input from the battery is probably run through a multivibrator to pulse the DC from the battery and and then stepped up 1 to 10 through a step up transformer. When you step up voltage you step down current by the same factor.

so take the 2.31 amps and multiply is by 10 to get your input current draw from the battery. 2.31amps x 10=20.31 amps.


at that power useage you will run a 100amp hour battery dead in roughly 5 hours. Now, if your stove uses less, it will last longer.

Get a 200ah battery and that will last 10 hours.

Do a search online for Deep Cycle Absorbed Glass Mat(AGM) batteries and buy the biggest you can find.

Even with the 512 you will need to buy a very big sealed lead acid battery. So you will still have the roughly 500.00 investment in the surefire 512 and then considerable investments in the battery.

It will definitly be cheaper to by the Xantrex.

Cheaper yet, a champion 3000.00 watt generator sold at lowes for 325.00. However, this must be run outdoors, our you will most assuradely die of carbon monoxide poisoning.

Now back to the formulas

average watts used/120volts= current draw. You always use 120 volts because that is average household voltage. That doesn't change.

What does change is the wattage you need, and the current draw.

AW/120=I

I/.90=output current

output current x 10= input current from battery.

battery capacity = amp hours or (AH)/ inverter input current draw. OR (AH/inverter input current=run time)

Even if you do get the Surefire 512H, I recommend a large battery like this one,

http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200337832_200337832

Mark