Power Inverter - Watts to Amps...

Dave___in___CT · Feb 7, 2004

Hi...

Looking into getting a portable power inverter... hooks to vehicle's 12 volt DC battery and converts it to AC power...

Inverters are rated in watts of output...
The hand power tools I want to power... like a drill... sawzall... are rated in AMPS... like 4.0 AMPS... 5.5 AMPS...
Circular saw is 15.5 AMPS...

How many watts are needed to run the drill & sawzall ?
Is 600 continous watts with 1000 watt surge enough ?

15.5 AMP circular saw ?

Should the supplying vehicle be running when the inverter is in use ?

Like to keep cost below $150... Occasional use...

Any recommendations for inverter brand? Model? Size?
Other ideas ?

Gas powered generators are too costly...

Thanks...

Dave...

ns_in_tex · Feb 7, 2004

Hi Dave,

Divide watts by voltage= amps, (1200 watts/120 volts=10 amps). Keep in mind this is running amps of the tool. A saw may double running amps on startup or when it binds in a board.

A few months ago, I purchased a Coleman Powermate PMP1200 inverter from Kitchen & Home Gadgets for 120.00 (online). My experiance was good.

If you are using it alot and heavy, I would suggest leaving the motor running, because 10 amps at 120 volt means 100 amp at 12 volt. It will take your battery down fairly fast. At this rate your alternator may not supply all the needed current.

John_Mc · Feb 7, 2004

That circular saw is going to take a pretty good sized inverter. 15.5 Amps is about 1800 watts. You might want to look at just getting a cordless circular saw instead (I've got an 18 volt Milwaukee cordless circular saw which I'm very happy with). You can charge up a few batteries before you head out to the job, or get an adapter to charge it from your car's cigar lighter.

This might let you go with a smaller inverter for the other tools you mentioned, or you can just get a set of cordless tools which all use the saw batteries. Milwaukee, Dewalt, Craftsman and others make some good packages which include a sawzall, drill, and circular saw. Go for the 18 volt (or higher) versions.

John Mc

dbelisle · Feb 7, 2004

I think you will find that a inverter to run a circular saw will cost as much as a small generator. I purchased an inverter in the price range your looking for and it does a great job on drills and small electronic stuff. I think it is about 800 watts.
Look at the small Coleman generators, I have one thats 1800 watts peek and has a 12 volt charger cable on it . I have used the 12 volt almost as much as I have the 120 volt.

They are reasonably guiet too.

I have seen them at Walmart for under $400.00 , about what you going to pay for a inverter that will run a skillsaw, and the inverter will draw the battery down faily quickly if you have a sizeable draw on it for any length of time.

Good luck

Mahindra 2810HST

Dave___in___CT · Feb 9, 2004

Thanks guys... !

Found some info. on inverters...
...as deerslayer says... I'd need a "True sine wave" type for my solid-state variable speed tools and cordless battery charger... and these are expensive...

Plus... as you say... the drain on my starting type battery will be too much and would probably kill it after several discharges/charges...

Think an inverter is not a good choice... /forums/images/graemlins/frown.gif

Now... I'm checking out smaller gas engine powered generators... specifically the "inverter" type ones...
1000w - 2800w continous output...

I don't want the typical low-cost higher output ones like at Home Depot... their useful wattage at 115v can actually be less than the rated wattage... like a 4000w rated one can only deliver ~1700w at 115v...

Yamaha & Honda have some nice inverter generators...
Inparticular the variable speed Ymaha's...
...the Yamaha 1000w #EF1000is inverter generator... ~$675 ~30 lbs...
...the Yamaha 2800w #YG2800i industrial inverter generator... ~$1150 ~60 lbs...

The 2800w is enough to power my refrigerator + more...
But I like the compactness, lower price of the 1000w one... but won't handle my circular saw...

Any input/thoughts on these ? /forums/images/graemlins/confused.gif

Thanks...

Dave...

tomnky · Feb 9, 2004

I think if You can swing the bucks go for a larger Honda that is Portable.You could always use it in case of a power outage , I personally would look at a two-fold use for it.

One doesn't realize the value of a good generator/inverter until they need one and then it is too late for what You have in mind.

A good generator/inverter is worth it's weight in the right situation!

SPIKER · Feb 9, 2004

Harbor freight has some gensets on clearance right now, 499 for a 4500/4000 rated generator with a subaru/robin engine. and only weight is about 110 lbs that is a elec start, the recoil start is 40 or 50 less.!

my brother has one of the colman generators a 5999 rated I think, really nice but he paid almost 900 for it with taxes. he used it about 4 times not even a full tnak and is selling it. not sure his asking price but I thinkhe said 500. he is in lodi ohio. not sure of you're location?

anyhow most people can use the 4000 or less wattage and be fine, and can back up the house in power outage as long as you don't run more than fridge & furnace with a light or two here & there.

Mark M /forums/images/graemlins/smile.gif

Dave___in___CT · Feb 10, 2004

Thanks guys... !

Dave...

have_blue · Feb 10, 2004

For $300, you can get a 2000W inverter (18a) AND a pair of 215ah golf cart batteries that will run a saw all day long. The golf cart batteries are true deep discharge batteries, and it won't hurt them to run them down to 25% remaining capacity.

Inverters are much better at handling high amperage tools than generators. I once saw a 5000w generator fail to start a 2hp air compressor. A 2000w inverter started and ran it just fine.

fractal · Feb 10, 2004

</font><font color="blue" class="small">(
For $300, you can get a 2000W inverter (18a) AND a pair of 215ah golf cart batteries that will run a saw all day long. The golf cart batteries are true deep discharge batteries, and it won't hurt them to run them down to 25% remaining capacity.

Inverters are much better at handling high amperage tools than generators. I once saw a 5000w generator fail to start a 2hp air compressor. A 2000w inverter started and ran it just fine. )</font>

Depends on which inverter you are using. These guys ( http://www.partsonsale.com/learninverters.htm ) sold me my inverter. They are as opinionated as they come and are in the business of selling product, so take what they say with a grain of salt. A 2000 continous/ 4000 peak inverter is 250 from them. A pair of t105 batteries is another 150. This combination is capable of putting out a full 15 amps of 120v for about an hour before the batteries are to cutoff.

My cheap table saw has a faceplate rating of 13a. My delta chopsaw has a faceplate rating of 15a. Using the chopsaw as an example and assuming an 80% efficient inverter, you will be drawing 188 amps from your 12v automotobile battery. This will drain your regular car battery in no time flat, and as we all know, automobile batteries do not like being flattened. In fact, do it a couple of times and you need a new battery. Next, most cars come with maximum 35 amp alternators. Towing package can increase that to 75. Those current ratings are at running speed. Output at lower speeds (i.e. idle) is reduced. I hope you get out of this little discussion that trying to run shop appliances off your existing car / truck battery is not a good idea.

A better solution is as have_blue said. Purchase a couple of T105 golf cart batteries for the inverter. Get yourself a dual output, high capacity alternator for your truck. Shop at the RV specialty sites / shops to learn about dual output high capacity alternators. Get a throttle kit for your truck so you can keep the rpms up without having to use a brick on the gas peddle.

Another thought I had when I considered this at one time was to look into a pto generator. Not a tractor PTO that has been discussed here at tractorbynet so many times, but an automotive PTO genset. Though, not sure what if anything the difference would be.. Many of the carpet cleaning vans use the vehicle motor through a pto transmission instead of a separate engine. It "should" be possible to get a genset hooked to the pto on your transmission if yours has one. I have absolutely no idea the cost of feasibility of this option, but am throwing it out as a thought.