Inverters - Do They Work?

[SLOBuds]

I would like to know if inverters work OK for power tools. I'm thinking about using one off my tractor as a poor-man's generator for small power tools.

Having no experience with them, I wonder if they work as published. Meaning, if I get a 400 watt inverter will it run 400 watt tools? Will it damage them in any way? Can I run my PC off one?

Thanks

 

[kennyd]

They work great, but look at the input requirements, they take a lot of DC current to make AC power. I would venture to guess your battery/alternator will have a hard time keeping up for long.

 

[Skyco]

KennyD is right-
Rough rule of thumb- an invertor draws 10 times the current out of your battery as it produces on the AC side. So a 400 watt load will be about 3.5 amps AC but will be drawing 35 amps DC out of your battery. As for a 400 watt invertor powering a 400 watt, it might, but my rule of thumb is use twice the invertor than your load, particularly if it is a motor and has a start up surge. Did an experiment once with an AC powered small refrigerator, while it took only 75 watts to run a 250 watt invertor wouldn't start it.
Other than that they work pretty well for most loads. The common ones don't have real clean AC, the waveform isn't a pure sine wave, so some electronic items don't like them.
I have a 2000 watt unit installed behind the back seat in my pickup, it runs power tools fine, but it can kill a battery pretty quick, the battery is a deep cycle unit installed under the truck bed and the invertor is hooked to it with 1/0 cables (big as your thumb)

 

[RonMar]

Skyco and Kenny are right, Watts are Watts regardless of the source. Power in Watts = current X voltage. Or P= I x E(P over IE). If you know any 2 values you can solve for the third by multiplying or dividing as appropriate. 400 Watts divided by 120V = 3.3A(P divided by E = I). That same 400W being drawn from a battery at 13V = 30A, plus a bit more for the conversion losses in the inverter.

Inductive loads such as drills, saws and refrigerator compressors can pull 2-3 times their normal running current during startup, so to feed a drill or saw with a 400W static load, may require as large as a 1000-1200W inverter. Most inductive loads(motors) also get most of their energy from the peak of the AC sinewave. Modified sinewave inverters approximate a sine wave with a series of steps and are typically a little flat topped. This deprives inductive loads of that energy so they will draw a bit more current to make up for it. Microwave ovens don't liked flat topped pulses for this reason and cook times can be much longer as they can't deliver as much energy to the magnetron with out a good ac pulse shape. Switching power supplies in computers also work a little harder on a mod AC sinewave. That being said, mod sinewave inverters will run most everything, just not as efficiently as a true AC sinewave.

As mentioned, this energy will need to come from your alternator on the tractor. Most tractor power systems are pretty marginal in my experience. Your alternator might not be adequate to feed a 30+ amp load in addition to charging the battery and running the instrunments. Short duration use could be covered by the battery, but the alternator will still try to make up for these losses while they are occuring. A 25-30A alternator might cook itself trying to feed even short duration 50A loads on the electrical system...

 

[ray66v]

Inductive loads such as drills, saws and refrigerator compressors can pull 2-3 times their normal running current during startup, so to feed a drill or saw with a 400W static load, may require as large as a 1000-1200W inverter.

RonMar is also right about the load. I fried my switch in my Sawzall last year this way.

Also be ready for your tools to sound differently than they do on regular AC.

For once everyone agrees???

 

[Mighty Dodge]

They will run small universal motors as in hand held power drills, circular saws etc. You'll need at least 750 watts, 1000 would be better. 400 watts doesn't have enough umph. I wouldn't use them on an inductive motor, ie table saw, drill press etc. they do require a larger amount of amp to startup.

M.D.

 

[tommu56]

If you use one dont skimp on the battery leads

For rough figuers if tool draws 3.5amps at 120 move decimal point to right so with out losses it will draw aprox 35 amps and most tractor alternators won't cover that for short bursts battery will put that out.

tom

 

[EastTexFrank]

I have a 1500 watt/3000 watt surge inverter. I use it to run an electric pole saw occasionally and other power tools when I don't feel like hauling out the generator. I have used it to run fridge/freezers during power outages although we had one big old fridge that it just couldn't start. The motor drew too much power to start it and the inverter wouldn't supply the 3000 watts surge for long enough to get the motor started and it would trip out. It'll start and run more modern fridges. Most of the bigger modern inverters have the facility to monitor the voltage of the battery supplying the power and will shut down if it gets down to something like 10 volts. Deep cycle batteries are probably better than auto batteries if you are going to use it often.

I should say that I put dual purpose, deep cycle batteries in the F350 and that's what I used to run the fridge, not one of the tractors batteries. I don't know if that is significant but it better be mentioned.

 

[cityfarma]

I have a 600VA inverter that I use for my caravan. I also have a 600VA petrol generator. If I want to use electric tools, I always use the generator as it can handle the starting surge where the invereter will always trip out.
As has been said before, you will need a much larger inverter than the power of the tool you intend to run on it.

Cityfarma

 

[SLOBuds]

Thanks all. Sounds like I have to buy one significantly larger than what is actually needed by the tool/device. And the required amerage may not be drivable by standard auto charging systems.

Unless I go with a very large inverter - which costs near what you will have to pay for a generator itself - its use will be limited to very small tools/devices.