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.

 

[SPYDERLK]

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.

Sorry, I couldnt post last nite because the link was bad. I have been running Xantrex 1000W inverters on BX1500 and larger tractors for about 8yrs. NO failures and I run the Remington 14" chainsaw, and [very carefully] a circular saw. You can do useful work with this inverter. Mine are old, but the successor is available right now at COSTCO for $50.
larry

 

[CATMAN]

400 watt inverters in our service vans(at work) will charge the laptop and run one 100 watt trouble light, but won't run two trouble lights. On the farm, I own a 1000 watt/ 2000 surge (from Costco) and it will just run a 4" electric grinder, but sometimes to get started, I have to shut off inverter, pull the grinder trigger and hold it in the "on" position, then flip the "on" switch on the inverter and the grinder would speed up. This only happened twice, but I needed to get a ruined wheel bearing race off of a spindle out on the road during harvest time(gravity box wagon). I had a spare hub and bearings to slap on it, temporarily, to get it home. Later, torched off the 4500 lb spindles and welded on 8000 lb spindles with larger bearings that had hubs that still fit the wheel bolt pattern.(Bigger is Better)

 

[ultrarunner]

YES... I've been running a Statpower Inverter 1500 in my service van since 90-91 without trouble. I did add a second battery and put in a higher output alternator.

It has an automatic "sleep" mode that will sometimes trip the inverter when a start my small skill saw or angle grinder. I found plugging in my drop cord with a 75 watt bulb and keeping it on prevents my Inverter from going into sleep mode and I can keep working.

I also use it to power a small Emglo Air Compressor

I think I paid around a $1000 for it back then... I didn't know anyone with one and it was something I stumbled on at the Oakland Boat and Yacht Show.

 

[anojones]

I've been investing in cordless tools to work around on the property but of course am always draining the batteries. Would it be reasonable to consider using an inverter to charge the battery packs rather than using the actual electric tools? This would save me from running back and forth to the house to swap batteries.

 

[SLOBuds]

I've been investing in cordless tools to work around on the property but of course am always draining the batteries. Would it be reasonable to consider using an inverter to charge the battery packs rather than using the actual electric tools? This would save me from running back and forth to the house to swap batteries.

I would not do that myself. You will have to charge the batteries for a long time, and most likely you will have to run your auto/tractor for that entire duration. That one charge could be pretty expensive given the cost of fuel these days.

It would be more cost effective to buy another battery probably. If you are doing the type of work that your tractor is with you running all the time, then maybe the battery charger concept works. But for me, I am being much more deliberate about turning off the tractor whenever not in use.

By the way, there is a good thread here on TBN about how long people are running their tractors in idle.

I took a look at the larger inverters. Ones that could drive some of my larger tools. Turns out that the price goes up significantly as the inverter gets larger. The more expensive that the inverter is, the more I think it is better to just buy a generator.

 

[cityfarma]

I would not do that myself. You will have to charge the batteries for a long time, and most likely you will have to run your auto/tractor for that entire duration. That one charge could be pretty expensive given the cost of fuel these days.

It would be more cost effective to buy another battery probably. If you are doing the type of work that your tractor is with you running all the time, then maybe the battery charger concept works. But for me, I am being much more deliberate about turning off the tractor whenever not in use.

By the way, there is a good thread here on TBN about how long people are running their tractors in idle.

I took a look at the larger inverters. Ones that could drive some of my larger tools. Turns out that the price goes up significantly as the inverter gets larger. The more expensive that the inverter is, the more I think it is better to just buy a generator.

I would disagree that there is a need to run the tractor whilst charging the tool battery from the inverter. Qualified of course by this depending on size of battery and how often it is charged. Most small battery tool battery packs only have a capacity of a couple of amp hours while the tractor has around 50 amp hours. This means that you can charge the battery a number of times before your tractor battery would be so low as to cause trouble starting.

I use a 150VA inverter in my 4WD many times to charge power tools without any problems.

Cityfarma

 

[Buckeye_Jim]

I have used various inverters for years and found them quite useful. As with anything you have a few gotchas though. Running power tools with a tractor would probably be an intermitent use for not too many hours at time. I would recommend 1500 watts. They will typically surge to 2500 Watts to handle starting current. In our service vehicles, we have used electric jack hammers and worm drive skil saws off these inverters. At these kinds of loads however, the wire from the battery needs to be large and very short. This is the biggest issue for larger power tools. We mount a 2nd battery in the back with the inverter connected with less than 12" cables. Pickup alternator systems are connected though a battery isolator which only charges the aux. battery after the vehicle battery has been charged. We buy the inverters at a local truck stop for around $ 300.00.

I personally would just use a small generator if I was out with my tractor. But if pressed, I would build a box with a battery and the inverter. Then carry the box to the point of use with the tractor. I wouldn't bother trying to connect it to the tractor electrical system. With a 100 Ahr. battery and 10 amp AC load, that should give you about 1 hour of run time. Since your use is typically intermittent, that may be 6 hours of say skil saw use, or maybe 2 hours of electric chain saw use. Charging would happen overnight with a small battery charger. I dabble with amateur radio and these modified sin wave units are way too noisy for the sensitive receivers.

Jim

 

[SPYDERLK]

I personally would just use a small generator if I was out with my tractor. But if pressed, I would build a box with a battery and the inverter. Then carry the box to the point of use with the tractor. I wouldn't bother trying to connect it to the tractor electrical system. With a 100 Ahr. battery and 10 amp AC load, that should give you about 1 hour of run time. Since your use is typically intermittent, that may be 6 hours of say skil saw use, or maybe 2 hours of electric chain saw use. Charging would happen overnight with a small battery charger. I dabble with amateur radio and these modified sin wave units are way too noisy for the sensitive receivers.

Jim

Thats work everytime you use it. Too much overhead. If your tractor has an automotive sized battery a direct plumb in mounted to the tractor is useful for drills, sawsall, low end circular saw. small chainsaw, etc and is always there when you need it. No overhead that you must play with each time you use it. 1000W Xantrex inverters are ~$50 cheap and will last years sitting on top of the hood if thats where you put it. They seem to be quite weather tolerant. I have a combined experience of about 12yrs counting 3 different setups. All still operate as new. No alternator problems. No battery problems. Bigger would be better for full applicability to all hand tools, but the real bargain seems to be in the 1KW unit.
larry

 

[schmism]

some are more efficent than others.

A friend is a broadcast engineer and often partially builds out the live broadcast trucks. he uses prosin inverters. two 2K watt units to run the equipment and a rack of about 6 diesel truck battery's to power them. They run a truck with AC off that setup for about 4 hrs without having to crank up the genny.

what the label says on the outside of the inverter can varry widly from what youd be able to draw off it successfully especially the lower watt ones (500 and below)

One paticuarly poor one had an output voltage of about 103V on a 13.5Vdc input with about a 15w load on it (running a laptop in my lap while on a cross country trip) But it was a cheezy 300w version for like $40 (the prosin ones go for like $800-1200 depending on options and wattage)

 

[SPYDERLK]

some are more efficent than others.

what the label says on the outside of the inverter can varry widly from what youd be able to draw off it successfully especially the lower watt ones (500 and below)

One paticuarly poor one had an output voltage of about 103V on a 13.5Vdc input with about a 15w load on it (running a laptop in my lap while on a cross country trip) But it was a cheezy 300w version for like $40 (the prosin ones go for like $800-1200 depending on options and wattage)

I believe the Prosin is a true sine wave inverter. It puts out a waveform just like house power. Good for everything, but expensive. All the ones that you pay less than $100 per KW for are modified sine output - a plain old square wave usually. The same energy is there as in the true sine, but induction motors and transformers arent as happy. Universal motors like in handtools work pretty well, as do lights. A regular voltmeter does not give you a true reading of the energy in the square wave relative to the sine wave. The sine wave will give a good reading on any AC meter, but for the square wave you need a true RMS Voltmeter to give the correct value. Other meters will read less. That 103V reading was probably not taken with a true RMS meter -- but then maybe it was a real bad cheapy and didnt make its speced 115V RMS.
larry