DC to AC power inverter to run electic tools?

[Soundguy]

Re: DC to AC power inverter to run electric tools?

I've run an inverter on my NH 1920 for extended periods of time.. but was on and off use for a couple hours.. 300-600 watts probably at max. Hand drill, etc. No noticeable drain on battery, as unit started fine after use... but then my tractor is closer to a tc40 or something like that.

I just noticed that harbor freight has a 1200surge/600load inverter on sale for 69 bucks... got an email flyer from them. Onder what the rest of their prices are...

Soundguy

 

[Inspector507]

Re: DC to AC power inverter to run electric tools?

Harbor Freight current prices

5000W........999.99
1750W........299.99
700W...........89.99
150W...........49.99 (on sale)
150W...........69.99 (on Sale)

 

[Bob_Skurka]

Re: DC to AC power inverter to run electric tools?

As for prices, they seem to run the gamut. Ebay seems to consistently have very low prices. Harbor Freight and Northern Tool also have low prices. I noticed the Northern prices are lower on the internet than they are in the catalogues they send me. We even have a supermarket chain (Meijer) in our area that sells inverters.


I am still confused as to what the net effect of running a 1500 watt/3000 watt surge inverter would be off the battery, with the engine running on my tractor.
-- Will it draw down the battery too much?
-- Will it overload the alternator?
-- Would I be better off running it with the engine off for shorter periods of time?

Again I anticipate modest useage, but it sure would be convenient to have available.

 

[R_squared]

Bob,

Try to find out the inverters current draw at maximum load (1500W). Rely on the manufactures specification as opposed to a calculated value. This amperage will help you determine a discharge rate. Also, find out the CCA's of your tractor battery, although this figure probably won't help much. The problem with automotive batteries is that the manufactures usually do not rate them in Amp-Hour capacity. A few automotive battery manufactures do give Amp-Hour ratings and they are based on a 20 hour discharge rate. An important note is that the discharge rate for an automotive battery is nonlinear. The proper way to obtain this is to perform a discharge curve for your own battery - few people will do this. Another point is that automotive batteries do not like to be discharged to less than 75% of their capacity (thin paste plate design) and they need to be recharged immediately after that. A final item is that automotive batteries can be charged at any rate that exceeds internal and surface discharge rates as long as the charge rate does not cause excessive gassing. What are the practical implications? Let's say that you find out your inverter draws 150 amps at full load and that your 600 CCA automotive battery has a 300 Amp-Hour rating. You would be able to run your inverter for two hours before exhausting your battery. At 75% capacity you would have .25x300=75 amps to expend. That means you could run your inverter for 1/2 hour before going below the 75% discharge of capacity. What factors in is the current the alternator/regulator is providing to the battery during the discharge. An automotive battery does not charge linearly either. The point is that there is not a simple, specific answer to your question. If you purchase an inverter, make sure your battery is in good condition and fully charged before going out for the day. Try to determine a best time estimate that you can use your inverter without going less than 75% of the batteries capacity. If your drill draws half the current of your miter saw, then you might get twice the time. Remember that the calculations are based on nonlinear charge/discharge curves. If you have a simple digital volt meter, you could periodically shut down the tractor and inverter and check the battery voltage. If it goes below 12.4 volts, then it's time to head back to the garage to put the battery on a charger. With the right observations and actions you should not harm your battery. Read 5030's advice on inverter types. A true sine wave inverter can safely power many more items.

 

[Bob_Skurka]

From what I can tell, it seems to all boil down to a couple things.

I can put an inverter on a tractor as long as I don't expect to power a city with it.

The inverter will drain the battery, (no surprise), but I should not have a heck of a lot of problems powering a drill to screw in a 100 deck screws or drill several dozen holes.

The alternator might be a problem and it may be overtaxed and fail under some conditions (too big of an inverter drawing too much load for too long) if the engine is running.

If I power up a circular saw, I should not expect to build a house with it on inverter power, but ripping several pieces of plywood or cutting a couple dozen 2x4's to lenght should not be a problem if they are not all done in one "production" type batch that will keep the saw running for an hour.

If the tractor is not running the battery will drain faster than if the tractor is on. But if the tractor is on, the alternator might be at risk. So running the inverter with the tractor off is probably safer for short use, and for heavy use I should run the tractor for a while between using the inverter to power a heavier load tool like a saw. But for low power consumption tools like a 3 amp drill, the engine can stay on while using the inverter to power the drill.

And, if I really want to get serious about it, I could put a large H.D. deep cycle high CCA battery under the hood, swap out the alternator for a larger one and not worry about the electical loads too much. But for fairly light usage of hand power tools out in the field far away from a regular power outlet, that is probably overkill, sort of like wearing both a belt and a pair of suspenders to hold up my pants when the friction created by over eating last night has already expanded my waist to a point that my pants have no chance of sliding off without significant tugging anyway.

 

[LAGEORGE]

Hello Bob, here is my experience with DC to AC inverters. The Suburbans we operate for television news come with inverters. They have 2000-watt sine wave inverters the size of 2 large shoeboxes. It takes a 200-amp alternator to run produce 2000 watts and run the truck running at fast idle. Often times we can see on the meters the deficit of power that the batteries are compensation with. Now the reliability of these systems is really bad the current Suburban I drive has gone through 6 alternators and 2 regulators. It uses large 2 0 cable to connect the system with the four batteries in the truck. I do not see how a small tractor can produce the power needed for anything more than 500 watts. Also the alternators in the tractors are really really small and very expensive and the power system is rates for about 40 amps max (most small tractors). So lots of electrical work may be needed to insure safe and reliable operation. Everyone is always complaining on the cost of parts I do not think people want to think about replacing alternators on a regular bases. I would go with a cheap PTO unit since you can use the tractor engine to generator 5KW or more power instead of the .5KW running the engine fast to turn a dinky alternator.

George

 

[Bob_Skurka]

George THANK YOU you wrote in english what I was trying to deduce from the more technical posts.

But since you seem to have a very practical knowledge of these things from a real world use of them in your vehicle, then how is it that a little John Deere garden tractor can have a 1000 watt inverter in it and still produce power? Or do you think it is something that is designed for such occasional and light usage that it will be unreliable if used heavily and will end up stressing the little tractor's electical system over time???

Or more simply put, if a 300hp Chevy Suburban with 4 batteries and a HD electrical system strains and groans to produce 2000 watts, how can an 18hp Briggs & Stratton produce 1000 watts? /forums/images/graemlins/confused.gif

 

[DavidJ]

<font color="blue"> Or more simply put, if a 300hp Chevy Suburban .... 4 batt .... HD electrical ...., how can an 18hp Briggs & Stratton produce 1000 watts? </font>

It's applying Ohms law. The Chevy runs at 12 volts so to get 2000 watts you need 167 amps. Those generators usually produce 120 volts, so they only need 17 amps to produce 2K watts.

As for running your inverter off your tractor.
You have to look at the usage. Those transmitters he's talking about run at a constant load so whatever the load is it's always that much. Ever how long they're on air they use the full load. Most tools are intermittent use items, so you only need the wattage for a short time that gives the system time to recover. The inverters that I have will not allow you to completely drain a battery. They have an alarm and a shutdown to prevent this from happening.

 

[Bob_Skurka]

DavidJ, the inverter I use in my Cherokee has a low battery shut off, and the 1500 watt units I'm looking at have the same feature. My question to you is do you use an inverter with your tractor, and if so, what size inverter and with why type of electical load?

 

[LAGEORGE]

I am confused? About the 17 amp thing. It takes over 167 amps DC to get 2000 watts AC right not 17 amps DC to get 2000 watts AC.

As for our power requirements it is true that our requirements are more of a constant 1400-2200 watt load but we do have a DC compressor and believe it or not lighting that can swell up power consumption big time into the overload range.
Your right a drill is not going to kill and alternator on it’s first day of school but when one wants to put a 2K inverter in a tractor, does one have to also keep in mind that it can only do that for 3 minutes at 500 watts only. If you are going to put in a 2K inverter then you better have the goods to produce it otherwise you will screw thing up. An inverter is a consumer and it will eat up every amp you can give it and more when asked to put out 2000 watts. I have also found inverters to be kinda dangers. You have lots of power both AC and DC and a short can cause thing to weld themselves and melt down.

I meant to mention the cost of inverters, cheap inverters produce square wave power not the clean stuff form Edison. It causes havoc in electronics and some pulse type motors. The reason they are so cheap is because they do not have to be clean just 120 volts. Using those inverters is like using low quality gas and knowing it, it will catch up to you. You are best to spend as much money as you can afford for the project. I would not choose less than a Stat Power unit for my home use. They seem to be built well enough for consumer use and have somewhat of a clean output but it is still a modified sine wave (square wave without the bad “square” word)

To continue the rant, my UPS backup power unit has a bigger battery than the one in my NH TC 24D. I do not see how I would not kill it in short order if I hooked up a 2K inverter and used it to capacity. Yikes.

So what have we learned? Yeah get an inverter but only up to 1K unless you can restrain yourself from using the full capacity of a 2K unit. Also 2K is a buzzword. 1K of clean power may cost double and more than the WalMart 2K unit costs.

But always keep in mind “you get what you pay for” and my personal favorite: “Theirs a reason it’s on sale!”

George