DC to AC power inverter to run electic tools?

Bobvt · Oct 30, 2003

You want to be careful using an inverter to charge power tool batteries. Many of the chargers can't deal with the modified sine wave. I have a 2,200 watt (2,600 for 20 minutes and surge to 4,400). It will charge my power tool batteries but never fully. One of my batteries (18 volt) now has a very short life; and I think it is because I used the inverter twice to try and charge it.

Bob

Bob_Skurka · Oct 30, 2003

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

At my office we have an emergency plan for power failures. We run the generator to a large UPS and the UPS then powers our main computer. It does "condition" the power coming out of the generator. So you will protect your electronic equipment from spikes, surges, low voltage, etc. Most UPS systems are specifically designed to provide safe power for computer and electrical equipment. Most are also very small and don't offer much run time, but that is not always a big issue.

At my home I have my electronic equipment (satellite upfeed, computer network, etc) powered in a very similar manner. Generator to the back up panel, panel to the UPS, UPS to the equipment.

The biggest downside to using inverters and even UPS units is that there is an inherant lack of efficiency. A typical inverter is probably 90% efficient. I have not checked the UPS units, but as they are battery back up units, I suspect they probably are also sapping off some efficiency so maybe they also run at 90%. If you are generating 5000 watts and you lose 500 of those to the inverter and then another 450 to a UPS unit, you gave up a large chunk of your available power.

Now if you run an inverter off your battery and then plug a UPS into the inverter and then try to run a power tool off the UPS I am not quite sure what will happen. I think that something like a 13 or 15 amp circular saw might simply drain things down pretty quickly, which is the original question I was posing in this thread. I just don't quite know how quickly. A simple 3/8ths hand drill might only draw 3 or 4 amps and should run for a long time without much problem. But your question of tossing in a UPS after the inverter might end up altering things a bit. I doubt if it would alter it too much. And if the UPS is not designed for the draw of an electric motor, the surge in the demand might ruit the UPS??? I just don't know that there is enough advantage to it to mess with it.

I am probably going to add a 1500 watt inverter to my tractor. I have figured out that the battery should be upgraded, but I will probably wait to do that until the current battery won't hold a charge. And near as I can tell, I don't want the tractor running while using power tools because it will strain the alternator.

DavidJ · Oct 30, 2003

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

There are basically 2 types of UPS's. Those that stay in standby offline and those that power the device hooked to them. The standby units have a small interruption when switching on (although only a few nanoseconds). They have no conditioning. The full on units condition and have no lag. Which unit do you have? It's hard to say. If it says it has conditioning then it's probably a full on unit. Lightening & surge protection alone usually provide no conditioning.

The only downside to hooking up the UPS is that you use some power to run the electronics of the unit that could otherwise be used to power the tool.

Soundguy · Oct 31, 2003

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

First.. there are some incompatibilities between the stepped output of some inverters and what your ups is expecting to see.. speciffically ferro-magneting inputs.. of some of the older designed ups's.

Second, keep in mind that there is a power loss in that extra step.. though i believe you would do better with a line conditioner after the inverter / generator. the line conditioner, like APC's Line-R is essentially the good parts of the ups, minus the inverter and battery. When I ran my electric repair business I used to be a dealer for the apc products.. fairly decent.. though their ups's, like many others, wont start a load on the otuput with having an acceptable input voltage that they were first running on before 'hand-over' to battery... If they sense a site fault.. like no ground reference, or reversed neutral, or low/fluxuating voltage.. they may not come on.. etc... I had no luck running the old 250's and 200's off a genny.. they showed site wireing faults, and like I mentioned.. even the new office-ups series won't start a load with no input... they really were only designed to maintain an existing load after handover from line to battery powered inverter.. etc.

good luck though.. you are in the right fram of mind.. I wouldn't run any sensitive electronic equipment direct off a genny output... some soret of emi/rfi and pahse correction, clamping/clipping, etc needs to be present..

Soundguy

Soundguy · Oct 31, 2003

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

</font><font color="blue" class="small">( There are basically 2 types of UPS's. Those that stay in standby offline and those that power the device hooked to them. The standby units have a small interruption when switching on (although only a few nanoseconds). They have no conditioning. The full on units condition and have no lag. Which unit do you have? It's hard to say. If it says it has conditioning then it's probably a full on unit. Lightening & surge protection alone usually provide no conditioning.)</font>

Most APC ups's, smaller than the matrix ups's, and the non smartups's, are all standby models.. and all offer power conditioning... and common, normal mode filtering / clamping, and clipping / surge protection..., as well as efi / rfi filtering... and ground fault detection..( though i doub't they do any phase correction while in standby ). The line-r model line conditioners run isolation, on a multitapped transformer.. so there is considerable filtering.. both by natural inductance, and via voltage adjustment via taps, etc... very quick handover times.... catches even before direct triac powered ( transformerless ) powersupplies crap out on the dropped sine wave.. etc.

Soundguy

Spencer · Oct 31, 2003

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

Soundguy, thanks for sharing your knowledge. I have another question that you may be able to help me with. I just bought a new Hewlett Packard laptop computer. I had an older HP that just couldn't keep up with me anymore. I had a DC power supply for the older HP that I got directly from them. It was an auto/airline adapter that put out 75 watts. HP does not make an auto/air adapter for my new laptop because it requires 90 watts of power. HP tech support is telling me that I should use a DC to AC inverter like we have been talking about in this thread. They told me to plug the AC power supply that came with the laptop into the inverter and use it like that. I do have a 175 watt inverter that I picked up on clearance a while ago for $13 but I am not sure I want to hook up my new laptop to it. I don't like the thought of converting the DC voltage from my van to AC with an inverter and then converting it back to DC using the laptop power supply. I would prefer to use a DC power supply from the van to the laptop and skipping the AC conversion. Unfortunately it doesn't sound like HP is going to be making any 90 watt auto/air adapters. Best Buy had a Targus Universal Auto/Air Notebook Power Adapter for $99 that looks ok.

What do you think? Am I correct in thinking I am better off with the Targus or similar DC power supply? Would it be fine to use the cheap VEC023 MAXX SST 175 WATT POWER INVERTER that I picked up for $13. I am assuming that having the battery in the laptop while using any external power source is always a good idea.

I travel around the country by van and I use the laptop for GPS/mapping navigation. My older HP worked great for around 4 years on that HP Auto/Air adapter. I sure don't want to do anything to harm the new laptop or the laptop battery. I also don't want HP to tell me something insn't covered under warranty because I used a aftermarket power supply.

Bob_Skurka · Oct 31, 2003

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

spencer, I looked at the Targus models but bought, for about $119 the iGo model.

It has been used to power 4 different laptops (3 different brands) and also has adapters (at an added cost) to power cell phones. Like the Targus, the iGo unit powers laptops on airplanes in cars and also direcly from an normal AC outlet. It comes with about a dozen different connectors so it will power almost any brand of laptop from an Apple to a Zenith. It was highly recommended to me by Apple and Compaq (which is a division of H.P.).

Soundguy · Nov 1, 2003

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

You are correct in assuming that multiple conversions will yeild multiple losses.. however in this situation.. it isn't too bad an idea. That small inverter won't run 175 watts all the time.. it will run according to its load.. pluss any losses in conversion..

Obviously that hp charger isn't passing 12v to the computer.. but rather something stepped down like 5v or 7.5v.. and they don't want to run a hi wattage resistor.. etc... so their answer is to use the available home adapter.

If it is a transformer style adapter.. you'r home free... it won't bee to picky if your inexpensive inverter is stepped sine wave ( or even square wave.. ). If it is a triac based power supply.. it may not be as efficient.. but will still work fine.

I'm guessing the hp ac adapter has some filtering built into it.. so that actually gives you a layer of extra protection you might not have on a direct dc hookup.. etc.. ( in case your alternator decided to dump 18v out all of a sudden.. etc

Anyway.. I've done the same thing you are mentioning.. or similar anyway.. I has a small upsonic ups, and the battery died in it.. I removed it, and made a big cigarette lighter cord and hooked it up that way ( battery was a 12v.. etc ).. and used that as my 'car inverter' for years for my computer.. etc. I made and recycled all sorts of junk back when money was tighter and junk was more prevalent.. and easy to come by.. broken.. for cheap / free..

Soundguy

JRP · Nov 1, 2003

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

5030,

You are right about starting current for an AC INDUCTION motor. Most small tools are universal motors. This means they have brushes and if were not for the variable speed switch they would run on AC or 120 DC. The best part about universal motors is that the starting amps is not 5x as it is for an induction motor.

Circular saws and drills will be universal motors, but air compresssors and standard table saws will probably have induction motors.

For an inverter system, get one that is at least one size larger than you think you will need.

They are cheap on ebay right now. search for "coleman inverter"

BobRip · Oct 30, 2004

Bob, I am an electrical engineer, but that does not mean I know everything about electricity. Here are my comments with no guarantee:
1 Use heavy gauge (2/0 that's with 2 zero. This is bigger than 2 gauge wire, much bigger. The inverter should have a recommendation, and it may suggest bigger wiring, then do it.
2. Keep this wire short between the battery and inverter, one or two feet if possible. Connect the inverter directly to the battery. Current will be over 100 amps. Keep the inverter cool.
3. A separate battery say 100 ampere hour or bigger paralled with the other one could be located in a separate location. this is not a bad idea, but may not be needed. Run the big wire between the inverter and the second battery and some slightly smaller wire directly to the other battery. I cannot give you an exact size but 6 gauge is rated at 55 amps continuously and should do. I don't know your tractor, but this sounds kind of extreme.
4. Instead of 3, put the largest battery that you can in the existing battery box and wire the inverter to it as described in 2.
5. Rev the engine up during and after use. The tractor alternator will only put out its full rated current at high speed. It will not charge the battery at full alternator rated current. Lead acid battery cannot be charged quickly with present technology.

The saw or almost anything with an electric motor draws a lot of current at start up and a lot less at no load. As you try to cut the current will go up. Start the saw unloaded and let it get to full speed before cutting wood. Don't load it too much.

Other options: Dewalt sells a battery charger for their saws and drills that can run off of a car cigarette lighter. This would be easy to add to the tractor. I have used their 18 volt saw to cut 2 X4. I think they claim 72 or so cuts per charge.

If you have not done wiring like described above, get an electrically knowledgeable person to give you a hand. I hope this is helpful, the inverter manual should have some good tips and they know their equipment best. You might want to give them a call and listen to their advice. Make sure that they are comfortable running a saw with it.
Good luck and be safe, a shorted tractor battery can put out several thousand amps if shorted and you don't want to be there when it happens. It can also explode. When you parallel batteries they must be connected postive to positive and negative to negative. It reversed an explosion might occur.