Introduction: Run AC Tools on Batteries Directly, Without an Inverter

Picture of Run AC Tools on Batteries Directly, Without an Inverter

The secret: Just do it. They're designed for that.
Nearly all power tools use a "universal" brushmotor that doesn't care if it gets AC or DC.
All you have to do is put 4 or more 12volt batteries in series and plug your tool in. I usually like to run my tools on about 70 volts DC (five batteries). They're a lot quieter that way and still have enough power.
If you want more power, just add more batteries. I think the gearbox of a circlesaw chatters less when it's running on DC. The batteries don't need to be nearly as healthy as what you'd need to power the same tools through an inverter.

Warning: All the warnings about tools, batteries, and electricity apply. If you want to get hurt you'll find a way, just like you would have without all this expert guidance.

Here I'm using a totally motley assortment of scrap batteries wired in series with my car battery.
If you have mismatched batteries the weak one will discharge first and need to be removed.
A lead acid battery is dead at 10.5 or 11 volts. Recharge then or it could stay dead.
You'll have to monitor them with a multimeter and write on the batteries with a sharpie so you remember what to expect.
I'm using one or more wimpy radioshack alligator clip cables, which make a decent fuse.
Don't try to put your solarpanels in series with your batteries for extra voltage. They can't deliver the starting current your motor needs. When the motor stalls that puts the whole series voltage across the solar panel which can be bad. The same effect means you want to take the weak battery out of the series as soon as the tool starts feeling weak.

To learn more about the junk battery powertool lifestyle, see the next Step.

Step 1: Happiness

Picture of Happiness

Here's my workshop. I'm at a free campground in the Everglades getting ready for a trip into the swamp. It's winter, which is the dry season. So it's 68 degrees and sunny most days. The pond is full of fish and alligators. Some of the alligators have been fed by people, which adds excitement to the situation.

Find free campgrounds with the Free Campground Directory.

My sun awning here is a mirrored "survival blanket" over a camo tarp. Don't bother with that, just get a real opaque silver tarp from CampingWorld. Home Depot, Lowes, etc. only carry the fake ones that make a solar oven that costs as much and won't prevent sunburn.

I do my cooking in a pressure cooker over a hobo stove. I don't have to watch the food cuz it won't burn before the fire dies down. I boil a dozen eggs or some fish stew on the bottom while I steam-bake a big bagel from my own dough in a stainless bowl floating ontop that. I grow my own sprouts for vegetables or eat the herbs that locals show me. So I don't need groceries and can stay away from towns a long time.

Every couple of days I'll drive a couple of miles til I have cell coverage and check my email to see if my life is still simple. I use my cellphone as a USB modem. My service is an old plan from Tmobile with a Motorola V188 phone. If I've been doing a lot of woodwork I'll gang up my batteries to recharge in parallel during the drive.

I sit in my comfy recliner in the shade and make cad drawings of Indonesian sailing canoes on my laptop. Solar panels charge my assortment of desulphated scrap batteries using bundles of christmastree lightbulbs as current regulators. I sip sun tea and nibble sprouts and a bagel with fish stew.

Colorful characters see my low-stress setup and come greet me like a long lost friend. They offer me beer and before long they're teaching me how to tune a spritsail like they did growing up in a Jamaican fishing village, or telling me what it was like to be imprisoned in "The Tombs" ("No privacy man! The worst!").

Step 2: Universal Motors

Picture of Universal Motors

This concept of running power tools on batteries, AC, or whatever source of electricity you've got is nothing new. Back in the day a lot of truck alternators had a high voltage DC output for powering tools.
Even now you can trick some alternators into putting out 110 volts DC by putting more current into the field winding. They never got around to changing the architecture of the alternator.
But you better disconnect it from your truck's electronics and batteries first.

Here's the motor plate on my Skil 100 planer. It says "Volts 115 AC-DC".
It doesn't care what flavor of juice it drinks as long as it's pressurized to around 100 volts.
This much-loved power tool was made almost unchanged from the 1930s til the 1980s.
Like most power tools, it has a universal brushmotor.
Once they they got the bugs out and got set up to make these motors in large volumes, the tool makers never got around to adding anything that that would make the motors incompatible with DC.

Some drills have a speed control that won't work on DC. Usually the drill will spin just fine, but only at full speed.


BlakeB38 (author)2016-11-15

For those asking if this will power game consoles you need enough batteries in series to make roughly 170 volts as inside the power brick is usually a switch-mode power supply that rectifies 120v ac to 170v dc. you are welcome

triumphman (author)2012-07-07

So what did you do when you finished playing Crocodile Gumby and your battery was dead! No way to start your vehicle is a bummer!

kedwa30 (author)triumphman2016-03-26

There's always a way. The first cars started with a hand crank. If it's a manual transmission, you can push-start it. You can put a hand crank in the chuck of a drill to make it into a charger. There's the solar cells. And of course you can always walk just far enough to flag someone down and get a jump start. :)

ecsaul23 (author)2015-08-10

Will this work for game consoles?

RileyM6 (author)ecsaul232015-08-27

that's what i'm trying to figure out too. Game consoles and guitar amps

kedwa30 (author)RileyM62016-03-19

Since game consoles and amps ultimately use DC, you can power them off a battery, but it's not as simple as connecting the terminals to the plug. The plug goes to a transformer which prevents the DC from passing on through. So you would need to know what voltage DC you need and where to patch it in. If the plug is a wall-wart that does all the converting to DC, then you can simply look at the output, get enough batteries to match it, then cut the cord or make a connector to hook the battery up where it plugs into the amp. But if the wall-wart only transforms it from, say, 120VAC to 12VAC, then I don't know if hooking up 12V DC will work, but it might.

kedwa30 (author)ecsaul232016-03-19

Game consoles use a transformer to convert the wall AC to whatever voltage DC they use, so in a word, no. But if you know the DC voltage your game console needs, you can directly hook up batteries to match that voltage, not using the plug or transformer. It's complicated because some game consoles need a variety of voltages. You can also use DC-DC converters to get whatever voltage you need from one 12 volt battery and those are usually a lot cheaper and more efficient than an inverter.

Wade Tarzia (author)2006-08-31

That's the life! If you are taking requests (and I'm still hoping to see "how to build a proa on the Majuro Atol beach with epoxy and dead vegetation") then I'm wondering if we could see an Instructable or two on Swamp Recipes -- i.e, how did you make your fish stew exactly? And etc.

TimAnderson (author)Wade Tarzia2006-09-02

One strange thing about living in a swamp or any camp-anywhere country, is that once you're out there there's nothing to spend money on. It's weird after a couple of weeks to still have the same five bucks, two dimes and a nickel in your pocket.

Wade Tarzia (author)TimAnderson2006-09-02

Did you bring your adz with you and use it a lot? (would seem to be a good swamp tool) I saw a whole box of old adzes at the Wood Boat Show last week but they were rather large two-handed ones and very pricey; reluctantly I dragged myself away. Hard to find a used/antique one-handed carpenter's adz.

dpatterson13 (author)Wade Tarzia2015-01-19

There is a company selling small yard madox's that would make a good starter tool. I don't recall the manufacturer but one could probably find it in a search. It was a yard tool, but when you picked it up (the small version especially) you knew it was all business. The small one was about $20, the next size was $30. Fairly rough forgings but nothing that wouldn't be removed anyway before it was put into use.

Wade Tarzia (author)dpatterson132015-01-19

I love getting replies to 8-year old threads -- it makes me think there is more solidity to this often ephemeral virtual digital world we are creating. I have, since this thread, found an excellent source of adz blades from a supplier to the Japan Woodworker tool catalog. These are adz blades for which you must build a handle -- he supplies the plans -- or go into the woods to find a proper crook to be shaped into one. These blades are LASHED on to the handle with a waxed nylon cord which he also supplies with the blade. I bought a small and a large. I have used the small several times -- it is excellent despite the too-light wood I used. Have not yet gotten around to building a handle for the large blade (which is not very large). They come honed and razor sharp. Carry on, and thanks for your reply!

triumphman (author)Wade Tarzia2012-07-07

I still have mine. Saw a guy on youtube build a log cabin by hand in Alaska. He had one. So I went out in my garage, found mine, and sharpened it and oiled it! I'm dreaming of course , that I may wake up from this dream and build my cabin!

TimAnderson (author)Wade Tarzia2006-09-14

I should do an instructable on adzes. There's a lot of variety. A straight-claw framing hammer would make a great adze if you could weld a cutting blade across the claws. Some people use a pickaxe with the pick cut off, but that's a big tool. If you can get a "cooper's adze" you'll be very happy with it. There's probably a dichotomy between "adze-thinking" cultures and "axe-thinking" ones. The Hawaiians used plane irons in their adzes when they could get them. Some pacific northwest tribes did the same thing, I saw video of that. The stroke they use relies on the iron bending to get the scalloped surface they want on their longhouse columns.

Wade Tarzia (author)TimAnderson2006-09-17

I have an antique cooper's adz, a bit too far gone to use except as conversation piece (though I have no problem with using a sound antique tool otherwise -- what is an antique, for that matter?). I was looking at a bowl-making adz at a local woodworker's shop. Saw the same ones in a catalog, and it said "honing required." The same brand at the shop had an 'edge' that was at least 1/16 thick -- more like "major grinding" required. I was pretty pissed and glad I didn't order it unseen. Yes, by all means, do an adz Instructable. Speak a little more about the one Mau Pialug made on your other site.

pfred1 (author)Wade Tarzia2007-01-10

I always wanted to make an adze out of an axe head. I do have a couple of adzes now, but they are difficult to come by. Axes on the other hand, its like they grow on trees or something. It sounds like a fun forging project to me. Maybe I'll get around to it someday.

Wade Tarzia (author)pfred12007-01-18

That would solve the problem of the handle-hole and steel quality, if you want to spend time forging (I have forged two things: a letter opener from a horse shoe under the guidance of a blacksmith, and then I went right home and used my Dad's acetylene torch to forge a Roman short sword (don't ask me why, I was much younger then!). Lot's of fun. Forge in the darkness to see the proper color of the glowing steel best). The problem I have had with non-tapered adz-handle holes is that the handles loosen up fast because the forces on the adz are slightly 'outward' (centrifugal?). I drilled a hole through mine and set in a nail for safety. The better handle holes are tapered in toward hand, which tightens the connection in use.

pfred1 (author)Wade Tarzia2007-01-24

Hmmm a tapered hole to hold the handle, that sounds like a good idea. All of this will have to wait until I have a forge setup at my new place though. It'll be worth it, the prices for specialty woodworking tools are obscene!

EmmettO (author)pfred12010-06-18

If anyone wants an adz, I can make one out of a masonry hammer in my forge. Or If you want a different size let me know. . .

sweetrocketsky (author)2014-06-23

You know, I thought that might be true. I was actually going to rig up some test to prove it to myself.

EmmettO (author)2010-06-18

I had seen a set up a long time ago (maybe on instructables?) where a guy used a circular saw and a few batteries to make an electric bike. Maybe it was you? I was going to try running my electric weed trimmer on a car battery but according to this, i'd prolly need several, which would be less than ideal. I wonder if 76 D cells in a bandoleer would have enough juice? Oh the horror!

astral_mage (author)EmmettO2014-03-04

look up on youtube 944 9 volt batteries.

hintss (author)EmmettO2010-11-29

IDK, but someone used like 40 AA batteries to power a laptop for like a few minutes

bhvm (author)2013-09-02

Amazing piece of insight! I never knew that power tools are dc compatiable. sadly it won't work with 240v tools, will it?

smokehill (author)2007-11-05

I've saved several of my cordless drills just to run directly off car batteries, eventually. As others may have noticed, a few years after you buy your nice cordless drill (saw, whatever), the company -- even big brands like DeWalt -- don't have replacement batteries. I know you can split the battery case and replace the cells, but it's sometimes tricky if it's a heat-sealed battery. Recycling these tools as 12v-direct seems like a simple recycle. I figure just splicing a 20-foot cord with a couple of clamps appropriate to the battery posts will yield a useful, "corded" tool away from home. Probably soldering is the sensivble way to attach inside the tool's handle. I have a couple of drivers who carry 14 or 18v cordless drills for repairs of my rental equipment, and this is my next effort to supply them power without the hassle of running out of juice mid-job. I suspect that running the tools with the engine idling won't affect the level of charge very much. I suppose one could use a cigarette ltr adapter instead of clamps, buy I like the idea of the juice coming thru BIG wires.

triumphman (author)smokehill2012-07-07

Idling, with the price of gas as it is is not very smart! Or thrifty!

Yerboogieman (author)smokehill2008-05-15

i saw that kipkay laptop battery thing and mine was a heat-sealed battery, which sucked

_soapy_ (author)smokehill2008-03-26

You'll get about 11 to 13V from the car battery when the engine is off, and normally 14.4V when the engine is running. Always useful if you need that little bit more power. I run my key machine off a battery pack and inverter, then back into a car charger, as I can then access ~12V or 13V or 14.4V easily, which boosts the power when cutting big steel blanks down.

pro2xy (author)2012-03-29

I dont care if Im reviving a dead 'ible (it never is dead).
I dont care if your batteries blow up into flames...!
All I know is that this is the LIFE Im CRAVING FOR!!!!!!!

Waaaaah!! Bliss!!

uberdeity (author)2010-03-07

A lot of electronic devices work from switched mode power supplies, which would work fine from a suitable-voltage DC supply; the first thing they do is rectify and smooth the incoming voltage so that it can be inverted again, so a DC supply would just pass straight through to the inverting stage.

Beware, though- if it's a transformer or motor coil that you're connecting to the battery, you'll just short out the battery and probably damage your transformer/motor coil.

liquidhandwash (author)uberdeity2010-03-07

I havent left any thing on dc that didnt work, on for any lenght of time, ops  that doest work unplug it.  it has cause no damage yet. I agree if you left it plugged in it would proabley over heat and die. It doesn't short out the batterers, or cause an damage to just check if it works, well not that Ive found so far.

uberdeity (author)liquidhandwash2010-03-08

You'll be okay for a few seconds, but DC through a transformer coil or motor winding is pretty much just a short if left for more than a few seconds. Well, more a few-ohms resistor placed across it than a short.

A car battery shouldn't sustain any damage for short periods- they're designed to provide hundreds of amps for a short time during starting the car. Just don't go off to find the manual with a non-working device hooked up to the battery!

Using non-lead acid batteries (i.e. if someone tried using a NiCad or Li-Ion pack from another device), you run the risk of serious damage to your batteries if you're hooking it up to a low-resistance coil.

hintss (author)uberdeity2010-11-29

all batteries are, IIRC, capable of providing infinnite current. its the duration that it can do that that matters.

as a sidenote, I my brother once shorted 2 AAs in series for about a minute without anything bat happening

schumi23 (author)hintss2011-12-17

ok, this is a bit late, but that would be because double AA's also provide only 3 volts(2 of them) and it wont to anything. however if it was even jsut 2 nine volt batterys, you woulda seen alot of heating up.

petre (author)2010-06-19

petre says: im an old timer electrician also. a DC or AC device draws current from the source. so, it doesn't matter how much current the source can provide it won't damage the device. if you draw more current than the source can produce the voltage will drop and overheat. a fuse is a current device. think about it. your batt is rated at what? and your tail light bulb is rated at .5 amp no way are you going to burn out that bulb. it will burn out if you over volt it.

jules15 (author)petre2010-06-21

So you could hook up an LED with 1.3 volts and 10 amps and it will be fine?

hintss (author)jules152010-11-29

it won't pull 10 amps: either the 10 amps figure is a maximum, on the current source is like a solar panel, and has a voltage/current curve that would cause it to overvolt

MaXoR (author)jules152010-06-24

Simpler analogy: Volts are like the size of a river coming off a lake. Current is how much water is in that lake, available to flow down the river. So with that in mind, you can float a small boat, or big boat.... both can float in the river, but an oceanliner is too large for the river, need a larger river.... however your lake would run out quicker because of the larger river needing more water to flow at the same speed. (And that is the calculation of wattage) If anyone needs help with my explanation..... ask!

petre (author)jules152010-06-21

petre says: jules as long as your batt is 1.3 volts you can do it. the current is whats available. think about it . my house breaker box is rated at 200 amps current 120 volts. if i have nothing turned on but a lamp it will not burn out. the lamp draws current from the breaker box. key word here is DRAWS current.

petre (author)jules152010-06-21

petre says: jules as long as your batt is 1.3 volts you can do it. the current is whats available. think about it . my house breaker box is rated at 200 amps current 120 volts. if i have nothing turned on but a lamp it will not burn out. the lamp draws current from the breaker box. key word here is DRAWS current.

maevonnie (author)2010-09-28

Oh my! That would be so cool to not have to use and inverter. They really can be the pits sometimes, like on the awnings at my house, they are retractable, and they need an inverter in order to run properly, which is such a pain!

liquidhandwash (author)2010-01-24

Thanks Tim for this great instructable, In this part of the world everything is 240 volts so I wire up 18 batteries and started pluging in everything I could find, Computer, Printer, flat screen tv, dvd, playstation, VCR, compact florescent lights, Phone and laptop chargers, switch mode battery charge. I found that as long as it doesn't have a transformer or an induction motor almost everything works.The stuff that doesnt work doesn't go bang it just wont go, no damage done.( I had a laser printer that threw a fit and jammed the paper but no damage) Do you have any problems with the switches arcing or burning out? I havent as yet but everyone says I will.

abadfart (author)2010-01-05

i miss my Datsun he could take anything you did except girlfriend's driving

Mtalus (author)2009-07-13

OK, so I'm 2 or 3 years late with a post. I hope this is still useful to someone. I run universal motor power tools from my truck alternator all the time. (I started doing this when the cost of an inverter with the needed capacity was very costly. Thankfuly this has changed now. ) My trucks alternator has an external regulator, so I can unplug the regulator and plug a jumper wire directly to the F (field) terminal of the alt. I replaced the output stud nut with a wing nut to allow quick disconnect of the battery from the alternators' output. I have an old extension cord end (12ga) that was cutoff early in it's life. I attached two heavy alligator clamps to the wires. Both have inline fuses. To use, with the engine off, I unplug the regulator and attach the jumper wire to the F spade. I detach the output wire and ensure that it cannot short to anything (it's other end is still hooked to the positive of the battery-be careful). I then hook the extension cord clamps to the output stud and ground. I double check that no wires are in danger of contact with moving parts and start the engine (I have everything wire tied in place and just connect/disconnect as needed). Then I connect the other end of the field jumper to a 12v positive (my truck has a grounded field). At idle I get about 35v with full current at 12v through the field. I then plug in a voltmeter to the plug end and increase the engine speed to get the voltage I need and hold the speed with a clamp on the linkage. My alternator tops out at about 135v. This is LEATHAL. Be careful. Potential problems: 1. Did I mention leathal voltages? Be very careful. 2. It's dangerous and embarrassing to have your car take off with a clamp on the throttle linkage. Make sure it is not and can not be put in gear. 3. The diodes in the alternator may not be able to handle the higher voltage but they are easy to replace with upgrades. 4. The engine's ignition system and the alternator's field are now draining a battery that isn't being recharged and may go dead if used too long. 5. Remember to reconnect the alternator when done. It's a hassle to get a jump when the battery goes dead at a later date because you forgot. 6. I'm certain there are other things that I just haven't had the pleasure to experience yet, so be careful...didn't I say that already? A good online alternator resource is "alternator secrets". Just do a search and you should find it. Sorry for the novella length.

TimAnderson (author)Mtalus2009-07-14

Great tips! thanks! do you have pictures? this is a whole instructable by itself!

Mtalus (author)TimAnderson2009-07-14

No pictures, sorry. I've been weaning myself off of electronics and now only use the library's computer. It kicks me off after an hour and rescues the rest of my day from surfing. Is there a 12 step program for this? I wish I had a good picture to post as it would add important info. I also have on-board air from a York auto air conditioning compressor. The compressor I used is from a '69 Mustang. It's made from cast iron and must weigh 50lbs! The aluminum units from mid '80s Volvos are half the weight. Having air, welding and power available on a mobile platform is very nice. I believe that there is an Instructable on adding air and welding; and he posted video. For welding I added an auxiliary alternator that I converted from Y to delta. The conversion lowers the peak voltage by the sq. rt. of 3, (1.73) and raises the current by the same; i. e. 60 amps to 100 amps. If I had been thinking straight at the time I would have brought all of the leads out from the stator windings so that I could switch from Y to delta and back externally. The unit as configured puts out about 80v peak. My angle grinders run fine at that voltage, so I can weld and grind with the same alt. Another benefit of two alternators is reducing the risk of "blowing" a vital unit of the vehicle. No one wants to get stuck at a jobsite, unless perhaps it's at a resort or something. One more comment: If using a string of batteries in series it's a good idea to use batteries of similar capacity to help avoid overheating one and having a nasty accident. That said I weld with 3 batteries in series, with an inductor, and am quite happy. I still have both eyes and most of my clothes are free of acid holes. Monitor them closely and don't let them heat up.

TimAnderson (author)Mtalus2009-07-14

I bet you used this gear to build even more cool stuff!

Mtalus (author)TimAnderson2009-07-28

Sadly, it's most often used to run a hedge trimmer or something equally glamorous and excitig. I remain optimistic though, not to mention it was fun to cobble it together in the first place. See what I mean? I just spell checked and see that I misspelled exciting. Fruedian slip of tig I'm sure.

panstar1 (author)2008-09-20

IF your going to be putting that many Lead Acid battery's in series (very bad Idea ) you should put a fuse in there ,or you will be swimming in sulfuric acid and shreaded battery parts if there is a short. Of course if you like the smell of lead acid battery's exploding ,you could just hook up 10 and watch the to end battery's find a new home in a million peaces !!! But really be careful acid in your eyes is not the same as soap in your eyes. There are kits you can buy that can supply you with 120 & welding options by simply running off of the alternator in your truck. & they have come down in price since they first came out so if you only power for a short time I would go that route it is better than carrying battery's around all the time ,even hooking the kit to a small tyota engine could work they don't use very much gas and there cheap there the only thing that is still in one peace !!!

austin (author)2006-08-31

hey is that sander from harbor freight? I work for them.

About This Instructable




Bio: Tim Anderson is the author of the "Heirloom Technology" column in Make Magazine. He is co-founder of, manufacturers of "3D Printer" output ... More »
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