Run AC Tools on Batteries Directly, Without an Inverter





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

About: Tim Anderson is the author of the "Heirloom Technology" column in Make Magazine. He is co-founder of, manufacturers of "3D Printer" output devices. His detailed drawings of traditional Pacific...

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

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

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.



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    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

    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!

    1 reply

    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. :)

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

    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.

    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.

    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.

    11 replies

    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.

    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.

    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.

    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!

    adz, made March 2010.JPG

    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!

    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.

    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.

    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.

    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.

    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!

    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. . .

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