Picture of Cordless Power Tool Conversion 18VDC to 120/240VAC
Necessity is truly the mother of all inventions....and my case was no different.  About a year ago, I found myself with a dead battery for my Ryobi 18V cordless tools and no means of getting a new one as I was working overseas. So I came up with a setup to run my tools off AC (household current) safely and with no worries of my tools dying halfway into the job.

Now I enjoy all the benefits of battery operated power tools just as much as the next guy....They're convenient, flexible, and you can usually get quite an assortment of tools that run off the same battery.  Then the inevitable happens....you get the dreaded blinking set of lights on your charger and the batteries die out almost instantly. Your faced with two options.....Drop $50-$100 on a new set of batteries or try rebuilding them yourself.  Neither one of those two options appealed to me nor did I have the time to order the parts from overseas.  As anyone in my situation might do, I scoured the internet for an alternative solution.  I found guys connecting car batteries to their drill...ummmm no thanks.  Then I came across the idea of using an old laptop power supply in place of the battery.....The voltage seemed right, but alas the wattage was too small.  Even at 180 watts, the biggest pc power supplies couldn't provide enough to overcome the start-up current of my battery operated circular saw or angle grinder. 

The principal of the pc power supply was sound, I just needed something bigger.  After a little more research I found that the common everyday laptop power supply is what they call a "switch power supply".   Turns out, switching power supplies are very common everywhere in the world, affordable and come in a variety of voltage and power ratings... I eventually chose a 350w AC/DC power supply produced by a reputable company called Meanwell with a voltage range of 15-18volts DC.

Wiring of the power supply to a dead battery is very straightforward, but the following instructable goes through the details step-by-step.
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traen28 days ago

I completed this project. I have a set of skil tools which are quite good. However, they were complete useless because of the battery situation. After the conversion, they now work adequately for the small home projects that I do a couple of times a year.

My setup looks almost identical to the instructable. The project was easy, quick and inexpensive. I cut through a rough cut 2x4 with my largest drill bit relatively easy and it wasn't even a wood bit. I cut through the same with the circular saw with some difficulty. I cut through the same with the recip saw pretty easily. That's all I need so, the project was more than worth it to salvage completely useless tools.

Having said that, JeremyA2 is right. The wattage/amperage is low. I wish i had gotten the SE-600-15 mean well power supply. It costs twice as much but, still about the same as a li-ion battery. I doubt the tools draw more than 40a. I think I'm going to call meanwell and see if they will do a swap for me.

Anyway, this instructable is awesome and the comments were also quite helpful.

BenRuss2 months ago

I have a set of Black & Decker Spitfire tools that I just picked up for free. One of the batteries I have managed to revive using my car charger but the other one is toast. I notice a lot of comments about the proper amps to get full power from your tools but I notice that you went with a unit that has 350W. Am I confusing Watts and Amp draw? I have seen people talk about only being interested in 400plus watts and others that say over 20 amps??

Do you find that you get full power and start-up with this set-up? if so, I don't think I want to mess around with my laptop converter, I will just drop the money and do this.

Thanks in advance.

franco40 (author)  BenRuss2 months ago

Hey Ben,

I'm not familiar with the Spitfire line from B&D.....Is it 18vdc?

Watts and Amps go hand in hand. A power supply rated for 350w will produce 19.4 usable amps at 18volts. A 400w supply will produce 22.2 usable amps at 18volts. (watts / volts = amps)

To answer your question regarding the performance of my setup, I've yet to stall the motor on any of my tools during initial start-up or under heavy loading. Recently I've connected a watt/amp meter to the power supply and both the saw and drill seem to consume the most power under heavy loading. But still no stalling and the performance doesn't seem to be deteriorating.

As for the laptop converter, don't waste your time....Been there, done that, and it will just stall under heavy load. The industrial powersupply mentioned in the instructable has built-in overprotection and I've spiked them over 40% on the rating without stalling them.....They are built for the abuse.

Hope this helps. Let me know if you need further help.


Anachrophile2 months ago

Great work, Franco. I haven't made it, but after an exhaustive search of the various options (rebuilding the battery with NiCd, LiPo, or LiFePo, buying new batteries), this is probably the most cost effective solution for getting new life from old tools for people who don't mind being attached to a box. I found good prices on the power supply (Mean Well model no. SE-350-15, I surmise) at Mouser and Jameco.

The voltage of these supplies being adjustable within a narrow range, I'd like to propose the possibility of moving up to the Mean Well HRP-450-24. The Mean Well chart says that its voltage can be lowered to 21.6v, and increased to 28.8 volts. Is this low number too high for 18v tools? My thinking is that if someone had 18v tools now, but wanted to move up to 28v tools in the future, this could cover both. (Clearly, 28v hasn't exactly caught on, though.) I'd appreciate the thoughts of someone more experienced in this area.

Personally, I'll most likely use the SE-350-15, a bargain compared to other options. A higher wattage model, the SE-450-15 is available for a little more money, for those those think they'll use the power.

jfritzy2 months ago

I am decent when it comes to working with electricity but am far from a professional electrician. I can do normal household repairs and things like that, but I find this conversion to be a little intimidating.

I have messed around with power tools and small machines but not really raw power supplies like the one(s) used in this instructional. Recently, I posted an Instructable about converting an air compressor by adding another tank and increasing the capacity. Working with compressors and the possibility of exploding the tank didn't worry me as much as working with electricity like this would.

Basically, it comes down to not understanding the science of it enough. Do you have any tips or reading material you could suggest to an amateur electrician?

Greg_NAtlanta4 months ago

I like your approach to this Instructable. I will be using this on one of my other battery powered tool needs. The only thing is that I'm taking the lazy way out on the Ryobi 18V project as I found on eBay "TWO Ryobi One+ P108 18v High Capacity Li-Ion Batteries P122 NEW" for $82.50. These are 4Ah each and I have purchased 4 and all are perfect. These are just too good to be true.

As I said earlier, I will be utilizing your project on my other battery needs and I thank you for that.

franco40 (author)  Greg_NAtlanta4 months ago
Hey Greg,

The price for Li-Ion batteries have dropped significantly since I originally posted my Instructable....Thankfully, it was just a matter of time.

Although I haven't invested in the new 18v Ryobi Li-Ion batteries, I have taken advantage of some of the smaller 12v Li-Ion options out there on the market, but not Ryobi. For what I do, the torque is more than enough and the weight and size savings is a great convenience. I'm sure one of these days I'll pick up some One+ Li-Ion, but it probably won't happen unless a big job come around to justify it. Too many other toys higher on my list.

Good luck with the setup and let me know if you have any questions.

P.s. I my latest rendition of this setup, I used a 50 caliber ammo can as the housing versus the cheapo plastic tool box. I also added a Watt meter to track current draw from the tool. Very happy with the results.
franco40 (author)  franco404 months ago

Here's an image of the latest PS.

The Fe Factor made it!5 months ago

Very nice! In order to avoid an incidental plug in of the tool directly into a 120V outlet I use a Neutrik power connectors on my DC line.

franco40 (author)  The Fe Factor5 months ago
Good thinking....The subject of accidental connection to a 120v outlet has come up with some of my readers.....I suggested a twist lock generator plug but your connector is much slicker. Where did you buy the match set of connectors?


I bought male and female pair


and http://www.parts-express.com/neutrik-nac3fx-w-powe...

sure, other options can be looked at, but I like how solid connection is achieved using this two plugs

rijack2 years ago
Awsome idea! I've thougt about this for my DeWalt 18V machines.
How did you figure out that 350W power supply was enough?
Did you measure, or looked up via specifications, or...?
franco40 (author)  rijack2 years ago
Hi rijack,

As I mentioned in my instructable, I originally tried a 180W power supply from a high end laptop but it just bogged down with any load. I looked around the internet and found the 350W which gave double the amps. I figured 20Amps should do it and if it was overkill, it wouldn't be by much. The motors of the tools will only draw as much current as they need. My cordless grinder has the biggest motor....if it didn't stall under load then I'd be safe.

I plan on putting a Youtube video showing the setup in action. With that I'll put an amp meter showing the current draw at startup.

Hope this helps.
pc-fan franco409 months ago

I like this article, thanks for the instructable and the info in comments!

A friend gave me an 18V battery drill with exhausted cells for free and I would like to modify it to run from the wall outlet without spending much on an expensive power supply.

I have found some examples of utilizing spare components, could a pc power supply be modded for the task? Or maybe something similar that is easy to find? I have a dozen of these PC PSUs rating from around 200W to 500W though they provide 12 volts output.

Cordless Drill to Corded - Modify Cordless Drill to Run from Wall

Power supply to my old Skil 2972

Any ideas or recommendations? THX

franco40 (author)  pc-fan9 months ago

Hey PC-Fan.....As I mentioned in my instructions, I found a 350w supply to be powerful enough to cover all my tools. A bigger supply like 500w would do the same job as the tool only pulls what it needs. Now for your question about using a 12v supply vs a 18v, you can try it although your tools might not perform 100%. I would suggest if you want to utilize the 12v supply, get a stepping transformer to bump the volts to 18.

fullfatc franco405 months ago
Hi Franco.

I have been trying this over the last couple of days with no results. I am trying to do this with dewalt 14.4v setup and have bought a hobby king switching power supply at 30a 14v-18v . But the unit has a o/c protection . Every time I put load on the drill it cuts the power supply out. I have tried thin leads and thick. Thin will run the machine but very weakly . Is there anything i am missing .

Please help

franco40 (author)  fullfatc5 months ago

Hey Fullfatc,

Sorry to here you are experiencing issues....I don't have any experience with the models put out by Hobby King, but they are a pretty reputable company. Have you tried their customer support? I recently added a Watt Meter to my setup to monitor the output. It might be worth to check your amp output. The unit might be splitting the 30amp output 50/50%, but I doubt it. It could just be a defective unit from Hobby King. Can you give me the model number of your unit? Add some pics of your setup and I'd be happy to check it out.


fullfatc franco405 months ago
Hi Franco ,

Thanks for coming back to me . I don't have any pics at the moment but the outputs don't split and my multimeter only goes to 10a so I can't check . It is the 13.8 - 18v 30a 540watt power supply. I have checked the voltage of course and wiring is good. But like I said if I use really thin wires it will run weakly. Thick wires will just cut straight out especially on circ saw and jig . It trips with overcurrent . What watts were you drawing at full torque
franco40 (author)  fullfatc5 months ago

Hi Fullfatc,

To your request, I took my circular saw to a 2" thick piece of oak. Surprisingly, the current I read off my Watt Meter showed an amperage draw of 28amps (~530W) when I intentionally made the saw bind. The max rated draw from my 350w power supply should only be 20amps at 18v so either my meter is off or my power supply is over clocked somehow....Regardless, under normal operation conditions (i.e. not binding the saw intentionally) I have no problem cutting 2x4s or 3/4" plywood with my Ryobi 18v saw using this setup. Could the overload protection of your power supply be a user variable feature? As for the wire thickness, I'm using a section of 16gauge extension cord from the power supply to the battery adapter.

franco40 (author)  franco405 months ago

Check out this website....


The power supply I have is "constant current limiting"....I couldn't find out what style the Hobby King version is, but since it was designed for charging batteries, it might have a different style overload protection.

The version I use can be bought for $50 on ebay:


fullfatc franco405 months ago
Hi Franco thanks for the info you have been amazing I thought it was the oc protection I have bought a similar product to yours although it's only 12v dc converters are only rated to 10a over here . Hoping the 2v won't make a massive difference . Highly annoyed wouldnt think the oc protection would need thinking about .

fullfatc fullfatc5 months ago
Hi Franco ,

What I meant is the 12v unit is rated at 350 watt 30a but a dc to dc converter is rated to 10a so I couldn't use one .

franco40 (author)  fullfatc5 months ago

Hey Fullfatc,

Sorry the Hobby King power supply didn't work out for you....I might have tried it myself if I wasn't so familiar with the Meanwell version. As for your new supply, I'm concerned with more of the 10a rating versus the lower voltage. Try it, but you might find the you don't have enough juice to overcome the startup current demand when you squeeze the trigger.

Good luck.


pc-fan franco409 months ago

Thanks for the tip and your quick answer, Franco40!
A suitable step-up transformer / dc-dc converter seems affordable (~15$)

jenkinsdan pc-fan9 months ago

You can wire transformers of the same voltage in parallel; I have also wired transformers in series to increase voltage. I WOULD NOT RECOMMEND THIS IN ANY APPLICATION THAT WAS LEFT UNATTENDED!

pc-fan jenkinsdan9 months ago

@jenkinsdan Thank you for confirming this option!

I have thought about this but a friend discouraged me saying that this would not be possible. Minutes ago, following your advice I found a nice tutorial about this:

Using Power Transformers In Parallel or In Series

Kinda hazardous how the host uses live electricity while connecting wires but the video is very articulate and comprehensible.


I would make sure to avoid it but what are the risks of leaving the connected transformers unattended? Heating and fire?

I think I will apply the safest, simplest, cheapest method available, but it is good to know that this would also work!

Wanted to let you know I realy appreciate you ingenuity and sharing in your tutorial on the ryobi. Followed your instructions and now have a functional power source. Thankyou!!!!!!
franco40 (author)  denis.matties7 months ago
Hey Denis......Happy to oblige. Hope you get many years of service out of the setup. Keep a lookout for some new ideas I'm working on.
JeremyA26 months ago

So out of curiosity I decided to test this. Since I own the exact same
Ryobi drill used in this instructable I hooked up an ammeter in series between
the drill and battery. Before testing the amperage I checked the
battery voltage. This battery has not been on a charger in a couple
weeks and still read 20.0 volts. With no load whatsoever the drill
pulled almost 4 amps at full speed (20 volts x 4 amps = 80 watts with no
load). I then decided to simulate a load by trying to hold the chuck
from spinning with my hand as I pulled the trigger. I recorded over 20
amps (My ammeter maxed out at 20) before I could even manage to pull the
trigger all the way and I wasn't strong enough to hold the chuck with
the drill running at full strength. So not even under a "full load"
this drill draws over 20 amps. (20 volts x 20 amps = 400 watts under
partial load). So even a 350 watt power supply would not provide as
much power as the battery would. You'd probably need closer to 500-600 watts to be completely equivalent.

In fact, if you look at Ryobi's actual corded version of this drill (


), it draws 4.5 amps at 120 volts, which is 540 watts.

I love the idea of having a 120V to battery pack adapter, and want one too just in case.

As an electrician may I strongly recommend that nobody ever uses solder on electrical connections that may carry more than 100W. It may melt and arc, causing a fire.

DICK WEED1 year ago

I've been thinking of buying Ryobi's hybrid string trimmer. If I do I'm going to take it apart and see what they did to make it able to run off batteries or AC. Might actually be cheaper and easier, especially the reconditioned ones.


franco40 (author)  DICK WEED1 year ago
Hi DW,

Thanks for the comment....I wasn't aware Ryobi had a product with hybrid capabilities. Dewalt had something years ago for its 24v tools, but it didn't catch on I think. Is it a recent development? The price looks good considering what your getting. Let me know how you make out.


I Googled a bit and found Ryobi also had a blower that was a hybrid too, not sure that they still make it though. These seem a bit different than the DeWalt in that you don't have a special plug in battery pack, you just slide a cover that exposes a 2 prong AC "plug" while it covers the battery hole. And there don't seem to be a lot of extra electronics tucked in anywhere or at least not that I can tell looking at on line pics and definitely doesn't look like it has a fan to cool an ac/dc converter. I'm wondering if they went the other way and put in an ac motor and then the battery DC is switch to AC. My electrical prowess is pretty limited but the inverters for DC to AC usually seem pretty big too, so there doesn't seem like enough room for that. May go buy one from the local HomeDepot soon since new is only 10 bucks more than these refurbed and see what they look like inside.

I bought it but only my wife and son used it to weed eat and trim. They didn't like it, thought it was to wimpy for what they wanted and they didn't like the auto line feed feature as it seemed to feed out line every time you stopped then started it again whether you needed more line or not. By the time I got back home that evening the'd already cleaned it up and stuck it back into the box to return so I never got a chance to look it over or investigate how they did the current type switching....dang it!

Oh and I found this site where a guy was looking for a conversion adapter


And he found this one and liked it


TomD88 months ago

I have the Dewalt 24V setup including the Ac adapter Its about as big as a 4.0 Li on battery a lil bigger we couldnt do same in a 18V Ni cad pack? quite larger than Li on compact batts.... i just wanna use drills battery pack cuz it fits well accepts the connection etc.... 5.5 x 2.7 x 2 in.. slide on battery 18 v ni cad

My personal favourite trick:
The cheapest source of suitable batteries is those sold for (serious) radio control models.

Take a cheap RC model battery pack with compatible voltage and capacity, and a matching plug.   Then make a five foot lead from the plug to the power tool terminals.

Then just drop the battery pack in your pocket, and conveniently use the power tool with much less weight in your hand.

And if it is a reasonably compatible voltage, and with an appropriate socket fitted, run it from a car battery charger when in the workshop.

If the car battery charger is a slightly lower voltage, the tool will run a bit slow.

If it's a higher voltage, the tool runs faster, but give it regular breaks to cool down or it will overheat !
RC battery packs are available with a wide range of discharge rates, indicated by a number followed by the letter C (e.g. 10C, 20C), where the number is the fraction of an hour in which the battery can be safely drained. For example, a 3000 mAh 20C pack can be drained in 1/20 h (3 min) and therefore can supply 1 A for 3 min.

Somebody please tell me if anything in italics was wrong, because I suspect that it was.
phase90 Ian012 years ago
Actually, the C rate is the drain rate that is a multiple of the capacity. The 3000 mAh pack that has a 20C rate means that it can provide 60 Amps continuous drain (3 Ah * 20). So, it can provide 3 Amps for 1 hour (3000 mAh) or 60 Amps for 3 minutes (60 minutes / 20 = 3 minutes).
Ian01 phase902 years ago
That makes a lot more sense. Thanks. :)
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