Cordless Power Tool Conversion 18VDC to 120/240VAC

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 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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The Fe Factor made it!8 days 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 Factor8 days 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


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 franco404 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-fan4 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.

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)  fullfatc23 days 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.


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)  fullfatc23 days 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)  franco4023 days 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:

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 .

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)  fullfatc22 days 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 franco404 months ago

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

jenkinsdan pc-fan4 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 jenkinsdan4 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.matties2 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.
JeremyA21 month 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

TomD83 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. :)
pc-fan Ian014 months ago

@DOTAU, @phase90, @ElectroFrank et al

OK, I have an 18V battery drill; the battery pack contains 15 pieces of cylindrical batteries with the text: "SC1.2V 1200mAh NiCd" – these look like the attached image. Their metal casing is rolled into paper.

How to properly calculate the parameters for a suitable power supply? amps, watts – I guess voltage would be 18V :)

What do the 'SC' letters mean?

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


Hi pc-fan, NiCd means Nickel-Cadmium cells which are 1.2V, so 15 in series makes 18V. 1200mAh is the individual cell capacity (1200 mAh = 1.2 Ampere-hour). The battery pack is therefore 18V, 1.2Ah, when new it should provide (about) 1.2A for one hour. But drills can take more like 10A, if so you might (theoretically) get full power continuously for about seven minutes.

To discover the maximum current that could be taken by the drill, remove the battery and measure the motor's resistance with a multimeter. The maximum current taken will be the voltage divided by the resistance. So if the motor shows 3 Ohms resistance, 18V / 3 Ohms = 6 Amps, so you would need a DC power supply providing 18V at (at least) 6 Amps.

(If the drill has a speed control, you would need to open it up and disconnect the motor to measure it's resistance.)

An ordinary cheap car battery charger giving 12V at 5A would do some work, but at much reduced power (the motor could then only take 12V / 3 Ohms = 4 Amps).

Power rating in Watts = Volts x Amps. A power supply unit must be rated at or above the maximum current drawn by the appliance.

Hi ElectroFrank, thanks for your precise and practical answer, this helps a lot! I will do this.

(SC is probably just the manufacturer's code name for the type of part.)

DOTAU phase902 years ago
3 Ah * 20 C = 3 Amps , not 3 Amp hours
phase90 DOTAU2 years ago
3 Ah (3000 mAh) is the rating of the cell or pack. If it is one string with nothing in parallel, they are the same. That means that the item can provide 3 amp hours of energy. In an ideal world, it is 3 Amps for 1 hour, 1 Amp for 3 hours, etc.
The C rate is the highest rate at which the cell (or pack) can be drained per the manufacturer's spec. In this case, 20 C. This means that the max drain is 20 times the capacity rating of the battery. 3A * 20C = 60 Amps. It only has a capacity of 3 Ah, so its theoretical capacity limits it to 3 minutes (1 hour = 60 minutes, 60 minutes/20C = 3 minutes). The reality of cell chemistries is that you cannot get the full useable capacity of the cell/pack at discharge rates higher than 1C due to internal series resistance and other factors.
In practice, the effective capacity of a battery is less at higher discharge rates. At higher currents, more energy is wasted as heat due to the battery's internal resistance. That's why batteries get hot when charging or discharging.

Please can anyone provide a link to a table of those RC pack codes ?  That would be extremely useful.
That is true. Some cell technologies are better than others in this respect, but yes it is harder to get all of the gas out of the tank at higher rates. It is the price we pay for being able to use it quick.
What are RC pack codes?
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