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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jeff822 months ago

Thanks for this. I plan on doing something similar soon. I was wondering about what power supply to use. I noticed that the one you got was a 15V and the device you are powering is 18V. Is there a reason why the 15V is sufficient? Would I be able to use a power supply as the following:

Thanks for your help.


That power supply is only 1.7amps, which means you can only supply 30watts to a tool. Most of the ryobi tools are designed to run at around 48 watts, so you will suffer power drops with anything less than 3.0amps

whitcwa jeff822 months ago

Batteries have internal resistance. When heavily loaded, their voltage drops. A regulated power supply has very little internal resistance. So a 15 or even 12 volt regulated power supply is plenty of voltage for an 18 volt drill. A couple of years ago, I connected a 34 amp 12 volt supply to an 18 volt drill and it has plenty of torque.

The Jameco supply has nowhere near enough wattage for a drill. Dewalt sells drills rated from 130 to 750 Unit Watt Output

Thorn-Boy2 months ago

Whilst doing some digging looking for suitable parts for a homebrew device, I

discovered this beauty!

The eFuel 30A Power Supply (£80.00)

Your eFUEL switching DC Power Supply is designed to use household
AC power source to power equipments that required DC power. The eFUEL
converts standard household power 100-240V AC to 12-18V DC power and can
supply up to 30 amperes of continuous power.


  • Two DC power outputs, up to 30a
  • Output voltage adjustable 12-18V
  • Large LCD indicates voltage and current amperes output
  • Two USB ports, 5 volts, 1000mA
  • Smart cooling fan
  • Over temperature protection
  • Overload protection
  • Short circuit protection

Or, better still this:

eFuel 1200W (15-30v) 50a Power Supply (£180)


  • 1 x DC power output, up to 50a
  • 3 x 10a Outputs (On/Off)

    Output voltage adjustable 15-30V
  • Large LCD Display
  • Two USB ports, 5 volts, 2100mA
  • Smart cooling fan
  • Over current protection
  • over voltage protection
  • overload protection
  • Over temperature protection.

    Short-circuit protection (on output)

There is also a 'eFuel 1200W (15-24v) 60a Power Supply', but I can't find the specs on the website.

Thorn-Boy2 months ago

Just a thought, but has anyone wrote to Ryobi and asked them to make one?

What kind if price would you pay for a 'Ryobi' made transformer?

I can think of several benfits, but can you think of any more?

I'll list the ones I can think of, but please list any more you can think of:

* Abilty to use mains power when lack of mains power is NOT an issue.
* Longer use times for those with limited number of batteries
* During 'Mains Use' the tool would be lighter (less user fatigue).
* Extended battery lifespan (if batteries only charged when 'Going Remote').
* Less Battery Changes' if working near mains power.
* Less batteries required by user.
* Less batteries produced by manufacturer (better for the environment).
* More environmentally friendly (less dead batteries going to landfill).

My cynical mind says that the reason something like this has not been produced by Ryobi (or other manufactures for that matter) is that it would impact on the future sales of the consumables, namely the expensive batteries.

So how many batteries do you 'Ryobi' users actually own?

Personally, I have four (albeit NiCad) and several chargers, but find I need to swap around a lot when using a few tools at the same time.

These NiCad batteries will die soon though as I've had them a few years now.

Personally, I jump at the chance of a properly made transformer.

No offence intended OP regarding the 'properly made transformer' phrase. I just don't fancy the idea of building one myself.

I would make the jump to 4 x Lithium, but the cost is ridiculously high to get decent batteries when they are only for home use and I would rather have just a couple and a tranformer for when working near mains power.

Nice work by the way.

DICK WEED5 months 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 WEED5 months 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.
vdv1017 months ago
Made it. Used it. Liked it. Thank you for this instructable!
danchanman11 months ago
I was wondering if a desktop power supply can be converted? But it only has 12v... Can it still work?
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.
DOTAU Ian011 year ago
phase 90 doesn't quite have it correct

The "C" rating tells you how much current relative to capacity, "mil Amp hour", that is safe to draw or charge your battery.

Amps = C * m A h / 1000 ( the /1000 is to go from mil amps to amps)

So a 1200mAh 10C battery is good for 12A (10 x 1200mA/1000)
A 1200mAh 15C battery would be good for 18A (15 x 1200mA/1000)

Exceed this rating for to long and excessive heat and catastrophic failure will surly follow.
phase90 DOTAU1 year ago
That is basically what I said. Rating * C for max continuous current draw. However, the C rate does not apply to charging at all.
phase90 Ian011 year 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).
DOTAU phase901 year ago
3 Ah * 20 C = 3 Amps , not 3 Amp hours
phase90 DOTAU1 year 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?
The pack codes you mentioned about C rate, 10C, 20C etc.   Or was what you already said all the info there was on that ?   I just wondered if there was any more data that might not be obvious to those less familiar with the RC "scene".
The C rate pertains to the cell itself.
The only pack codes that I know of are the ones that describe the construction (# of cells, negative electrode, positive electrode, shape of cell, size (diameter, width, height)) as given in IEC 61960. This is a standard for secondary (rechargeable) cells for portable applications.
Ian01 phase901 year ago
That makes a lot more sense. Thanks. :)
as an adapter for old tools that could be used on the bench it is a good idea I have been hanging on to some obsolete tools with dead battery packs now I have an option. A while back I while looking for something else I found out the RadioShack now sells many replacement batteries for many obsolete tools.
privatier1 year ago
Here is a cheaper source for your transformer: go to a place for recyling electronics and pick up a UPS. They contain transformers which are powerful enough. Connect the primary side to AC, and the secondary side to a bridge rectifier (35A, <$3), no capactor required. For long heavy duty work mount the rectifier on a heat sink. A CPU cooler from an old computer works just fine. Note that this solution has no inherent current limiter, so do not short the output!
Also, huge waste of time.
franco40 (author)  zappenfusen1 year ago
Hey Zapp,
You have a right to your opinion and I respect that, but to each their own. I'm sure there are guys out there that can make use of what I've instructed and that's why I did it. My needs overseas dictated I have a set of cordless tools. You might not be aware of this little fact, but consumers in the U.S. are privileged when it comes to availability and price of products. In southeast Asia where I'm currently working, you can't get a decent set of 18v tools for less than $1000!!! So I when I needed tools I brought them from the U.S. and I didn't want to drop a wad of $$$ on something that might get stolen on the job site. When the battery died, I improvised. Enough said.

I value and appreciate good well made tools just as much as the next guy, but my Dewalts, Porter Cables and yes....Milwakees stay home.
Sorry for the long winded reply & if I offended. I have been wiped out of tools several times in a 30 year career but if I can't use my tools for the purpose I purchased them they are waste of money. I have worked for contractors using my tools since the 1st theft and refusal of my employer at the time to replace them. I continue to supply my own tools with my employer supplying consumables. On the occasion I was relieved of a tool the cost of consumables increases accordingly. Maybe underhanded but have had no complaints from employers. Their insurance may not replace lost personal tools but they haven't seemed to mind replacing said tools through unexplained increases in consumable's cost even when my drill bit, blade purchases, etc. briefly rise to match cost of stolen tools. I guess I'm fortunate to be employed by persons appreciative of the fact I always have the required tool available without searching an entire job-site. I still believe purchase of cheap (Ryobi) tools beats the adaptation of PWM power supplies of adequate output to power a cordless tool. Please accept my apology,
I appreciate your reasoning and well know the sinking feeling when quality tools grow feet and are never seen again. $1000.00 for a rechargeable Lithium set-up would reduce me to corded tools also. The corded tools do have an appreciable increase in torque and speed over battery operated though and in your situation I believe, given the cost, I would stick with corded exclusively and invest in heavy duty extension cords. If job site theft is a main concern when purchasing, choosing, and comparing available tools I believe I would locate workmates a tad more respectful of others tools. There's nothing I hate more than a derelict attempting to sell stolen tools on a jobsite for 1/10 what they actually sell for. I'm adverse to the cost of the required XFMR to supply needed power for cordless tools. I have been fortunate that the majority of jobs I've worked on were inhabited by person's aware that my tools are my living and have respected that fact . Sorry If I offended yet I still feel converting cordless to corded kind of defeats the original purpose, convenience, and increase in utility of the new cordless offerings. In the States availability of High end cordless tool's is evidently 1/2 what you are paying in your locale giving great credence to your solution. I must insert I've a Milwaukee Magnum 1/2" Holeshooter which is 20 years old and will outlive every cordless I've ever purchased as will the Sawzall, Circular saw, etc., Eliminating the umbilical cord though will always increase productivity while decreasing frustrations to an extent making cordless indefensible when power isn't available. You would be amazed the situations absent of mains power making cordless necessary. Good things to be said for both but in my mind if theft dictates selection of needed tool I once again thank my lucky star's for the market I labor in. I will forever have my original corded Milwaukee's purchased when I realized the offerings of local Electrical contractors consisted of the cheapest tools they could find due to the conscienceless, thieving, tool less electricians (?) they insisted on hiring. When the manufacturer's developed cordless my 1st purchase of a Dewalt 14.4 volt drill, though Ni-cad, became my constant companion and now you would have a fight if you attempted confiscation of my newest Li-ion cordless tools. I'll never relinquish my corded tools as there's still jo
jobs they excel at (18" ships augers!), things only the outrageously priced and over the top 36 volt cordless are evidently meant for as well a stroking the Male ego. Sorry if I offended and good luck with those "footed" tools.
This appears as a joke. Divorce Ryobi, decide your needs and purchase appropriately
Go one or both. I've corded Milwaukee's 30 yrs. old and like new, as I've complete cordless Makita's which are unbeatable. The time is coming when this debate shall be moot. I remember the thrill of my 1st 14.4 V DeWalt drill. Amazing!
mhafiz11 year ago
Wow!very detail instruction.good job!
abadfart1 year ago
very nice i thought about building one inside the battery so it would be self contained
ac-dc abadfart1 year ago
Not reasonably possible. A manufacturer using high density construction might barely be able to do it but a self-made supply of that power density seems very unlikely, not to mention that the power density is too high from an overheating perspective.
DeWalt used to have one for their 24V tools that was pretty slick. It snapped in where the battery went and had an integrated fan. I am loving this, though! I think it will absolutely be my next project. I have a decent size collection of 18V Ryobi tools as well and when you start using several at once there don't seem to ever be enough batteries. It saves duplicating tools I only have in cordless and bought that way on purpose!
DeWalt DW0247 AC-DC Converter.JPG
franco40 (author)  abadfart1 year ago
Hey abadfart,

Sounds like a great idea but you might find it hard to fit hard to fit a powersupply big enough into the confined space. Good luck and drop me a line if you can get it done. Loved to see it work.

I'd love to see the opposite. I made the mistake of buying a battery powered Dremel, and boy would I love to be able to plug that thing in...
onemoroni11 year ago
If I am correct you wired a standard A/C appliance cord with a standard plug to the old battery? I would be concerned about confusion even though you know what the deal is. I did a similar project for my 1/4 inch impact. I just used a computer power supply and a long length of appliance cord wired directly using the 12v output. It is a little slower, but does the job every time.
lloydrmc1 year ago
Nice project, well documented and illustrated ("photoed"?). i share other people's concern about using an unsuitable plug/socket combination. May I suggest something more suitable and readily available?
estructor1 year ago
Great idea. (I have a commercially made DC adaptor that snaps into my Ryobi 18v tools.) A big caveat with your set-up: Am I right you hard-wired a North American type 110v 3 prong AC cord onto this DC adaptor you made? Because you are overseas and surrounded by different socket receptacles, you may be "protected" from someone accidentally plugging this straight into an AC wall socket. (though a traveler w/an int'l transformer adaptor might try it...) For the Instructables audience, I strongly suggest you advise that the best practice would be to use a unique DC type plug from your construct to the power supply; one that cannot be plugged into any wall socket, anywhere in the world. A plug end with two terminals such as seen in autos, or even a cigarette lighter type plug. We can't assume that innocent passersby will know the hidden protocol behind your use of a widely recognize plug standard and NOT plug it into a wall socket with bad results. But ability to use these handy DC tools w/out OEM batteries is a good scheme. Thanks!
franco40 (author)  estructor1 year ago
Hey estructor...I've updated my Instructable based on the caveat you mentioned. Let me know what you think
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