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I have a number of Ryobi One+ tools that have enough power and quality for me in most cases. They all share the same 18V battery form factor which means that I can invest in 2-3 batteries and use them for any tool, which is nice. However, for longer jobs I would like the option of plugging the tools into an electrical socket and run off of that, to not have to charge or change batteries all the time.

Understandably, companies make lots of money from their battery sales and aren't interested in providing such a solution themselves. I would also break the warranty if I did something like this. However, practically, this this possible?

There are 3D-printed products that act as an adapter from a regular 18V laptop transformer and lets us plug that cable into the empty battery socket of a power tool. These are quite expensive and some reports vary on how well they work compared to the actual batteries. Before buying them I would like advice on if I can build one myself, and what transformer specifications would be necessary.

None of my tools or batteries specify the number of watts they consume at maximum load. When fully charged my multimeter says they output 20V DC. There must be a limit in the batteries so the tool doesn't drain the entire battery instantly and burn up, but is it possible to calculate that somehow without jacking in the multimeter between the battery and the tool and putting it under load? I don't think it would be safe to attempt that. My idea is that if I ran the tool from a 100-120W 20V transformer, or whatever the power I would need, it would simply be a matter of properly connecting the positive and ground wires to the tool battery socket. The easiest way would likely be to sacrifice a battery by taking it apart, removing the battery cells and rewiring it from the transformer. Is this very foolish or not?

Thanks for any help. I have some wired tools that are more powerful, but would really like to use my Ryobi kit both ways when their power is enough.

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    Don't bother – Caius Jard Feb 26 at 10:48
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    Aside from the power supply considerations making it unfeasible, the inconvenience of having to swap a battery once every couple of hours is nothing compared to having to trip over a cord and transformer that you lug everywhere you go – Caius Jard Feb 26 at 10:51
  • " removing the battery cells and rewiring it from the transformer." Are you planning on adding a rectifier in there somewhere. Removing DC cells and adding AC from a transformer won't work. – JACK Feb 26 at 16:07
  • This is foolishness. I have a One+ drill with two batteries, and the first (having been discharged and then placed on the charger) is always fully charged by the time I wear out the second. A power supply to "mimic" a lithium-ion battery is not at all trivial, and using one rather than the correct battery will void the bleep out of your warranty on the tools. If they are out of warranty already, the fact that you risk damaging them from dubious power supply is still valid. – Ecnerwal Feb 26 at 16:56
  • "There must be a limit in the batteries so the tool doesn't drain the entire battery instantly and burn up" -- if you believe that, then do more learning before attempting a project of this type. That's an important issue that you need to understand. I agree with others' statements that if you are rotating 3 batteries on chargers (i.e. put the flat battery on the charger you took the fresh one out of), you'll never outrun the charger. – Harper - Reinstate Monica Feb 26 at 17:39
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No reasonably-sized and priced 20V PSU will be able to deliver the power that your 20V tools need. You are trying to design a corded tool that can last through a big job. The correct solution is to buy actual corded tools. Just the ones that you actually need for such big jobs. Plan B would be to buy more, bigger, batteries and a multi-battery charger that you can keep near your work location.

I don't know what current is drawn by battery-operated tools but we can guesstimate. A typical corded 120V saber saw or rotary saw is rated at 10 or 12 amps, therefore consumes say 1400 Watts. At 20V that means a tool with similar power needs to draw 70 amps from the battery. You could improve this guess by rigging up one of your tools to actually measure the current from the battery but let's start with this. You are looking for a 20V 70A PSU.

Forget about laptop PSUs .... even the biggest ones the size of bricks meant for whacko-crazy gaming laptops only provide a small percentage of that power. A typical laptop PSU is 65W. Big ones are over 100W but nowhere near 1400.

20V 70A PSUs do exist, but they are very expensive, well over $500 and they are enormous and typically designed for permanent installation in a workshop. They are specialty items. You won't find one that is practical or economical for your intended use and it certainly would not be more convenient than charging and swapping batteries.

One last thing: If you did manage to rig something up that could deliver the kind of power you want to your tool, you would probably electrocute yourself. Unless you designed it with the same safety standards as an AC-powered tool. Double insulated cables, sockets, and plugs, fuses, etc etc ... all the things designed to protect you with dangerous power delivery. Are you going to design and build that into your 20V solution? No. So you'll eventually get killed. Just go buy one or two corded tools!

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Sure you can build a dc supply for your corded tool.

You ask how to calculate the power supply size. Take a known battery with a known amp hour rating. Many batteries state the AH on them some may show a value like 3300 ma hours this makes the number look bigger but in this case it is 3.3 amp hours. Then put that tool under a normal load and see how many minutes it lasts. Calculating the use will be only as accurate as your load. Now for safety double the value you came up with or even 5x and size your components based on that. If trying to go simple transformer there are 18v models out there and full wave bridges rated at 20 amps in small packages you can put in a project box and have your low voltage dc feed the tool.

This could be a fun project and cost less than a new corded tool but is it going to be something that you use? I have thought about it I have Vmax batteries up to 6AH that makes the tool heavy but it lasts long enough for me to get the job done in most cases if I wanted light it may be an option but I have not done it because I already have corded tools in every style of battery tool I have.

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  • It would be nice to know which specific tools OP is talking about. I myself don't own a battery-powered saber saw, rotary saw, angle grinder, etc. For the tools that I do own, 20A seems reasonable and your suggestion may be viable. My guess in my answer was for higher powered tools that in fact I don't own, so I worked backwards from corded equivalents. Do you have a battery skilsaw and does it last 10 minutes on a 3.3Ah battery? – jay613 Feb 26 at 14:51
  • @jay613, yes I have a battery, grinder, recip & skill style saw they are the power hogs unlike impact drivers, drills, grease guns. On the power hogs a 5-6 ah tool lasts long enough for most Jobs in some cases a 2nd battery is needed. I have friends that use the smaller batteries and they are fine for impact drivers but large load tools like grinders kill them fast. I am not sure if your 70 amps is realistic my charger outputs 4a and charges my tools in an hour or less depending on battery temp. I think 30 amp would be sufficient based on that I don’t think any of my tools last less than 15m – Ed Beal Feb 26 at 15:11
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    An issue with your methodology is that it does not account for peaks in power draw. That 3.3AH battery can provide 50A for a second to power through something. A 20A PSU... not so sure. – Olivier Feb 26 at 15:22
  • I just threw out the 20 amp as a number of a full wave bridge that could be purchased I have them up to 400 amps on my shelf I was thinking more along the lines of 30 amps. if a 4 amp charger can charge the battery in an hour 4 amps if the battery lasted for an hour. 8a for half hour. 16 amps for 15 minutes (about what hogs last) and 30amps for 71/2 minutes. That’s how I did a quick calculation sure you can come up with all kinds of numbers a battery provides infinite current under a short right? No the battery capacity and internal resistance limit what they can provide reality vs ohms law. – Ed Beal Feb 26 at 15:31
  • Hmm something to consider. Laptop PSUs and the very expensive ones I mention in my answer provide clean, precise power. Maybe you don't need clean or precise to spin a DC motor. In which case the approach in this answer might produce what you suggest at a cost less than buying corded tools. Or maybe there are electronics in the tool between the battery and motor that will get fried if your PSU is very spiky. Let us know. :) – jay613 Feb 26 at 18:38

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