Replace tool batteries with switching power supply - Page 1
Forum section: electronics / beginners

author: Signal32
author_rank: Frequent Contributor
timestamp: January 29, 2021, 10:08:11 am
content: Hello,I have a bunch of Ryobi 18V Tools that operate on batteries only.Sometimes I use a tool for extended periods of time in the same place - not really taking advantage of the cordless feature and having to use lots of batteries.So I am wanting to create a "Corded battery" - basically have an AC->DC power supply that feeds power to the tool via a battery-like interface - so the tool thinks it's using a battery but it's using an AC->DC switching supply.The 18v is actually 4 cells of Li-Ion, meaning a max voltage of 21v.The replacement power supply needs to be rather high amperage (20A+) to be able to handle the high current draw of the tools.Now, I can't really find a (cheapo) 21v high-amp power supply but there are a bunch of cheapo 24v power supplies, like this:https://www.ebay.com/itm/DC24V-20A-Switch-Power-Supply-Adapter/143741964539. I know that I can't adjust the voltage to any value, and that I have to stay within a few +-%, so I'm wondering if ~14%(24->21v) adjustment would be OK.Q1: Is there any fundamental issue with replacing batteries with a AC->DC power supply ?Q2: Is it possible (and safe) to adjust the voltage on the 24v power supplies, I see a Youtube tutorial that says you can do this via changing a resistor ( see video at bottom of post ).Q3: Anything else that I am missing / should consider ?Thanks!

author: jpanhalt
author_rank: Super Contributor
timestamp: January 29, 2021, 10:18:04 am
content: I did that once with an old (circa mid-1980) Sears electric screwdriver. Much lower current and voltage than today. Modern tools effectively have a battery present test and temperature detector as safety circuits in the battery. You may need to simulate those functions to get it to work.Do you have a dead battery you can dissect? If so, and if your supply is adequate, it should still work. Going from 18V nominal to 24V may be OK, but considering that brand, there may not be much margin for overvoltage, which will give overcurrent and more heat.

author: beanflying
author_rank: Super Contributor
timestamp: January 29, 2021, 11:26:19 am
content: The problem you will run into mainly is the inrush current which may depending on the supply shut down as it will consider the output shorted. More likely you will blow the output fuse (assuming it has one). If the drill is variable speed (likely) if you try running it at 24V nominal you may blow the speed controller in the drill.As to varying the voltage by that amount it will be circuit dependent so general advice will be just that unless you have a specific supply. Some of the better Meanwell supplies for example have a potentiometer for that purpose as standard, the variation available on these is generally an unknown on the datasheet unless someone have tried before?

author: ledtester
author_rank: Super Contributor
timestamp: January 29, 2021, 06:06:11 pm
content: Here is a teardown of an typical electric drill, you can inspect yours to see if it is similar:https://youtu.be/Fg0lnY8RfxM?t=3mAs for the major components:* motor -- I'm sure the motor can handle 24V* MOSFET -- you can check yours, but 60V is very common for these kinds of MOSFETs* control circuitry -- the one in the video has a zener for voltage regulation; if yours also has some sort of voltage regulation you should be ok hereFound this review & teardown of 18v Ryobi cordless tools which might help:https://youtu.be/IoTr4LhQC4Y?t=8m35sIf your battery pack has a third contact it might be a temperature sensor which the tool senses to make sure the battery is not overheating.

author: Infrared_Fred
author_rank: Regular Contributor
timestamp: January 29, 2021, 06:19:54 pm
content: Quote from: beanflying on January 29, 2021, 11:26:19 amAccording to the datasheet for a 24V 100W Meanwell Supplyhttps://www.meanwell.com/Upload/PDF/LRS-100/LRS-100-SPEC.PDFthe onboard trimpot pot allows the voltage to be adjusted to 21.6V.