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How Can Cordless Tools Replace Corded Tools? The Math Doesn’t Add Up!


We talk about the cordless job site pretty frequently. As manufacturers push into more powerful cordless tools, the concept of switching out your corded tools without power trade-offs is compelling. But how can cordless tools replace corded tools? The math doesn’t add up.

How Can Cordless Tools Replace Corded Tools? Just the Facts

  • Batteries run lower voltages than the 120V coming out of the wall
  • To match 15-amp corded output, batteries run much higher current
  • An 18V battery has to push 100 amps to get 1800 watts of power

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The question came through on our Milwaukee RedLithium High Output Battery article and it’s a really good one. Here’s the rationale:

120 volts x 15 amps = 1800 total watts

18 volts x 15 amps = 270 total watts

or even…

36 volts x 15 amps = 540 total watts

…and we can keep going, of course. Any cordless tool producing 15 amps can’t possibly be as powerful as a 15-amp corded model. There must be something more.

How Can Cordless Tools Replace Corded Tools? More Current!

How Can Cordless Tools Replace Corded Tools?Running as much as 100 amps to power a tool seems awfully high, but that’s exactly what’s going on in the battery.

18 volts x 100 amps = 1800 total watts

Notice that as you increase the voltage, the extra current you need comes down.

36 volts x 50 amps = 1800 watts

In order for the battery pack to only provide 15 amps of current to match what you get out of the wall, it would also have to be wired for 120 volts.

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Keep in mind that many manufacturers list a “Max” voltage, which is the voltage at the pack’s highest charge state. It quickly drops 10% down to its “nominal” voltage where it operates most of the time. So, you’re looking at a tool that would be 133V Max to match the 120V coming out of your wall.

In case it comes up on Final Jeopardy, that would be sets of 37 cells.

20V Max Vs 18V: Setting the Record Straight

What’s Next?

When I spoke with Paul Fry, Cordless Guru for Milwaukee Tool (my title for him, not his official one), he gave me a little more insight into how cordless tools are replacing corded tools. He said the original lithium-ion tools that came out years ago were only able to produce a few hundred watts out. With better cell and tool technology, they’re now able to get a few thousand watts out.

The only question remaining is how to manage that kind of output with a meaningful runtime. For now, getting 1800 watts to match 15-amp corded tools is not only doable, but it’s also effective.

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