Using battery operated tools on power supply.

Old 01-12-15, 12:10 PM
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Angry Using battery operated tools on power supply.

Hello All,

I have a set of power tools (drill, saw, etc...) that run on an 18V rechargeable battery that came with the tool set.
I constantly have to charge them and then if I have a cutting job that is heavy or takes long then the batteries drain and the blades do not spin fast enough to get a good cut.

So I thought why not replace the batteries and just connect to a power supply source so that I can get constant power and thus never run out of power or the need to re-charge.

I replaced the battery with a transformer that would give me an output of 19V and 3A. I found that it works pretty much on most of the power tools I have except on the circular saw tool. I find it hard to believe that the circular saw would require more Amps than 3 Amps. This is not a heavy duty saw.

So my question is how can I get the saw to work with my transformer ?
(Do I need more Amps ?)

Note that I find that using the reciprocating saw works if only I get it going very slowly and then gradually it reaches it max power of running.


Old 01-12-15, 12:27 PM
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Yes.... you need a power supply with higher amperage capability.
An 18v 10A supply is probably what is needed.
Old 01-12-15, 12:41 PM
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Funny how my old, some over 40 years old, drills and circular saws are still turning. Battery tools have their advantage, but long life and tough jobs are not among them.

Sometimes dragging a power cord around is less of a hassle than climbing down 3 lifts of staging to get a new battery.

A few years ago I did see a power corded unit that plugged in to replace the battery. I don't know what brand it was, but it must not have been mine or I would have bought it in a heart beat.

Old 01-12-15, 12:42 PM
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There is a reason for corded power tools. They can deliver more power in a consistent, safe manner and are equipped with the proper size wire, insulated to specs and usually UL approved. What you want to do will void any warranty and liability to the manufacturer of the tools. If you have a need for a consistent long running power tool then you need a generator that can meet the demands of a on the job power tool. Plus what you want to do is unsafe because if power drops suddenly while a cut is being made that can cause injury.
Old 01-12-15, 12:49 PM
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I have a top of the line (at the time) Dewalt 18 volt cordless 1/2" hammer drill. I love it. That said, the cheap, $30 Craftsman 3/8" corded drill I have at the bottom of the tool box has way more power.

Cordless tools have their time and place but a corded tool will almost always perform better. Rather than screwing around with what you're trying to do, I would buy new corded tools.
Old 01-12-15, 01:00 PM
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I agree, while cordless tools can be handy - they shouldn't completely take the place of a corded tool Sometimes I'm surprised at what my 19.2 volt drill can do but it will never do as much as my corded drills can do.

Older batteries won't hold a charge as long as they did when they were new so buying a new battery pack might help BUT any time that the job requires you to constantly change out battery packs - that job is better tackled with a corded tool!
Old 01-12-15, 04:26 PM
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I see a lot of discussions on the pros and cons in using Corded Vs Cordless but I am surprised to see PJmax suggesting 10A.

I don't think these batteries have the capability to supply that much current. or do they ?
Old 01-13-15, 07:45 AM
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Originally Posted by raminee
I don't think these batteries have the capability to supply that much current. or do they ?
You betcha they do. Especially the newer Li-Po packs have so much ability to dump instantaneous current that they have a reputation for exploding into flames if they malfunction. Seriously.

Even the oldest Ni-Cd packs were assembled with approx. 12ga. wire.
Old 01-13-15, 09:29 AM
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Batteries especially lithiums have a tremendous ability to deliver a lot of power in a short period of time. Starting a circular saw takes a lot of power initially to get the mass of the blade spinning. You may sometimes even notice that corded tools will dim the lights when you pull the trigger.

I used to fly RC helicopters and it always looked odd to have a small little battery pack with big fat wires coming out of it. The heli weighed less than 2 pounds and had a 45 amp controller for the motor. It didn't need anywhere near that much amperage most of the time but if you spooled up the rotor quickly or flew it hard it took a lot of power.
Old 01-14-15, 06:20 AM
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I have one cordless tool that uses a 24V lithium pack that had a couple cells go bad so I repaired it. Each battery in that pack is rated at 1.2V 50A instantaneous so that's 1200 watts available power. I was intimidated to be working on it.

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