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Running a cordless drill from an AC transformer

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Running a cordless drill from an AC transformer

Postby Mike G » 05 Oct 2020, 08:51

Is it possible to get rid of the battery from a cordless drill, and run it on mains electrickery via a transformer?

Obviously I'm not proposing to operate it as a drill, but as motive power for something else. It's just that both the power, controls, and the chuck would be very useful to have in the final device, so suggesting other alternatives, especially including circuitry, won't really help.
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Re: Running a cordless drill from an AC transformer

Postby HappyHacker » 05 Oct 2020, 09:32

Should not be a problem as long as you stick rectification, to get DC electrickery, in as well.
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Re: Running a cordless drill from an AC transformer

Postby 9fingers » 05 Oct 2020, 09:41

HappyHacker wrote:Should not be a problem as long as you stick rectification, to get DC electrickery, in as well.


You might need a capacitor too in order to provide high enough peak current to get the motor to start especially if it will be loaded during start up. You might need the old battery pack case to house the capacitor in conveniently.

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Re: Running a cordless drill from an AC transformer

Postby Mike G » 05 Oct 2020, 10:20

Hang on.........if 18V DC starts and runs the drill perfectly well now, why would I need more than that to start and run it if I provide that 18V via a transformer?
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Re: Running a cordless drill from an AC transformer

Postby Mike G » 05 Oct 2020, 10:26

HappyHacker wrote:Should not be a problem as long as you stick rectification, to get DC electrickery, in as well.


Does that happen after the transformer? So 240v AC > 18v AC >18v DC? Or does is happen at the 240V stage....240v AC > 240v DC > 18vDC?
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Re: Running a cordless drill from an AC transformer

Postby 9fingers » 05 Oct 2020, 11:38

If only it were that simple Mike.

A battery will be 18vdc nominal but will be able to deliver large currents in order to get a motor started and indeed to do serious work upto the design limits of the drill. You have not said how much work your application needs.

Some basic theory you need to understand.

A transformer (alone) will (should) deliver its rated voltage at its rated power/current BUT the voltage will rise by at least 10% off load ie most of the time in your application I suspect(?) This is called the "regulation" of the transformer. There is also the variability of the mains input voltage to consider. I'll leave that out for now.
Perfect rectification will give a voltage = root 2 times the ac voltage but minus about 1.2 volts to allow for real world rectifiers assuming you are using a full wave bridge rectifier.

so 18v tranny times 1.1 x root2 -1.2v will give a shade under 27 volts No Good for your drill eh?

Something like a 12v transformer should get you to 17.5v off load but a tiny bit less than 16v on load which might do unless the drill is ex lithium battery and it might shut down*.

Some experimentation will be advisable under real world conditions.

Using a much bigger transformer that you think you need will reduce the 10% voltage drop with load

* some lithium drills do their battery management ie low voltage cut off in the battery pack itself in which case the problem goes away. If the drill does the sensing then there could be a problem.

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Re: Running a cordless drill from an AC transformer

Postby Mike G » 05 Oct 2020, 11:50

There's a good reason I hate electrical stuff..... :)

The load isn't likely to be much, and will be continuous. The gearbox will deal with any starting issues. It's a spinning threaded rod/ travelling nut type of mechanism I have in mind. The speed of travel isn't critical, so I can set the drill on a low gearing but spinning at maximum revs. I have an old drill, but it is of such high quality that I might just buy a cheaper new drill without batteries to provide the workings.

From what you are saying it seems that the rectification happens after the voltage drop.
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Re: Running a cordless drill from an AC transformer

Postby 9fingers » 05 Oct 2020, 12:49

I have a number of Bosch green 7.2v drills. Perfectly good just dead batteries.
I could experiment on one and then send it to you if you like?

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Re: Running a cordless drill from an AC transformer

Postby Mike G » 05 Oct 2020, 13:27

Kind of you Bob, but I suspect a 7V drill won't quite be man enough for the job. However, doing the experiment with a rectifier and transformer could be really useful, so if you get bored one day that might be a really worthwhile exercise.
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Re: Running a cordless drill from an AC transformer

Postby 9fingers » 05 Oct 2020, 13:39

Mike G wrote:Kind of you Bob, but I suspect a 7V drill won't quite be man enough for the job. However, doing the experiment with a rectifier and transformer could be really useful, so if you get bored one day that might be a really worthwhile exercise.


The experiments on the drill must be done with the target drill and proposed transformer.

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Re: Running a cordless drill from an AC transformer

Postby Mike G » 05 Oct 2020, 13:55

If I do that experiment it will consist of seeing if the drill runs without emitting smoke. :lol: No other parameters will be measured.
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Re: Running a cordless drill from an AC transformer

Postby Alasdair » 05 Oct 2020, 14:05

Mike G wrote:If I do that experiment it will consist of seeing if the drill runs without emitting smoke. :lol: No other parameters will be measured.


That sounds like the 'cigarette foil or nail in the fuse board' type of electrickery that I was brought up with. "If it blows the fuse then stick in a bit paper from a fag packet, if that burns then a 6 inch nail will sort it". That worked until the meter went on fire then we knew it wasnt going to work.

:lol: :lol: :lol:
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Re: Running a cordless drill from an AC transformer

Postby Robert » 05 Oct 2020, 16:27

If you've got the charger for the drill maybe bodge some wires from the charger to the battery terminals and leave the battery still connected (fitted) to the drill. That way the battery provides the starting current and the charger enough to run continuously.
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Re: Running a cordless drill from an AC transformer

Postby AJB Temple » 05 Oct 2020, 16:38

OK, this is going to sound odd but....if you are willing to buy a cheap donor cordless drill, why not just buy a cheap mains power drill and do away with the transformer and complexity?
Don't like: wood, engines, electrickery, decorating, tiling, laying stone, plumbing, gardening or any kind of DIY. Not wild about spiders either.
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Re: Running a cordless drill from an AC transformer

Postby Andyp » 05 Oct 2020, 16:43

What is it that you are trying to make Mike? There might be a better way of getting there that you haven’t thought of yet.
I do not think therefore I do not am.

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Re: Running a cordless drill from an AC transformer

Postby Mike G » 05 Oct 2020, 17:06

AJB Temple wrote:OK, this is going to sound odd but....if you are willing to buy a cheap donor cordless drill, why not just buy a cheap mains power drill and do away with the transformer and complexity?


I think that a 240V drill probably spins too fast. The mains drills I'm familiar with don't have a gearbox, and I see this as needing a low gear.

The idea is a TV raising gismo in a cabinet in the lounge.
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Re: Running a cordless drill from an AC transformer

Postby MY63 » 05 Oct 2020, 17:44

Mike I have 2 black and decker firestorm drills I think they are 14 v this is the only picture I have in the back ground behind the daft dog.

ImageIMG_0350 (1) by my0771, on Flickr

Both drills work I have a couple of chargers and a saw with six batteries but only one battery works.
You are welcome to them if you can use them.
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Re: Running a cordless drill from an AC transformer

Postby Malc2098 » 05 Oct 2020, 17:45

Peter Parfett goes about it slightly differently.

[youtube]ajV5UXPk_Zo[/youtube]
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Re: Running a cordless drill from an AC transformer

Postby Woodbloke » 05 Oct 2020, 17:59

[quote="Malc2098"]Peter Parfett goes about it slightly differently.

Just to go slightly off topic for half a mo', this chap was a full colonel in the Royal Signals and was at one time in charge of security arrangements in NI during the time of 'The Troubles'. He used to live in Gillingham (Dorset) quite close to me and I spent a very pleasant day with him a few years ago at his home and workshop. He also suffers from athritis quite badly which you wouldn't realise seeing his videos - Rob (sorry for the 'detour' Mike)
I no longer work for Axminster Tools & Machinery.
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Re: Running a cordless drill from an AC transformer

Postby Mike G » 05 Oct 2020, 19:25

MY63 wrote:.......Both drills work I have a couple of chargers and a saw with six batteries but only one battery works.
You are welcome to them if you can use them.


That's really kind of you Michael. Without wishing to look a gift horse in the mouth, if one of these has a robust gearbox and a working reversing button then it would be great if it's going spare. Let me give you a few quid for the postage etc.
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Re: Running a cordless drill from an AC transformer

Postby MY63 » 05 Oct 2020, 21:30

Mike the only issue I had was batteries both worked well. I bought one new battery then realised it was half the price of a new drill. One of the big sheds had a deal on Ryobi so I jumped to them.
They are in the small shed I will get them out.
How will I know if the grear box is good?
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Re: Running a cordless drill from an AC transformer

Postby Mike G » 05 Oct 2020, 21:54

If they're still of use to you Michael then hang on to them, seriously. If you're going to chuck them, I'll have one, but don't part with it if you're in any doubt. It's always handy to have two or three. As to the gearbox.....if everything works OK then that's good enough.
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Re: Running a cordless drill from an AC transformer

Postby MY63 » 05 Oct 2020, 22:24

Mike I will never use them I am not sure why I kept them if you can use them that is fine with me.
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Re: Running a cordless drill from an AC transformer

Postby MY63 » 06 Oct 2020, 12:13

Mike

Image2020-10-06_12-06-35 by my0771, on Flickr

Image2020-10-06_12-06-50 by my0771, on Flickr

Both chucks turn freely on both speed settings, I have not foung the charger yet if you need it i will keep looking.
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Re: Running a cordless drill from an AC transformer

Postby 9fingers » 06 Oct 2020, 13:28

Mike,
One point you might want to consider in your design is whether you need to reverse the drill to lower the TV.

Simply reversing the supply to a variable speed drill with the drill trigger taped to the "on" position will not reverse the drill but will instead let the magic smoke out.
Furthermore once the trigger is depressed, most if not all drills prevent the reversing button from operating.

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