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Running a cordless drill from an AC transformer

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Re: Running a cordless drill from an AC transformer

Postby AJB Temple » 06 Oct 2020, 17:03

I might be wrong about this but I was under the impression that low powered DC motors produce very erratic torque when run at low speed. I thin this is to do with commutator gaps (is that the correct term?), which become more gappy in practice when the armature is tuning over slowly. The gaps are not noticed when the motor is spinning fast.

My knowledge is sketchy and stems from trying to help my son (now studying aeronautics) develop a moving rotor system for a drone project he was doing. The design required the blades to rotate at low speed during system checks and for the motor to be capable of being tilted (to simulate pitch change as I recall). It was very difficult stop jerky motion. He resorted to a gearing system but that added weight.
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Re: Running a cordless drill from an AC transformer

Postby Mike G » 06 Oct 2020, 18:42

The drill trigger will, I think, be separated from the machine and used in a two-way switching arrangement with a switch on the outside of the cabinet. The machine's original switch would simply be used to switch it off at the end of each run, be that up or down, so it should never go from up to down whilst in the middle of a run. The change of direction function would be similarly organised with a mechanical device controlling it, again, only at the end of a run. I think.
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Re: Running a cordless drill from an AC transformer

Postby 9fingers » 06 Oct 2020, 18:49

Mike G wrote:The drill trigger will, I think, be separated from the machine and used in a two-way switching arrangement with a switch on the outside of the cabinet. The machine's original switch would simply be used to switch it off at the end of each run, be that up or down, so it should never go from up to down whilst in the middle of a run. The change of direction function would be similarly organised with a mechanical device controlling it, again, only at the end of a run. I think.


Sounds like you are up to speed with the potential issue Mike :eusa-clap:

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Re: Running a cordless drill from an AC transformer

Postby Mike G » 06 Oct 2020, 18:57

Well, it was the ease of controlling the switching that was the primary reason I thought about using a cordless. That, and the chuck for ease of attachment to the works I'm thinking of making.
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Re: Running a cordless drill from an AC transformer

Postby timothyedoran » 07 Oct 2020, 15:24

I might be i bit late to the party. When I lived on a canal boat I knew of people running 12v power tools directly from 12v car/leisure batteries.
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Re: Running a cordless drill from an AC transformer

Postby 9fingers » 07 Oct 2020, 15:37

timothyedoran wrote:I might be i bit late to the party. When I lived on a canal boat I knew of people running 12v power tools directly from 12v car/leisure batteries.


That is worlds away from what Mike has been suggesting. Leisure batteries will be able to supply
loads-a-current to start a drill motor so no issues.

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Re: Running a cordless drill from an AC transformer

Postby Mike G » 07 Oct 2020, 18:38

Yeah, I ran a cordless from my car battery when camping in Africa.
It's already DC, so you're halfway home before you start. And most 12V car batteries are delivering 14 or 15V anyway before the voltage regulator sorts it out.
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Re: Running a cordless drill from an AC transformer

Postby Jonathan » 07 Oct 2020, 19:07

Mike G wrote:Yeah, I ran a cordless from my car battery when camping in Africa.
It's already DC, so you're halfway home before you start. And most 12V car batteries are delivering 14 or 15V anyway before the voltage regulator sorts it out.
I built my off grid timber house using an old Makita hooked up to old 12v battery.

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Re: Running a cordless drill from an AC transformer

Postby AJB Temple » 07 Oct 2020, 21:25

Mike G wrote:Yeah, I ran a cordless from my car battery when camping in Africa.


OK, I have to ask. Who needs a cordless drill when in Africa camping? Urgent bit of bookcase building? :D
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Re: Running a cordless drill from an AC transformer

Postby Mike G » 08 Oct 2020, 07:14

:lol: :lol:

Repairs to vehicle or camping kit. I remember using it to rivet the frame of my rooftent, for instance.
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Re: Running a cordless drill from an AC transformer

Postby Lons » 08 Oct 2020, 09:44

AJB Temple wrote:
Mike G wrote:Yeah, I ran a cordless from my car battery when camping in Africa.


OK, I have to ask. Who needs a cordless drill when in Africa camping? Urgent bit of bookcase building? :D


I'd have though that was obvious, when being attacked by lions fend them off with a cordless drill. :) :eusa-whistle:
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Re: Running a cordless drill from an AC transformer

Postby 9fingers » 08 Oct 2020, 10:35

Lons wrote:
AJB Temple wrote:
Mike G wrote:Yeah, I ran a cordless from my car battery when camping in Africa.


OK, I have to ask. Who needs a cordless drill when in Africa camping? Urgent bit of bookcase building? :D


I'd have though that was obvious, when being attacked by lions fend them off with a cordless drill. :) :eusa-whistle:



Li-Ion drill would be best for that job I guess? :lol:

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Re: Running a cordless drill from an AC transformer

Postby Mike G » 08 Oct 2020, 11:12

Presumably there is a transformer and a rectifier inside the battery charger for any drill. Could I not just run a cable from the battery charger terminals to the terminals in the drill?
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Re: Running a cordless drill from an AC transformer

Postby 9fingers » 08 Oct 2020, 11:26

Mike G wrote:Presumably there is a transformer and a rectifier inside the battery charger for any drill. Could I not just run a cable from the battery charger terminals to the terminals in the drill?


Absolutely not Mike. The charger is especially designed to be connected to a battery not a motor load.

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Re: Running a cordless drill from an AC transformer

Postby Mike G » 08 Oct 2020, 11:33

How about a car battery charger? That outputs DC at a suitable voltage for a car battery (presumably 12 to 15V).
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Re: Running a cordless drill from an AC transformer

Postby DaveL » 08 Oct 2020, 11:42

Mike G wrote:How about a car battery charger? That outputs DC at a suitable voltage for a car battery (presumably 12 to 15V).
That would still need a capacitor to smooth the rectified AC output and it must not be just a trickle charger, they would not supply enough current.
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Re: Running a cordless drill from an AC transformer

Postby Mike G » 08 Oct 2020, 11:49

Hmmm.....

Why is this so difficult? There must be a bit of kit which takes 240V DC in and outputs 15 to 18V DC out without me having to get "Electronics for Dummies" and a new soldering iron.
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Re: Running a cordless drill from an AC transformer

Postby DaveL » 08 Oct 2020, 11:58

Well you could get one of these, but you need to know how much current the drill needs.
https://www.ebay.co.uk/itm/264759172436
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Re: Running a cordless drill from an AC transformer

Postby Robert » 08 Oct 2020, 12:40

Mike G wrote:Presumably there is a transformer and a rectifier inside the battery charger for any drill. Could I not just run a cable from the battery charger terminals to the terminals in the drill?


Which is almost what I said the other day. You need the battery still fitted as well as the charger to drill wiring. The battery does the hard work when required and the charger just tops it up.
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Re: Running a cordless drill from an AC transformer

Postby stevegruk » 09 Dec 2020, 17:54

Mike

This is probably miles too late but....

Yes you can but as others have said you need a rectifier and a big smoothing cap. The sizing of all of this depends on your load which determines how much electrical power you need.

A safer an easier way is to buy a nice safe enclosed switched mode power supply such as one of these, but again you need to select one with enough power:-
https://uk.farnell.com/w/c/power-line-p ... rt=P_PRICE

Although you could, I’d not use the drill own switch or mechanical direction control just use a double pole changeover relay and wire direct to the motor in the drill. I’d use a micro switch to control the direction relay.

Hope that helps.
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Re: Running a cordless drill from an AC transformer

Postby sunnybob » 09 Dec 2020, 18:44

Buy the kit Mike, or youll burn your house down.

https://www.hiddentvlift.co.uk/our-prod ... pathway-13

I bet youll spend that on the home made pieces.
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Re: Running a cordless drill from an AC transformer

Postby Mike G » 09 Dec 2020, 21:09

sunnybob wrote:Buy the kit Mike, or youll burn your house down.

https://www.hiddentvlift.co.uk/our-prod ... pathway-13

I bet youll spend that on the home made pieces.


Oh ye of little faith..... :lol:
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Re: Running a cordless drill from an AC transformer

Postby Mike G » 09 Dec 2020, 21:12

stevegruk wrote:Mike

This is probably miles too late but....

Yes you can but as others have said you need a rectifier and a big smoothing cap. The sizing of all of this depends on your load which determines how much electrical power you need.

A safer an easier way is to buy a nice safe enclosed switched mode power supply such as one of these, but again you need to select one with enough power:-
https://uk.farnell.com/w/c/power-line-p ... rt=P_PRICE

Although you could, I’d not use the drill own switch or mechanical direction control just use a double pole changeover relay and wire direct to the motor in the drill. I’d use a micro switch to control the direction relay.

Hope that helps.


Hi Steve, and welcome.

As it happens, that is precisely what I've got. Everything self contained within a box, so pretty foolproof. I reckon I'll be starting work on the electrics this coming weekend, so we'll see what we see.
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Re: Running a cordless drill from an AC transformer

Postby Sheffield Tony » 09 Dec 2020, 21:57

sunnybob wrote:Buy the kit Mike, or youll burn your house down.

https://www.hiddentvlift.co.uk/our-prod ... pathway-13

I bet youll spend that on the home made pieces.


That looks awfully like a windscreen wiper motor.

Having designed control electronics for a few motors, I have been caught out more than once by underestimating the stall current. For the wiper motors 15A might be seen. I wouldn't be surprised if it is more for a drill motor. The PSU will see that briefly on starting. The other common oversight is where the energy goes when braking / stopping. Most controllers direct it back to the battery to get rid of it. Mains PSUs don't always like that.

Not sure I've been all that much help here - sorry.
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Re: Running a cordless drill from an AC transformer

Postby sunnybob » 10 Dec 2020, 06:53

Back in '89, I was the secretary of a target shooting club. I bought 5 turning target units that were using windscreen wiper motors They had huge torque, snapping a man sized target frame through 90 degrees almost as fast as you could see. They ran off full sized car batteries that in the end I rigged up to be on permanent trickle charge because the targets drained the batteries so quickly.

Its all about the torque, so DO NOT under estimate 12 volt dc power requirements. :shock:
8-)
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