Windscreen Wiper Motors

[davidimurray]

Hi

I've built myself a mechanical hacksaw which is powered by a windscreen wiper motor. However I'm having problems driving it. I've got an old knackered battery from my motorbike - but this doesn't have enough grunt left it in. I then got hold of a 12V 24A DC power supply which works - but after a couple of min the motor gets red hot and I'm worried it is going to fry itself. I'm guessing that I need to find a way to limit the current ?

Any ideas?

Cheers

Dave

[baggo]

Hi David,

You're probably overloading the motor anyway using it as you are. They are not designed to drive a heavy load and I doubt if the motor will last long in your application. I presume you are using it because of the built in gearbox to give the reciprocal motion?

John

[chris vine]

Hi David,

Surely a 12v car battery charger would be the easiest thing. I am sure the motor will be 12 v unless it is from a lorry and I would think 10A is probably sufficient so most small chargers will cover it.

Chris.

[Lurkio]

Hi Dave,
My first post...had to make one sometime, so here goes!
I agree with Baggo, the motor probably isn't man enough for the job and will most likely eventually fail.
You could try cooling it, though...perhaps a small fan designed for PCs etc....they are readily available for 12V operation. Some fins attached to the motor also would help, obviously.

Lurk.

[houstonceng]

David

Modern motors quite often are designed to run hot to the touch. They are designed to a price. Insulation materials are better and stand higher temps than the old shellac varnish.

Wiper motors are often in a cool air-stream on a car anyway, so may run hotter without cooling.

Finally, wipers aren't a heavy load so Baggo and Lurkio (Was his first post "The Prologue" ?) are probably correct.

Have fun
Andy

[davidimurray]

The basis of the saw is from an article in Model Engineers Workshop - there were 2 parts - part 2 had the wiring in it and guess which part I can't find.

I did try a car charger but the one I have at home is a clever one that examines battery condition before it will charge. Hence it won't drive the motor as it is not a battery. The problem seems to be that as the load increase towards stall, the motor will draw near infinite amounts of current - I think that's correct, hence I need to limit the max current.

The motor is apparently from a Fiat. When you say a motor doesn't have to do much consider the weight of all the water it has to 'lift and shift'. From my experiments with the saw so far, its not going to set any records for speed, but I want to leave it chugging away in the background - I seem to spend far too much time sawing up material.

Cheers

Dave

[Tel]

I read somewhere that these motors generate around 1/2hp. I know that I've used 'em on various projects with a fairly heavy demand with no problems.

[davidimurray]

When I was using the old battery from my motorbike, it took two hands to stop the blade going - that is holding the frame and not the blade

Cheers

Dave

[ron]

These motors are quite powerful. with a charged battery they should do your job OK, don't know about the modern ones but the old Lucas ones were suitable for continuous running, that's what the Triumph TR6 used for it's petrol pump motor for the mechanical petrol injection, they also drew quite a heavy current in this application, it's advised to modify the wiring to a separate heavy feed via a relay. They also run very hot, to the extent that a common mod was to fit a cooling coil to stop petrol vapourisation in hot weather,
Ron

[jackrae]

Might sound daft but try reversing the motor direction - they often have a preferred direction of rotation to compensate for thrust off the worm gear. If it has permanent magnetic pole pieces this is a simple job of reversing the feed polarity. If it is a series would motor you'll need to get into the windings. (However I suspect it won't be)

Another thing is the supply voltage - bike batteries are fairly low ampere-hour capacity and if , as you say it's already "knackered" then you are probably "writing in yellow" in the snow.

Fit a decent car sized battery and be prepared to be amazed.

Jack

[davidimurray]

Thanks guys - what about this 24A power supply I have? Do you reckon that is too large?

The motor gets hot very quickly with this psu - perhaps 60 seconds you can start to smell toastiness. And you can feel the outer casing is getting warm.

Cheers

Dave

[havoc]

Might sound daft but try reversing the motor direction

This is actually a good idea.

If you are running it of a power supply, does it tell you the current it draws? If so, then calculate the power it draws when loaded and when not loaded. (do the same running the other way)

[chris vine]

Hi again David,

Have just read your post properly this time and see your psu is 24A not 24V....

I am sure this should be easily sufficient as there are very few fuses in a car over 20A.

If your psu is really 12v and the motor starts to smell toasty and or burns out, it seems that it is probably defective anyway.

No problem, just go down to the breaker's and get another one.

I am pretty sure a wiper motor should be powerful enough for a hacksaw, there is quite a load on a long wiper blade especially when the screen is almost dry. Also the old fashioned type with the hefty bowden cable type of drive had a lot of friction to overcome.

Good luck,
Chris.

[mmaidnz]

Hi,David.I'm using a windscreen wiper motor as a drive for my mill drill table feed.Mine is from a 70's honda civic,and it is certainly man enough for the job.Mine is powered by a computer power supplies' 12v rail,and it works well.
If the motor is overheating,the load is possibly too much for it.
I'd find a bigger motor,possibly a 12v truck one if you can get it.
The amperage of your supply is only relevant if it's insufficient,but at 24A that's unlikely.

[havoc]

Well, unless that is a 24V power supply, not a 12V one that can deliver 24A. In the latter case it would not surprise me that it gets hot.

[Tel]

My w/w powered rod binding lathe draws 2.5 amps on lo speed, 4 on hi.

[davidimurray]

Right

Did a bit of an investigation last night - found that when I installed the blade this had pulled the frame alignment out of square and was binding. Motor still gets warm but not as bad. It took about 10 minutes to cut through a 1/2" square bar with 2 rest stops included in this time.

Not fast - but the finish was brilliant - probably save that much time squaring the bar off when I come to machine it!

Cheers

Dave

[ChrisCrosskey]

Hmm... sort of glad to see this discussion on here cos my current project is a Duplex hacksaw ands one of it's possible power sources is a wiper motor, though given how cheap gearmotors can be picked up on ebay I'm keeping my eye out on there for a little single or three-phase 120rpm or thereabouts gearmotor.... as an example I've got a 3/4HP Allen-Bradley motor and a 1HP Hitachi inverter on my ML7 and not only was it a transformation in terms of less vibration and more power than the old single-phase 1/3HP (which was rubber mounted but still more vibey than the new rigid foot) but I got the whole lot for about 60 quid...... If I go 12V I have to bring 12V source down to the shed, single or three and I don't
chrisc