12v DC Motor

Graham

2 Amps seems quite high without any load, but if it is that high then your PSU needs to cope with the much higher starting current and the laptop supply is probably unsuitable.

If you measured the motor current running of a battery charger and used an inexpensive multimeter, the indicated current may be erroneous. Some battery chargers just rectify (no capacitors) the output of a transformer (17 Volts on one I looked at a couple of days ago). Only when the charger is connected to a battery does the output become proper DC which would then give a reasonably accurate reading on a meter.

Regarding motor rotation direction, without examining its construction the safest option is to run the motor in the same direction as it did when it was wiping windows.

Ian P

Hi Ian and Jason. Used a car battery as power source running motor when I checked the current. Meter is a digital 'Precision Gold'?, don't think it was cheap, came to me from bros. estate. When powered from a battery charger (Heathkit) ammeter on the charger indicated about 2.5amps at start-up then dropped back to around the 2 mark when running. Haven't run the motor direct off the laptop psu as didn't know what to expect giving 18.5 v to it and didn't want to risk damaging it. Could try a bulb in the circuit.

As to motor direction, I've had to make an extension shaft fitted to the tapered threaded end that drove the activation bracket for the wiper set-up to mount a sprocket, which led me to rotate anti clockwise to pre-empt any loosening issues when in use, could cross pin that so I could rotate clockwise if anti clock is dodgy.

The electrics are proving more problematical than the mechanical components LoL.

Cheers

GW

The wiper motor I use for feeding the table of my mill runs forward, and backward with no problems, 18 volts is no trouble, these motors will take up to 24 volts.

Ian S C

Your motor must have better armature thrust arrangements than the majority of car windscreen wiper motors. Car manufacturers are highly ingenious as shaving the last fraction of a penny/cent off the cost of every component. In the long run simplifying and reducing the number of components is actually better for the customer, for as well as there being less to go wrong, they can spend the money and concentrate on better specs for the parts that are essential.

Most if not all wiper motors use a worm and pinion, neither gear will be bothered which way its rotating but In its intended application the motor armature end thrust is always in the same direction so the manufacturer caters for that properly. The armature end float in the non thrust direction might only be limited by a thin walled plastic sleeve (part of the rotor insulation). Its perfectly adequate when wiping but might not last long if the motor is reversed.

For reversing operations there is a much more suitable motor in the doors of modern cars. The window driving motor also has a worm and pinion reduction but it designed to be reversible.

Ian P

Latest update Guys. Tried running the motor direct off the laptop psu at 18.5 volts (checked with meter) as Ian said but motor wouldn't run. Don't really want to buy an electric window motor with regard to the rotation question so will pin the extension shaft. Now I've finally managed to corner my neighbour who is a retired BT development engineer. He's saying that the design of these psu is not suitable for doing what I am trying to do, he did try to explain the technicalities but he lost me after 10 seconds or maybe not as long as that. As it runs off a battery charger he says use one of those, looks like Neil's suggestion! was the way to go, though he's going to see if he has a suitable transformer/rectifier/capacitor etc in his bits and pieces to build something up. If not will try to pick up the smallest charger in physical size with the necessary capacities that I can. Thanks for all the help and suggestions, really appreciated.

Cheers

GW

The The motor will have very low resistance when stopped, and the PSU probably sees this as a fault and refuses to deliver current. A 12V motor I have here takes 7A when stalled, at 18.5V that would be over 10 amps when run off a low-impedance supply like a lead acid battery. The PSU will think it's been shorted out.

You need an 'unintelligent' PSU or a transformer based one.

Neil