vacuum cleaner motor reversal?

In message , Phil L writes

It is, as they say, a total load of bollocks

It hasn't occurred to you that a motor that sucks also blows out of the other end? Isn't it easier to just point the existing exit at whatever you want to blow at?

Never seen one like that (outside of cartoons anyway). On our old cylinder machine you just connected the hose to the opposite end of the machine if you wanted blow instead of suck.

Given that we're on AC now I don't suppose this would make a great deal of difference. If they ever did reverse at the flick of a switch, the switch must have been doing more than swapping live & neutral.

Tim

What does make a universal or induction motor always start and run the same way?

Most vacuum cleaners use series wound motors and to reverse those you need to get inside it and reverse the connections to the field windings. Which may not be possible with a sealed design. Other possibility is to reverse the fan on its spindle.

Swapping the plug connections won't do anything - the mains does just this

Universal and induction motors are two completly different beasts

universal's are basically a dc motor, direction is hard wired in.

Wrong, although if it has brushes with a commutator it's a "universal" (AC/DC) motor and swapping some simple internal connections will do this. Too difficult to explain in ASCII, but I'm sure web searching will turn it up. Purely AC motors won't reverse (for simple levels of fiddling).

It's AC and is reversing 50 times a second anyway.

You need to reverse the connections to the field coil wrt the armature. The motor might / might not run too well in reverse.

Derek

My experience with model aeroplane propellors tells me that won't work. ;-) Reversing the motor will.

If the fan is actually a centrifugal compressor that won't work either. Neither will reversing the motor.

Derek

Wouldnt work. Even if you did contrive to reverse the motor direction, all vacuums use at least a 1 stage, often 2 or 3 stage centrifugal fan which just doesnt work rotated the other way!

Tim.

Phil L wrote on 17/12/2008 :

Doing that will make nil difference to the direction. Only swapping one of either the field coils or brush connections will change the motors direction.

Even if you get the motor spinning backwards, many of the designs seem to be a semi centrifugal design compressor, so it will probably not make much difference to the air flow direction.

They do already blow, at the opposite end to the end they suck. Could you perhaps modify the output end to accept a pipe?

Dry vac motors are cooled by the inward air blowing over the motor & exhausting around the periphery of the motor. They do 'blow' but through a series of small peripheral vents, so its difficult to channel the airflow - and if its restricted too much it can cause overheat.

Wet/dry vacs discharge air around the periphery or via a tangential tube, depending on the turbine. Tangential discharge motors are usually only found on carpet cleaning machines, but they make excellent blowers.

The top picture here

Not in any microwave I've seen. Mine always goes anticlockwise (as do most others I've seen).

Tim

Depends on the type - "synchronous" is just a characteristic of how fast the motor runs, there are several ways to build them. Most of these are fixed to go in one direction (either magnetically by slugging, mechanically with a press-button ('30s clocks), electrically, or switchably) so as to make them reliably self- starting. If it's the simplest sort and really doesn't care, then it needs flick-starting.

Many non-time-critical "synchronous" motors are also not quite synchronous, as they use a little inbuilt slip to give self-starting.

It's the inbuilt slip, or phase lag, between an induction motor rotor and the stator which gives rise to the restorative force that cases the motor to turn - in effect the rotor is always playing "catch up" with the stator. By definition it is then "synchronous" with the supply, speed control can be achieved by increasing the number of poles/windings but there is an underlying synchronism with the supply frequency in there somewhere. At rest there is maximum phase lag equally in both directions and the forces on the rotor are balanced - a flick will set it going either way as AD says. A capacitor is the normal addition - this forces a small phase lag in one direction when the motor is switched on - it starts to move and the normal forces take over.

Some had a mechanical means that wound up a kicked the motor in the opposite direction if it started backwards.

Sharp microwaves go both ways oh er misses

So does our Panasonic. First button push, it goes clock wise, start it again and it goes anti clockwise. Never noticed if it changed direct on one run though. I'm usually tending to other cook at that time.

Dave