240volt switch used with 12volts?

[Vass]

any reason I cannto use this "COLUMBUS 400 PNEUMATIC TIME DELAY SWITCH" on a 12volt battery to a motor?

[Invisible Man]

Can't see any problem as long as it can cope with the DC amps.

[dennis]

The voltage needs to be higher than the supply so a 240V switch should be fine on 12V.

All switches have different ratings for AC and DC switching. In general you need to look at the maximum current it will switch to see if it will break that current without welding itself. The current will be significantly lower for DC switching.

[Vass]

cool, ta

[Peter Parry]

It all depends on the motor.

The switch is rated at 6A AC (3A AC on inductive loads) On DC that rating will probably be less than 1 Amp. The switch capability depends upon its current handling capability and the current breaking capacity of the switch. It is the second which is much lower at AC than DC.

A pneumatic switch may also have a relatively slow switching action, this will derate it more on DC.

Motors are inductive loads and generate high current sparks at switch off.. You can protect the switch to some extent by fitting a snubber across it - 0,1mfd and a 47R resistor in series.

[Dave Plowman (News)]

How much current does the motor take? Motors are inductive devices which produce back EMF when switched off and likely to cause arcing on an AC switch - unless very small.

[The Natural Philosopher]

Three possible reasons.

1/. Current is excessive for the contacts. Motors on 12v take big startup currents and generate nasty flyback voltages when the current is cut..

2/. Contacts are not designed to suppress a DC arc. AC tends to kill the arc a bit quicker, as there are periods of 'no voltage'

3/. Its a solid state switch designed for AC only..;-)

[Vass]

any other ideas then, I need people to casually switch on as they walk by and it run for a short while

[Peter Parry]

The switch you are looking at isn't electronic so it will work happily on 12V. Whether the contacts will survive depends on the motor rating

- if you can let us know what it is you can get a more precise answer. If not you can always use the switch to switch a relay and the relay to control the motor.

[geoff]

In message , "dennis@home" writes

Did you mean rated voltage there, braniac ?

With high current low voltage applications on mains switched, you can get a build up on the contacts which, over time, increases the contact resistance.

You can also get switch burn due to the back emf stored in the motor windings on switch off

[Dave Plowman (News)]

Use the switch to operate a relay with 12 volt coil. A car 30 amp one would be ideal - the coil on those draws about 0.1 amp. They're about a fiver in Halfords - or pennies from a breaker.

[dennis]

I meant what I said.

Did you mean mains switches there, braniac?

Hint.. don't start nit picking when your English is so poor.

[The Natural Philosopher]

Don't get me wrong, it may work. It may not work for long. It may not work at all.

What you concoct to do this depends on your skills and what stuff you have to hand.

Id probably do something with a CMOS chip, a resistor and a capacitor and a power transistor.

[Vass]

skills? 50-50 stuff - zero

Whoosh!

Will try the push button, its only got to work for 3 weeks.

[Dave Plowman (News)]

If you gave details of the motor it might be possible to make an educated guess.

[dennis]

I would guess that its the wheel chair motor he is attaching to his turntable.

It shouldn't take much power as its low geared and lightly loaded from what has been posted in the other thread. Probably 1-4 amps.

[Vass]

absolutley no writing on the motor or gearbox, so I have no idea sorry should have said

[Toby]

To be fair, your post was ambiguous, I assume you meant "The RATED voltage OF THE SWITCH needs to be higher than the supply so a

240V switch should be fine on 12V."?

[dennis]

It wouldn't have made much sense in another random context.

However geoff is a pita that just likes to try and score points even though he isn't very good at it. As you can see he understood what I posted but feels the need to try and make out he knows more. I don't know why he does this but its his problem to work on. I don't expect him to take the hint either as its too subtle and he won't understand it.

[Peter Parry]

Wheelchair motors loaded can draw 20 -40 amps, they are usually rated at 250W continuous and 500W peak. Although they won't draw anything like this in the application contemplated they also have horrible switching spikes. If it is a wheelchair motor I'd be inclined to put a relay on the switch (a very simple job) and switch the motor on the relay contacts.

If you salvage (or buy) a "standard" Bosch type car relay the contacts will be numbered.

Connect relay contact 86 to bty negative. Connect one terminal of the pneumatic switch to bty positive. Connect the other terminal of the pneumatic switch to relay contact 85 Connect relay contact 87 to battery positive.

Connect the motor negative to battery negative. Connect motor positive to relay contact 30.

These relays all use standard Lucar blade connectors.