# Special type of switch needed

Discussion in 'Electronic Components' started by smpaladin, Sep 18, 2004.

I am new to electronics and I need to know if there is a type of
switch that will assist me in reversing the polarity of an
electromagnet, as in the picture here

I've asked this question before in a different group, but I keep

What I want is a switch, like the green switch in the picture, that
will alternate the input/output currents between two wires, as long as
an outside current is applied to the switch. This way, I will be able
to reverse the polarity of an electromagnet as long as the outside
current is applied to the green switch. Is there any specific type of
switch that will accomplish this?

2. ### Peter BennettGuest

You can either use a DPDT switch, or use a DPDT relay, with an SPST
switch to control the relay.

If the wiring from the battery to the electromagnet is located where
you can easily reach it, I would use a simple DPDT switch.

If you want to be able to switch polarity while you are some distance
from the battery and electromagnet, then the relay and SPST switch
might be more appropriate.

What you have shown in that drawing is a relay and SPST switch.

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Peter Bennett, VE7CEI
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3. ### William P.N. SmithGuest

You do indeed need a DPDT relay, the normally closed contacts wired
straight through and the normally closed contacts wired in reverse.

Is this for a class? If not, (how) are you planning on implementing
this circuit?

4. ### Watson A.Name - \Watt Sun, the Dark Remover\Guest

It's called a polarity reversal switch. See the diagram at the bottom
under double pole double throw switch. http://www.1728.com/project2.htm

You can wire a double pole, double throw relay similarly.

5. ### Watson A.Name - \Watt Sun, the Dark Remover\Guest

You forgot 'normally open'.