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Dc motor 2 direction switch

by ramonegumpert
Tags: h-bridge
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Mar1-10, 11:44 PM
P: 186
Hi experts,

is it possible to have a simple 2-directional switch using just 2 12v coil relays (having normally opened and closed contacts)? Is this equivalent to a h-bridge or must a h-bridge be used? The triggering is from a 555 to the relay coils.

I tested my circuit but it does not seem to switch polarity even though the relays switched! This resulted in only 1 directional spinning for the half cycle and then the in the other half cycle the motor halts which i suspect is due to shortcuiting.

But the circuit seemed to work at times bi-directionally. So, this is why i like to confirm if 2 relays can perform a h-bridge.

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Bob S
Mar2-10, 01:09 PM
P: 4,663
You need a single DPDT (double pole double throw) relay or equivalent wired as a cross (X) switch. There are two types of DPDT relays; make before break, and break before make. You need the latter.

Bob S
Mar3-10, 06:30 AM
P: 186
Sorry Bob S and forummers,

I think my relay is of type Single Pole Double Throw, not DPDT. My appologies.
Here is how it looks like :

There are 2 contact points for the switch (common) : one is the normally opened and the other is the normally closed.

I am using 2 spdt relays as my h-bridge controlled by a 555.

I wish to confirm that this is feasible as a h-bridge. Currently, my configuration is not working properly and only momentarily does it oscillate between 2 directions.


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