Dual-drive DC motor with relay

Thread Starter

Michal Mičuda

Joined Nov 15, 2016
8
Hello, I need to control 6 DC motors, direction and speed. H-bridge would be great, but i would need 24 transistors. I found simple schematic, with one relay for controlling direction and one transistor for controlling speed. I have one question, in H-bridge there are protective diodes on transistor, but in this schematic with relay I've got no idea how to connect it or if I have to connect it at all. (only on transistor for controlling speed). I appreciate all answers.
 

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crutschow

Joined Mar 14, 2008
25,648
You might consider one of these. Some of them are dual-bridge, so you would only need 3 of them.
You might also consider PWM for controlling the motor speed using a 555 timer. It's more efficient, dissipating little heat, so shouldn't require a heat sink.
 

PhilTilson

Joined Nov 29, 2009
86
MOVs are bidirectional which is needed in your circuit as the voltage across the motor can be either polarity.
Yes, but the diode should be placed across the two common contacts of the relay, through which the current flows unidirectionally!

And in answer to an earlier question, yes - polarity IS important! The diode must be reverse biased in the normal direction (ie diode -ve to the +ve side of the supply) otherwise you will quickly begin sending smoke signals with your transistors!

Finally, what's wrong with using 24 transistors? I suspect they would be cheaper than six relays! Or use the IC H-bridges mentioned by Crutschow.
 

Thread Starter

Michal Mičuda

Joined Nov 15, 2016
8
What's wrong? That 24 transistors willl cost me arround 24€ and 6 transistors plus relay arround 10€ and I found IC for max 1A and that's too low for me, so i can add diode across the transitor like in normal h-bridge?
 
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