provide a mechanical interlock and keep the four ones safe, I call this the Xzibit (Pimp My Ride) solution. Funny story: in some forum some people were discussing about adding two more relay to the first four to -somehow.

Every possible configuration is ok, and that's not the case with four relays. By the way, the module is also optocoupled, therefore the control circuit is two times protected from the power side of the device.Īs you can see in the second image it doesn't matter if you don't provide a delay or if you give a wrong input, the motor won't behave in the right way (well, you are providing a wrong input, what do you expect? miracles?) but the circuit and the power supply will suffer no damages. With this solution you'll have only four possible outcomes, which are all safe and that won't damage anything. The wiring is quite easy, you only have to connect the power supply plus and minus 'at the same side' of the two relays. If you discard the H-bridge, transistor based or four relay based, and if you take a two relay module ( amazon, bangood)and follow this wiring scheme you'll be able to properly control a DC motor in both directions without any risk of short circuit and without spending unnecessary money. Moreover, because of shit happens, the situation could be worse: if you overload a relay you risk to melt its contacts and you might not be able to open it also using the proper command input, so aven a brief mistake can lead to a destructive runaway.īeside the safety reasons 4 relays are not an optimal solution because only two relays are actually required, so happy days: a better solution actually do exist and it's even cheaper! Step 2: Second Solution (good) Yes, indeed, it's generally valid for every H-bridge but the transistor module is faster, it use smaller current and it's mostly used paired with a microcontroller (maybe with it's own library). You may replay: ok, good to know, but you would have the same issue with transistor based H-bridges, with relay or bigger contactor is only a little more time expensive. If you have both S1 and S2 or S3 and S4 closed at the same time you'll short the power supply, and this could cause damages to the power supply and/or the circuit itself. This means that you need to introduce at least some delay between the operations. On the paper is not a big deal, in reality a 'little yet not negligible' amount of time is phisically required to open a relay. In order to change the spinning direction you have to open S1 and S4 and then close S2 and S3. In this case you can safely close only one of the switches on the right (S3 or S4), for instance we can assume to have the S4 closed, so the motor is spinning in one direction. For example: lets pretend that the top lef switch (S1 in the image) is closed. If you do the opposite bad things will happen because of an inherent issue. The main issue is that the H-brige requires a precise control of its switches: you must first open a switch and only after a little delay close the other one. While the concept is theoretically valid the practical application isn't so effective. Long story short: the four NO connections (NO means 'normally open', the relay's contacts that don't conduct current when the relay is not active) are set up as the conceptual H-bridge switches. Several projects use four relay to build a mechanical copy (relays are mechanical switches) of a transistor H-bridges. The first solution is somehow suboptimal but still it's the usual solution that you'll see surfing the web.

Then what should you do to a big DC motor? Step 1: First Solution (bad) Moreover most transistor based H-bridge doesn't provide galvanic isolation (even if it's theoretically feasilble it's just not a feature of the most common h-bridge modules), and this could also be an issue for your project if it's sensitive to electrical noise. Second: this task becomes harder as the motor becomes bigger, at some point the required current can't be managed by the most common h-bridge modules.

The most common devices are the Arduino's 'Motor Shield' ( amazon, banggod) or the L298N module ( amazon, banggod), which is the same concept of a motor shield but its control pins are designed to be more accessible. Since i mostly saw 'less than optimal' solutions i decided to write this tutorial.įirst: as long as the motor is 'small enough' the cheap and easy solution is to use an H-bridge transistor based control module. I saw several ways to approach this probelm, some are clever, some aren't so smart. In several projects one big task is the control of a DC motor, and by 'control' i mean start/stop and switch between cw and ccw movement and to proper use some endstops.

Bidirrection motor code arduino relay