Introduction: Simplified 'H' Bridge

Picture of Simplified 'H' Bridge

This is a simple circuit to control the direction of a DC motor, with the capability to turn it off.

Step 1: Nothing to It...

Picture of Nothing to It...

There is really nothing much to explain. A simple switch will give you the capability to reverse and switch on/off your motor. A switch, like anything else can wear out, but with only one part to deal with, you have less of a chance of paying for a bunch of more expensive components when it comes time to replace them.

Step 2: Wiring the Switch

Picture of Wiring the Switch

This diagram shows the DPDT switch, with a center OFF position (NEEDED if you want to be able to turn your motor OFF) The + and - are the battery terminal hookups to the center (COMMON) terminals of the switch. The numbers (1 and 2) indicate the connections made inside the switch when the switch is in the ON (1) position or the ON (2) position. NOTE the blobs. It shows that the wires are connected. All other wires are just passing over each other. One other thing... You can use TWO SPDT switches side by side so long as you physically clamp the toggles together to achieve the same effect. Having the switches in the opposite directions will connect both switches to either positive or negative on the battery, and your motor won't be running.

Comments

amando96 (author)2009-03-31

ohh way beter than relays for sure, although for robots not the best option, but for big motors like couple hundred volts, pretty usefull :tup:

Pazzerz (author)amando962009-03-31

You can actually use a servo from a cheap ( as in cheap) RC car to move the switch. It works. Those servos can be cannibalized and used to move a lot of different things and even some hard to move things with a little gearing or leverage. I bought a 'cheap' car for $11 and got my money's worth out of it for my own robotics.

mecfr (author)2008-06-08

hi i can see how this will replace the H bridges. but using the same switch [three states that has on-off-on) how can i connect it to limit the current (or how many times the motor turns?) thank you in advance for your help

Pazzerz (author)mecfr2008-12-18

You would need a motor controller with current limiting, and a feedback system to tell you how many turns/degrees(whatever) the motor has taken like with a servo motor. Stepper motors can be controlled with a single IC and some transistors, etc, with the IC controlled by the number of pulses input into it. Each pulse moves the motor to the next coil position, BUT there is no feedback in such a system, unless you make one for it. This is why the more you want out of a motor, the more involved it is, and usually more costly. The exception is widely used motors with these capabilities that are manufactured in such quantities that it is cheaper to buy one rather than make one (unless you're doing it for the experience). The switch (above) can be replaced with a single relay for electrically controlled projects, which will come in handy for those 'mobile' projects where you don't need to be chasing it around to switch directions.

Pazzerz (author)mecfr2008-06-09

If you want more control, replace the switch with current limiting transistors or ICs. The amount of turn can be controlled via feedback from a counter or position sensor such as servo motors have. The circuit here represents the simplest way I know to switch a motor between forward/reverse/on/off. The point of this instructable was to poo poo the over complicated designs I have seen on here and elsewhere. If it is computer/processor control that you want, fine. This will still be the simplest way to go with very little modification. I see too many people going the over-complicated route with these microprocessors when they are totally not needed. My Rule: Build it simple, then let the microprocessor take over where your brain and hands did the work.

unclelar (author)2007-08-23

Would this work on an AC motor?

Wyle_E (author)unclelar2008-12-10

It depends on what kind of AC motor. Series-wound ("universal") motors, like the ones in AC-powered portable power tools, can be reversed by reversing the connections to the brushes, but you have to get inside the motor case to do that. Reversing the connections to the whole motor won't work; that's why series motors run in one direction on AC. One simple approach is to use a permanent-magnet DC motor, a bridge rectifier and a reversing switch on the DC side of the bridge.

Pazzerz (author)unclelar2007-08-23

Actually, I wouldn't think so. There is a little more involved with an AC motor. There is a sight with a question and answer about this at:

http://en.allexperts.com/q/Plant-Automation-Controls-2477/AC-single-phase-gear.htm

This may be just for this particular motor, but it does give you an idea of what may be needed. I've dealt very little with AC motors even before I went to school for electronics. The easiest were 3 phase motors.

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