DC motor control - is this schematic good?

Here is schematic for DC motor control. Using this I can drive motor in both directions and also send short pulses to motor, to move it only a little bit in desired direction.
Let me explain schematic in detail.

PWM controller is powered using 12V DC (Vin). Modulated signal (Vout) is input signal of first DPDT relay. Depending on which relay is energized, direction of rotation of motor is changed.

D1 and D2 are there because of back EMF protection. D3 and D4 are there to enable me to drive motor in opposite direction when it goes to limit in one direction.

Using left 4PDT (ON-OFF-ON slide type) I choose whether motor will be powered for long time (as long as one of relays is energized) or for short time (one of relays is energized for short time using pulse signal generated using 555 circuit).
Lets say that we choosed on left 4PDT that voltage which drives motor is "long" (lets call this first ON position of left 4PDT, it is of type ON-OFF-ON).

Using right 4PDT (ON-OFF-ON, momentary) I choose which relay will be energized. Pay attention that in whatever "ON" position is right 4PDT, it will short one part of 555 circuit (one side of C2 with pin 2). You will see soon reason for this

When left 4PDT goes in second ON position, then 555 circuit gets power supply (12V DC) and it is ready.
Right 4PDT now has not only function to choose specific relay (thus driving motor in desired direcion), but also to cause process of generation of short pulse using 555 circuit by short connecting one side of C2 with pin 2 (here is where I found this pulse generator **broken link removed** , thanks to AlbertHall). Generated pulse energize specific relay for short time so motor rotates in specific direction only for short.

Is this ok? Is there something what should be changed? I didn't choose values for capacitor and resistor in 555 yet because I still don't know exactly what will be pulse duration. I have normally closed wtiches, DPDT relays and PWM controller.
Motor is linear actuator (**broken link removed**), it should arrive in few days.
I should buy other components. Motor amperage is 3A max.
This is PWM controller I have http://www.ebay.com/itm/162002954574?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT
DPDT relays are **broken link removed** .
Which diodes should I use for D1, D2, D3 and D4?
Is this power supply (12V DC) good for this application **broken link removed** ?

etf said:

. D3 and D4 are there to enable me to drive motor in opposite direction when it goes to limit in one direction.

Click to expand...

How does this work?

12V DC should be good for your application but make sure about the current rating of the power supply and the quality of the adapter that you are going to choose

Hi,

I see no mistake, therefore I expect it works.

But it could be more easy.
Half the wiring can do the same. A simple solution need only SPDT relays and DPDT sliding switches.

Klaus

Thanks for replies.
@c_mitra, limit switches are NC, when one of them is opened (when motor reach one of limits) there is no path for current so motor stops (diode across NC switch which is opened is reverse biased). However, when I change polarity of motor voltage, that diode becomes forward biased and enable motor to move, although switch is opened
@hobbyckts, max. motor current amperage is 3A but I will probably buy 12V DC 6A. One thing that I don't like about power supply from ebay is that it is from China
@KlausST, I would like to see your solution There are a lot of wires in my schematic and that is drawback, but I have full control of motor using only two 4PDT switches (one is used to change direction of motor, second is used to select type of voltage - continuous or pulse).

Hi,

for example: **broken link removed**

look for : "Using two typical SPDT (Single Pole Double Throw) relays to control a DC motor:"

**********
and: To control the relay coils...you don´t need to switch both wires. Leave one wire continously connected with GND and only control the 12V to the relay coil.


Klaus

etf said:

Thanks for replies.
@c_mitra, limit switches are NC, when one of them is opened (when motor reach one of limits) there is no path for current so motor stops (diode across NC switch which is opened is reverse biased). However, when I change polarity of motor voltage, that diode becomes forward biased and enable motor to move, although switch is opened .

Click to expand...

That much is clear. However, I do not see the two DPDT switches (just below D1 /D2 on the left), how they are providing power to the motor. In the connection shown in the diagram, the motor is not supplied with any power.

If you are feeding a DC motor with AC (with which it is not going to run) but once you put it with D3 or D4 which makes it into DC, that is going to be simple. But the actual power to the motor must be reversed, not only putting a diode.

Hi,

That much is clear. However, I do not see the two DPDT switches (just below D1 /D2 on the left), how they are providing power to the motor. In the connection shown in the diagram, the motor is not supplied with any power.

If you are feeding a DC motor with AC (with which it is not going to run) but once you put it with D3 or D4 which makes it into DC, that is going to be simple. But the actual power to the motor must be reversed, not only putting a diode.

Click to expand...

I´d say the schematic is correct.
Activating one relay moves the motor in one direction.
Activating the other relay moves the motor in the opposite direction.
Activating none or both relays make the motor to stop. (free run, no break)

Klaus

@c_mitra
Left DPDT (it is relay) is connected to Vout - modulated voltage from PWM controller and that voltage drives motor. When both DPDT relays are deenergized (like on schematic) there will be no path for current to motor (same for situation when both relays are energized). When one of relays is energized there will be current path to motor and motor will rotate (direction depends which of relays is energized).

And in fact, both relays can't be energized in same time