relay needed... help

[serpentine5]

hello forum folks.
I am a total novice to electronics... but am very mechanical minded. I have a project before me that I need a little assistance with. I was hired to do the electrical part of the installation of a water feature (water fountain in a condo) and after the boss got to know me he is depending upon me to wire up the electronics too.
what we have is a touch screen computer interface with a control program installed on it. the computer is connected to a control modual that has sensors and relays built into it. this allows the pumps and valves to be controlled from the computer.
what I now am faced with is connecting the resivour drain valve to the system. this valve only has a single 12v positive and neutral. the power has to be applied for 2 seconds to open the valve, then the polarity needs to be switched and power applied for 2 seconds to close the valve. I cannot change the polarity with the computer or the control modual. so I was thinking there might be a 6 prong relay I can connect the pos and neutral to on one end, the pos and neutral of the 12v power supply to the other and connect leads from the relays of the control modual to the other two free pins of this relay. when control mod relay 1 applies power to the relay, the relay opens the pos to pos and neutral to neutral and when control mod reply 2 alloys power to the relay the relay opens applying pos to neutral and neutral to pos effectively reversing the polarity to the valve.
is this possible? do they make a relay as such as I described above?
if not, what is my option?

thanks very much for any and all info, serp

 

[davelectronic]

Relay control

Hi there, ive wired up a few relays for motor servo control, relays come in many contact/pole arangements, your aim seems more to do with the control system, the relay part is not to hard to do, but i suspect a timing circuit is needed to tiriger the sequence, ive done remote control relay circuits, but not single timing control via a timing circuit, maybe another member can ilaberate on this timing relay multiple control circuit. I think thats the way forward. Dave.

 

[serpentine5]

the timing part is covered with the program on the computer via the control modual.
what I need is something that will allow me to safely reverse the polarity on the 12v circuit without backfeeding into itself or the power supply, or the control.

 

[serpentine5]

ok, I have a 8 pin relay here that I have been tinkering with. if connected like:

1-4 on one side, and 5-8 on the opposite side. Power from the control comes to 1 and 5, the valve white to 2 and red to 6, and power pos to 3 and 8 and power neg to 4 and 7. when there is no power to the relay, it would always be closed between 2 and 4 and 6 and 8. when the power is applied to the relay, it would open 2/4 and 6/8 and close 2/3 and 6/7. this would operate the valve in the manner we need it to work.

do they make a larger one that would leave the switches in the open position on both sides instead of one open and one closed until power is applied? I guess I could use two of these and tie them together so they would always be in the default open position, but them both could be commanded to close at the same time and burn the valve up....
if a larger one I would need it to take one neutral and two positives on the power activation side to tell it to close one set of switches or to close the other, without being able to close both at the same time.... that way I can switch the valves power source from correct to reversed, and then the times would cut power to the relay after 2 seconds causing the relay to go back into the default open position on all switches.

 

[davelectronic]

Relays

There probably is a relay that will meet your spec, i dont know of one. Two relays are an option wired in the way that you need if wired correctly nothing will burn out, but you need the sequence of switchings to be correct. Dave.

 

[duke37]

In order to change the motor direction you need a two pole change over relay. Connect the power to the common contacts and the motor to the unenergised contacts and also swopped over to the energised contacts. This ensures that the motor cannot be connected both ways at once. If it were, it would not damage the motor, it would damage the power supply due to the short.
I think this is what you suggest in the previous post.
Another relay would be necessary to define the application time. This could be as simple as a singe pole make relay.

Two similar relays could be wired so that each could only be energised when the other was not energised, this may make the control simpler.

Incidentally, the terms line and neutral are normally used on AC cicuits and can cause confusion if used on DC circuits.

 

[davelectronic]

Relays

You seem to have a good idea of direction, no schematic so a bit tricky t visulise, diodes if big enough block voltage going where you don't wont it. Dave.

 

[duke37]

I attach a diagram of two 2 pole changeover relays with a switch for each direction. If you are using semiconductor switches, do not forget a flywheel diode across each relay coil.