circuit to reverse motor direction, 24v

[H73iiPz]

I may have put this question in the wrong place before, but here is what I need help doing. I am trying to build an auto matic door for my wife's chicken coop. It is all 24V. I plan to use a lawn sprinlker timer, i.e. station 1 open: station 2 close. The timer runs for 1 minute. I have micro switches to stop the up travel and down travel. I need a circuit to reverse the polarity of the motor so it can run in in two directions. The door will usually open in AM and close in PM. So the 1 min run on the timer is not a problem. It will be off in plenty of time for each action.
Thanks

[pebe]

You could use the circuit on page 1 of the other topic about chicken coop doors, to reverse the motor. If you want to use that, feed the 12V rail from your 24V supply by using a 7812 12V regulator (that gives a common negative rail) . Remove the connections between the top contacts of the relays and the 12V rail, and connect them to your 24V supply instead.

[H73iiPz]

Thanks, so much. However, I was trying to make it as simple with the fewest parts as possible. The transformer voltage from the lawn sprinkler timer is 24v as is the motor.

[pebe]

It is possible to use a single relay for reversing, with On = door up and Off = door down. But there has to be some way of steering the timing pulse to toggle the relay. A single 555 could do it if both poles of the timer are 'free'. But most suitable devices will not work at 24V (the absolute max for a 555 is 16V) so a voltage regulator to drop the voltage is still required.

To make up a steerable flip flop using discretes would probably take more components.

It is possible to make a simpler circuit if your timer was programmable to give an output for the entire time the door was to be open (instead of just a pulse). It would a simple matter to switch the relay then.

[H73iiPz]

Thanks for the help. It looks like, from what you describe, I may heve to use two relays. One for up with +- polarity and one for down -+ polarity. I have acess to a number of 24v relays. Now I need to know which kind, i.e. spdt, etc. and how to wire the circut. The sprinkler timer has a common wire and one for each station. The micro switches have a com and NO and NC connections.

[pebe]

Are the timer's connections 'free'? ie. are they not connected in any way with the 24V supply?

[H73iiPz]

The timer has a 24v power supply deliverng constant power to the 24 hr. clock which is programed to turn on a station in turn delivering 24v power to the station timer of one or more minutes as programed. It is a standard residential irrigation system timer.

[pebe]

That's not the question I asked. Let me put it another way.

I need to know how to connect up the contacts of the timer. So can you tell me if Is there any electrical connection (ie. can any resistance be measured) between any of the timer contacts and either 0V or +24V of the power supply?

If there is a connection, does the contact for each position connect to +24V when its timer is On? And does it connect to 0V when the timer is Off?

[H73iiPz]

The contacts to get power to what would be irrigation valves (24V) are com and each station. When the timer calls it activates power to the com and a station. Otherwise there is 0v between the com and any station. The only power is to the 24 hr. clock.

[pebe]

Here is the circuit – about as simple as it gets.

The motor direction is controlled by two SPDT relays REL1 and REL2, with contacts S1 and S2. When REL1 is energised, it puts +24V on the LH side of the motor to open the door. When REL2 is energised, +24V is put on the RH side of the motor to close the door.

The limit switches are wired using the ‘Common’ and ‘Normally Closed’ contacts, so that at the end of the door movement, the switch operates and breaks the contact. The drawing shows their positions when the door is closed and the bottom limit switch has gone open circuit.

Operation is simple. The ‘Open’ timer will put forward bias on to the base of TR1, REL1 will operate and the door will start to open. When the door operates the top limit switch, TR1 will switch off and REL1 will de-energise. The 'Close’ timer will operate TR2 and REL2 in a similar way.

If the motor is trying to close the door instead of opening it, just change over the motor connections.

The 2N3704 connections can be obtained here:

http://www.datasheetcatalog.org/datashe ... 2N3704.pdf

Best of luck.

[H73iiPz]

Thanks. It looks pretty straight forward. I am assuming 6K8 and 2K3 are the diodes. It looks like the relays are 4 pin?? You have to forgive me. Im 72 and the majority of my basic electronics involved vaccuum tubes, risitors - condensors, etc. The first experience was building a cat's whisker radio right after WWI.I.

[pebe]

Th 6K8 and 2K2 are 1/4W resistors. The diodes are the two devices across the relay coils; with their cathodes to the tops of the coils.

In case you are not sure, the three terminals on TR1 and TR2 shown in the circuit are (from the top) C, B and E.

The relays are SPDT types, ie. each has a common connection that can switch between two other contacts - the normally closed one will be marked 'NC' and the other will be normally open and marked 'NO'. Each relay will each have 2pins for the coil and 3pins for the contacts, but there may be 4pins for the contacts - ie. the 'Common' connection may be duplicated.

You said you may have some relays lying around, so if you can let me know their makes and types I can possible give you a bit more info on them.

[H73iiPz]

My schematic symbals are refreshed, Thanks. I'll get back as soon as I get the relay information.

[H73iiPz]

I finally received the correct relays and all the other parts. They originally shipped DPDT. They are 8 pin SPDT. NTE R14-5A1515-24 24VAC #R95-121.
I am not sure what you mean to orient the diodes "with their cathodes to the tops of the coils." They are smaller than a grain of rice. Also, when speaking of TR1 and TR 2, is C,B and E - Collector, Base and Emitter?
Thanks

[pebe]

The diodes must be connected so that correct polarity is observed. There will be a ring painted around one end of the body near the lead-out wire, and that wire is its cathode.

Yes, C, B, and E stand for Collector, Base and Emitter .