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Preventing a possible 12v short circuit

smilegr8

Dec 30, 2021
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Good evening everyone !

My very first post here :)
I was wondering if somebody can spare few min to have a look at the diagram / sketch I have attached and advise how to solve the issue I have .
Basically I need to power a 12v liniar actuator via 2 different timer switches , one switch has the outputs reversed so the actuator can retract

1 timer switch will be on for 60sec at 14:30 and the other timer switch will be on for 60 sec at 21:30
A short circuit is certain if somehow both timer switches will be on at the same time ( let say one switch fails )

Happy to pay for a coffee if somebody can solve the mystery for me in a simple way as i'm a total beginner :)

Happy 2022
 

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Bluejets

Oct 5, 2014
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The way how I see I think you have the diodes will not work.
Cannot see actual diode polarity in your so-called diagram.
Most here don't work for beans....:):)
 

AnalogKid

Jun 10, 2015
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That timer has + and - inputs and + and - outputs. When the timer is *off*, is there any continuity between the input and output terminals? For example, are the two - terminals connected all the time, and the timer breaks only the connection between the + terminals?

ak
 

smilegr8

Dec 30, 2021
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That timer has + and - inputs and + and - outputs. When the timer is *off*, is there any continuity between the input and output terminals? For example, are the two - terminals connected all the time, and the timer breaks only the connection between the + terminals?

ak

Good evening- yes I think so at least that's what i can understand from the diagram below .
Thank you Iurie
 

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crutschow

May 7, 2021
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If both timers are on at the same time, there won't be a short if they are applying power from the same 12v supply.
 

smilegr8

Dec 30, 2021
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If both timers are on at the same time, there won't be a short if they are applying power from the same 12v supply.
Yes both timers will have the same source however for the actuator ( dc motor ) to travel in both directions second timer has the output polarity the other round
 

smilegr8

Dec 30, 2021
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Dec 30, 2021
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That timer has + and - inputs and + and - outputs. When the timer is *off*, is there any continuity between the input and output terminals? For example, are the two - terminals connected all the time, and the timer breaks only the connection between the + terminals?

ak

Thanks for asking about continuity, considering that two terminals are connected all the time - my already poor designed diagram is a total failure:)
I will probably go for a manual DPDT momentary switch instead

Thanks everyone for your time
Regards Iurie
 
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crutschow

May 7, 2021
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I will probably go for a manual DPDT momentary switch instead
Sorry I didn't properly understand your requirements, thus my incorrect previous response.

You can use two 12Vdc SPDT relays in a bridge configuration, activated by the timers to control the actuator as shown below:
It will not cause a short even if both relays are on at the same time (it would just apply +12V to both actuator connections which means it's OFF).
upload_2021-12-31_8-59-47.png
 
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smilegr8

Dec 30, 2021
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Sorry I'd didn't properly understand your requirements, thus my incorrect previous response.

You can use two 12Vdc SPDT relays in a bridge configuration, activated by the timers to control the actuator as shown below:
It will not cause a short even if both relays are on at the same time (it would just apply +12V to both actuator connections which means it's OFF).
View attachment 53737

Thanks Crutschow

I ll print it out and ask my neighbour ( electrician) to read it for me before i mess it up : )

Happy 2022 !
 

crutschow

May 7, 2021
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I always pick relays with a normally closed contacts so they can be interlocked like this.View attachment 53738
I think that's essentially that same circuit as my post #12.

The diodes in my circuit are to prevent contact arcing and erosion from the high reverse transient voltages otherwise generated by the relay coil and actuator inductances.
 
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crutschow

May 7, 2021
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I ll print it out and ask my neighbour ( electrician) to read it for me before i mess it up : )
If you aren't aware, the lines in the schematic represent wire connections, and a dot on the wire indicates the two wires are connected together. The two wires can be connected together at any convenient point in the physical circuit (such as a relay terminal).
 

smilegr8

Dec 30, 2021
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If you aren't aware, the lines in the schematic represent wire connections, and a dot on the wire indicates the two wires are connected together. The two wires can be connected together at any convenient point in the physical circuit (such as a relay terminal).
Thank you !
 
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