Wire 2 Relays,so that is impossible for both to be energized at the same time

[settra]

hello forum! i want to wire two relays, in a way, that if the one of two is energized, then it is IMPOSSIBLE, for the other one to get energized..
the catch is, i cant use any of the terminals, appart from the ones that oparate the coil.... anyone has a design that could do that??
thanks!

 

[ClydeCrashKop]

Single Pole Dual Throw switch?

 

[settra]

i dont understannd what you ask you mean how many terminal the relays have?? i will be using "2 channel " relays..



maybe a circuit like that will work?? :
https://imgur.com/hXzK605

 

[mbarazeen]

..the catch is, i cant use any of the terminals, appart from the ones that oparate the coil....
thanks!

so you cant wire one coil via other relay? you can use additional relays? or some electronics? whats your working voltage?

 

[settra]

the relays are 5v, 2 channel relays. each channel has 3 terminals (input, NO,NC )
on the 2 channels, there will be +16v on one channel, and GND on the other channel.
i can use other relays/elecltronics. the above design uses N-channel FETs. but i am looking for the simpliest possible solution

 

[ClydeCrashKop]

Using a Single Pole Dual Throw switch, only one or none can be energized.

 

[settra]

yes the siwtches will be single pole dual throw. the problem is, there will be 2 switches so one can be on one state, and the other one on the other... (the second "Switch" is actually an arduino that also controlls the relays)

 

[alec_t]

the second "Switch" is actually an arduino

Are you saying the Arduino also has a SPDT switch? Or is this switch a port which can be set as an output and can pull high and low?

 

[dougy83]

This may do what you're after. The diodes across the relay coils are to protect the transistors when power to the relay is turned off.
The SW1/SW2 inputs should probably be driven by totem-pole outputs or similar, or the leakage of the schotykey diodes may turn the transistors on slightly.

 

[settra]

no, no i have a program running on my pc, that has two buttons that you can press ( an SPDT switch). it comunicates via serial with the arduino, and then the arduino sets high or low the pins, in order to energize the relays.

 

[settra]

dougy83, yea cool! it seems like it would work !!

 

[ClydeCrashKop]

The plot thickens…

 

[settra]

 

[crutschow]

dougy83, yea cool! it seems like it would work !!

Yes. Just make sure the two diodes at the transistor bases are Schottky types or the circuit won't properly inhibit the OFF relay from turning on. You could use regular diodes if you also add an extra diode directly in series with each transistor base.

 

[eTech]

Here's a sim..

1 with diode's
1 with schottky's

 

[crutschow]

Here's a simulation with an added standard diode on each input (no Schottkys). Note that whichever relay is energized first prevents the other from being energized unit the first one goes off.

Note that this circuit may allow both relays to energize concurrently if both inputs are simultaneous.

 

[KeepItSimpleStupid]

when you say impossible, I think of a mechanically interlocked relay: https://www.galco.com/shop/AC-Mechanically-Interlocked-IEC-Contactors These are used on transfer switches. Electrical protection isn't good enough.

 

[eTech]

Hi

Railroads use the method shown in this attachment a lot in safety circuits. Once a relay is energized, the other is locked out. The contacts are made of carbon so they don't weld together.

The relays in the attachment are shown in their de-energized state.

eT

 

[settra]

both the interlocked relays, and the diagram with the schotky diodes, seem to do the job perfectly !!
(i tend to prefer the intelocked, cause its really, really impossible for the relays to energize at the same time ) but what i will finally choose, depends on what relays i will be able to find, and how many channels they will have!!
thanks allot for your help guys!!