using diode to strictly control path of 24v ac?

[hvacr9]

I have a hot water heat project that has 6 zones.6 seperate pumps are powered by six seperate spst 24v coil relays.I now have added another circuit that I want powered whenever any ONE relay is energized.

Can I just use six diodes one off of each hot leg of coils down to the added circuit relay.

Is there another way or am i way off track?

Im trying to avoid having to buy 6 dpdt or dpst relays since I already have panel wired and just currently want to add circuit.

Any help or suggestions on how to achieve this would be greatly appreciated !!!!

 

[kchriste]

Are you sure that the relays have AC and not DC coils?
If the relays are controlled by 24Vdc, then some diodes will probably work. Don't forget the back EMF diode for the new relay.

 

[hvacr9]

thanks for your response the relays are definately 24vac Im just tryin to power the last relay whenever any one relay closes without backfeeding 24vac to other open relays

 

[Roff]

What controls the existing 6 relays, e.g., switches, relays, electromechanical timer, etc.?

 

[kchriste]

If the relay coils are all fed by a common rail, then you could use diodes to half wave rectify the AC from each relay into DC to switch one DC relay. Do you have a schematic of how the 6 24Vac relay coils are wired?

 

[hvacr9]

basically the common leg on all relays are daisy chained together.Each thermostat will close when ther is a call for heat and 24 vac goes to other leg of coil.I want to power one more relay with 24vac off each thermostat relays without the current backfeeding to unenergized coils.Im not an electronics person whatsoever,just good with relay logic and am trying to keep from changing all the relays to accomplish this task

thank you for the reply could you explain exactly what to use to rectify that 24vac to ? dc

common transformer 110-24vac powers all relays

 

[Roff]

If the relay coils are all fed by a common rail, then you could use diodes to half wave rectify the AC from each relay into DC to switch one DC relay. Do you have a schematic of how the 6 24Vac relay coils are wired?

I had the same thought, but wanted to explore the control scheme first, in the hope that there might be some extra contacts on whatever was doing the switching. Thermostats probably don't have any.
If the capacitor is large enough to keep the ripple down to a few volts, it may take several seconds for the relay to drop out when power is removed. That might not be a problem.

 

[Roff]

Hvacr9, how much current does your additional relay draw, or what is its resisstance?

 

[hvacr9]

thank you both for replying,let me say again that I am not into electronics whatsoever although it fascinates me. could you explain the diodes I need and or give me a schematic on how to wire them.the dc relay is the perfect cheap solution I just dont know how to rectify the voltage and what voltage dc relay to get

 

[Roff]

thank you both for replying,let me say again that I am not into electronics whatsoever although it fascinates me. could you explain the diodes I need and or give me a schematic on how to wire them.the dc relay is the perfect cheap solution I just dont know how to rectify the voltage and what voltage dc relay to get

What sort of load will you be switching with the DC relay? Is it OK if it doesn't drop out for a few seconds (it might be less) when power is removed? We need to pick a relay before we can select diodes and a capacitor.

 

[hvacr9]

my fnal relay I dont have yet Im only switching a 2 amp load at 110 volt.

drop out time is not an issue

 

[Roff]

Selecting a relay is a can of worms. What sort of environment will it be in? How do you want to connect the wires to it (solder?)?

 

[hvacr9]

just a simple spst spade terminal relay would be fine environment is enclosed electric panel with six other relays.

 

[kchriste]

What electronics suppliers do you have in your area that have an online catalog?
Here is a concept circuit:

 

[hvacr9]

radio shack I suppose.....your link didnt come up on your post

 

[kchriste]

I doubt that RS will have what you need. I assume you are in the USA?
Take another look at the link above.

 

[hvacr9]

half wave rectification ...would I go with a 12 volt relay? radio shack website search engine ...(capacitor and diode returns alot of different items...they do have the 460 you mentioned just not sure about the diodes

 

[hvacr9]

what is the r1 in your schematic

 

[kchriste]

If you leave the capacitor out and add a catch diode, you would get an average of 10.6V pulsating DC across the coil. The relay may chatter and hum a lot. If you use a capacitor (Rated for 50V) as shown in my diagram, then you get around around 33V of relatively smooth DC. You'd use a resistor (R1 in my diagram) to drop this down to 24V.

 

[hvacr9]

thank you thank you ok lets say I have a relay coil 2000 ohm then how would i size cap and resistor