Trying to wrap my head around uses for a relay - would this work?

[MrEd]

I have never used relays, and am trying to figure out how they might be of help in my system. Would the below work:?

I have a Honeywell L4006b on the side of my tarm, when it gets upto 160 it kicks on the C3 circulator. I'd also like to use this information (the information being that the tarm is above 160) to signal my load circ that it is OK to run if any zones are calling for heat (and to prevent the load circuit from running if there is no heat to be had from the tarm).

I could add a second aquastat with a 18G wire back to the zone valves/end switch to accomplish this, or I was wondering if a relay would solve this problem, and if so, which one.

I am thinking that a 24V wire on the control side of the relay that connects when the L4006B gets to 160, is there a relay that could then turn on a Grundfos 15-58 directly *and* close a loop on a 24V wire that then tells the endswitch to turn on the second pump (50 feet away) or would additional parts be needed?

Would this be a recommended use of a relay? or am I thinking the wrong way? Can I relay complete two circuits for me, one at 120V and one at 24V? Would this be called a single-throw, double pole or is this a double-pole, single-throw relay?

BTW: In case you all can't tell, even though my tarm was up and running last year, I am finally delving into the control aspects - last year I did a lot of turning switches on and off at the right times...and this I need to make things run more automatically.

 

[Nofossil]

I wish I could find a good relay tutorial on the web. You are hardly the first person to ask these questions. I went through the same process years ago, and all I can say is that it's worth taking the time to wrap your head around relays and relay logic.

Basically, relays have three characteristics that matter in most applications: Coil voltage, contact type, and contact current carrying capability.

Think of a relay as a switch that's controlled by electricity instead of by hand - the switch will be in one position when power is applied to the coil, and in the other position when there's no power. Simply choose a coil voltage and power type (AC or DC) that matches the power that you have available to control the relay.

Inside the relay, there can be one or more sets of contacts. In general, there's no significant difference in price to have two sets of double-throw contacts (DPDT). That gives you a good deal of flexibility. For one thing, you can switch different voltages with each contact set. Double-throw contacts give you a common contact that switches between two additional contacts - one when the relay is not powered (the 'normally closed' contact) and another when the relay is powered (normally open).

Even if I only need single pole single throw (SPST) I'll order DPDT just to have the extra flexibility down the road. The only time there's a significant price penalty is for relays that switch large loads.

As long as you're under 10 amps of load, relays are generally small and cheap.

 

[Mid Michigan]

To answer your question you need a double pole relay. It could be a single throw or a double throw.
Yes, you can put 120VAC on one pole and 24VAC on second pole.
If you hook a relay to L4006b this will give you the ability to use the info for more than one thing. You can easily buy 4 pole relays if you wish to. Same info for four different things.
Be sure relay contacts are rated for load you are applying to it. The contacts are rated for 120VAC and the horsepower or amps of your pump you are good to go. You should oversize the contacts some for the pump as the start up current is always higher than the running current. If they are rated high enough for the 120VAC the 24VAC shouldn't be a problem but you want to make sure the amps still fit with in the rating.
Also keep in mind the coil voltage must match the voltage output of your controller. Which I believe is 120VAC for your situation.


SPST single pole single throw is one switch that can be turned on or off, can be purchased normally open or normally closed, open means you will turn something on when coil is energized, closed means you will turn something off when coil is energized.
SPDT single pole double throw is one switch that can be turned on or off also but you have the option of having the device normally on or normally off. This can be wired either way as above without worrying if you purchased the right one. If your logic is backwards just switch to opposite side of contact.
Normal position is the position the relay will be in with no power on the coil. This is what state it would be in if your power goes off.

DPST same as above except there are two sets of contacts meaning you can switch two different things with the same coil.
DPDT same as above except there are two sets of contacts meaning you can switch two different things with the same coil.