Where to find VAC to VDC Relay

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BlueDevil

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I am looking for a VAC to VDC Relay. Roughly 3-32VAC Input and 2-24VCD Output. Doesn't necessarily have to fit those specifics but that would be preferred. Everything I come across seems to be VDC to VAC.

Any ideas or suggestions?
 

prcguy

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Are you asking for a relay with a coil that is 3 to 32VAC and contacts that will handle 2 to 24V DC? A solid state relay will handle a wide range of input or coil side voltages like 3 to 32V DC but a relay with a coil will be rated at a specific voltage like 12, 24, etc, otherwise the coil will not energize properly at lower voltages and will overheat at higher than rated voltage.

I've not shopped for solid state relays recently but there should be some available that will take AC or DC on the input and output side.
prcguy

I am looking for a VAC to VDC Relay. Roughly 3-32VAC Input and 2-24VCD Output. Doesn't necessarily have to fit those specifics but that would be preferred. Everything I come across seems to be VDC to VAC.

Any ideas or suggestions?
 

bharvey2

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Solid state relays can work well but they come with some caveats. If your load is resistive, (like a heater or incandescent bulb) you don't normally have to worry about the type of relay. If your load is inductive, (say a big transformer in the power supply) a "random turn on" not "zero crossing relay is what is recommended. A "zero crossing" relay can be rough on inductive loads.
 

BlueDevil

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I cannot seem to locate a Solid State Relay that will accept VAC input near the 24V range.
 

prcguy

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You can simply rectify the AC for a solid state relay input using a diode and capacitor. There is no current to speak of and a half wave rectifier using only one diode and a few uf capacitor should work fine. I would also put a small load resistor around 1K ohm across the relay input to discharge the capacitor faster.
prcguy




I cannot seem to locate a Solid State Relay that will accept VAC input near the 24V range.
 

bharvey2

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I cannot seem to locate a Solid State Relay that will accept VAC input near the 24V range.
Can you please clarify both your control voltage and load voltage? I can compare to several I have and maybe give you a good part number.
 

Rred

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Relays don't do that.

Relays do not convert AC to DC, or vice versa. They also don't convert voltage levels.

So if you need to do what you said you need to do, you'll need a transformer to change the AC voltage level, followed by a rectifier to make the AC into DC, followed by a voltage regulator to adjust the voltage at the output.

You might find all that in one digital switching power supply, but given the odd voltage levels good lucking finding it.

I'm thinking a description of exactly wtf you are trying to do, would shed some light on what you really need to make it happen.
 

RFBOSS

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Taking your post at face value here is a link to one that looks like it would work.

32 volts AC coil and 28 volts DC contacts.

A socket for 4 or 5 dollars and you are good to go. I will admit to soldering to the pins for my own DIY, but for something somewhat more professional, a socket is recommended.
 

bharvey2

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Brandon,

Here is a SPDT mechanical relay:
Magnecraft 781XAXM4L-24A
Control voltage is 24VAC Contact voltage is 20A, 277VAC or 28VDC

If you're looking for a solid state relay, look for a DC to DC relay with the proper voltages and rectify the control voltage as PRCGuy suggests.

A possible DC/DC relay is a Crydom D1D40-4269 or equivalent.
Control voltage is 3.5-32VDC Load is 100VDC max 40A
Keep in mind that with solid state relay, you'll get a voltage drop across the output.
 

RFBOSS

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A little more expensive maybe but no socket needed, sounds good to me. The one I posted was the first one that I found.
 

prcguy

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If you are starting with 24V AC for a solid state relay control and you rectify with a diode and capacitor to make DC, you'll end up with something close to 34V DC so keep that in mind. You might have to make a simple voltage divider like a pair of 470 ohm resistors in series across the 34V and feed the relay control from ground and the center junction of the two resistors, leaving you with about half the voltage.
prcguy

Brandon,

Here is a SPDT mechanical relay:
Magnecraft 781XAXM4L-24A
Control voltage is 24VAC Contact voltage is 20A, 277VAC or 28VDC

If you're looking for a solid state relay, look for a DC to DC relay with the proper voltages and rectify the control voltage as PRCGuy suggests.

A possible DC/DC relay is a Crydom D1D40-4269 or equivalent.
Control voltage is 3.5-32VDC Load is 100VDC max 40A
Keep in mind that with solid state relay, you'll get a voltage drop across the output.
 

BlueDevil

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I need a Relay that can handle approximately 16-24VAC as it is being powered by my HVAC thermostat. The input amperage is very minimal. On the output side I essentially just need the relay to create a closed circuit. There is about 4-6VDC with very minimal amperage that will flow through the Relay.

I need VAC input because a VDC Relay cannot handling the 50/60Hz Alternating Current. I like the Solid State Relays, especially for their size as I am going to try and put this in a standard electrical outlet box.
 

RFBOSS

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A small change in your terminology may help. When talking about relays and someone says they want a relay that can handle XX, most people will think about the rating of the switched contact not the control signal.

It may be more clear to say that you need a relay that will operate from XX volts and switch XX volts and current.

As you may know not all solid state relays will switch DC. A lot of solid state relays use thyristors and they will not switch DC. There are solid state relays that use power mosfets for switching and they will switch DC and the manufacturers will specify that they will switch DC.

"The input amperage is very minimal."

The input current (the current used to control the relay (solid state or mechanical) will be determined by the device used. It can vary.

A quick look at some of the solid state relays showed a range of just a few milliamps to as much as 25 milliamps. The control voltage tends to vary with the control voltage, the higher the control voltage the higher the control current. This is the amount of current needed to control (switch on) the solid state relay. Just something to keep in mind.

Since you mentioned solid state relays, I found this solid state DC switching relay at Jameco. Its control voltage is DC not AC, but it will switch DC. If you rectify your AC control voltage, it looks like this device will need around 20 milliamps of control current to turn it on.

I took a quick look at some of the larger parts houses such as Allied Electronics and found similar things to the Jameco part. I just took a very quick look, some of the larger parts houses may have solid state relays that can be controlled with and AC voltage and switch a DC voltage. It may be worth a look or maybe someone here knows of a specific part. It has been awhile since I have had to do any specing of parts.

I took a quick look at AC coil mechanical relays and there are a lot of 24 volt AC coil relays and they are small enough to meet your requirements but they need north of 35 milliamps to operate. I know there are some sensitive AC coil relays out there, I just did not stumble across any.

I do not know if needing 15 to 30 milliamps or more to operated the relay (solid state or mechanical) will be an issue for you.

Again, and I may have missed something, but I seem to be the only one that has mentioned that not all solid state relays will switch DC.
 

RFBOSS

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I do not know exactly what you are trying to do and what electrical codes may be involved, but this aside... and after I wrote my somewhat short :D:D post above, my mind shifted gears from relays.

I would be very, very easy to build a circuit to meet your goals.

A diode and capacitor to rectify the control voltage, a few resistors and a transistor and you are golden.

And although you did not mention it, if you needed some type of hysteresis (turn on/turn off delay) our friend the ubiquitous LM 555 would take care of that.
 

mikewazowski

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I need a Relay that can handle approximately 16-24VAC as it is being powered by my HVAC thermostat.

I was going to recommend that you check with an hvac supplier as 24vac is used as the control voltage for hvac's but I'm assuming you've already done that.

You might try looking for another application that uses 24vac as a control voltage.
 

Soundy

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This will do what you need, for less than half the price of the Amazon listing above: R14-11A10-24 | Relay - 24VAC Coil DPDT 10A (probably closer to 1/4 the price if you figure the exchange). Check local electronic parts suppliers, most should carry something similar.

Switched contacts on a mechanical relay aren't DC or AC specific so it doesn't matter which you're switching.
 

RFBOSS

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"The input amperage is very minimal." Referring to the current used to control the switching device, solid state or mechanical.

BlueDevil has not told us how much current is available to control the relay.

24 VAC HVAC control relays would seem to be the answer.

But again we do not know about coil current and whether or not it will be an issue.

I might guess not, but with out additional information, we can not say for sure.

"Switched contacts on a mechanical relay aren't DC or AC specific so it doesn't matter which you're switching."

Actually the contacts on mechanical relays are rated for AC and DC with the allowable breaking voltage being much less for DC than AC, because it never goes to zero like AC at the zero crossing point.
 

KI7HYI

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Relays do not convert AC to DC, or vice versa. They also don't convert voltage levels.

So if you need to do what you said you need to do, you'll need a transformer to change the AC voltage level, followed by a rectifier to make the AC into DC, followed by a voltage regulator to adjust the voltage at the output.

You might find all that in one digital switching power supply, but given the odd voltage levels good lucking finding it.

I'm thinking a description of exactly wtf you are trying to do, would shed some light on what you really need to make it happen.
They did when they were called vibrators.
 
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