Ever need to put 120 VAC into a 24VDC Input?

[Bob A.]

Just wondering if anyone ever came up with a simple and effective way to do the conversion? If so, I'm curious about what worked over time.

Bob A

 

[Mickey]

Interposing relay.

 

[bernie_carlton]

Electro-mechnical Relay - if low speed, solid state relay if higher speed

 

[leitmotif]

Step down transormer and rectifier?

Otherwise I am curious to see if you have better luck - every time I did 120 into 24 I got this smoky stuff. Let me know what I did wrong.

Dan Bentler

 

[The Plc Kid]

This is what i use http://www.ab.com/en/epub/catalogs/12768/229240/229266/229643/229703/

Standard for normal stuff

SSR for high speed stuff.

 

[dahnuguy]

opto coupler

 

[Clay B.]

Interposing relay.

Pretty much this covers any voltage miss matches. You can even do the same thing for outputs.

Just remeber the 3 gotcha's on using solid state relays.

1) You may need a pull down resister
2) Polarity matters on both sides of the relay.
3) If you short them to ground the relay generally stays shorted not open. Mainly happens on AC Solid State Relays

 

[Norml]

I'm assuming that you are powering a PLC 24VDC input. If the application can stand a short power-up delay, you could use a small cheapo 24VDC power supply of the wall-wart variety and just switch it on or off.

 

[robertmee]

I'm assuming that you are powering a PLC 24VDC input. If the application can stand a short power-up delay, you could use a small cheapo 24VDC power supply of the wall-wart variety and just switch it on or off.

Yeah, I want my PLC inputs and processes relying on a cheapo wall-wart

 

[paulcs]

A solid state I/O module. Available as normal or inverted logic.
http://www.power-io.com/products/iac.htm

 

[rdrast]

Lots of replies here, but we also go almost exclusively with the AB DIN-Mount devices listed by Kid above.
We also use them for outputs that have to drive inductive field devices (like solenoids) or large contactors, etc.

A nice feature, is that the small relay module (or SSR Isolator if you choose) is replaceable from the top, without removing the whole base or un-wiring anything.

 

[jayc12155]

Solid state relay or Electro-mechnical relay will do.

 

[TheStarr]

Here is another DIN rail relay. Same as the AB but made by Phoenix Contact and available through most electronics dealers.

Part# PLC-RSC-24

Can't beat the price, here is Allied's: http://www.alliedelec.com/Search/ProductDetail.aspx?SKU=090SPEC&MPN=PLC-RSC+24UC%2f21-21

We have had these clicking away for years with no problems.

 

[interd0g]

Transtronics has a range of opto-isolators fro various voltage conversions eg 24/24 24/120/ 120/24. Right now I am grappling with he 120vac to 24vdc version which unfortunately has a half-rectified DC output which must be smoothed.

 

[jrwb4gbm]

Here's just a wild guess at a solution. Perhaps you could put a resistor-capacitor type surge suppressor across it to smooth it out, might not work due to time constant being wrong.
Something like in this link:
http://www.newark.com/jsp/search/productdetail.jsp?SKU=97K8283&CMP=AFC-GB100000001