Converting an AC-to-DC RF receiver.

[The Nice Guy]

I have a RF reciever that operates on 120Vac which controls two relays with 120Vac outputs. I need to convert it to 24Vdc outputs. I presently have a stepdown transformer with a 120Vac primary to a 24Vac secondary soldered in-line to two legs from the 120Vac power tranformer...which is connected to a Dc rectifier...which is soldered into the relay circuit to provide 24Dc when the relays are energized. My question is this...is there a better way?

 

[Torben]

I have a RF reciever that operates on 120Vac which controls two relays with 120Vac outputs. I need to convert it to 24Vdc outputs. I presently have a stepdown transformer with a 120Vac primary to a 24Vac secondary soldered in-line to two legs from the 120Vac power tranformer...which is connected to a Dc rectifier...which is soldered into the relay circuit to provide 24Dc when the relays are energized. My question is this...is the a better way?

Welcome to the forum!

If you can post a schematic or diagram that would make it easier to help.

Do you have a datasheet for the relays? If not, what are the markings on the relays?


Torben

 

[The Nice Guy]

diagram

Please see attachment.

 

[The Nice Guy]

Is it possible to just directly connect the stepdown transformer and rectifier to the 120Vac output at the lug block to power the 24Vdc motors?

 

[The Nice Guy]

schematic

Please see simple schematic.

 

[The Nice Guy]

I know the relay will handle the load because everthing is presently hardwired in and opereational, but I thought it would be easier to just connect to the relays to get the same results. Yes or no?

 

[Torben]

Please see simple schematic.

Can you post a real image file like, say, a PNG or even a BMP? Word documents are not suitable for posting graphics, and the graphic in the Word document you posted is all blurry and unreadable. As far as I can tell all that's on it is a drawing of the relay board and its terminal block, which doesn't tell me anything since there is no information about what hooks up to what and no indication of what your modifications are.

The reason that I asked about the relay markings and datasheet is that just because a relay can handle 120VAC does not necessarily mean that it can handle that much DC--or even lower. Just because a relay works for a while on a given load doesn't mean that it will be terribly reliable if it's not rated for that load--the contacts could give out sooner than expected.

In any event, it sounds like what you have could work. That's about all I can tell with the information given. Again, if you have any datasheets, model numbers, the markings from the relays, etc, that would really help.


Torben

 

[Torben]

One thing I forgot to mention: the 24VDC you are getting now is DC only in the sense that it's all on the same side of 0V--it's not really a steady DC voltage. You need smoothing capacitors to convert the pulsing DC into a smoother voltage (which will be higher than 24V). If you want a good, well-behaved voltage source, you should also use a voltage regulator such as an LM317 after the smoothing capacitors to make sure you get a steady 24VDC output even when loaded. As it is, even with smoothing caps, the voltage will sag with increased load.

How much current capability do you need? The values of the smoothing caps and the regulator you choose (if you need one) will depend on that.


Torben

 

[The Nice Guy]

I know the relays are capable of handling the load. Instead of connecting to the stepdown transformer to the power transformer located next to the relays and installing jumpers and bridge on the pcb to channel the vdc after the rectifierthrough the relays...would it be easier to just connect the stepdown transformer and rectifier from the 120vac relay output to get the required 24vdc to power a dc motor?

 

[Torben]

I know the relays are capable of handling the load. Instead of connecting to the stepdown transformer to the power transformer located next to the relays and installing jumpers and bridge on the pcb to channel the vdc after the rectifierthrough the relays...would it be easier to just connect the stepdown transformer and rectifier from the 120vac relay output to get the required 24vdc to power a dc motor?

It might be easier. I don't know--too much depends on information I don't have. It sounds like if you just took the 120VAC from the relays and ran it through rectification and filtering that you would need to build two copies of the rectification/filtering circuit: one for each relay (but it would be easier to hook up to the existing relay control board). If you did it the way you originally described, you'd just need to build one--as long as the one you built was up to the task of powering both motors, one motor, or no motors at the same time depending upon the state of the relays.


Torben

 

[The Nice Guy]

Thanks for your input and info! Gotta go...Good Night.

 

[Torben]

Thanks for your input and info! Gotta go...Good Night.

Good night! Good luck with your project. Check back in the morning. Chances are that one of our more experienced members may have added some more information here. We have real pros on the board. Me, I'm just a hobbyist.


Cheers,

Torben