Can some one please help me I am newbie so I am trying to go from 240vac to 24vdc . I was thinking a transformer from 240vac to 24vac then a bridge to 24dc only problem I only have a vague idea how to make one .could someone please take the time to tell me in detail please . Also is this the cheapest way of doing it ??. By the way it is to power a actuator thanks a lot Keith

 

Hi Keith. A couple of things. AC voltage is measured using the RMS(Root Mean Square) technique. Ignore the details of why this is true for the moment. The peak value of an AC waveform which is measured with an RMS value is 1.414 times the RMS value. From 24 VAC this would be:

\(24 \times \sqrt {2} = 33.94 \; \text Volts\)

When you use a bridge rectifier on the 24VAC you'll get about 32.5 VDC out of that. This might be too much for your actuator.

 

Transformers are expensive. It would be cheaper and if it is switched mode, lighter and smaller to use a ready made wall wart (a plug-in power supply). It would also take care of the safety of the mains connection.

 

Hi Keith. A couple of things. AC voltage is measured using the RMS(Root Mean Square) technique. Ignore the details of why this is true for the moment. The peak value of an AC waveform which is measured with an RMS value is 1.414 times the RMS value. From 24 VAC this would be:

\(24 \times \sqrt {2} = 33.94 \; \text Volts\)

When you use a bridge rectifier on the 24VAC you'll get about 32.5 VDC out of that. This might be too much for your actuator.

Thanks better try something else

 

Transformers are expensive. It would be cheaper and if it is switched mode, lighter and smaller to use a ready made wall wart (a plug-in power supply). It would also take care of the safety of the mains connection.

Thanks sounds good to me .

 

@Tryin2learn. Capacitor is not needed on rectified AC for any inductive device. the x 1.414 does not apply.
So the output is OK for a 24vdc device with just the bridge.
Here in N.A. hardware stores sell a cheap transformer that does the job.
Max.

 

Thanks better try something else

Sure. An 18 VAC transformer will give you 25.45 volts peak less about 1.4 for the bridge diodes or just about 24 Volts peak. If what Max says applies to your actuator it should be perfect.

 

Never seen a 18vdc transformer?
You will need 24vac secondary when using no capacitor, the 1.4 factor only comes in when capacitors are used.
This allows the use of the more common 24vac secondary.
Max.

 

Why are you even trying to "roll your own" power supply?
Just buy a 240VAC to 24VDC power supply (wall wart or whatever)..

You didn't give any specifics on current that this "actuator" needs though.. That would help provide better answers/solutions..
You may just need something like this..
http://www.mpja.com/24-Volt-Adapter-Power-Supply/products/571/
or maybe this..
http://www.mpja.com/24-Volt-Power-Supply/products/541/

Post the current requirements for your actuator..

 

Hi'ya what I have been trying to do is when I switch my extractor on it switch's a actuator on on the outside wall to pull up a steel plate that is covering the extractor hole to keep draughts out ( we are living on top of a hill and it's surprising how much draught comes through a 12 inch hole ) the plate will lower when I switch the extractor off much like a sash window going up and down . The plan so far is to use a onrom LY2N_J dpdt relay the extractor is 24vdc so I was going to take the power from the fan motor Connexions on to ins 7-8 of the relay and loop them on to a PSU to drop the current down to 24 vdc to move the actuator up and down . I understand I will have to take the output from the PSU back to the wiper terminals 5-6 on the relay .OK so far ?? Then I connect the actuator to pins 1-4 to raise and lower the plate . Does everything done OK . One further question do you have to observe polarity on these relays ??. Thanks for your you

 

I made a mistake there the extractor is 240 vac

 

This the datasheet for the LY2N relays:
http://pdf1.alldatasheet.com/datasheet-pdf/view/117194/OMRON/LY2N.html
[EDIT] try this link instead:
https://components.omron.com/compon...B9FF347100085257201007DD582/$file/LY_0911.pdf

 

. One further question do you have to observe polarity on these relays ??. Thanks for your you

Not unless they have the BEMF diode internal, which I believe this series does not.
Max.

 

One further question do you have to observe polarity on these relays ??

The LY2N relay has an LED indicator and with a DC coil polarity does matter - pin 8 positive, pin 7 negative. Page 12 of the datasheet I linked to.

 

Sorry can't make head nor tail of them drawings so positive of the fan terminal goes to no pin no 8 and negative to in 7 OK .what about 24 vdc coming from PSU I understand they go to the wipers pins 5-6 do I have to observe polarity ??

 

Specs on the actuator?
Does it have internal limit switches to stop its motion at the up and down points?
If not you are going to need to add limit switches also..

What you want to do is drop dead simple.. But we need info on the components you are using..
Then getting you a diagram of the whole thing is simple..

 

Thank's for all your help finally I hope .Do you have to observe polarity with pins 1-2 n/c and pins 3-4 n/o thank's again Keith

 

Specs on the actuator?
Does it have internal limit switches to stop its motion at the up and down points?
If not you are going to need to add limit switches also..

What you want to do is drop dead simple.. But we need info on the components you are using..
Then getting you a diagram of the whole thing is simple..

Yeah all I am struggling with is the connections on the relay .Yes the actuator has limit switches and like I said 24 vdc

 

I am assuming that the actuator is motorized? If so what is the rating of the motor?
The rating charts for the contact life and current capacity only cover DC resistive loads
Max.

 

Hi'ya if this helps just looked at actuator details all it lists is lifting capacity etc . Then says no load current 1 amp load current max 3 amp .hope this helps Keith .

I am assuming that the actuator is motorized? If so what is the rating of the motor?
The rating charts for the contact life and current capacity only cover DC resistive loads
Max.

No idea max just says heavy duty linear motor high performance 75n 165lbs .