Hi All

I have a 240V to 24VAC transformer to generate the voltage for some AC solenoids. Is it possible to use the 24VAC, through a suitable AC to DC module, to generate a DC voltage for the rest of the electronics? Ideally, the DC voltage would then be stepped down via a DC-DC converter.

 

Is it possible to use the 24VAC, through a suitable AC to DC module, to generate a DC voltage for the rest of the electronics?

Yes. Providing the load isn't high enough to affect operation of the solenoids.

 

Hi All
Is it possible to use the 24VAC, through a suitable AC to DC module, to generate a DC voltage for the rest of the electronics? Ideally, the DC voltage would then be stepped down via a DC-DC converter.

What DC voltage and current level is required for the rest of the electronics?
Here's a complete Module that can do that. Five models available with 5, 12 , 15, 24 and 54 volt outputs at varying current limits.

 

Well, anything about 14VDC 1A is sufficient.

 

Well, anything about 14VDC 1A is sufficient.

Look at this Module.

 

Excellent, I can use the one that outputs 15V.

I wonder if they do a 240 to 24VAC transformer as well. I will check their website out.

 

Excellent, I can use the one that outputs 15V.

I wonder if they do a 240 to 24VAC transformer as well. I will check their website out.

I thought you said you already have the transformer.

 

I thought you said you already have the transformer.

Yes, If they have one,I could purchase it all from one source

 

Well, anything about 14VDC 1A is sufficient.

What is the current rating for the transformer and what current do the solenoids require?

 

What is the current rating for the transformer and what current do the solenoids require?

I have been using these in past
TRA2400001 | Carel 3VA 1 Output Chassis Mounting Transformer, 24V ac | RS

I am also thinking 3VA is to little as well?

 

Keep the AC and DC supplies separate.
Low voltage wall adapters are readily available at low prices at second hand stores.

 

Yes, this custom design needs 24VAC

So I planning

240VAC -->24VAC-->15VDC

The 24VAC transformer needs to be adequate for both my relays and the transformer.

Or is it better to do the following on the PCB
240VAC -->24VAC
|
----------> 15VDC

I am thinking that with option 2, the 24VDC would not need to be as powerful?

 

Solenoids will pull down the supply voltage. They also generate a lot of noise spikes when switched on and off.

That is why I suggest using two separate supplies.

 

Ok , I aim to make small 2 L PCB with the both 24VAC transformer and 15VDC working independently but both connected to 240V. Is this a good approach?

 

For AC to DC conversion, do the math first. Full-wave bridge or half-wave centre tap will give different voltages.
24VAC will give about 26V x 1.4 = 36 VDC which is too high for 15 VDC output.

Calculate the power dissipation of the 3-terminal linear voltage regulator. Your aim is for an overhead voltage that is just right.

Another solution is to use a buck or boost SMPS (switch mode power supply).

 

Ok , I aim to make small 2 L PCB with the both 24VAC transformer and 15VDC working independently but both connected to 240V. Is this a good approach?

Yes and I would suggest using this 15V Module.

 

Oh yes, that is what I use generally, but I had thought about the other module as it would work with 24VAC

 

Yes and I would suggest using this 15V Module.

I have seen some systems, for example, irrigation units, where entire systems work of the same 24VAC power supply. How would they achieve it all with 24VAC?

 

I have seen some systems, for example, irrigation units, where entire systems work of the same 24VAC power supply. How would they achieve it all with 24VAC?

The system would have the necessary DC supply running off the 24VAC.
In irrigation units the DC current required would probably be minimal as it would be mostly for logic control of the solenoids.

 

The issue is not how much current the low voltage DC system requires. The concern is how much current the 24 VAC solenoids require. The supply voltage will drop if the power source is inadequate for the load.

My irrigation system is not connector to AC mains because it sits in the greenhouse with no access to AC power. It runs off of a 12 VDC SLAB (sealed lead acid battery). It does not use solenoids. It uses water valves that are driven by 3 VDC motors at less than 100 mA. The motor requires power only to open and close the valve which takes about 2 seconds to operate.