Driving an SSR input from a DC power adapter

[dmaxweb1]

well total isolation is the obvious advantage
you dont get any isolation with a FET, huh !

a small DC votage say 6V switching 240VAC mains
to some extent SSR's have now fulfilled that job, but even then for many applications good old mechanical relays can often be physically smaller


Dave

I have a very basic SSR question. I understand the function of a SSR but my question concerns the DC power supply. I want to switch a 110VAC circuit with a panel mount SSR rated 3-32 VDC input. Can I use a common wall adapter (i.e. cellphone power supply) to convert to 3VDC 200mA as the DC power supply? I know the SSR minium switching input is only a couple of mA but will 200mA be too much for the SSR?

Thanks

 

[KrisBlueNZ]

Hello and welcome to Electronics Point

I have moved your question to a new thread and sent you a PM so you will be able to find it.

Yes, you can drive the SSR from a supply rated at 3V and 200 mA.

The 200 mA part of the adapter's specification is the maximum current that it's designed to supply. The actual current you draw from it will be determined by what you connect it to.

When it's not connected to anything, no current flows. When it's connected to the SSR input, some current will flow, but if the SSR is specified to accept 3~32V at its input, it will include some kind of current regulation that will limit the current to much less than 200 mA. So the adapter will not be damaged.

If you post the manufacturer and part number of the SSR, we can double-check.

 

[dmaxweb1]

Hello and welcome to Electronics Point

I have moved your question to a new thread and sent you a PM so you will be able to find it.

Yes, you can drive the SSR from a supply rated at 3V and 200 mA.

The 200 mA part of the adapter's specification is the maximum current that it's designed to supply. The actual current you draw from it will be determined by what you connect it to.

When it's not connected to anything, no current flows. When it's connected to the SSR input, some current will flow, but if the SSR is specified to accept 3~32V at its input, it will include some kind of current regulation that will limit the current to much less than 200 mA. So the adapter will not be damaged.

If you post the manufacturer and part number of the SSR, we can double-check.

Thanks for your help. The SSR is a Crydom D2410

 

[KrisBlueNZ]

OK, the D2410 has a current regulator in its input path, so it draws about 10 mA at any input voltage from 5V to 30V. At 3V it draws a bit less than 10 mA but it is still guaranteed to operate. So a power supply rated for 3V and 200 mA will be fine.

 

[dmaxweb1]

Help for my Brewery Project Please

OK, the D2410 has a current regulator in its input path, so it draws about 10 mA at any input voltage from 5V to 30V. At 3V it draws a bit less than 10 mA but it is still guaranteed to operate. So a power supply rated for 3V and 200 mA will be fine.

Hi
Need a bit more help.
What I'm trying to accomplish is operating a 24vdc .5A NC solenoid valve with a simple wall outlet power supply of 24vdc .75A. I had hoped that by switching off the 110vac to the power supply, the 24vdc would immediately drop to 0. I was wrong - the voltage slowly drops to zero. Do these power supplies have capacitors (or ?) that take time to bleed off the voltage? I need the voltage to drop to zero so that the solenoid valve closes immediately. Is there a way to do this?

The 3vdc question is my previous post is for operating a liquid level float switch that will use an SSR to switch the 110vac to the 24vdc power supply mentioned above.

This is for my home brewery project and I need to get it up an running so I can restock my bar.
Thanks in advance.

 

[BobK]

You could switch the 24V output instead of the in input.

Bob

 

[KrisBlueNZ]

Yes, the power supply does have a capacitor. As BobK says, you can switch the output - i.e. connect an SSR or relay contact between the 24V DC output of the power supply and the 0.5A solenoid valve, but not that SSR - it's only designed to switch AC.

You can get SSRs that are rated for DC. And you don't need a 10A rating, obviously! With a DC circuit, you should put a reverse-connected diode (e.g. 1N400x) across the SSR or relay contact, to suppress the back EMF from the solenoid. (Google those keywords for more info.)

You might get away with something cheaper - an optocoupler driving a Darlington transistor, for example - but an SSR that can switch DC is probably your simplest option.

If you describe the control signal - what it comes from, how it is generated - we may be able to suggest something else.