I have on order an LED driver and I want to use it as a simple 12v DC output to control a Solenoid Valve. The Driver says Constant Current & Constant Voltage. I obviously don't want 1A pumped into the Solenoid. I will of course put a Diode in to protect against back EMF.

Have I chosen the wrong type of Transformer? I will be using a relay to switch the solenoid on and off with the output of the LED Driver as the feed to the solenoid (I will probably put the relay on the input side of the LED Driver so it is not always on).

Thanks in advance.


It's not clear if the power supply you've chosen is constant current or constant voltage type. Also it's not clear how clean is the output of the power supply, being LED specific, it might be outputing some nasty triangle wave as usually LEDs don't care and chinese manufacturers don't care, but solenoid would care - in the worst case it be switching on and off rapidly.

In any case, you will not be pushing 1A via solenoid rated for 540mA, provided output of the power supply does not go higher than 12V, so it's safe to test it.

  • \$\begingroup\$ "2. Constant current and voltage" EDIT: I'm saying how vague the description is \$\endgroup\$ – Funkyguy Jul 9 '14 at 17:30
  • \$\begingroup\$ @ShannonStrutz what does it mean? \$\endgroup\$ – miceuz Jul 9 '14 at 17:31
  • \$\begingroup\$ Yeah that was confusing to me too, I was assuming it had different pins depending on if you wanted C.Current or Voltage (hopefully). When I get one thorough I will try and get the datasheet and test it. \$\endgroup\$ – Unstable Jul 9 '14 at 17:36
  • \$\begingroup\$ I think its just chinese-english for "This works, don't question it, goodbye" It only has two input and two output pins. I don't see a configuration jumper or switch or anything. \$\endgroup\$ – Funkyguy Jul 9 '14 at 17:36
  • \$\begingroup\$ @ShannonStrutz for £2 I will test it, as long as I'm not going to blow things up. \$\endgroup\$ – Unstable Jul 9 '14 at 17:53


In some supplies with connections like the one shown the two screws are the terminal screws. In other cases these may just hold a cover in place. If those are terminal screws then you will have AC mains on the screws when in use. (I have seen this done).

Provided it is in fact an isolated supply (see PK's comment) it should work OK.
A supply for LEDs may have some noise but if it is a switching converter this is liable to not bother a solenoid. If it is an iron core conventional transformer - possible but unlikely due to relative costs nowadays - it can have 100 HZ ripple (2 x 50 Hz UK mains frequency) but for LEDs this would need to be low enough to not grossly affect a solenoid.

Quality of such low cost supplies CAN be such that it blows up along the way and worst case it may apply mains to the output if it does blow up - even if it is an "isolated" supply. Be prepared to have the solenoid destroyed and mount it so it does not kill you or burn the house down if it dies.

DO NOT be overly put off by the above safety advice - it applies to many low cost mains powered products - it's just that people don't give enough consideration to such things. In many cases even poorly made equipment lasts indefinitely. But some definitely doesn't.

I would usually 'pop the top' on such supplies to see how they have been built. This can be distressingly easy to do in some cases) A glued back together wellish built supply may be a better bet than a nicely sealed death trap.

INFORMAL test. - "Don't try this at home" (you know what I mean).

Measure input to output DC resistance on a high Ohms range. Resistance should be VERY high if not essentially infinite. If not, ask further. Pros and cons apply.

Next: Power up on mains with output disconnected and measure using AC 250V or higher meter range between output (either lead) and house wiring ground or house wiring neutral. If there are capacitors between output and input (for noise suppression purposes) Vout will be at ABOUT Vmains/2. If so you will be able to get a tingle from the output relative to ground if operated isolated. This is not a fault per se - it is based on regulatory requirements (which may not bother your manufacturer) and even top quality supplies MAY do this. Grounding one output lead will stop this happening. A floating output that has Mains_AC/2 on it via capacitors will happily destroy some equipment - ask me how I know :-(.

Then, if there is very high or infinite resistance and no caps evident, "megger" it with an insulation tester or similar if available - see below.
If a tester is not available, using suitable connections and due care, connect mains AC from one input lead to one output lead !!! Usually done with an extension cord and crocodile clip leads powered from a minor distance away.
Using tester or mains, apply voltage.
If it goes bang, it may have done so anyway in far more dangerous circumstances.
If it survives this test it is NOT a guarantee that it is safe - just an indication that it's not utterly terrible. Some ARE utterly terrible and weeding them out is worth GBP2.29 in experience gained.


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