0
\$\begingroup\$

I bought a 12 V, 30 A LED power supply for a chemistry experiment (electrolysis). The power dropped to 0 and the onboard LED in the power supply started blinking when the anode and cathode were in the water and electrolyte.

I read about a similar situation, and the behaviour seems to be due to overcurrent; a protection function of some adapters.

How can I make this work like a regular adapter? Are there other methods to control this current issue?

led power supply blinking

Short clip showing the blinking. Ignore the wire colors. I thought it was due to the wiring, but it wasn't.

LED Power supply inside picture

\$\endgroup\$
7
  • \$\begingroup\$ Your solution probably has a very low resistance, and the power supply is overloaded. Buy a laboratory power supply so you can control the current and voltage; and measure the current. A laboratory power supply can be put in constant current mode. \$\endgroup\$
    – Mattman944
    Sep 23 at 0:32
  • \$\begingroup\$ note: the stripped ends of the wires are too long ... the end of the insulation should be inside the screw compartment \$\endgroup\$
    – jsotola
    Sep 23 at 0:49
  • 4
    \$\begingroup\$ you might be able to put some resistance in series to limit the current. Something like an automotive headlight bulb might do the trick. If you use a H4 bulb, you have the choice of two resistances - high beam or low beam. You get a visual feedback as to how much current is being drawn. Note - the bulb gets hot! \$\endgroup\$
    – Kartman
    Sep 23 at 2:22
  • \$\begingroup\$ If it's a LED power supply, see if it has a constant current (CC) mode, and use that. Otherwise the filament auto headlamp of Kartman is an excellent idea. \$\endgroup\$
    – Neil_UK
    Sep 23 at 5:48
  • \$\begingroup\$ Is lowering the electrolyte concentration to increase the solution's resistance an option? If not, I'd go for Kartman's Light Bulb. \$\endgroup\$
    – ocrdu
    Sep 23 at 7:08

1 Answer 1

3
\$\begingroup\$

I found the PSU's schematic but I'm not going to share it here.

The converter is a TL494-based half-bridge converter having CV and CC control. This means that as long as the output current is below the pre-set value (around 40 A as I can see) the converter runs in CV mode and regulates the output voltage; but once the current exceeds the pre-set value the converter drops into constant current (i.e. regulates the output current) and loses voltage regulation, therefore output voltage drops.

In your case, if your experiment causes a significant current draw then the converter should limit the current and decrease the output voltage accordingly. As the load tries to draw more current the output voltage will drop more until the voltage drops below some threshold.

If the output voltage drops below that threshold the converter will assume that there's a short circuit so the short circuit protection will kick in. Different designs have different short circuit protection implementations such as periodic restarts (hiccup), latched stop, etc. Yours seems to have the first type: The converter forces itself to restart hoping to see the load within the specified range but triggers the short circuit protection. That's why you see a blinking LED indicator.

\$\endgroup\$
5
  • \$\begingroup\$ Thank you Rohak seems thats the case so whats the solution for this? as you know electrolysis means very very low resistance in water can perhaps adding PWM helps? \$\endgroup\$ Sep 23 at 21:36
  • \$\begingroup\$ @AminMyCard PWM won't be solution because full current will flow for a non-zero time. You may try limiting current by adding resistance such as light bulb as others suggested above. \$\endgroup\$ Sep 24 at 16:28
  • \$\begingroup\$ so in the end i have to add some sort of resistor to mimic real load for power supply can you help me out what ohm & wattage need for this, sorry about delay reply Internet is blocked in IRAN due protests \$\endgroup\$ Sep 27 at 12:06
  • \$\begingroup\$ Well it's hard to tell because I don't know if your experiment requires voltage or current. If only the current is what you need then simply the resistance should be higher than or equal to 12V / 33.3A = 360 milliohms. But, as I said, I don't know what voltage and current you need. \$\endgroup\$ Sep 27 at 12:23
  • \$\begingroup\$ finally i got my internet back, electrolysis need currents any voltage above 2.5V only heat up the solutions \$\endgroup\$ 7 hours ago

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.