0
\$\begingroup\$

I am plating my vias with electrolysis, and I need to safely limit the current so it doesn't go over 30 amps.

The power supply I'm going to order is, you guessed it, 12V 30A.

I've calculated the need for a 0.4r resistor, but good luck finding a 0.4r resistor rated for 360+ watts.

I'm following this guide, unfortunately they don't mention how many volts you are supposed to use, they only give you a calculation for the current. (They do say 0.25v, but only when you are first putting the board in the bath)

Is there anything else I can do? Hopefully that doesn't break the bank?

I just had an idea while writing this, would using 4 100 watt, 2 ohm resistors in parallel work(to get it to 0.5r)?

\$\endgroup\$
  • \$\begingroup\$ You could look for a constant-current power supply. Maybe look for LED drivers, since LEDs are also driven based on current. \$\endgroup\$ – immibis Apr 23 at 0:39
  • \$\begingroup\$ I added a link to the power supply in my main post, it says its for LED's, but I don't see anything about constant output. On another note, I was using my adjustable bench PSU, running only 5 amps through it, but the wires started smoking. I was going to change the cables to something that could handle it, but was worried it may damage my PSU, even without the smoking cables. Would a bench supply fall under the constant-current type supply? \$\endgroup\$ – LittleRain Apr 23 at 0:46
  • 1
    \$\begingroup\$ If your bench supply has a current limit knob, then it will be safe from damage from overcurrent because that's what the current limit is for. (just because the actual supply is safe doesn't mean your wires won't catch fire though as you found out) \$\endgroup\$ – immibis Apr 23 at 0:57
  • \$\begingroup\$ Ok thanks a lot immibis. \$\endgroup\$ – LittleRain Apr 23 at 1:12
  • \$\begingroup\$ Assuming you've ordered that beast, which is a wide compliance-current constant-voltage power supply, you should now search for a DC-DC Constant Current 30A Converter to provide what you really want: a wide compliance-voltage constant-current power supply. \$\endgroup\$ – jonk Apr 23 at 7:21
1
\$\begingroup\$

You don't want to spec a power supply for your project based solely upon the maximum current it can provide, as standard supplies aren't intended to operate at maximum current. While most switching power supplies should have over-current protection to save them from damage, an over-current event would place the power supply in failure mode. A current limited power supply is what you need. A current limited bench/rack power supply would also suffice in your situation, and may also be an advantage based upon the fact that you could also adjust the output voltage in order to experiment with the best voltage/current combination for your application.

You mention that very low voltage is required for initial immersion, so it may be likely that a similar low voltage may be optimal for completion of the process, with 12 Volts being way too high. If you are experimenting, then some sort of adjustable voltage/current power supply would be a necessity. Unfortunately, bench supplies that can provide 30 Amps of current are not inexpensive.

The resistor idea is not really a reasonable solution. Even though it could protect your load from over-current, it could still shut down a standard power supply, and while in operation, would dissipate any excess power as a large amount of heat.

As a side note: I'm not an expert on stick welders, but I understand they have very large transformers that provide very low voltage at extremely high current, with the current or voltage being adjustable. You might explore using a low powered stick welder as a source of your power.

If you can eventually find the "sweet spot" for your current/voltage requirements, a permanent solution of a very powerful transformer may be your answer. Many people rewind secondary coils on MOT (microwave oven transformer) cores to provide very high current at low voltages, and multiple windings (or a tap on a single winding) could be wound that could be switched between if you needed to change voltages when going from the drop stage to the plating stage of your process. You could then use resistors to regulate your current if you already know your demands, assuming that the secondary transformer windings can provide enough current.

Alternately, you could build a transistor circuit for the MOT to fine-tune the output current limit, which would require you asking a separate question, if it has not already been asked and answered.

\$\endgroup\$

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.