Hi guys, I have a lab supply that I made out of a 1200w computer power supply and I was wondering how I can get around it going into protect when I draw current quickly. I know it’s not really designed to deliver a load really quickly but I’m drawing well under what it can do but I think it’s to quickly. I was thinking of adding some reservoir caps if that would work???
Cheers
Cheers
switching power supplies do not like caps to be placed on the output, some will go into protection
i solved the issue by putting diode bridge on the output, then followed by caps, it stopped going into protection
i solved the issue by putting diode bridge on the output, then followed by caps, it stopped going into protection
What do you mean "draw current quickly?"
Can you give an example of what you do that causes the power supply protection mode to kick in?
There may be a better way to solve this than "throw big capacitors at it."
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As for adding capacitors to the power supply output causing problems as others have mentioned, that happens because the capacitors look like a short circuit to the power supply until they are charged up.
PC power supplies are supposed to protect the PC from damage (or at least a fire) if something goes wrong. "Goes wrong" includes drawing more current from it than intended - even for just a very short period.
The problem with large capacitors on the output of a PC powersupply is that they will look like a short circuit for a moment when the power supply is turned on.
What is often done is to place a small value resistor between the power supply output and the capacitor. That keeps the capacitors from looking like a short circuit to the protection circuit.
Alternatively, you could place a large value inductor between the power supply output and the capacitor. That slows the inrush current and again prevents you capacitors from looking like a short circuit to the power supply.
Another solution is to use a negative temperature coefficient (NTC) resistor between the capacitors and the power supply output. NTC resistors start out with a (relatively) high resistance that goes down as they warm up.
Whatever you do, keep in mind that anything you use prevent big capacitors from causing the protection mode to kick in will also mess with the voltage regulation. The 12 volt output will not be 12V anymore. It'll be lower, and more subject to fluctuations caused by load changes.
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The bridge diode suggestion has at least a couple of drawbacks:
- It drops the output voltage by over 1 volt. You have two diode drops in series at all times between the power supply and your circuit.
- The current rating of you power supply is effectively only the current rating of your diode bridge. If your 1200 watt power supply can provide 100 amperes at 12 volts, then you will have to find a diode bridge rated for 100 amperes or else your bridge will die when you try to draw full current from the power supply.
To summarize. If PS with transformer you may need to include soft start circuit not to blow fuses after you add extra capacitors. Starting from 40+mF per channel you need to start considering soft start.
With switching P.S. simplest way is CRC filter (R usually in a range of 0.1-0.75+ Ohm) just to make sure that switching PS over-current protection not tripping.
With switching P.S. simplest way is CRC filter (R usually in a range of 0.1-0.75+ Ohm) just to make sure that switching PS over-current protection not tripping.