I’m building ~175w grow light using an Xbox 360 200w power supply. The power supply is 12v output and is supposed to be a pretty good power supply, you have to trick it to run (short 2 wires) but Google hits seems to say it’s decent.
The light has 3 channels of 2s XM-L2’s driven at ~60W, each channel driven by its own buck converter running in CC mode. 7.0A @ 8.32v=58.24W per channel
The problem is the PS shuts down immediately if you try to power it up with all 3 buck converters hooked up but runs them all just fine if you power the PS with only 2 on and turn the other on a few seconds later.
Is there any way around this? Something I can do to the Xbox power supply to make it not trip its protection at startup?
I turned one of the buck converters down to 5A (so the whole system would be ~156W) and it starts up just fine there but the light is for a friend and I need it to be plug and play at the full 175W, no ducking around with it turning tiny pots and having to measure current…
Anyone used a 360 power supply for anything? I figured 175w should be safe on a 200w supply but like I said it doesn’t start up till I’m down at 156W. How much does a 360 actually draw?
Some buck converters I’ve tried over the years have a massive voltage spike when turning on, triggering the power supply’s shutdown. Putting on a cap on the input solved it.
So just to clarify, you can turn it on with the two buck converters at full and the third turned down. It remains stable if you then turn up the power on the third buck converter?
If that’s the case, I’d wire a set of two switches. Tell him to turn on switch one, wait five seconds, then turn on switch two. The second switch does nothing except flip a relay that bypasses a circuit limiting the third converter’s power.
Correct. I can also switch the 3rd on, at full power, and that spike doesn’t shut the others down (but that’s still different that firing all 3 up at once, at full power)
The problem with using two switches is how people use grow lights; a timer turns them on and it’s all automated.
She’s growing exactly what you think :zipper_mouth_face:
I have found most computer power supplies are not very efficient. I think 85% efficiency is probably close as an average. So your Xbox power supply probably isn’t giving you the entire 200w. I used a computer supply for a 100watt 12 volt RF transmitter I had. I had 2 power supplies available at the time a 400watt ATX and a 650watt ATX. The 400watt would trip the protection in the supply once in a while but the 650watt one would power it just fine. This particular RF tranmitter pulled 23amps at full bore 100% duty cycle.
Take that info for what it is. It was just my experience with these two particular supplies and one transmitter. I have since quit using switching supplies and stick to linear regulated supplies and lots of time deep cycle batteries.
If you plan to change the power supply I would recommend you a HP Common Slot power (460W Platinum) supply from Ebay. (10 - 20$)
The are silent, significantly less sensitive to load spikes and reach even at lower load high efficiency up to 94%.
The usual problem is the initial surge to charge up the caps is high enough that the power supply senses a short circuit in the output, and shuts down. Generally this can be avoided by placing a small high current inductor between the cap and the supply. A few millihenries is usually enough, and once things stabilize the small inductor no longer has any real effect. The inductor significantly reduces the inrush current to charge the caps, and that reduction is enough to prevent the supply from sensing a short circuit. This is often done in high power supplies to protect the rectifiers from damage during the initial start.
I have used a XBOX power supply for years, to power my icharger. Never really pushed it near it’s limits though.
Sounds like mattheww1950 has the fix.
I know you have probably already checked but I was Just wondering if your wire size is big enough to reduce V drop for the given distance?
