I'm doing a quick and dirty project to build a resistive DC load to test some ATX12V SMPS. I've got access to a bunch of 5 ohm, 50W power resistors at a bargain price, and I have some aluminum and copper bar stock for heatsinks. I need ~800W total load, about ~700W @ 12V, ~75W @ 5V, and ~30W @ 3.3V.
I'd like to use a rotary switch to vary the +12V load by 2.4A at a time. A local shop as some 6 position switches. So one of those would allow me to vary the +12V load between 0A and 12A. Get 5 of them and I have 0A to 60A, or 720W. Great! Do the same thing with 3x for the +5V and 3x for the +3.3V and bam.
Here's the problem though. That means I need 55 power resistors. That's a couple hundred bucks. Ok. I was expecting that. But it also means about fifty bucks in IRF740s with my current design, and any transistor I can find that will do the job is around the same price or more. I also need some diodes. And some resistors, but I have access to a ton of 5% 0603s so no biggy.
How can I condense my design to use fewer semiconductors? The power resistors I already have sourced and they're my best deal, but I feel like I can use fewer transistors and diodes, but it just ain't coming to me right now. It's been a rough day; I need a beer.
Any advice?
I'd like to use a rotary switch to vary the +12V load by 2.4A at a time. A local shop as some 6 position switches. So one of those would allow me to vary the +12V load between 0A and 12A. Get 5 of them and I have 0A to 60A, or 720W. Great! Do the same thing with 3x for the +5V and 3x for the +3.3V and bam.
Here's the problem though. That means I need 55 power resistors. That's a couple hundred bucks. Ok. I was expecting that. But it also means about fifty bucks in IRF740s with my current design, and any transistor I can find that will do the job is around the same price or more. I also need some diodes. And some resistors, but I have access to a ton of 5% 0603s so no biggy.
How can I condense my design to use fewer semiconductors? The power resistors I already have sourced and they're my best deal, but I feel like I can use fewer transistors and diodes, but it just ain't coming to me right now. It's been a rough day; I need a beer.
Any advice?