Why Use Two Power Supplies?
To be clear, we’re not referring to computers that use redundant power supplies. These computers have two PSUs in them at the same time, but only one of them is actually supplying power. Redundant power supplies are usually used in servers where you want to avoid interruptions from a blown power supply. The second unit seamlessly takes over if the primary unit fails.
No, here we’re talking about using two PSUs simultaneously to share the load of powering the components of a computer. There are two main reasons anyone would consider using two separate power supplies in their computer.
The first reason you might want to do this is that you’re trying to power a computer that no single PSU has any chance of handling. This mainly happens in high-performance computer builds such as cryptocurrency mining rigs with many GPUs. So one PSU handles the GPUs, and another handles the rest of the computer.
The second reason is budgetary. Instead of replacing a perfectly good existing power supply with an expensive high-capacity model, it’s possible to add another modest unit for an overall cost-saving solution. You may even have a second PSU in a drawer somewhere you can repurpose this way.
The Drawbacks
So if this is an option, why don’t a significant number of people do it? There are many reasons why connecting two PSUs to one computer may not be the best idea. The most important thing to consider is that desktop computers were not designed to work this way. In particular, your motherboard was only designed to control one PSU at a time, so you need one of several workarounds, which we’ll discuss below.
Apart from the relative “jankiness” of fudging a second PSU into your computer, where do you put it? Desktop computer tower cases are almost all only designed for a single PSU. You can buy dual-PSU cases for high-end workstations or extreme gaming systems. That covers the first common scenario of building a system that needs more power than a single high-capacity PSU offers, but it’s not relevant to users trying to save money. After all, if a budget-conscious user is spending money on a fancy case to hold two PSUs, you may as well just buy one new PSU with enough power.
This means you’ll need a jury-rigged solution that’s neither easy on the eyes nor necessarily safe and practical. At best, it’s a temporary measure until you can afford one large new PSU. Perhaps the biggest drawback is introducing another failure point to your computer, especially if the two PSUs run close to their maximum capacity.
How Does It Work?
Assuming that someone has their heart set on running two PSUs, how does it even work? Remember we mentioned above that motherboards can only control one PSU simultaneously? It tells the PSU when to turn on and shut down via the ATX connector, which on most current motherboards is a 24-pin connector. Even if you plug the second PSU into the wall and hook it up to your GPU’s external power ports, the PSU won’t run on without the right signal.
In the early days, when this was purely the practice of mad science, brave PC enthusiasts would use a paperclip or a soldered wire to bridge the pins in the ATX connector, telling the PSU to turn on. Then they’d control the PSU’s power using the power switch on its back (if it has one) or the switch on the outlet. Using this method takes some finesse since both the PSUs need to be turned on simultaneously, or you risk instability or bootup failure. Even then, in some cases, the extra PSU would sometimes turn itself off or otherwise misbehave.
The paperclip method is dangerous, unreliable, and, today, completely unnecessary. There are two ways to make this setup work. The first is to use a PSU tester to turn it on and keep it on. However, not all testers will let you run the PSU indefinitely and will turn it off automatically after a set amount of time. So unless you have the right model that can be (mis)used in this way, it’s not a solution.
The closest thing to a permanent solution is to use a dual-PSU ATX adapter cable or a dual-PSU Sync Starter. The adapter cable is simple a factory-made equivalent of bridging the right pins on the second PSU, but with the advantage of letting your motherboard control power-on and shutdown for both PSUs. This is a cheap and simple solution, but a worrying number of people in the reviews for these cable adapters indicate that they can melt or even start a fire in your PC. That doesn’t inspire much confidence!
On the other hand, the sync starter board uses power from one of the primary PSU’s SATA or Molex connectors as a signal to start up the second PSU. According to the product descriptions for these more sophisticated sync starter boards, there’s no heat generated in the board itself, which means there’s little risk of anything melting.
You Probably Shouldn’t Do It
While it’s undoubtedly very cool that it’s even possible to run multiple PSUs in one computer, we can’t recommend it. Unless you’re a crypto miner, extreme workstation user, or an extreme gamer with components running at the ragged edge of performance, there’s little reason to try this yourself.
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