Have you ever turned on your Eurorack case only to be greeted by wildly blinking lights on every module? Your power supply might be suffering from current inrush problems. What is current inrush and how can you protect against it? Read on to find out!
All power supplies are rated as to how much current they’ll supply to the +12v, -12v, and +5v rails. A good general rule is to find a power supply (PSU) that can provide 30-50% more current than you need on each rail. For example, if ModularGrid suggests you need 700mA on +12V, you should be look for a PSU that can supply 1-1.5A on +12v.
But sometimes, this might not even be enough due to a situation called “current inrush”. Basically, the total current required by your modules is different at different times. When you first power on your modules, especially digital modules, they tend to draw more current – sometimes even more than is listed on ModularGrid! This is “current inrush”.
If the total current drawn by your modules is more than the PSU can supply, strange things happen. I’m told this isn’t risky to modules, but it can be a bit scary. In my first case, this started happening when I added a couple of new digital modules. Sometimes, when I powered on, all the lights in the case would start blinking rapidly at the same time and nothing would work. The first time this happened, I thought I had fried everything! The power supplies I was using were rated for +3A on +12v and -12V and 1.5A on +5v. This should have been plenty, but for some reason, during startup, it wasn’t.
After doing a lot of research, I found 2 great solutions:
Intellijel TPS80W and TPS30W bus boards
These bus boards are great for so many reasons! They have noise-reducing features such as star-distribution and triple 120 degree phased power, short circuit and over-voltage protection, and super accurate voltage. But the best part (for the purposes of this article) is their “soft start” feature. Basically, during power up, different parts of the board are powered up one after the other in sequence. This prevents all modules from kicking on at once and overloading the power supply by drawing too much current. It’s brilliant!
Note – some may not like the shroudless headers on these boards because not having them means you’ll have to be extra careful about how you plug in your modules so as to make sure you don’t connect them backwards. Personally, it doesn’t bother me. A bit of extra care when plugging in modules is always a good thing.
These are my recommendation if building your own case from scratch. I use them in my 126hp 6U cases, personally. The description on the TPS80W says it’s intended for cases up to 104hp/6U, but I’ve never had a problem with power in my cases, even with power-hungry modules like BitBox and the WMD Performance mixer in the same case.
For more information and specs: Intellijel TPS80W Triple Power Bus Board (Intellijel.com)
WMD Soft Start Module
If you don’t want to replace your bus boards altogether, check out the WMD Soft Start modules. These handy little devices plug into your existing power connections and can provide soft-startup capability to a single module. At around $30/apiece, this is a very affordable and easy to install solution.
For more information and specs: WMD Soft Start Module (WMDevices.com)