Why isn't it powering up?

Fletcher-Moorland-Capacitors-Replacement

If one of your machines hasn't started up again after a shutdown, you can bet it's one of these that's the culprit!

These electronic components are capacitors. Well, Electrolytic capacitors really. You will find many of these in all electronic circuitry, built onto printed circuit boards (PCBs).

Their function is to store charge in a circuit. Their general construction is two ribbons of aluminium foil separated by an electrolyte soaked, insulating material. Imagine a sandwich, the foil is the bread, and the insulator is the filling. Then it's rolled up, very much like a Swiss roll, and stuffed into the small can like container that I'm holding.

So, when you switch your machine on after a period of shutdown, and it doesn't power up.

What's going on?

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Most machines use power supplies to power electronic systems. These power supplies are a switch-mode power supply (SMPS), you may have heard of that term? It is a type of power supply that is small and efficient, and it is used in power and control electronic systems.

There is one part of this power supply that is the pre-charge circuit. No, I'm not going to go all technical here, I'm keeping it pretty simple. It's the part of the circuit that limits the inrush current in the power supply. Lets' just say that these power supplies need this part of the circuit.

Now, back to the capacitors. These things age with age and use. Recall I mentioned an electrolyte-soaked insulator? This electrolyte dries out over time and use. When that happens, the capacitor isn't able to do its job, it can't store the charge it's designed to.

This is where dried up capacitors become problematic; they're a time-bomb in your equipment. Once the capacitor in a pre-charge circuit has done its job on power up, it's then not needed, until the machine needs to be powered up again.

Imagine a machine is switched on for 24 hours a day, there is no problem at all. But that capacitor will be aging, it will be drying out, it will be wearing.

You switch a machine off for a shutdown because you think it's the right thing to do to save energy. Then you come to switch it on again. Guess what? that capacitor can't do what it's supposed to do. Your machine doesn't power up.

Then, which is quite common, you keep trying to power up your machine. There might be a bit of a bang, and some smoke appears. You certainly have a problem then!

There are a couple of things you can do to prevent this power up problem though. One is to leave your machine powered up. This is perfectly acceptable, it will be drawing some power, but it's more likely to start up again when you need it.

The other is to have your automation equipment overhauled, i.e. servo drives, power supplies, inverter units that are in your machines. The capacitors and other ageing components can be swapped out for new ones. Then you'll not have this problem for a good number of years.