I’ve had a couple of questions about capacitors during the Thanksgiving holiday weekend. First a quick warning: Capacitors actually hold electricity, so even if the tanning bed is unplugged, you can get shocked badly if they aren’t discharged. Personally, I unplug the bed, then turn the bed on, which helps. This is the same idea on how a TV can kill or hurt you, even if it is unplugged, as the capacitors still are charged. So be careful.

First, some schooling: A capacitor is a pretty simple device. You can make one at home using aluminum foil and wax paper. Imagine taking two sheets of foil (conductors) then placing the wax paper inbetween them (insulator). This has to be done so there is no way that the two sheets of foil can ever touch each other. Now roll them up tight and solder a connector to each of the two sheets. That is the two poles, and this actually holds electricity when charged. If you want to get fancy, you can submerse the entire thing into a liquid that is dielectric (can’t conduct electricity) to dissipate heat. The size of the sheets, plus the thickness and type of wax paper determines the capacity of the capacitor. And yes, this really works, although not as well as those produced by more exacting standards, such as in a factory.

In addition to storing electricity, they can be used as a filter (installed in series mode instead of parallel). This is the little cylinder you see on tweeter wires, which filters out the bass frequencies and prevents damage to the tweeter. You also see this on old cars that have points, called a condenser (the word condenser is just another word for capacitor, just less used). They make Tesla coils work. If they didn’t exist, you wouldn’t have a computer, TV or radio. Your toaster and light bulbs would still work fine, though.

These seldom go out on tanning beds, as they have no moving parts and are pretty stable. When one finally dies, it is usually unevenful. Usually. Once in a great while they go out in spectacular fashion, burning up some wire, or perhaps exploding. Only twice have I ever seen one that had exploded. One in a tanning bed, and one in a car stereo system with lots of 12 inch woofers. In both cases, it sounded like a shotgun and did damage to the sheet metal. Obviously the owners were not amused, but again, this is very rare. In otherwords, don’t lose sleep over exploding capacitors but don’t be careless either.

Capacitors can work like a bladder tank of sorts: When the electrical current is high, they soak up power. When it is low (such as when you first start the bed) they release power. This happens very fast. They also serve to act as a buffer and even out and filter the incoming power a bit when used in this fashion.

Not all beds use large capacitors. Beds that have magnetic, electronic or high frequency ballast use smaller capacitors that are built into the ballast themselves. Choke style beds use the large offboard capacitors that we are talking about here. How many, and what rating depends on the number of lamps, and the preferences of the manufacturer. Some beds use less total capacitance as a way of saving money, others use many to make starting and running smoother. How much you need per lamp is a broad range, not a simple fixed amount. To a point, the more the bed has, the better.

Of course, the question was “how do they connect inside a tanning bed?” and I will let this image explain this. For a two pole capacitor, in a tanning bed or most anything else, this diagram works.

Hope that helps clear up a few things about capacitors!

Dennis