Dear Friends,

I though today I would add an article that would help in a more general way. I get a lot of emails that are confused about the different parts of a tanning bed’s electronic system, and the relay (or contactor) in particular. This post will cover the most basics of this important, and sometimes faulty part. For our purposes, the terms “relay” and “contactor” are interchangeable and mean the same thing. Both terms are used in the electrical industry.

Dennis
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What is a relay (or contactor) and what does it do?

The contactor/relay is the ON/OFF switch for many tanning bed, particularly older units. Not every bed has a relay, but most with 28 lamps or more, and many with 16 or 24 lamp do have one. They all look different, but the basic operation is the same. They all serve a single function, to act like a “light switch” of sorts, turning the bed on and off. The unit shown is a “reed” style relay, whereas the larger type commonly found in many beds is a “plunger” style. I used the reed style in this example because it is easier to cut apart and show you the principals.

All tanning beds have a timer. In units with a timer but no relay, all the current flows through the timer, then on to the ballasts and lamps. In beds with timers and relays, the timer only carries enough current to turn the relay on and off, and the relay itself carries the full load of current (hense the name “relay”, as in, the control is relayed over to this device).

Relays have three or four basic connects, and an electromagnet:

1. Coil terminals. Two contacts on the relay that are powered by the timer. When these two contacts have electricity put to them, the relay is ON. When you disconnect power (the timer runs out) then the relay turns off. Typical markings are A1 and A2.

2. Line side. This is where the main power from the wall connects to, the “line power”. Relays can have 1 to 4 or more of these terminals, usually numbered something like T1, T2, T3, T4, etc.

3. Load side. This is the other half of the relay that is connected to the ballasts, then lamps. When the coil is ON, power flows across the relay from the LINE side to the LOAD side, thus the unit is on. When the coil is OFF, then the circuit is broken and the bed is off. Relays can have 1 to 4 or more of these terminals, usually numbered something like L1, L2, L3, L4, etc. When the power is on, power flows from T1 to L1, from T2 to L2, etc. but they don’t ever cross. Basically, this is like having multiple switches in a single device.

4. N.O. Normally Off terminal. Most relays don’t use or have this feature, but the ones that do (like the example shown, used in SunMaster beds) then you can have a device to be ON only when the relay is OFF. This sounds counter to what the relay does, but this allows you to have a fan, special lighting or other devices on only when the bed is off. Again, most beds don’t have or use this feature.

5. Electromagnet. This is a coil of wire around an iron core. When you put power to the coil, it flows through this coil of wire and creates an electromagnet. This attracts a metal plate inside, which moves toward the magnet, and acts as the switch. As long as the electomagnet is ON (power applied to the coil) then the unit will make contact and the device will be on. As soon as you stop delivering power the A1/A2 terminals on the coil, it springs back away from the contacts and the bed is off.

Click on this image to open a new window with a larger version of this image. Note, this relay is cut open. You would normally not see the coils and switching mechanisms.

The center post in the image is the line, where the incoming power is connected to. In a reed style relay, this is the part that moves. It normally rests (and connects to) the N.O. contact if so equipped. This provides power to those terminals when the unit is off. When the electromagnet engages, it attracts the metal plate on the right, which pushes the switching plate to the left, disconnects the Line from the N.O. terminal, and instead connects it to the Load. This turns the bed on. (My hand is pushing the plate manually to demonstrate this. Normally it would be to the right when off.)

Ok, not too terribly technical, but that is the basics on how a tanning bed relay/contactor works. Hope this helps you budding technicians!

Dennis