Troubleshooting a Mercury Vapor Ballast

A ballast on a white background.
  • 1 hours
  • Intermediate
  • N/A
What You'll Need
What You'll Need

The mercury vapor ballast is a device that works with mercury vapor lamps. If the lamp isn't working properly, you will need to troubleshoot to see what is going on with it. If it is a fix you decide to do yourself, it can save your money and time. Let’s take a look and see just what needs to be done in order to troubleshoot a mercury vapor ballast.

The Components

There are two different components of the mercury vapor ballast and they are the transformer and the capacitor. In order to tell when there is an issue, they need to be tested individually to find out which component is not working and if it should be replaced or fixed.

The Transformer

The transformer has leads that need to be hooked up to be tested. You can start with the 120V lead and continue with the other one marked COM. They need to be hooked up to the 120V line. To measure the output voltage, you need to find the ones marked CAP and COM and take the measurement with at least the CAP side disconnected using a voltage meter. You should get a reading of 240 VAC. If that is not the reading you get, then the transformer is bad and needs to be replaced.

The Capacitor

To test the capacitor, re-attach it to the transformer’s CAP lead. Measure the voltage from the COM and the capacitor lead that is black. If the capacitor proves to be fine, you will get a reading of 240VAC, but if the capacitor needs to be replaced, then your reading will only be 0-2 VAC.

Testing the Mercury Vapor Lamp

You should now test the mercury-vapor lamp. Plug it into an outlet and take measurements of the voltage that goes between the capacitor lead that is black and the COM. This will tell you whether the lamp and the capacitor are good. The voltage should read 15 VAC, but it should ramp up to 130VAC within 5 to 10 minutes. This will indicate if the lamp is defective. The voltage should read 240 VAC if the lamp is no good and something with one of the components of the mercury vapor ballast is not working.

With the right equipment, you can test the mercury vapor ballast yourself. It is not a difficult process. Each of the ballasts will need to be tested. The ballast that was tested above is the 100W MV advance ballast. The ballasts all come in different voltage sizes. The manuals should be able to tell you what the correct voltage is for the model you want to test. There are guides that can help with finding the proper voltages for the different sizes, as well. If your equipment is not working properly, then it is time to start troubleshooting and find out what is not working correctly.