Failed High Voltage Contactor

This contactor was used to replaced the Furnas contactor installed as original equipment when the transmitter was manufactured in 1986.  Furnas is no longer in business, thus the ABB A145-30 was substituted. It purchased from directly from Broadcast Electronics for an FM35A transmitter:

ABB A145-30 contactor
ABB A145-30 contactor

It was installed about 18 months ago and has been in nearly continuous use since.  The broken white plastic housing surrounds the contactor coil and is responsible for pushing and holding down the contact fingers.

ABB A145-30 contactor coil cover
ABB A145-30 contactor coil cover

Looks like the coil is running too hot and damaging the plastic. This resulted in a failure of the contactor to make and no high voltage to the transmitter PA.  Obviously a problem.  I spoke to BE about this and they did not have a good answer.  Actually, what they said was “That contactor is rated for 220 amps,” which is true enough. The only thing that I can think of is the coil is rated for 208 volts and the transmitter is connected to a 240 volt delta service.

A new contactor was ordered and installed yesterday.

I will investigate the coil voltages further, but for now, the 27 year old transmitter remains on the air.

Broadcast Electronics FM35A
Broadcast Electronics FM35A

8 thoughts on “Failed High Voltage Contactor”

  1. Perhaps it’s time to install a series resistor to reduce the power in the contactor coil. Once you determine how much voltage is needed to pull the armature in all the way, you can calculate the resistance value. The hold-in voltage is probably lower than the pull-in voltage. Some 100% duty cycle contactors will get warm though.

  2. Yeah, I’d be wondering about coil voltage, rated vs. actual. Any more, a lot of them are mix & match, with either field-swappable coils or at least same-footprint versions in all the popular voltages.

    (There are usually more-rugged versions to be found — if there’s room for one and the station owners will pay the price. ABB hasn’t been covering themselves in glory, IIRC.)

    Primary voltage mismatches are a real gotcha and not everyone is comfy with the differences between, say, a 240 V delta and a 208 V wye. This sometimes includes the original installers and/or electricians.

  3. I do believe I’ve been in that transmitter room with the former engineer many years back! Was the antenna at that station replaced recently? A friend noticed that it looked like the Brown Shively is now a Grey Shively.

  4. @David, we keep the CRT turned off unless we are tuning the transmitter, which is why it still works
    @Roberta, I think I am going to put a voltage dropping resistor in series with this coil to prevent further failures as Bob has suggested.
    @Mike, I don’t know, have you ever been to the WEBE transmitter site?

  5. I added a battery back-up hand-off control relay years ago to a control system
    where the control voltage was the incoming 120v AC, and I did not like the excess current
    and heat on the coil. I added 100 ohms to the coil circuit, and it still pulls in very reliably, while keeping the coil current much lower. Still happy after 15 years.

    There have been some times I wish I could have increased coil current; a chattering
    MEMA 4 Westinghose contactor which chewed up the auxiliary contacts repeated over several
    days….while we ran with a flat blade screwdriver jammed in the gap of the the contactor
    plunger to stifle the buzzing.

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