What causes rectifier stacks to buzz loudly? I've got a Harris FM 25K (power supply) in which these stacks are currently buzzing loudly, and have been for about a week now, and we're starting to get concerned. Voltage coming into the building is exactly where it should be (all phases are 240 +/- 3 volts). None of the parameters on the transmitter have changed either. I used to encounter this with a Continental 816R, but usually only when I just turned it on (and eventually the stacks would quiet down after being on for 10 or 15 minutes).
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Power Supply Rectifier Stacks
- Thread starter Brian Bowers
- Start date
If you have a scope, look at the incoming waveform of the AC.
If there's a big "standing"spike riding the AC wave, it's going to buzz and it may or may not be a problem.
First you have to find out if the source of the spike is your equipment or outside.
It can partially be the noise of all the switching power supplies connected to that service, but in a 3 phase system, it would
most likely be one very bad and noisy offending device on the same distribution transformer as you.
If the incoming AC waveform is fairly clean, it could mean somthing is drawing down the DC and a higher than normal
current in the rectifiers might become audible buzzing. And that would need some looking at.
Filter caps may be failing in some way.
I don't know if this model gives access to DC current, if it does, I'd wonder if DC current is higher than normal.
If there's a big "standing"spike riding the AC wave, it's going to buzz and it may or may not be a problem.
First you have to find out if the source of the spike is your equipment or outside.
It can partially be the noise of all the switching power supplies connected to that service, but in a 3 phase system, it would
most likely be one very bad and noisy offending device on the same distribution transformer as you.
If the incoming AC waveform is fairly clean, it could mean somthing is drawing down the DC and a higher than normal
current in the rectifiers might become audible buzzing. And that would need some looking at.
Filter caps may be failing in some way.
I don't know if this model gives access to DC current, if it does, I'd wonder if DC current is higher than normal.
Are your certain that the buzz is coming from the rectifier stacks and not from the laminations on the plate transformer?
I would shut the transmitter down (be sure to kill the power breakers and use your Jesus Stick to discharge the HV section) and check for loose connections on the plate transformer and on the rectifier stacks.
Also check to make sure that all mounting hardware is tight.
Keep a close eye on the high voltage meter. The buzz may be caused by shorted turns on the plate transformer. If you have a few shorted turns, the problem will get worse and you'll probably see that your plate voltage begins to change. If the shorted turns are on the transformer primary, the HV will go up. If the shorted turns are on the transformer secondary, the HV will go down.
I would shut the transmitter down (be sure to kill the power breakers and use your Jesus Stick to discharge the HV section) and check for loose connections on the plate transformer and on the rectifier stacks.
Also check to make sure that all mounting hardware is tight.
Keep a close eye on the high voltage meter. The buzz may be caused by shorted turns on the plate transformer. If you have a few shorted turns, the problem will get worse and you'll probably see that your plate voltage begins to change. If the shorted turns are on the transformer primary, the HV will go up. If the shorted turns are on the transformer secondary, the HV will go down.
I'm almost positive. I haven't pulled the panel of the power supply yet, but looking inside, I can seen the stacks run across it, and as I run my ear next to the cabinet, the loud buzzing is next to all of the stacks. This station has no working backup, so this won't be easy trying to diagnose. Usually Plate Volts runs around 9,000 to 9,200. It currently is running at 9,000. I admit, nothings been tightened or cleaned in the power supply for at least 7 years, if not more. I really hope it isn't the plate transformer.
I don't know if the HT series power supply cabinets are much different from the 25K, but I have a couple of HT-35s that have buzzy solenoids in the supply vault. It is disconcerting to hear it, but it doesn't seem to affect the transmitter operation. Sometimes you can tap the side of the vault and make it quit. I seem to recall that there is a service bulletin from Harris about this.
Something in the power supply for our HT-20 would very often buzz loudly. I believe it was the contactor and Harris said we should tighten some bolts or screws on it, can't remember exactly which ones. That helped but didn't totally fix it.
We could make make the buzzing totally go away by turning off the plates for a second. Sometimes it would take 2 tries. Once it was quieted it would stay quiet until the next time the transmitter power was recycled. It was like this for many years, the buzzing never seemed to hurt anything.
We could make make the buzzing totally go away by turning off the plates for a second. Sometimes it would take 2 tries. Once it was quieted it would stay quiet until the next time the transmitter power was recycled. It was like this for many years, the buzzing never seemed to hurt anything.
Mysteriously, the rectifier stack growling has since quieted down. Not sure why.
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