WOW! What a way to get me out of my blogging slump! I burst forth with this spectacular failure.
One of my radio clients on Cape Cod has been beset with with a spate of severe failures of his 5KW class transmitter. First, a RF module died, reducing power by about 600 watts. I should have let enough alone! But in the interest of good engineering practice and doing the right thing for my client, we sent the transmitter back to the manufacturer (it’s really not field serviceable).
The newly repaired transmitter lasted 1 day when he lost 2 more modules, resulting in a reduction of power by about half. It’s a real gamble, depending on which multiple modules you lose, output power can vary from the value equal to the two modules to 1/2 of the power rated. The manufacturer was honestly embarrassed by this failure and did right by us, but the long and short of the story, the transmitter is starting to rot from the inside out due to the humid marine environment.
In all cases I managed to arrange a loan of a transmitter of about 1/2 the power. The two stations are good friends and help each other with donations, trades and promotions, so the engineering part of equipment loans was no big leap.
Now we are up to speed… the transmitter lasted about a month and suffered a total failure on a dark and stormy night, with no error logs, no alarms, it simply doesn’t make any power, though you can see current consumption as it tries, but nothing comes out of the output. The manufacturer was totally stumped though he suspected the directional coupler, the very last device that measures forward and reflected power, was defective… oh boy was he optimistic!
We theorize that the air became humid during an intense rainstorm. The low pass filter developed condensation, and after a brief power outage, the condensation dripped, the voltages swung around finding their place on startup and an arc developed. A huge arc as shown by the pictures(s).
This is the downside of going with an “economizer” method of air conditioning. A high end A/C unit will pull in outside air during the winter months, but it takes into consideration humidity and dew point. In the early spring, it might be cool enough to still take in outside air, but it will be humid and wet. Add salt air to this mix, and things start to oxidise and rot.
So the long and short of this is, don’t try to second guess your A/C scheme or your contract engineer. Though it may increase your electric bill a little, call this insurance! In the Northeast US I can see pulling in outside air from early November to early March, with the odd wet day off.
I hope to build up a humid, temp, air pressure, etc, sensor to control the A/C vs. the intake fan very soon. It will also log those parameters for later review and fine tuning. More on that later, as 90% of the work has been done, just not blogged.