The original article is available HERE.
This Over-voltage Crowbar Protection unit was running from April 2024 day and night without any disruptions. About a week ago I noticed that the ZS Link Hub Network radio was off one morning when I entered the Shack. The Power Supply was running but there was no life in the "black box" which housed the Crowbar circuitry.
The first thing I checked was the fuse that normally go up in smoke if the protection circuitry "kicks in". There was nothing wrong with the fuse. The next item to check was the BT152 Thyristor. It tested OK. Next would be the MC3423. Replaced it and still no power. A closer look at the Veroboard revealed that the output (positive) track to the Motorola radio has lifted from the phenol board. The copper track was cracked and there was no connectivity. Well this told me that the Veroboard tacks could not handle the amps drawn from the power supply. When I constructed the unit this was one of my concerns but I thought that with only the radio connected this would not be an issue. Continues daily use proved otherwise and the Vero PCB track failed.
According to the original Vero spec the area of a strip is equal to 39g which is rated to carry 2 amps for 1 second before fusing. Well if this holds true then the Veroboard that I used lasted surprisingly well. Fixing the unit was quite easy. I joined two tracks together for the input and output side and soldered a 2.5 mm solid tinned copper wire on top of the tracks. This is not optimal but I am sure that it will be able to carry the load and hopefully last longer than the Vero board strip. In the event that it fails again I will use 3 - 5 mm tinted copper wire to which I will connect the main crowbar low amperage circuit board. After all the main circuit board only suffice as sensing unit.
After the modification, the board was placed back into the "black box", the wires connected and the unit switched on. It fired right up. The Motorola specs shows 7.0 Amps current drawn on TX @ 25 watts and a standby current of 400 mA. I am sure that the 2.5 mm copper wire and the added track will be more than enough to handle the necessary current. Time will tell!
Finally: I will be playing around with a few other Crowbar Protection- and Reverse Polarity Circuits. More on this in future postings.
