James White redesigned the “standard” 12 Volt turn signal flasher to use a MOSFET output, then he modified the design to successfully run on 24 Volts for bus & truck applications.
At about the same time that James was doing this, Can-Car Rail approached us to develop a 36 Volt flasher for their rail coaches. I thought it would be easy! Whoops, not so fast…
Well, oh my Lord, 36 Volts DC is nasty. My first attempt to just use my modified 12 Volt design was a complete disaster. The three lead-acid car batteries that we used for development just provided so much power that the 2N5301 output transistor overheated and failed on the first flash into a short. The 12V and 24V designs could flash into a short indefinitely (Ed Van Humbeck drove around with a flasher wired directly across his car battery for about 6 months in 1980/1981 to prove that it could easily handle it).
The FET Flasher didn’t perform any better.
Instead, I had to develop a completely different design, right from scratch. I used some of the same concepts, although I had to change components – the 2N5301, for instance, is only rated for Vceo to 40V, so it had to be changed. The supply to the 555 timer had to be modified to handle the high voltage. The drive stages had to be changed to handle the voltage translation and the drive requirements of the new output transistor.
The biggest change was that the 36V flasher got a “ground return connection”, which allowed it to be constantly powered, instead of having to scavenge the operating current from the bulb current.
We had to change the mechanicals as well – the original 12V and 24V flashers were simply placed into a plastic cap along with a heatsink/mount made of a piece of bent & punched aluminum, then the cap was filled with epoxy. The But, like all challenging designs, it was 36V flasher needed much better heat dissipation for several devices, so it was designed as a flange mount device, a circuit board mounted on top of the “W” shaped metal mount, then covered with a lid.
The design was a challenge, the result was a success, but we didn’t make many units – perhaps a few hundred. But, that’s the difficulty – you can’t tell ahead of time, what will be a winner, and what will be a loser. You just have to do your best, and take on the ones that look reasonable.