OhTheAgony
here for the chicks
I even got some instructions done to go with them! Pretty unusual for me. As I said earlier, I believe these things will be self limiting. If the voltage is too high, early signs of combustion will happen. Nobody wants that. The sweet spot here is 13.5 to 14.2 volts, less than one volt difference between the low and high range.
I don't know how you are instructing your customers of course, but to be honest I wonder if that might just be to hot for most 20 ohm valued Ohmites if you leave it there for too long Rick.
I ran mine (with a resistance of 23,4 ohm) on 13,8 to 14,2V most of the time (like 12 hours per day on average), and it blew this week
I have used it on a unregulated PSU that in hindsight produced around 15,7V at peaks (the voltage constantly throttles up and down with that one) for weeks before I got a proper variable PSU though. And before that I stuffed my UD between pillows and whatnot to keep it up to temp, so it could very well be the damage was already done back then. But if you want to be certain if they can take it perhaps you want to leave one of your average or hotter running units on 14V for a few months in a row to see if it survives.