Crowbars

If you do something stupid with an electronic power supply, sometimes they are equipped to sense it and throw a crowbar across the output to protect the insides. Picture a Jacob's Ladder running, an evil scientist cackling maniacally, and a hero sneaking through the shadows carrying a crowbar--he then poises to cast his payload into the crackling storm of electricity--

If you're reading my blog, you probably know by now that something rather technical shows up once in a while. This is one of those posts.

I'm checking out a Con Avionics HS26-13.5 analog power supply. It weighs a good 30 lbs. and is rated at 24-28 VDC at 13.5 A. This particular unit has been dropped on its head. The front right top corner has been displaced a good inch into the volume of the machine.

I could tell the case would short a couple of contacts inside if it were powered up, so I resolved to get the cover off. Well, first thing to do is take an odd silver (matte aluminum) box off the back. It's a -Con Avionics OVH26-13.5. Google says "con avionics ovh26-13.5" doesn't exist. At the moment I think it's merely a sophisticated external overvoltage crowbar circuit.

It's connected across the output. It has large bolt-mounted diodes or SCRs of some kind and an MCR648-2 mounted on the outside on a moderate heat sink. The supply is "HS26-13.5" while the attachment is "OVH26-13.5," so it seems to me we have Over Voltage Handler or somesuch with a common voltage-current pair with the supply proper.