An autoformer the basic unit should be inherently tough as nails. Hard to damage. A secondary transient voltage protection device would or should be located close enough to the basic voltage correction device that it would suppress voltage transients that degrade the insulation of the voltage correction device. Got it?
Devices that use wall warts or AC/DC voltage converters really do not care a heck of a whole lot about wide voltage spans. But excessive transient voltage events degrade transistors, capacitors, IC's, etc. in the devices.
Has anyone out there taken apart a transient voltage suppressor device (referred to as a surge guard)? Is there anything more than a series of metal oxide varistors inside? To be UL approved the device must have a fuse inside. Single/overall fuse protection is a pure neanderthal grade design. Each MOV should have a backup WHEN not if the first MOV gets tired and dies. Individual fuses. Same for Transient Voltage Suppressors. Avalanche diodes. Paralleled and individually fused. I use Gas Discharge Tube (3-leg) protection against Armageddon-like events.
Simple MOV only devices do not have the reaction time of avalanche rectifiers. High frequency transients slip by the MOVs.
Avalanche rectifiers by themselves do not have the capacity that a slower reacting MOV has.
A major event such as crossed power line, shorted pole transformer, or nearby lightning strike will blast through avalanche rectifiers and MOVs and burn them out. Enter the Gas Discharge Tube device. It buys enough time to allow a lightning feeder to ionize a path to earth negative. Power pedestal, shore power cord, and suppressor device all go up in smoke. But a protected RV stands a good chance coming out unscathed. This theory is not hypothetical. It has saved the interior electronics of three homes that I am aware of in Mexico. One galvanized steel power drop pole was melted on the tip, the meter was shattered, and the 8 gauge feeder wires were carbonized. The bolt fried the suppressor to ash, and it's ground wire disappeared. But all the electronics in the home continued to function once the damage was repaired. Done right, this stuff works.
But when I run across ads for upper end suppressors that boast Gas Discharge Tube, Avalanche TVS, and MOV protection, the price is cruel. The components are not that expensive. Hell, a 44,000 joule Vishay MOV costs fifty seven dollars retail. I have several pounds of MOVs, avalanche diodes and GDT's that'll be here next weekend. The BIGGEST capacity units available.
