devices for surge protection

MEXICOWANDERER wrote:
Alternator avalanche rectifiers are rated 28-32 volts. Since they are in a major circuit they do limit total system transient voltage events to.......28 - 32 volts.
My personal ideal is SEVENTEEN POINT ZERO VOLTS clamping.

Automotive transients involve other factors and completely different solutions. This science is well defined by manufactures who design this stuff and by international standards.

SAE J1455 and ISO 7637-1 defined automotive transients up to 270 volts and energy up to 50 joules. These are high side or extreme numbers. Alternators rated at only 28-32 volts are woefully insufficient - easily fail.

SGS Thompson, one of many manufacturers who address this threat, define load dump (a destructive surge on 12 volt systems) as
peak voltage 80 to 100 volts and duration 300 to 400 milliseconds.

SGS Thompson also admits in a 1996 application notes that

The protection at the alternator level is a quite new concept and all the technical problems do not seem to be completely solved.

Electronics found in normal residential and commercial service are insufficient for automotive applications. Therefore automotive electronics tend to be more expensive. Power supply chips that operate up to 40 volt in most electronics are insufficient in automotive environments. Similar chips for automotive applications are rated at 60 or as much as 100 volts. Automotive environments are that harsh.

Automotive electronics are more expensive due to robust parts designed for and required for that harsh environment. Anything designed for 12 volt operation should withstand at least 60 volts.