thanks ghurd and woofer .
its just i see a lot of 12 dc heaters for sale on sum sites .
there not cheap. old post from ghurd talked about small 12dc coffee maker type thing
from flea markets.
as it happens i have one at home. it will boil water from the car cigarette lighter socket . i also got it from a flea market.
but ghurd said about 5kw . yes i know i cant use that on a dc system .
it would just buckle the battery plates.
but whare do dc heating element start and finish .also ac heating elements begin
the coffee maker element is 140 watts. so it says .so might use 11 amps.
ive seen 300watt heaters ac.
there are plenty dc elemts for sale . is it just the wattage that is different.
ive taken sum apart its just a wire inside covered in ceramic or sumthing.
and a outer metal jacket.
so its the wire inside that heats up.
so is it just a matter of watts . lower is ok for dc and higher you need ac.
why do i want to know. its just the dc rated are so expensive.
while the ac rated are cheap.
looks to me there made from the same stuff. thats what is confusing me.
just a thicker wire inside. it must be a special wire that don't melt .
when i get interested in sumthing i like to understand it or how it works.
so is it one law for dc and another for ac?