Protecting 12V electronic equipment

[Richard C. Ferryman]

I have various electronic items on board which are rated at 14V and
16V DC max. I am fitting a 20" LCD TV this winter and that is rated
at 16V max. Although so far I've not had a failure I'm concerned at
spike protection and voltage regulator failure giving high voltages.
I had considered some hefty 16V zeners with suitably fused feeds to
act as protection.
Could low drop-out regulator ICs help to regulate down to a nominal
12V, but how do they work if the input voltage drops below 12V?
Any suggestions welcome. I am off in the spring on an extended trip
of around 5 years duration and am currently preparing for as many
eventualities as possible.
Richard

 

[Ed Price]

Read the discussion entitled "Are zap stoppers really needed
on alternators?" starting about 11 Jul.

Properly constructed mobile electronics don't use
conventional voltage regulators that max at 30 some volts.
Typical 12 volt transients are discussed as 50, 60 and 270
volts. Do they charge more for mobile electronics only
because it says mobile or maritime? No. They must also design
for transients unique to 12 volts systems.

That 14V and 16V DC max rating would be voltage continuous.
You need further specs. How many transient volts can it
withstand? Is it designed to withstand load dump transients?

Don't use zener diodes. Use avalanche protection diodes
with names such as Transzorb and Transil.

I agree completely; I regularly use Transzorbs on my 28 VDC military
designs. In mission critical (read that as flight controls or ordnance
systems), a combination of protection is used. For instance, something like
a transzorb, for quick clamping of a very fast risetime transient. And a gas
discharge tube, to handle a longer duration, higher energy transient. And
passive LC filtering too.

Compatible operation of multiple systems on a common power bus requires
co-operative measures by all manufacturers. All the protection can't be in
the alternator alone. There are commercial and military standards which
define the vehicle power bus environment. A reputable manufacturer will
produce a product that doesn't inject deviations onto the bus in excess of
what everyone else on the bus is prepared to accept. A reputable
manufacturer will claim product conformance to a known vehicle bus power
quality standard, and/or provide accessible technical performance data.

Of course, that's a perfect world.

BTW, this brings up a subject that is constantly being discussed; the "can I
install an xxx in my boat?" topic. If the manufacturer is reputable, and
intended operation from a vehicle power supply as an option, then the answer
is usually a yes. But, if the manufacturer expected their gadget to operate
off a simple battery, or a 12 VDC wall-wart power supply, then the design
may not be capable of withstanding the vehicle power bus deviations. Proceed
at your own risk, as you are now your own systems integrator.


Ed
(recently described as not quite ready for the kill-file)