On Apr 12, 1:46 pm, "Roger Long" wrote:
Since I'm only concerned when the starter is engaged, how about wiring in a
bypass with a NC relay that opens whenever the engine key is turned on?
When the alternator is going, low voltage shouldn't be a problem and I would
then have no voltage drop when sailing and drawing on the batteries. Since
I have a diesel, the engine is stopped before I turn the key off.

If that starter motor created spikes so destructive as to overwhelm
protection already inside electronics, then a typical zener diode is
only a bucket trying to stop a flood. Why is maritime electronics
often more expensive? Properly designed electronics include circuits
that make a trivial 'starter motor' spike irrelevant. Low voltage
also is not destructive and is made irrelevant by those same circuits.

Meanwhile, a destructive transient is called load dump. So critical
as to be defined even by SAE J1455 and ISO 7637-1 standards. Also
easily created if special consideration is not made to battery
switchover circuits.

Load dump is defined by one manufacturer with peak voltages of 80 to
100 volts and duration of 300 to 400 milliseconds. ISO defines it as
a voltage spike of up to 270 volts.

Most 12 volt electronics designed to withstand load dump are rated
for at least 60 volts. Examples of why a power adaptor is not
purchased on price and why another poster has never seen such damage.
How many replies even knew that load dump (not a starter motor) is the
destructive transient. A problem so common and so well understood as
to even be defined with SAE and ISO standard numbers.

Meanwhile, designs to make load dump irrelevant also make lesser
'starter motor' spikes also irrelevant.