[PUP] 3 wire systems

[2elnav at netbistro.com]

----- Original Message ----- 
From: "Allen, Harris" <hallen at wbdiesel.com>
> It should be noted that the voltage threshold on the E-Plex system is
> 32V and I believe that the octoplex system is the same. A runaway
> alternator can easily take out parts of the system. Lightning strikes
> are currently an unknown on these systems. A electrical contractor in
> North Carolina that I do business with estimates that the cost of a 3
> wire system is about 25% higher than a conventional one. For the time
> being I would stick with a conventional system as I know that for the
> most part it will survive a lightning hit.
> Harris

REPLY
Good point Harris.  That may explain why my older technology system has 
survived as well as it did.  Back in 1996 I first built a system  using 
relay logic.  Although I was vaguely aware of  high end autos using digital 
systems back then  I lacked any firm  information on  what they were using.
The system would be less vulnerable in a 12 V  system but now that most new 
builds are going 24V  it also moves the 3 wire digital operating system 
closer to the maximm threshold.
One solution is to go high tech  and use only regulated  DC  into the 3 wire 
system.  It's expensive and would  negate the potentrial cost savings.
I know of one high end RV manufacturer  who documented 50% savings on  the 
total installed cost of a  3 wire system compared to  hard wire old style 
in  their similar but older model.  But this is also in a production shop 
with many identical copies of the same model being built.  By comparison 
most boat builders  are one off or  limited quantity production.

I would argue that  we should not toss out the baby with the bathwater. 
Tthe topology of a 3 wire system  offers  considerable  benefits  in terms 
of wire weight reduction and reduction  in wire duct congestion. Taking  one 
step backwards  to relay logic  may seem retrogressive but is still ahead of 
what we are doing at present.


Arild