Date:         Wed, 05 Jun 1996 03:33:04 -0700
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         jwakefield@4dmg.net (john wakefield)
Subject:      Re: 87 Vanagon: 3rd choice for gauge

william.warburton/OU=tritec@dsw.govt.nz wrote:
"It should be possible to locate the series resistance close to the 
battery and other high current paths and have the actual meter on the 
dash with relatively light cabling linking it to the "sender" 
resistance."
 Then he closes his note with "Cheers," to which I can only say three 
Cheers for William.  What a perfectly wonderful insight.  Why didn't I 
think of that.
  Now it's true that most ammeters would be destroyed by most people who 
tried to perform this meter modification, but the idea's still great, and 
were I with VDO or competitors, I'd have Bill's external resistor version 
as an option, with a tiny fast blow fuse.  Using a second small internal 
resistor, this fuse would still protect the delicate movement moter 
windings.
  Now if I had to vote for the third meter, it would certainly be a 270 
degree swing analog volt meter with a range from 10 to 15 volts.  Why so 
specific?  First of all, you need accuracy to be able to KNOW static 
battery condition.  Yes, that's right, any good photo electic energy book 
publishes a chart showing the voltage vs. percentage of charge that's 
left.  That's the basis for the crudely effective battery condition 
display in the Westfalia kitchenette.
  Faced with a late night remote camp gathering situation where you 
feared the battery might not restart the motor in the morning, you might:
1) Turn off the TV even though you're engrosed in the plot.
2) Offend others by retarting now for a high speed idle recharge period.
3) Take a chance.
  In this situation, an ammeter is as informative as your speedometer, 
which is to say, useless.  You already know the load per switched on 
device.  But with an accurate volt meter, you have no need to doubt what 
percentage charge remains.
  It was suggested that an ammeter told more about the charging system 
than an ammeter.  I believe that's wrong.  The one thing that an ammeter 
does better than a volt meter, is inform how "active" a battery is.  An 
active battery is one that can QUICKY (that's a rate) accept and deliver 
large current levels.  New batteries are super active, old ones approach 
the grim recycler by becoming less able to deliver/accept high current 
levels.  So after a long weekend's discharge from using the coach 
appliances, an active battery will pull current like mad, whereas the 
tired one will pull less for longer.
  Now the volt meter readings in this situation can tell you just how 
your charging system is pulling that load.  So an informed observer can 
know a lot from either, but for the Westy camper, the dual function makes 
the volt meter my choice.
	John Wakefield