Date:         Wed, 16 Jun 2010 01:24:00 -0400
Reply-To:     Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject:      Re: How to modify Bosch regulator for remote sensing.
In-Reply-To:  <4c158f96.814ee50a.280c.2428@mx.google.com>
Content-Type: text/plain; charset="US-ASCII"

More umph can be a good thing! Keeps the battery and alternator sales up.
Has anyone thought why VW uses 13.8 volts? As for voltage drops across the
system, there are some design benefits such as providing some limitation of
alternator load at high current demands.

13.8 volts keeps the batteries at or just below the gassing threshold. While
it will not fully charge them it prevents damage from long trips. For
discharged batteries you do not want to bulk charge above this voltage
either. In fact proper bulk charging should be current limited (25% A/H
capacity tops) and the voltage allowed to climb. Putting 14.5 volts on a
discharged battery will result in immediate gassing and battery damage.
Brighter lights and faster fans! How much? Keep those spare bulbs handy.
Alternator heat load! If the voltage at the alternator is increased 10%, It
can make 20% more heat,(assuming a given current). Remember that the
alternators limit is function of its internal resistance so at full loads it
has to dissipate 1/2 the power it produces as heat.

Just keep the stock regulator set up and upgrade some of the wiring. And add
some fuses and fuse links for protection.

Dennis


-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Edward Maglott
Sent: Sunday, June 13, 2010 10:10 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: How to modify Bosch regulator for remote sensing.

This is all interesting.  I like the idea of getting more umph up to
the battery, and from there to my aux battery.  Keep us posted on the
failsafe considerations you are developing.  btw, what do you mean by
"float."

Edward

At 04:41 PM 6/12/2010, David Beierl wrote:
Excellent point.  Something bad could definitely happen.  On this
>unit and I presume all of them, if you float the input the alternator
>will go to full output which with a small load might be a very high
>voltage.  The sense input draws 8-9 ma at 14.5v, so to failsafe it
>would need a suitable resistor across where the internal bus was
>cut.  I'll figure out what suitable is, but it shouldn't be critical.
>
>Now if the sense lead is *grounded* that will definitely drive the
>thing to full output.
>
>I haven't addressed the situation yet of the alternator output no
>longer driving the battery, but the sense input still connected there
>-- effectively it's the same as floating the input, since it will be
>immediately carried down to the loaded battery voltage.  Looks like
>the systematic solution to that would be to get the 30 terminals of
>the ECU/Fuel relays off the direct alternator wire and feed them from
>up forward somewhere, either the fuse/relay panel 30 terminal or
>direct from the battery.
>
>Another solution would be to use a diode to bridge the cut instead of
>a resistor.  That way the internal regulator voltage should never go
>more than a diode drop above the regulator set point.  Not ideal,
>would want a warning probably; but not instant disaster either.  And
>put a quarter-amp fuse in the sense lead, so it would blow if the
>lead was grounded.
>
>Have I missed anything?
>
>Yours,
>David