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VAL Digest V1 #13



VAL Digest         Sunday, September 21 2003         Volume 01 : Number 013




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Topics in Today's Digest:

Re: [VAL] Battery question
Re: [VAL] Battery question
Re: [VAL] Battery question
Re: [VAL] Battery question
Re: [VAL] Battery question

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Date: Sat, 20 Sep 2003 08:50:32 -0500
From: dean <dean@xxxxxxxxxx.net>
Subject: Re: [VAL] Battery question

It may be over simple but all I have to do is to UnPlug the light cable
between the truck and the trailer.
I only do it if I am going to be stopped for over 4 hours or more. Like
over night or taking in some event.
This will stop the drain on the truck system.

If I was to use a Diode I would have a voltage drop in the charge line
that would keep the batteries in the trailer less than a full charge.

Dean

On Friday, September 19, 2003, at 12:43  PM, Joann Wheatley wrote:
>
> Is the Bargman connector what I need in order to charge the batteries 
> whilst driving? and does it have a disconnect that all by itself (i.e. 
> not manual) prevents the trailer batteries from draining the tow 
> vehicle battery? If not, could you please recommend such a device?

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Date: Sat, 20 Sep 2003 09:03:03 -0500
From: "Dr. Gerald N. Johnson, electrical engineer" <geraldj@xxxxxxxxxx.net>
Subject: Re: [VAL] Battery question

Dean, one diode has two failings. First it doesn't isolate the trailer
from draining the tow vehicle battery, and second there's that diode
drop to keep the trailer battery from being fully charged. It takes TWO
diodes (and two diodes are part of the classic charging isolator), one
from the alternator to the vehicle charging circuit, the other from the
alternator to the trailer charging line. Then since most alternators
base their charge reference on the charging circuit, not their output
terminal, they automatically adjust for the diode drops and charge both
batteries equally. Though the relatively thin wires to the trailer
battery do slow its charging rate. My dad tried to use only one diode in
his '86 F-150. A wiring short shorted that diode and burned the wire
open, then he didn't charge the trailer battery at all.

The alternative is a relay that's only enabled when the engine is
running that connects the charging line from the tow vehicle battery to
the trailer battery. That's they way the factory tow package in my '98
F-150 does it. I don't know if the relay is run by the engine computer
or the ignition switch. It would be simple wiring to do it by the
ignition switch but better by the computer which knows if the engine is
turning because it has to create the ignition pulses. I'll try to see if
that is identified in the wiring diagram CD. Its hard to trace.

Gerald J.
- -- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.

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Date: Sat, 20 Sep 2003 11:07:31 -0500
From: Mike Keith <mkeith@xxxxxxxxxx.com>
Subject: Re: [VAL] Battery question

At 09:03 AM 9/20/2003 -0500, you wrote:
>Dean, one diode has two failings. First it doesn't isolate the trailer
>from draining the tow vehicle battery, and second there's that diode
><SNIP>
>The alternative is a relay that's only enabled when the engine is
>running that connects the charging line from the tow vehicle battery to
>the trailer battery. That's they way the factory tow package in my '98
>F-150 does it. I don't know if the relay is run by the engine computer
>or the ignition switch. It would be simple wiring to do it by the
>ignition switch but better by the computer which knows if the engine is
>turning because it has to create the ignition pulses. I'll try to see if
>that is identified in the wiring diagram CD. Its hard to trace.
>
>Gerald J.
>--
>Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
>Reproduction by permission only.

Dean and Gerald,

I would use a low oil pressure switch, one that loses ground when the oil 
pressure goes low. Using a 12V Solenoid Relay from an electric golf cart 
(like a ford starter relay, except rated continuos duty) Run the 12VDC line 
from the truck battery to the solenoid, then to the bargeman 
connector.  supply 12VDC to the coil of the relay, and run the ground to 
the low oil switch.




Mike

Mike and Marianne Keith
75 Argosy 26'  81 F100
New Florence, MO
GR8R STL unit #4503
Nil Illigitimi Carborundum RAH

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Date: Sat, 20 Sep 2003 10:20:44 -0500
From: "Dr. Gerald N. Johnson, electrical engineer" <geraldj@xxxxxxxxxx.net>
Subject: Re: [VAL] Battery question

Mike, you may work too hard but your use of the low oil pressure shutoff
works well. I checked the wiring diagrams on my '98 F-150 and the
trailer relay in the towing package is supplied coil power from an
ignition switch line that's only energized in the run position, not in
start, off, or accessory. That keeps it really simple. Just a matter of
locating the correct ignition switch load line.

One more thing needed is a 30 amp or so circuit breaker in the charging
line between the truck battery and the solenoid relay contacts.

And despite Dean's reluctance, the dual diode isolators work very well
ALL the time, no chances for forgetting to disconnect and no wiring
damage from trying to charge the starting battery from the trailer
battery. But it does take TWO diodes which do come with heat sinks in
the standard isolator packages which can be miswired, then they don't
work well. Wired right they work very well.

Gerald J.
- -- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.

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Date: Sat, 20 Sep 2003 11:25:03 -0700
From: Joann Wheatley <jwheatle@xxxxxxxxxx.edu>
Subject: Re: [VAL] Battery question

Dean - thanks, that sounds simple enough. I assume you refer to the big 
plug that goes from the trailer into the truck's receptacle that has to 
be connected for the lights. I'll do that way.
Jo Ann
>

> It may be over simple but all I have to do is to UnPlug the light cable
> between the truck and the trailer.

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End of VAL Digest V1 #13
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