Date:         12 Jun 1996 09:44:27 -0700
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         "Harvey Chao" <Harvey_Chao@smtp.svl.trw.com>
Subject:      Battery Isolator

Mail*Link(r) SMTP               Battery Isolator

 
SyncroHead@aol and jwakefield@4dmg.net have talked about coach battery
charging and the problem with the 0.6v voltage drop from a solid state battery
isolator.

The theoretical fully charged voltage (after surface charge is bled off by
sitting ~12 hrs or by brief discharge) is 12.72 volts.  ANY applied voltage
higher than that will result in some charging of a fully charged battery, and
more charging of a partially charged battery .  The exact amount will depend
upon the health (usually represented by the internal resistance) of the
battery and the voltage difference between the battery and the applied
voltage.  For example a healthy battery dischared down to an open circuit
voltage of 11.5 will charge at a rate of  the difference between the applied
voltage and 11.5 divided by the internal resistance.  A typical healthy
battery has a very low internal resistance, 0.1 ohms or a lot less.

The accepted output voltage from you alternator typically ranges between 13.8
and 14.4 volts.  So if you have the alternator set low at 13.8 (this is
usually a "float voltage, you can supply this to a car battery 'indefinitely'
w/o risk of overcharge and the current flow will typically be measured in
miliamps).  However, it will take a bit of time at this voltage to recharge a
discharged battery.  If you set the alternator to 14.4 volts, even after you
subtract the typical 0.6-7 volt drop across the isolating diode, you should
still be able to apply 13.8 volts to the battery.  The risk here is you may
tend to overcharge the starter battery.

A possible solution is to get an adjustable regulator for your alternator, set
it's output 0.6 volts higher than you want, say a little higer than 14.4 and
put an additional diode between the alternator output and the starter
battery's "+" terminal.  This way, both batteries (starter and coach) have the
same voltage drop and don't overcharge.  Since the starter and other normal
vehicle electrical loads are connected directly to the starter battery
(downstream of the diode) they will get regular current flow from the battery.

I have attempted to enclose a PICT file to show this schematically.

For
  Your
    Information
dcp'90




begin 666 Untitled 1
M``46```"``````````````````````````4````(````5@```!`````)````
M9@```"`````#````A@````H````"```!```````````!```!````#F[Y4+7]
M^5"U_8````"`````4$E#5$-$<G<!``````````````````````````````!5
M;G1I=&QE9"`Q````````````````````````````````````````````````
M````````````````````````````````````````````````````````````
?``````````````````````````````````````````!%
M````````````````````````````````````````````````````````````
M````````````````````````````````````````````````````````````
M````````````````````````````````````````````````````````````
M````````````````````````````````````````````````````````````
M````````````````````````````````````````````````````````````
M````````````````````````````````````````````````````````````
M````````````````````````````````````````````````````````````
M````````````````````````````````````````````````````````````
M````````````````````````````````````````````````````````````
M````````````````````````````````````````````````````````````
M````````````````````````````````````````````````````````````
M```````````````````````,;O____\!E`*)`!$"_PP`________``#__P``
M`HD```&4`````````*$`P`-Y)5!O<W138W)I<'0@2&%C:R!B>2!-:6ME($)R
M;W)S(#$R+S<O.3`-+T1I<V%B;&5.97AT4V5T4D="0V]L;W(-"7L-"75S97)D
M:6-T(&)E9VEN#0DO<V5T<F=B8V]L;W(@#0D)>PT)"7!O<`T)"7!O<`T)"7!O
M<`T)"75S97)D:6-T(&)E9VEN#0D)+W-E=')G8F-O;&]R('-Y<W1E;61I8W0@
M+W-E=')G8F-O;&]R(&=E="!D968-"0EE;F0-"0E](&1E9@T)96YD#7T@8FEN
M9"!D968-+V)C87)R87D@=VAE<F4@>PT)<&]P#0EB8V%R<F%Y(#(@>PT)"2]D
M82`T('!S(&1I=B!D968-"0ED9B!S971F;VYT(&=S879E(&-S('=I#0D),2!I
M;F1E>"`P(&YE>V5X8V@@9&$@861D(&5X8VA]:68@9W)E<W1O<F4@<V5T8VAA
M<G=I9'1H#0D)8W,@,"`P('-M8R!D82`P('-M8R!D82!D82!S;6,@,"!D82!S
M;6,@8PT)"6=R87D-"0E[(&=L?0T)"7LQ('-E=&=R87E]:69E;'-E#0D)9&$@
M,BX@9&EV(&1U<"!M;W9E=&\@<VAO=PT)?6)I;F0@<'5T#7T@:68-)0TE(%5S
M960@=&\@<VYA<"!T;R!D979I8V4@<&EX96QS+"`Q+S1T:"!O9B!T:&4@<&EX
M96P@:6XN#2]S='`@>R`@)2!X('D@('!L("!X('D@("`@("`@("`@("`@("`@
M)2!3;F%P(%1O(%!I>&5L+"!P:7AE;"`@*&%U=&\@<W1R;VME(&%D:G5S="D-
M"71R86YS9F]R;0T),"XR-2!S=6(@<F]U;F0@,"XR-2!A9&0@97AC:`T),"XR
M-2!S=6(@<F]U;F0@,"XR-2!A9&0@97AC:`T):71R86YS9F]R;0U](&)I;F0@
M9&5F#0TO<VYA<&UO=F5T;R![("4@>"!Y("!M("`M("`@("`@("`@("`@("4@
M;6]V971O+"!A=71O('-T<F]K92!A9&IU<W0-"7-T<"`@;6]V971O#7T@8FEN
M9"!D968-#2]S;F%P;&EN971O('L@)2!X('D@(&P@("T@("`@("`@("`@("`@
M)2!L:6YE=&\L(&%U=&\@<W1R;VME(&%D:G5S=`T)<W1P(&QI;F5T;PU](&)I
M;F0@9&5F#0``&O_______P`!``K_____`90"B0`)````````````40"F```!
M'`!M``<``````"(`"@`F````H0"V``0``0`!`!H`````````!P`!``$`"?__
M________`%@`!P``````(P```*$`M@`$``$``0`'``$``0`B`*8`-@"+``<`
M`````",```"A`+8`!``!``$`H`",`'$`'@`L`/@`-@$%`#$!!0`V`/@`,0#X
M`"P`^``Q`04`!P`!``$`<``>`"P`^``V`04`,0$%`#8`^``Q`/@`+`#X`#$!
M!0`A`#$`^`"@`(T`!P``````(P```*$`M@`$``$``0`'``$``0`B`#$`AP#<
M``<``````",```"A`+8`!``!``$`H`",`'$`'@`(`/@`$@$%``T!!0`2`/@`
M#0#X``@`^``-`04`!P`!``$`<``>``@`^``2`04`#0$%`!(`^``-`/@`"`#X
M``T!!0`C<0``H`"-``<``````",```"A`+8`!``!``$`!P`!``$`(@%^`#8`
MG0"@`(P`#/_?_H(``0`*_H'_W@`6`F@`!P``````(@`````````C````H0"V
M``0``0`!``<``0`!`",D```'```````C````H0"V``0``0`!``<``0`!`"(`
M"0`(&P``!P``````(P```*$`M@`$``$``0`'``$``0`B`!(`#!(``*``C0`,
M`"$!?@`!``K_____`90"B0`'```````C````H0"V``0``0`!``<``0`!`"(`
M&0$#`.<`!P``````(P```*$`M@`$``$``0`'``$``0`B`#\!!@#F`!K_____
M__\`"0```````````#$`=P#O`1\!0``'```````C````H0"V``0``0`!`!H`
M````````!P`!``$`"?__________`#@`&O_______P`)````````````,0!X
M`;$!(0("``<``````",```"A`+8`!``!``$`&@`````````'``$``0`)____
M______\`.``'```````C````H0"V``0``0`!``<``0`!`"(`=@$4`+L`!P``
M````(P```*$`M@`$``$``0`'``$``0`B`#`!!PT```<``````",```"A`+8`
M!``!``$`!P`!``$`(``-`04`#0'9``<``````",```"A`+8`!``!``$`!P`!
M``$`(@!X`=@`E0"A`)8`#`$````"```````````,_NS_G0`!``H``````!D`
M#P`'```````B`````````*``F`"A`)H`"/_L;X```!N``"P`#``5"4AE;'9E
M=&EC80`#`!4`#0`8`"X`!````0``*A0!*P``H`"9`*``EP`C````H0"6``P!
M`````@``````````#/\V````(P```*``F`"A`)H`"/_L;X#__^6``"D``2L`
M`*``F0"@`)<`(P```*$`E@`,`0````(```````````P`YO_>``$`"@``````
M'``G`",```"@`)@`H0":``C_]9,````+@``-``P`*``*```'0V]A8V@@"@"@
M`)D`H`"8`"H.!T)A='1E<GD``*``F0"@`)<`(P```*$`E@`,`0````(`````
M``````S_-0`$`",```"@`)@`H0":``C_]8\`___6@``H``H```A3=&%R=&5R
M#0``H`"9`*``F``J#@="871T97)Y``"@`)D`H`"7`",```"@`(P`#`#"_P<`
M`0`*_H7^_@`:`8@`(P```",```"A`+8`!``!``$`!P`!``$`(R0```<`````
M`",```"A`+8`!``!``$`!P`!``$`(@`)``@;```'```````C````H0"V``0`
M`0`!``<``0`!`"(`$@`+$@``H`"-`*``C``,_SD`!@`!``K^B_XW`"``P0`'
M```````B`````````",```"A`+8`!``!``$`!P`!``$`(R0```<``````",`
M``"A`+8`!``!``$`!P`!``$`(@`)``@;```'```````C````H0"V``0``0`!
M``<``0`!`"(`$@`,$@``H`"-``P!R`%T``$`"O____\!E`*)``<``````",`
M``"A`+8`!``!``$`!P`!``$`(@%X`1@`J``'```````C````H0"V``0``0`!
M``<``0`!`"(!<0'8`*\`!P``````(P```*$`M@`$``$``0`'``$``0`B`#$!
M%"T```<``````",```"A`+8`!``!``$`!P`!``$`(@`-`=A/``"A`)8`#`$`
M```"```````````,_JO_T0`!``H``````%0`60`'```````B`````````*``
MF`"A`)H`"/_V60#__X&``"@`"@``"E1O($-O86-H(`T``*``F0"@`)@`*@X/
M0F%T=&5R>2!,;V%D<RP-``"@`)D`H`"8`"H.$$%S<W5M92!I<V]L871E9`T`
MH`"9`*``F``J#@YF<F]M(%9E:&EC;&4@#0"@`)D`H`"8`"H.$'-T87)T97(@
M8F%T=&5R>0T`H`"9`*``F``J#@5L;V%D<P``H`"9`*``EP`C````H0"6``P!
M`````@``````````#/\=`"@``0`*```````X`$\`(P```*``F`"A`)H`"/_V
M(P```%^``"@`"@``#%1O('-T87)T97(@#0``H`"9`*``F``J#@IA;F0@;W1H
M97(-`*``F0"@`)@`*@X0=F5H:6-L92!R96=U;&%R#0"@`)D`H`"8`"H.!6QO
M861S``"@`)D`H`"7`",```"A`)8`#`$````"```````````,`BG_10`!``H`
M`````#@`4P`C````H`"8`*$`F@`(__7>````.(``*``*```+06QT97)N871O
M<@T`H`"9`*``F``J#@UW:71H(&]U='!U="`-``"@`)D`H`"8`"H.#&%T(#$T
M+C0@=&\@#0"@`)D`H`"8`"H.$#$T+C8@=F]L="!O=71P=70`H`"9`*``EP`C
$````_V%R
`
end