Date: Thu, 22 Feb 2007 11:40:26 -0800
Reply-To: Jake de Villiers <crescentbeachguitar@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Jake de Villiers <crescentbeachguitar@GMAIL.COM>
Subject: Re: was fav 12 V acc, now 2nd battery relay system
In-Reply-To: <45DDBBD2.9060609@gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
" I don't see the risk of connecting a
deeply-discharged aux battery to the engine battery as long as the
alternator can provide the current and that current can reach at least
as far as the engine battery."
+1 As Mike Collum pointed out, there is no risk. I drove Dixie for six
months with a totally snookered house battery, and the only drawback was
having to re-configure the stereo every time I fired her up.
The current just goes right past the useless battery-like object into the
12V radio, lights, etcetera.
Jake
On 2/22/07, Michael Elliott <camping.elliott@gmail.com> wrote:
>
> (Is this a top post or a bottom post or a don't care group?)
>
>
> Hi Frank, Yeah, I see what you mean, but I don't see it as a real risk.
>
> If a 1315 is being used, and if the aux battery is deeply discharged,
> and if the wire between the two batteries is fat, the aux battery will
> suck current from the starter battery when the two are connected. If the
> alternator is unable to provide enough current to keep the voltage
> sensed by the 1315 above 12.8 volts, the 1315 will disconnect the aux
> battery, wait a bit, then try reconnecting it. A smart system, an
> advantage.
>
> In a relay system, like mine, the batteries are not bridged until the
> alt light goes dark (I am still not clear, exactly, in electrical terms,
> what conditions cause the lamp to go out, but presumably it indicates
> that the alternator is powering everything sufficiently well to be
> charging the engine battery). If the aux battery is deeply discharged,
> and if the wire to it is fat, then there will be a lot of current
> through that wire when the relay closes. Now, if the alternator has
> enough current capacity to provide the needed current, then the aux
> battery will not be dragging down the engine battery because the
> alternator will be providing what is needed to keep voltages where they
> need to be, at the same voltage. If they are at the same voltage,
> current will not flow from one to the other. The engine battery might
> not be getting much charging at this time, since the majority of the
> alternator's current will be going into the aux battery.
>
> [If you put 13 or 14 volts onto two batteries that are connected in
> parallel, the battery that has been more deeply discharged will draw
> more current -- from the source, not the other battery unless the source
> can't keep the charging voltage at 13 or 14 volts. If the charging
> source can't and the voltage drops then the more fully-charged battery
> will be providing the charging current into the less-charged battery.
> But if all things are equal, like battery types, and wires having
> sufficiently low resistances so they don't limit currents and all that,
> the strongest source provides the charging current.]
>
> If, however, the alternator can't provide enough current to be charging
> my engine battery and aux battery at the same time, or if the wire from
> the alternator to my engine battery is skinny while the wire from my
> engine battery to the aux battery is fat, the engine battery might be
> called upon to provide some or all of the current that the aux battery
> wants. If a 1315 was monitoring the voltage at the terminals of my
> engine battery, it would disconnect the aux. If it was monitoring the
> voltage some other place it might not, depending on whether the whole
> system sags or not. The relay system is dependent upon the alt lamp to
> tell whether it can connect the aux battery. I presume (again, don't
> know) that the alt lamp will light if the alternator can't drive the
> system voltage up then it would disconnect the aux battery. Again,
> voltage drops caused by wire losses affect the operation of this: a fat
> wire between the two batteries and a skinny wire from the alternator to
> the engine battery would cause the alternator to think thing are better
> than they are and maybe not light the alt lamp. That's one situation
> where the 1315 is better, since it monitors the engine battery while the
> alt lamp seems to know more about the conditions back at the alternator.
> But if the alt lamp ain't happy, the relay disconnects the aux battery.
>
> A second advantage to the 1315 is that it does wait a bit to try to
> reconnect the two, while the alt lamp might go right out as soon as the
> relay disconnected the aux battery, causing the relay to reconnect,
> causing the alt lamp to light again. Wash, rinse, repeat.
>
> I do see those as two distinct advantages that the 1315 possesses.
> However -- and here is where folks who know Vanagon wiring real well can
> correct me -- I don't think that the engine battery is at much risk if
> it is connected to a deeply-discharged aux battery because I am assuming
> that the wire from the alternator to the engine battery is fat enough to
> deliver the current the aux battery wants so that the engine battery
> isn't much bothered. If the aux battery is totally hosed, then all bets
> with the relay system are off, as I described below in my post of a
> couple days ago.
>
> My aux battery is a deep cycle Group 27 under the bench seat. While it's
> not identical to the starting battery it's not so different that I'm
> worried about overcharging or undercharging one or the other. Besides,
> the long wire run to it from the relay provides a bit of a voltage drop
> which limits charging current if the battery is deeply discharged. I
> don't normally let it get below 50% depth of discharge anyway.
>
> I'm not arguing that the relay system has all the advantages of the
> 1315. I think the 1315 is cool, and see that it has two clear features
> that make it desirable, but I don't see the risk of connecting a
> deeply-discharged aux battery to the engine battery as long as the
> alternator can provide the current and that current can reach at least
> as far as the engine battery.
>
>
> --
> Mike "Rocket J Squirrel" Elliott
> 71 Type 2: the Wonderbus
> 84 Westfalia: Mellow Yellow ("The Electrical Banana")
> 74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
> KG6RCR
>
>
>
> Frank Condelli typed:
> > In a message dated 21/02/2007 11:56:49 A.M. Eastern Standard Time,
> > LISTSERV@GERRY.VANAGON.COM writes:
> >
> > Hi Frank, I'm not seeing any normal conditions where my relay system is
> > at a disadvantage when compared to the 1315. My starter battery is
> > always connected to the charging source, just like in a system using
> the
> > 1315. My aux batter is connected to the starter battery/charging source
> > under only two conditions:
> >
> > 1. The alternator is putting out enough voltage to extinguish the dash
> > ALT lamp. What's that -- 13 volts or more? Bridging the aux battery to
> > the starter battery under these conditions is appropriate unless the
> aux
> > battery has suffered a major failure, in which case all bets are off
> > with my system.
> >
> > 2. I have operated a switch to manually bridge the aux battery to the
> > starter battery/charging source by applying voltage from the aux
> battery
> > to the relay coil. This would be done in the case where the starter
> > battery is low and I need to steal some power from the aux battery to
> > pump up the starter battery. There also should be no problem unless the
> > starter battery has suffered a major failure.
> >
> > I did use the phrase "normal conditions" in my opening paragraph, and I
> > noted above two unusual conditions which involve the near or total
> > meltdown of one or both batteries. In the situation where the aux
> > battery was hosed, the 1315 would allow a fellow to keep driving
> because
> > it would refuse to connect the bad battery, whereas my system has no
> > such safeguard. If the starter battery is low, both systems allow a
> > fellow to bridge the aux to it for starting, but if the starter battery
> > was massively failed neither system would help.
> >
> > The 1315 does not require metering: it appears to be smart enough to
> not
> > connect ugly-dead batteries to the system. So that's an advantage --
> but
> > to me, not much of one because I like meters -- even with a 1315 I'd
> > monitor battery voltage.
> >
> > So, unless I'm missing something, the 1315 only provides two advantages
> > over the relay system: no-brainer operation (always useful when you
> have
> > a squirrel's brain) and it refuses to connect a hosed aux battery.
> Those
> > two may be advantages enough for some folk to recommend the 1315 to
> > them, but to say that "relay systems work but not well," is a bit much.
> >
> >
> >
> >
> >
> > Mike, this is all well and good and correct, however your missing one
> > important point. Using a relay system has both batteries connected
> together as
> > soon as the engine starts and the alternator red light goes out we all
> agree on
> > that ? OK, so if that is true and the aux battery is dead and your
> staring
> > battery is full what happens ? Well, what happens is the main battery
> will
> > try to dump it's charge into the aux battery until they both become
> equal. The
> > rate at which this happens depends on the size of the wire used to
> connect
> > the two batteries and the speed at which the alternator can keep up
> replacing
> > the missing voltage in the batteries. So, this is not a problem if you
> don't
> > mind changing two batteries more often than usual as ordinary car
> batteries
> > do not like to be discharged and charged constantly. That was the
> reasoning
> > behind using a deep cycle battery as the aux battery. So then we're
> back
> > where this thread all started. The only deep cycle battery that sort
> of fits
> > under the seat is the OPTIMA Yellow Top which we see by recent
> experience is a
> > piss poor battery ! So.......some of us have gone back to using a
> regular
> > car battery with a good warranty as the aux battery. Those of us
> who have
> > done this most likely already have the 1315 as it is required to charge
> the
> > OPTIMA correctly in a two dissimilar battery situation. It also make
> more sense
> > to charge the batteries independently and this is what the 1315 does
> best.
> >
> > Cheers,
> >
> > Frank Condelli
> > Almonte, Ontario, Canada
> > '87 Westy, '90 Carat, '87 Wolfsburg (Forsale) & Lionel Trains
> (_Collection
> > for sale_ (http://members.aol.com/Fkc43/trainsal.htm) )
> > Vanagon/Vanagon Westfalia Service in the Ottawa Valley
> > _Frank Condelli & Associates_ (
> http://members.aol.com/Fkc43/busindex.html)
> > _Vanagon Stainless Steel Exhaust Systems_
> > (http://members.aol.com/Fkc43/stebro.htm)
> > _BusFusion_ (http://members.aol.com/BusFusion/bfhome.htm) a VW Camper
> > camping event, Almonte, ON, June 07 ~ 10, 2007
> >
>
--
Jake
1984 Vanagon GL
1986 Westy Weekender "Dixie"
www.crescentbeachguitar.com
| 
