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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
Comments: To: Michael Elliott <camping.elliott@gmail.com>
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


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