Just a quick note on batteries in parallel. If one battery is not agood as the other the
bad one will discharge the good one to it's level. If one has an internalshort it could wipe
out the whole system. Both batteries should be bought as a pair andmonitored closely.
The usual reason batteries go bad is the "stuff" (lead compound) flakesoff the plates and
builds up in the bottom of the plat housing (the case). When the "stuff"gets high enough it
starts shorting the plates out and causes a "cell" (internal part ofa battery) to go bad. It
could be solved by making a deeper bottom so more stuff cold buildup before shorting the plated,
but they couldn't sell as many batteries.
Always My Best,
R.M.Andrews

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Jim Dunmyer wrote:

> Tom,
> I'll still maintain that as long as the recommended charging voltagesare pretty close, I
> wouldn't worry about it. Remember that they're in parallel anyway,so the applied voltage is
> actually the same. Unless your isolators are something unusual, theyonly prevent one battery
> from backfeeding another, they really don't do anything for the charging.
>
> With your type of travelling, I can see why you want a good electricalsystem, but you were
> certainly abusing it by running the water heater! <<grin>>
>
> I'm now off to look at the sites you listed below, thanks for theinfo!
>
> <<Jim>>
>
> Tom H. wrote:
>
> > Jim,
> >
> > The rated charging voltages is pretty close but the internal resistancesand capacity are
> > not. However, perhaps my concern is overly cautious although Ihave always understood that
> > mixing different battery types and sizes is not a good idea.
> >
> > As far a being a moot point, in fact the situation of normallyrunning off of batteries and
> > moving often is a situation that I often find myself in. SinceI work full time, our trips
> > are typically logistically planned so that we cover a lot of milesin the beginning and
> > often stay at boondock sites since we are only stopping for sleep.I have been in
> > situations several times over the past couple of years where wedid delete the batteries
> > and were only able to recoup small recharging from the tow vehicle.However the major
> > reason for this deletion was that my previous hot water heaterwas electric only, which we
> > used through an inverter, and thus this would rapidly run us down.Just this week I
> > finished final installation of the PrecisionTemp 500 LP continuous/instantaneouswater
> > heater. Everything appears to be working well and we'll be testingit next week on a 10
> > day trip to FL (our first trip since November '98).
> >
> > The E-meter that I have discussed was actually purchased at http://www.rvsolarelectric.com/
> > although I have since seen this same meter at West Marine and atJade Mountain. It is
> > described on the Jade Mountain web site (http://www.jademountain.com/metr.html)as:
> >
> > E-Meter: New reading as a % of charge with digital precision. Abreakthrough in
> > versatility, information and cost. Complete, accurate (99.95%)data on your battery bank.
> > Displays amp hours, volts, amps, kilowatt-hours, state of charge,consumption rate, and
> > more. Also acts as a digital ammeter, letting you know how muchpower each DC load draws.
> > Optional RS-232 computer output. 0-50V, requires 500 amp shunt.Excellent all around meter:
> > highly recommended!
> >
> > I am very impressed with this meter as I can program it for instantaneousreadouts of A-hrs
> > as well as remaining A-hrs in the battery bank. As you surmised,it uses a shunt to
> > measure the current while the battery bank data was input by meas denoted in the battery
> > information. I am not using the RS-232 output because I am satisfiedwith the information
> > I can presently get from the meter as it is.
> >
> > Tom H.
> >
> > Jim Dunmyer wrote:
> >
> > > Tom,
> > > The rated charging voltage of those batteries is probably prettyclose, and actually
> > > MUST be identical because you have only one source, and they'reessentially paralleled
> > > while charging. It is not a problem to parallel different batteriesas long as the rated
> > > charging voltage is the same. Note that you cannot place mismatchedbatteries in SERIES
> > > (such as 6-volt golf cart batteries), even to the point of havingthem differ
> > > significantly in age.
> > >
> > > The forklift battery connector that I mentioned is a 2 pole,heavy plastic job, with a
> > > big handle to pull it apart. The contacts are huge, plated, spring-loaded,and "wipe" as
> > > the connector is engaged/disengaged. Depending on size, they'llhandle handle a couple
> > > of hundred amps for lengthy periods of time; forklifts oftenhave #4 cable going to
> > > these connectors. This connector wouldn't replace the Bargman,but supplement it.
> > >
> > > The whole thing might be moot anyway: a fancy hookup to the vehiclewould be needed only
> > > if you are normally running off battery power and are movingoften enough to charge it
> > > up. Plus, using a lot of battery, and driving for only a fewhours. I'd think that
> > > extensive boondocking would warrant solar panels or perhaps asmall DC genset. (in case
> > > anyone is interested, there's lots more to them than simply beltingup an old car
> > > alternator to a lawnmower engine!)
> > >
> > > Did you say that you have one of those "E-meter" gadgets? Canyou elaborate on how it
> > > works and what it does for you?
>
> --