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Keep Your Chassis Batteries Charged
Are your chassis
(engine) batteries charged when you are parked and plugged into shore power?
You say, yes of
course...are you positive? For sure your RV or House batteries are connected to
the charger/inverter when you are plugged into 'shore' power, but your engine or
chassis batteries may not be!
Many coach builders
do not wire the engine batteries into the charger/inverter for 'shore' power
charging, rather relying on the engine alternator to charge them while driving.
They have differing reasons for not hooking the batteries together so they can
be charged together...most notably the fact that the two different batteries are
different type
batteries for different jobs.
The
Engine/Chassis
batteries are auto type batteries for large starting currents
and quick recharges. Diesel engines usually have two 'auto' batteries of the
same type to provide large starting currents and longer cranking times. These
auto batteries now days are usually a sealed type, requiring little
maintenance...or "maintenance free". While not totally maintenance free, at
least you don't have to worry about water levels in the cells. Keeping the
batteries and terminals clean is about all that is required for these batteries.
These auto batteries are NOT designed to be deep-cycled and recharged many
times. You can only deep-cycle these type batteries a couple dozen times before
they go bad. They are designed to deliver high starting currents for short
periods of time and be quickly recharged by the engines alternator
with voltages typically as high as 14.4
-14.6V (different than RV batteries).
However, the
RV or 'House'
batteries are deep-cycle 'marine' type batteries designed to
be deeply discharged (boon docking) with carefully controlled recharging cycles
with voltages around 14.2 - 14.4V
(different than auto batteries).
They can be deep cycled & recharged several hundred times depending on several
factors. These RV batteries are vented to allow gases (hydrogen) generated
during the recharging cycle to escape. These type batteries need regular
maintenance to maintain the proper water levels in each cell. Note the water is
'boiled' off during recharging, not the acid, so water is all that needs to be
added ...DISTILLED water only please!
Note:
There is a new type RV deep-cycle battery called the AGM or Absorbed Glass
Matt that IS sealed and IS near maintenance free. Some coach builders are
providing these newer type batteries. They are very good, but pretty expensive.
Your coach literature should tell you what type batteries you have. For an
in-depth article on these new batteries. . .see the Nov. 2004 issue of Motorhome
magazine, pg.50.
Assuming you have the
conventional lead-acid type batteries, they are most likely NOT hooked together
for charging, due to the DIFFERENT
charging conditions required. Most charger/inverters are programmed to
properly charge deep-cycle batteries, NOT starting batteries.
How can you tell if
they are hooked together? While parked and plugged into 'shore' power,
your power monitoring system will tell you the voltage of your RV/house
batteries.
-
If your monitor
system has a switch to also tell you the voltage of the engine/chassis
batteries...then they are not hooked together.
-
If your monitor
system only has one position on the volt meter, use an external volt meter and
measure the voltage on both sets of batteries. If they are hooked together, they
will read about the same voltage. . .if the voltages is significantly different,
they are not hooked together.
SUMMARY:
If your RV/Chassis
batteries are not hooked together with the Engine/Starter batteries, you may
want to consider using an external
charger to keep the Engine batteries topped-off while you are parked.
Today's newer
motor homes have 2 to 3 slide-outs (even quad slides) plus leveling jacks and
are often run from the Engine/Chassis batteries instead of the house/RV
batteries and draw a sizeable load. The coach builders are not very careful on
how many circuits they wire on the engine battery circuit.
With no re-charging while parked, your
engine batteries will not last as long as you might expect.
Regular Lead-Acid batteries will
discharge about 12% per month with no load and no charging.
You can tell if your
slide-outs and jacks are run from your Engine batteries by measuring the voltage
after you shut the engine off (12.6v to 12.9v or higher), and then again during
or after you put your jacks down and your sliders out (12.0 to 12.4 or lower). I
finally measured the current drain on my engine batteries with everything
'off'...0.6 to 0.7 AMPs! That is ~650ma of continuous drain on the engine
batteries...during storage that will drain your batteries in a couple of weeks
to very low levels, which will damage your batteries...in two weeks my 3 yr. old
FTL batteries got down to 11.8V...BAD.
Note: Some
high-end coaches do have a 'differential monitoring' system that monitors the
voltage on both strings of batteries and uses a relay to switch the
Inverter/Charger between battery strings to maintain a proper charge on both
sets.
SOLUTIONS:
-
External
Tri-state charger - several good brands exist to safely keep
your engine batteries charged. This is the solution I recommend. I use a Sears
Diehard Tri-state charger. It has an automatic regular mode, a deep
cycle mode and a start mode. My external charger, when set on the automatic 2 amp - slow
rate will initially go as high as 8 amps, then taper off down to 2 amps, then to
zero as it reaches full charge. . .it will top them off quicker than a small
trickle charger. It will cycle on/off to keep the engine batteries at full
charge. It will not over charge them.
The model no. is
200.713101, however, it is over 5 years old and may not be a current model
number. Note - this is not a special charger...it is just a plain ole
Sear Diehard Battery charger that has 3 modes...2 amp auto - 10A auto deep cycle
- 60amp manual start. I have a convenient compartment next to the batteries
where I carry the charger. Since it is portable and not wired in, I remove it
occasionally to charge the car batteries when we forget and leave a dome light
on all night!
-
Wired-in
trickle chargers - there are a couple commercial products I've
heard about like the Trik-L-Start by LSL Products; Echo ~ Charge by Xantrex; and
Start_It by Vector Electronics.
-
The
Trik-L-Start
connects the engine batteries to the RV batteries with a
charge controller in
between.
It contains isolation diodes so you can charge the engine
batteries, but can't accidentally drain them. The only draw back I saw was a
charge current of 5 amps. That will trickle charge the engine batteries, but
that will take several hours to bring them to full charge, depending on how
drained they were. For more info see the LSL web site -
http://www.lslproducts.com/TLSPage.html for $48.95. Winnebago sells
them in their store for around $60. A few owners, early on complained to
Winnebago and received one for free. My understanding now is that Winnebago has
stopped supplying the unit for free.
-
Echo ~ Charge
- Thanks to Bill Wright and Ray Egan for the links to the Xantrex Echo-Charger info.
Product Features
15 A maximum charge
current
Automatically adjusts
for 12 or 24 volt battery banks (both battery banks must be the same DC
voltage and
battery type)
Automatically
switches on/off without affecting the in-house battery bank or over-charging
Uses excess current from the primary
charging source
Built-in thermal and
over-current circuits
Reverse polarity
protection
Easy three wire
installation
One year warranty
See
http://www.xantrex.com/web/id/8/inter.asp click on the RV
Catalog (pdf file), then go to battery accessories...Echo Charge
-
Start_It
by Vector Electronics - stocked at Camping World ~$30
Start-It®
1.5 amp on-board automatic float charger trickle charges 12V battery as needed
and turns off when battery is fully charged. Level indicator shows charging
status. Built-in circuit protection guards against overcharging or short
circuit. Ideal for cold weather battery maintenance and improved starting
performance.
http://www.campingworld.com/browse/skus/index.cfm?skunum=24849&tab=spec
 BatteryMINDer
is a Battery Charger:
Available in 6, 12,
24 and 36 volt models
Amps dependent upon voltage required
Maintenance Free
Deep Cycle – Golf Car, Marine, Solar
Charges SLA/VRLA, AGM and Conventional wet liquid batteries
Polarity reversal / short circuit over temperature protection
Charge indicator shows correct connections plus
'blinks' when battery reaches full charge
Charges any size battery from U-1 up to 8-D
Charge/Maintain up to 4 batteries (of similar type - in parallel)
http://www.batterymart.com/batteryminder.php
-
Home brew
-
-
Some folks have wired their two battery strings together, using diodes
and hopefully in-line fuses. . .but I
don't recommend you
do this. . .
-
Wire/cable needs to
be big enough to handle the current draw...
-
Diodes need to be the
right size and wired with the correct polarity...
-
In-line fuses should
be used for over current protection and need to be sized correctly...
-
Wiring your two
different battery types together using the house charger/inverter is NOT a good
idea as explained above. The two different type batteries have different
charging voltages, different internal resistance, different charging rates, etc.
-
If it's really hot
weather and you choose to run your generator running down the road to cool the
coach in addition to your auto A/C, your generator will activate the RV charger
to charge the RV batteries AND the engine alternator will be charging the engine
batteries. IF you have the two batteries tied together, even with an isolation
diode, the engine batteries will be seeing a charge from the engine alternator
AND the RV charger/inverter...not good.
-
Wiring mistakes,
slips, accidental short circuits with wrenches, etc. can cause serious injury,
fire or cause a battery to explode! Short circuited batteries will provide an
infinite amount of current for a few milliseconds. . .long enough to do serious
damage, like melt your wrench, vaporize your wedding ring, maybe explode,
splattering sulfuric acid on you and your surroundings...be careful!
-
Using the
MOM or Booster
Switch - I recently heard from some readers that he and some
friends came up with the idea of 'wedging' closed the Booster or Momentary
switch that is used to tie the two battery strings together so the shore power /
charger can charge both strings of batteries. Here is an anonymous quote...
- "Just read your article about batteries on the
CAT RV Club website. I found it to be an excellent source of valuable
information and presented at the "Batteries for Dummies" level, which is
appropriate for me."
- " I have been keeping my batteries charged using
a "trick" shared by several friends. Most coaches have a Momentary switch
which uses the RV battery power to help the chassis batteries to start the
vehicle. This links both systems together, momentarily. I was told to place
an object under the spring loaded momentary switch to hold it in the ON
position and that will cause the shore power to charge the coach batteries.
Gee, maybe that's why I have to change out ALL of my batteries once a year.
Ya think??? Any way, thanx for the good info.
"
Thanks for the input! I never thought
about using the MOM switch but my guess is that you guys are not the first
or the last to come up with that idea. Guess we now know why the MOM switch is
designed to be Momentary.
Besides needing different charging
voltages, cycles, steps, etc. the different types and brands of batteries
have different plate construction and therefore different internal plate
resistance...this causes parasitic current drain between different type
batteries when hooked together.
So, if you left them connected with no
shore power, the batteries would 'drain' from one set to the next, depending
on which set had the lower internal plate resistance.
During charging, the shore powered
inverter/charger is set for charging RV deep cycle batteries at around 14.2
- 14.4V while the engine batteries need a higher voltage around 14.8V to be
properly charged.
The same condition applies for mixing
battery brands together in any battery application...always use the same
brand and the same 'age' batteries in any application, dry or wet.
Bottom line - don't
mix different types or brands of batteries in the same circuit.
This chart
illustrates the 3 levels with good charging. Bulk that typically starts at
around 12.2 to 12.6v...rises to the Absorption level of ~14v followed by a Float
or maintenance level of ~13.6v.
If you have comments
or feedback, send an email to -
webmaster@freightlinerchassisownersclub.org
Created 4/01/05
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