New Owner Questions About Electrical Stuff

[Jamo]

We have a new (to us) '89 Winnebago Chieftain, 27 feet with a 454 Chevy engine.  There are two switches on the dash labeled "Aux Battery" with "Off" and "On".  Question: does it matter where I leave this switch when everything is shut down and shore power is not plugged in?  Also, there is another switch labeled "Battery Mode" with "Dual" and "Mom" below the switch.  What is this switch used for?

Also again, The coach batteries are two 6 volt golf cart batteries and they are toast.  They are frozen and the sides of the cases are bulged out. I'll be replacing these two batteries in a few months.  Do the golf cart batteries provide any advantage over regular, deep cycle batteries? 

John

[DaveVA78Chieftain]

Pdf page 23 of the 1989 Winnebago Operators manual

[Jamo]

Thanks for the pdf file.  Unfortunately my computer and service are too slow to download all 82 pages. (I waited 11 minutes and only had part of the first page downloaded.) Any chance you could just send me page 23?

Thanks,

John

[DaveVA78Chieftain]

BATTERY CONDITION METER AND SWITCH -Optional
This gauge allows the driver to monitor the state of charge of batteries in the motor home. The
battery condition switch is used to select the battery to be monitored. Depress the left side to
monitor the automotive battery; the right side to monitor the auxiliary battery.
To obtain an accurate reading:
1. The battery mode switch must be in the neutral position.
2. Both the automotive engine and the auxiliary generator engine must be stopped.
3. An interior light should be turned on to provide a small load which draws off battery surface charge.

BATTERY MODE SWITCH
A & C Body Motor Homes
The battery mode switch is used to connect the auxiliary batteries to the automotive electrical
system, allowing them to be recharged by the engine alternator while driving. The momentary
(MOM) position can be used to provide additional starting power from the motor home auxiliary
battery, if for some reason the automotive battery is discharged.

DUAL Position- Automotve and Coach Batteries are connected together
Neutral Position - Automotve and Coach Batteries are disconected
MOM - Press while turning ignition key to Start position

CAUTION
Damage to the automotive alternator can occur if·the 110 volt auxiliary generator is
started while both btteries are connected. Never leave the battery Mode switch in
the DUAL position while parked as it could allow both batteries to discharge.

AUXILIARY BATTERY SWITCH - Optlonal (A Body Motor Homes Only)
This switch allows you to conveniently disconnect the auxiliary battery during prolonged storage
periods without the need for removing a battery cable in the battery compartment. This disconection
reduces the possibility of battery drain by electrical devices (such as clocks) which are
energized continuously.
  Press the switch momentarily and release to connect or disconnect the battery. The switch is
spring-loaded and will return to the neutral position when released. An indicator light located next to
the switch will be illuminated while the auxiliary battery is connected to the system.
  The auxiliary battery switch is intended to be used to disconnect the auxiliary batteries during
extended periods of non-use or for seasonal storage. It shouId not be used in an attempt to
"save' the auxiliary batteries while using the 110 volt system.

CAUTION
NEVER disconnect the auxiliary batteries while the utility power cord (shoreline) is plugged into
either the generator or an external receptacle. Electronically sensitive equipment, such as
TV's and VCR's or high-amperage equipment, such as the refrigerator and electric step, may be damaged If
operated while auxiliary batteries are disconnected.

[Rickf1985]

To add to what Dave said, when you disconnect the batteries with that switch they are totally disconnected and they will not charge either. The relay that operates that switch works off of the power in those batteries so if they are totally dead it will not switch over. You will need to get a solid 12 volts to the system to get the latching relay to switch over. You might want to get those batteries out of there while they are frozen, if they thaw and spill acid all over you are going to have one hell of a mess to clean up. Nature is on your side right now holding it all together.

[Jamo]

Dave and Rick thanks for all that great information. I'll print this stuff out and go up to the rig and fiddle around with everything to see what I can figure out. Any thoughts on whether two six volt golf cart batteries are any better than a single (or two) twelve volt batteries for the coach?

John

[DaveVA78Chieftain]

From my perspective, one 12VDC vs two 6VDC batteries in series comes down to cell construction which also means two 6VDC batteries will typically take up more space than one 12VDC battery.

Automotive 12VDC batteries are designed for high amperage over a sort period of time (e.g. engine start).  As such they are designed with many thin lead plates.  So, since the concern is high amperage over a short period of time, the Cold Cranking Amp (CCA) rating is a measurement of the number of amps a battery can deliver at 0°F for 30 seconds and not drop below 7.2 volts. This design also allows for faster recharging by a engine alternator.  Discharging them below 50% capacity can damaging them resulting in short battery life.

6VDC Deep cycle batteries (e.g. golf cart batteries) use much larger plates that are more suited to constant amperage draw over time.  This beefier plate design also stands up better to being discharged below 50% capacity though that is still not good for any wet cell battery.  It is this heavier construction that provides the longer life of 6VDC wet cell batteries.  These batteries are rated in amp-hours which is how many amps can be drawn from the battery over 20hrs.  Example, a 100 AH battery can supply 5 amps over 20 hours.  With that said, you are at 50% capacity (50 AH) at approximately 10 hours.  That means a 6VDC battery pair  rated at 220AH only has 110AH of usable energy if you do not want to start shortening total battery life.

12VDC RV/marine batteries construction is in between those 2 versions (a compromise).  Used for both engine start and/or trolling motor operations.

So, the generally accepted optimal design is a automotive battery for the chassis, and two or more pairs of 6VDC batteries for the house.

With that said, one concern is if you use the alternator to recharge the house battery set in this optimal design, is that you are placing the automotive battery in parallel with the house batteries.  A weak chassis battery can drag down the house batteries in this condition because they are all trying to achieve a balanced voltage setting.  The alternator has to work much harder in this situation in order to bring what it sees as one large battery bank.  So, effective use of the DC system requires keeping all components in good working order.

[Jamo]

Dave, thanks for that great explanation! Maybe by Spring I'll have a handle on this rig and its systems.

John

[Jamo]

One last thing about my frozen coach batteries: When I remove them will I be able to use either the generator or shore power for interior lights without getting new batteries installed first?

John