Chassis Batteries Discharging

[Walt Pocock]

Hello, Thank you all for sharing your expertise on these complicated rigs.
My current problem is my chassis batteries will go dead from a full charge in about 48 hours. When the coach is unplugged from shore power, main switch off and Echo Charger disconnected the batteries will go from 12.8V to 5V in 48 hours. I don't know what is still hot after the main switches are off so I don't know where to start looking for the fault.
Thank you for any suggestions.

[Keith Moffett]

Walt, better minds than mine will no doubt help.
Let me suggest that you post the age of the batteries, type (wet or gel), fluid level and condition of connections.
This will help others help you.
Also, by main switch are you refering to the switches in the battery compartment or the one by the entry door?

Keith

[Walt Pocock]

Kieth, Thanks for the head's up.
The batteries are wet and about two years old. The connections are great. The switch is the main in the battery compartment. I should have noted that the batteries will stay charged if I disconnect them.
Thanks   

[Lawrence Tarnoff]

Guys ...

I, too, am interested in the answer as my coach chassis batteries on a couple of occasions have died.  One of the posters suggested in another string that the Delco radio may be drawing from the chassis battery.  My batteries were new last fall.  Like Walt, if I turn off the switch in the battery compartment there is no problem.

Larry

[Gerald Farris]

Walt,
The ECM (engine control module) for the C12 on your coach is wired to the chassis batteries before the cutoff switch, and it has nearly a 2 amp constant draw for the keep alive memory. To solve this problem, the coach needs a charging source (either solar or shore power) or a heavy duty marine style disconnect directly at the chassis batteries. 

If the batteries are disconnected from the ECM, the keep alive memory is lost, but it will be rewritten in about a minute after power is restored. 

Gerald

[Dave Atherton]

Walt, Gerald is 100 percent correct on your battery drain. This is one area that many people have
problem with ( power to the ECM. ) The connection is direct to the ECM from the battery's that has
a inline fuse. another problem that follows dead batteries is incorrect voltage from ECM to sensor's,
engine will not start until correct voltage to sensor's is present. Dave Atherton

[Mike Groves]

Walt,
The ECM (engine control module) for the C12 on your coach is wired to the chassis batteries before the cutoff switch, and it has nearly a 2 amp constant draw for the keep alive memory. To solve this problem, the coach needs a charging source (either solar or shore power) or a heavy duty marine style disconnect directly at the chassis batteries. 

If the batteries are disconnected from the ECM, the keep alive memory is lost, but it will be rewritten in about a minute after power is restored. 

Gerald

All,

They may have done something different between the 1999 and 2000 year Marquis.   I store my 1999 a month at a time, with only the disconnects switches off for both House and Chassis, and I've not run down the chassis batteries yet.  The lowest I've seen them is at 11.7V after a month away, and I store undercover at a storage facility.  I had read about the batteries running down on this forum, so at first I returned after each week to check and run the generator, then 2, then 3, then a whole month.  So, must be a different approach pre 2000 year. 

Any other 1999 Marquis owners notice this on theirs?  Sorry a bit off topic, but I find the difference interesting and wonder why the 2000s would drain so quickly (48 hrs?).

Thanks, Mike

[Michael Rump]

All,

After reading the posts about chassic battery discharge on the C12, I am also interested in learning about the marine switch to eliminate battery drain.  I believe our coach was always stored with shore power on, and therefore never experienced the referenced battery drain.

What should I look for to determine if this is applicable to our coach as we plan to store it without shore power?

Thank you in advance!

[Edward Buker]

Mike,

12V batteries are essentially dead at 12.2V so I am not sure how your batteries will hold up if they end up at 11.7V repeatedly. Normally you would not be able to start the engine without using the switch to tie the house bank in at those voltage levels.

If you can go a month and start the coach normally without the back up battery bank involved it could also be that someone has modified the wiring and moved the ECU voltage source to turn off with the coach switches.

Later Ed

[Edward Buker]

Mike,

If you have a DC amp meter capable of measuring 5 to 10 amps, you would remove the chassis + main lead that goes to the coach from the starting battery bank and put the meter in series with it. You should have all known loads like lights turned off. If you see between 1 to 2 amps you are powering the ECU. If you see .25 amps or less you are probably not powering anything but minor electronic memory items like in the dash radio. If you see the normal ECU load between 1 and 2 amps and you were leaving the coach unplugged to a 120V source for an extended period of time beyond several days, you would disconnect the main plus battery lead and leave it disconnected until you return.

Later Ed

[Mike Groves]

Mike,

12V batteries are essentially dead at 12.2V so I am not sure how your batteries will hold up if they end up at 11.7V repeatedly. Normally you would not be able to start the engine without using the switch to tie the house bank in at those voltage levels.

If you can go a month and start the coach normally without the back up battery bank involved it could also be that someone has modified the wiring and moved the ECU voltage source to turn off with the coach switches.

Later Ed

Ed,

I will admit to never having tried to start it after a month without first starting the generator.  The generator has always started even at 11.7V, so that's been my bridge - not the house batteries.  Doesn't take long, after the generator has been running to start the coach.  I'll be going down in a couple of weeks (that will be over 1 month) and I'll see what happens.

Thanks,
Mike

[Michael Rump]

Ed,

Thank you for the information for checking the ECM draw and the battery work around.

Best regards,

[Walt Pocock]

Thanks everyone for the comments and input on my battery draining problem. It appears all that should still be connected after the main switch is off is the ECM and possibly the clock in the radio which are minimal drains (2 amps +/-). Since my batts will go dead in 48 hours with the main switches off and the solar on I must have a situation unique to my old blue Beaver.
I will use the volt/ohm/amp meter to identify the actual draw.  The only other thing I can think of is to check the switch itself and, if it's OK, continue to disconnect  the positive cable when parking for short or long term. 
Thanks again, Walt

[Andy Clark]

Hey, Walt.... Careful with the "Old Beaver" stuff, eh?  <GRIN>

Andy

[Keith Oliver]

Walt:

On my own "old Beaver" I put in a positive disconnect at the negative terminal.  I found a knife switch at an RV store.  Seemed like tailor made for the job.  I never had that problem again.