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Topic: Perplexing 12v Charging / Starting Problem - 1994 U240 (Read 522 times) previous topic - next topic

Perplexing 12v Charging / Starting Problem - 1994 U240

I hate electrical problems and it looks like I have two.  Since they both started at the same time I imagine they are related.  I've chased this for the last two days and offer it to you folks to impart any wisdom!

1) The batteries fail to charge with shore power, but ALL will charge with the generator OR engine running
2) The engine will not start with all new and/or verified good, charged batteries unless the boost switch is on

This is on a new-to-me 1994 U240.  There are 2ea 12V 8D batteries in the last storage bay on the rear driver's side and 2 Optima red top automotive batteries in the engine bay mounted very near the bumper.  As I'll describe shortly, the set-up is a bit confusing as it appears they are all wired together... ie no specific starting and house batteries.

After a 3 day trip in the boonies  in cold weather (an anomaly for this coach as its home is Lake Havasu, AZ used with shore power 98% of the time) I realized the batteries were toast even after a load test by my mechanic not long before the trip.  After 2 nights we changed our plans to camp at a park with shore power.  The last day the coach wouldn't even start with the boost switch on unless generator was running, but the alternator would take over on the road.  We got home, no problem.

The 2 AGM 8D batteries that came with the coach were at 10.5v even after a week of being plugged into shore power at home awaiting time to replace.  The coach wouldn't even start with the generator running and boost on after that week.  I replaced both with lead-acid since dry camping is minimal and the price was so much less.  The two optimas tested fine and are holding a charge.  The amp-hour meter showed +2 after installing and running the genny as a matter of maintenance.  I worked on the heater motors (lube) and ran those for about an hour the same day along with other 12v systems.  The amp-hour meter was at -20 or so when done but I plugged in shore power assuming they would charge back up.  2 days later the meter was at -33 with nothing left on!

I realized with my trusty multimeter, that no batteries get charged when connected to shore power (no doubt the problem the last day of the trip).  On the voltmeter above the doorway, I show just a little less than 120v and positive polarity coming in.  The same plug charged the coach the weeks and months before.  This is the case with the boost on or off.  All breakers were checked on the bed and on the Freedom 25 inverter/charger.  I also checked the settings on the inverter remote panel.

ALL of the batteries charge when the generator is running.  The power is fed to one of the 8D's and transferred to all of the others.  This is the same with and without the boost switch.  After a few hours running the genny the new batts. were back to near 0 on the amp-hour meter.

ALL of the batteries charge when the engine is running.  Again, with and without the boost switch.

My problems accumulated:

The engine failed to start although the dash was showing 13v.  The starter engaged but could not turn the motor.  With boost on, it fired up perfectly.  I turned my attention to the optimas.  Long story short, I disconnected them completely from the system and the same problem existed.  No boost, no start and perfect starting with boost.  The optimas are not the starting batteries.  They are tied into the 2 8D's.
 
I continued to chase around with my multimeter until I disconnected all but one 8D battery.  The coach still had power and the same problem existed (no boost no start and start with boost on).  It appears that all that is going to the other 8D is the main leg that ends up at the inverter.  All systems are connected to the other 8D.

Questions:

-What is causing the boost issue? The boost or ignition solenoid? Regardless of how the batteries are wired, all was fine before.  No boost was ever needed.  What is the boost tied to if all batteries are wired together, or is this just another symptom?

-What is causing the no-charge issue.  The DC switch?  How would this tie into the issue above?

-Are the batteries connected correctly?  Should the isolation happen (automatically) somewhere else on the coach?

Please tell me it's something simple!

Re: Perplexing 12v Charging / Starting Problem - 1994 U240

Reply #1 –
OK, I can describe how it was wired from the factory-- no idea how subsequent owners modified it:

Alternator charges both battery banks from either shore power or generator.

CONVERTER was standard, and ONLY charged house bank from either shore power or generator.

Inverter charger was an option-- again only charge house bank from either shore power or generator.

SO, while plugged in, the house bank should remain above 13.0 VDC.

If no subsequent charger added, the chassis batteries will continue to drop in voltage.

If house bank above 13.0, the use of the BOOST switch should allow an easy start, as it adds the fully charged house bank to the chassis battery.

 
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Perplexing 12v Charging / Starting Problem - 1994 U240

Reply #2 –
Quote from: wolfe10 –
OK, I can describe how it was wired from the factory-- no idea how subsequent owners modified it:

Alternator charges both battery banks from either shore power or generator.

CONVERTER was standard, and ONLY charged house bank from either shore power or generator.

Inverter charger was an option-- again only charge house bank from either shore power or generator.

SO, while plugged in, the house bank should remain above 13.0 VDC.

If no subsequent charger added, the chassis batteries will continue to drop in voltage.

If house bank above 13.0, the use of the BOOST switch should allow an easy start, as it adds the fully charged house bank to the chassis battery.

 

My idea would be to isolate the starter lead and hook that onto on the 8D's and leave the other 8D and optimas connected.  Would this pose a problem considering the wiring upstream? 

What would cause the boost switch to operational on only one battery?

Re: Perplexing 12v Charging / Starting Problem - 1994 U240

Reply #3 –
Quote from: 454Rocket –
My idea would be to isolate the starter lead and hook that onto on the 8D's and leave the other 8D and optimas connected.  Would this pose a problem considering the wiring upstream? 

What would cause the boost switch to operational on only one battery?

Not sure I understand.

Yes, one 8D in good condition and fully charged will be fine for starting your Cat 3116.

Optimas are generally start batteries, so suspect the pair of them are the start batteries.

I would not recommend mixing wet cell 8D's and the Optimas in the same battery bank-- they are different kinds of batteries.

And, the boost switch COMBINES the two battery banks.  Easy to verify.  Check voltage at each bank-- will be different.  Engage the boost switch and check voltage again.  The two banks will be the same since they are not "combined".
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Perplexing 12v Charging / Starting Problem - 1994 U240

Reply #4 –
I have been through similar problems. The very first thing I would do is Remove and clean/wire brush all cable ends,. It sounds like the engine batteries are not getting a good ground. That would keep them from charging and from supplying full power to the starting system. Also, clean the cables that attach the house batteries to the Inverter/isolator, these are bolted together on the rear of the house battery terminals.They have a tendency to build up a carbon like substance that causes the continuity to fail. Last but not least check the isolator itself to make sure it is working properly. Good Luck...  ^.^d 
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Gerry & Brenda
CHARLOTTE HARBOR, FL
1994 Grand Villa - # 4466
U300 Unihome - 6V92 Detroit
4 speed Allison - Jake Brake