Alternator or Battery Problem Don't Know

[sean_keadle]

I have a 71 Winnebago with a Dodge 318.  The Dual Battery Switch doesn't work.  When you put a jumper cable from the Coach battery to the Chassis battery it will start.  When you remove cable it dies.  I pulled alternator took it to Oriley's to have tested, and it passed.  So I replaced the Voltage regulator.  Still have same problem.  Behind the battery compartment, there is a solenoid (looks like a old Ford starter relay)  and a breaker.  I went to a local RV parts place got new breaker, but said they didn't have solenoid.  I replaced breaker but still having same problem.  Any help would be appreciated.

[DaveVA78Chieftain]

When you put a jumper cable from the Coach battery to the Chassis battery it will start.  When you remove cable it dies.

Sorry but that says dead chassis battery.  First get that fixed.

Get yourself a voltmeter.   You need to make sure that when the engine is running you have 13.8 to 14.5 volts across the chassis battery terminals.  That tells you the charging system is working properly.

Once thats all working ok, then you move over to the constant duty solinoid.


When 12VDC is applied to the small terminal (from NORM/DUAL/MOM dash switch) the relay energizes cross connecting the chassis and house batteries.  No voltage is applied when dash switch is in NORM position.  12VDC applied in DUAL/MOM position.  Ignition key also has to be on to get voltage to the solinoid.  You can normally hear the switch energize/deenergize.
Replacement solnoids are available at RV and Marine supply places though some auto supplies do carry them.  It is NOT a starter relay.  It is called a constant duty solinoid designed to be energized for hours at at a time that can handle a minimum of 100 amps.

Dave

[LJ-TJ]

Hey Dave what wire do you hook up to the left side? What wire goes to the little center pin? What wire goes to the right side? What side does the house battery hook to? What side does the Gen set hook to? Thanks Mate.

[DaveVA78Chieftain]

The Generator always goes to the house battery side.

As I said above, small (center pin) is wire from the dash switch (small signal [dash switch] controlling high amperage signal [battery]).

Does not matter which side you connect to.  Just make sure generator is connected to same side as house battery (B+).  Chassis battery (B+)connects to opposite side.  See battery portion in figure below which is for a 74 or later rig (electronic ignition).

The solinoid relay is nothing more than an On/Off switch.  It is designed to be ON for extended periods.   You can not replace it with a Ford starter relay because the starter relay is not designed to be ON for extended periods and will fail fairly soon.

Dave


Link to actual picture: http://i286.photobucket.com/albums/ll120/BaileyDave/Winnebago/StartingCircuit.gif

[LJ-TJ]

  Thanks Dave

[sean_keadle]

Ok please don't take this as arguing, I'm just wanting to fully understand.  My redneck logic tells me if the alternator is working properly; if I pull of the jumper cables off the battery after the engine is running the alternator should be pumping out enough vaults to keep the engine running.  I know that doesn't work on new cars but it allways served me well in the past with old one.  Also does the dual battery switch operate the constant duty solenoid?

[DaveVA78Chieftain]

Not seen as arumentative.  You made a good observation and it deserves an honest answer.

Yes, the dual battery switch (typically labeled in a Winnebago as Norm/Dual/MOM) operates the constant duty solenoid.

The battery disconnect test you performed is based on the premise that the only things that can be defective are the alternator, reulator or battery.  It does not acciunt for wiring or connector issues.  Additionally, the battery acts as filter during normal system operation.  It absorbs voltage spikes that can damage sensitive equipment like radios.  Thats why it is normally not viewed as a effeciant test method.

I have not said that the charging system is working.  I only said the battery was bad and needs to be replaced.  Once you have that portion resolved then you can dig deeper into other possible issues.  Can you use one of the house batteries in place of the chassis battery for the purpose of testing?  Yep.  Just be aware that if the house battery is a true deep cycle battery then you could damage it.  Deep cycle batteries are not designed for the high amperage draw of a starter.  Ok for once in a while but not on a regular basis.

You will find a description of the charging system and troubleshooting info on my web site:
http://dave78chieftain.zxq.net/index.html
Menu is on the left side.
There is not much to the charging system.  Most likely you have a bad connection.

Dave