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Topic: Chassis batteries not charging when engine and generator running (Read 1387 times) previous topic - next topic

Chassis batteries not charging when engine and generator running

I just noticed the when I run the generator and the engine is running the chassis batteries do not charge - dash voltmeter is around 12+ volts .  I get a reading of around 13.5 when I turn on the boost switch.    Of the many things that could be wrong, any ideas on where to look first?

Problem solved!  See reply #23
Larry Rubin
2004 U295 38' build 6278
2014 Jeep Cherokee

Re: Chassis batteries not charging when engine and generator running

Reply #1 –
Larry, I would start by checking the isolator under the bed, using a VOM, check voltages, 1 at a time, center post goes to engine driven alternator the outside 1 goes to chassis battery, other goes to house batteries.
Good place to start.  With rear engine runnng at fast idle, you should have about 13.5 to 14.5 on center post, then about 1 volt less going to each other pose due to drop thru the diodes.
If not, I would guess the might be a problem with the isolator.
Sounds like the contactor is working that connects both together.
Maybe some one will provide a simple wiring diagram for your coach.
Good Luck
Dave

Re: Chassis batteries not charging when engine and generator running

Reply #2 –
Larry,
 
Are you sure that the engine alternator is charging when the engine is running alone?  Others with more knowledge will provide more specifics, but when my alternator was shot, the only time my chassis battery charged was when the "boost" was turned on with the generator running.
 
If you want the chassis batteries to charge while the generator is on without hitting the boost switch, add something like "Trik-L-Start", which allows charging when coach is plugged in or when generator is running. Unlike the Boost switch, Trik-L-Start has a diode ? that prevents a weak coach battery from discharging the chassis battery and vice versa.
Don Hay
'92 Grandvilla, U-280
The Hayfever Express
Build #4055
'97 GEO Tracker
Life is like licking honey off a thorn.

Re: Chassis batteries not charging when engine and generator running

Reply #3 –
Larry, Don is asking a very good question, which is "Are you sure your alternator is charging your chassis batteries?"

When I read your question, I thought of several questions to ask, which you would have to answer before I could answer your question.

Here is why:
Battery voltage readings can be very misleading.
Dirty connectors between your chassis batteries and the dash voltmeter could result in voltmeter reading lower than the battery voltage, or in eratirc readings at dash voltmeter.
Whie discharging, battery voltages will be low.
While charging, battery voltages will be high.

If you have a "battery voltage - state of charge" table you will see that voltage of 12.7 volts = 100% charge, while 12.2 volts = 50% charge. However, 12.2 volts can occur with a 98% charged battery while providing 160 amps to your inverter to run your convection oven. Turn off the inverter and the battery voltage will rise back up spontaneously, rapidly at first, then more slowly over the next few hours (yes hours). If you take a voltage reading two hours later it will be close to the reading you really need to determine the state of charge, however, 10 hours later, the voltage will probably be a little higher. I say probably because temperature also effects battery voltage, so a winter time reading of 12.2v is somewhat different than a summer time reading of 12.2v.

The boost switch "ON" closes a solenoid which connects chassis batteries to coach batteries making one larger battery bank.

With boost "OFF", dash voltmeter shows chassis battery voltage with ignition on. The generator on or off will not effect this reading. The main engine on or off should effect this reading. You should see 12+v with engine off and 14+v with engine on.

With boost "ON" dash voltmeter shows (chassis + coach) battery voltage with ignition on. The generator on or off should effect this reading. The main engine on or off should also effect this reading. You should see 12+v with engine and genset off and 14+v with engine or genset on.

The alternator output is controlled by the chassis battery voltage but charges both chassis and coach batteries (via the diode isolator block - mine is behind the driver rear tires). The generator, which is started by the coach batteries, charges only the coach batteries unless the boost is on or you turn on your converter.

Here is what I would do:
With everything off, check voltages of chassis and coach batteries at batteries for a couple days. Start main engine with boost off and check voltage at coach batteries. If 14+v at batteries, all is well. Now check dash voltmeter, if still only 12+v, look for bad wiring or connectors. If only 12v or less at chassis batteries, check alternator output.
Wyatt
96 U320 40 WTFE, build 4943
84 Toyota Supra towd
2015 Jeep Wrangler towd
Victoria, BC, Canada

Re: Chassis batteries not charging when engine and generator running

Reply #4 –
All excellent info and I will follow your suggestions to check things out (as best I can since the house batteries are buried inside the front bay so checking at the batteries themselves is loads of fun)  - I'll get back with results.
Larry Rubin
2004 U295 38' build 6278
2014 Jeep Cherokee

Re: Chassis batteries not charging when engine and generator running

Reply #5 –
It is as I first described it.  The generator effects the chassis batteries voltage.  With the generator off and the engine on, I get 14+v measured at the chassis batteries  Turn the generator on with the engine running, the voltage slowly goes down to 12.5+v on the chassis batteries  - measured at the batteries, at the battery isolator, at the dash voltmeter and at the accessory plug on the dash (the last two being about half a volt lower.)  Turn the generator off and the chassis voltage immediately goes up to 14+v and confirmed at all 4 measurement points.  The house batteries voltage act as you would expect it to.

I have not checked the alternator output at the alternator although as I say, with he generator off, I am getting 14+v with the engine on.   

Could the trouble be in the isolator?
Larry Rubin
2004 U295 38' build 6278
2014 Jeep Cherokee

Re: Chassis batteries not charging when engine and generator running

Reply #6 –
Larry,
It appears that somehow the generator is loading the chassis battery when it is on as indicated by the voltage drop.  The only thing I can think of is that somehow the generator starter's source is the chassis battery, not the house batteries and the starter is staying engaged.  I would not think that the generator's starter would draw more current than the engine's alternator would put out unless it is like mine which requires about 1000 RPM before it starts providing power.  Please lets us know what you find out.
John Cooper
'91 GV 36'
Oshkosh chassis
Cat 3208T 300HP

Re: Chassis batteries not charging when engine and generator running

Reply #7 –
Thanks a heap to Mike for listing some combination's.  That got me thinking that since there are 5 items that may be on or off - Engine, Shore Power, Generator, Charger (I have a Prosine on which I can turn the charger off), and the Booster switch, then there are 32 combination's.  Now a few of these aren't very interesting, e.g. everything off, but it became a fun exercise to document the charging possibles for each combination.  So here is a table showing all 32.  Note that I have no claim to accuracy of the charging and not charging  columns because I just used some simple logic vs. any real knowledge.  Please, please take a look and let me know what needs to be changed.  And I'd like to fill in the last column with more trouble shooting ideas if the charging and not charging isn't as it should be.    That of course, is what got this thread started.

Larry Rubin
2004 U295 38' build 6278
2014 Jeep Cherokee

Re: Chassis batteries not charging when engine and generator running

Reply #8 –
Correction to the notes on the table I attached to my last post ---- my problem is combination 10 not 2 as listed in the notes
Larry Rubin
2004 U295 38' build 6278
2014 Jeep Cherokee

Re: Chassis batteries not charging when engine and generator running

Reply #9 –
There is at least one scenario that would cause the symptom:  chassis battery charged by alternator UNLESS the generator is on (and therefore powering the inverter/charger to charge the house battery).

If the alternator sense wire is incorrectly installed on the house battery lug of the battery isolator instead of the chassis battery lug, the alternator/regulator would "sense" that the batteries are fully charged when the generator/charger are on since they would be starting to charge the house bank in bulk mode at 14+ VDC.  Therefore, the alternator would properly read that the battery was fully charged and NOT charge.

So, the alternator would not be charging either bank and the inverter/charger would only be charging the house bank.

Brett Wolfe
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: Chassis batteries not charging when engine and generator running

Reply #10 –
Quote
There is at least one scenario that would cause the symptom:  chassis battery charged by alternator UNLESS the generator is on (and therefore powering the inverter/charger to charge the house battery).

If the alternator sense wire is incorrectly installed on the house battery lug of the battery isolator instead of the chassis battery lug, the alternator/regulator would "sense" that the batteries are fully charged when the generator/charger are on since they would be starting to charge the house bank in bulk mode at 14+ VDC.  Therefore, the alternator would properly read that the battery was fully charged and NOT charge.

So, the alternator would not be charging either bank and the inverter/charger would only be charging the house bank.

Brett Wolfe

Brett - that did it!!!! Thanks so much for figuring this out.    I did have to replace the isolator a while ago and the alternator sense wire was zip tied to the wrong battery wire (the house) so of course I installed it with that battery wire on the same isolator lug.

So mystery is solved.

----------------------------------------------------------------------------------------------------------------

Now that this is solved, I'm wondering if it would be a good idea to start a new thread to cover the conversation a about the inverter / charger panels.  This way, folks would more easily find it.
Larry Rubin
2004 U295 38' build 6278
2014 Jeep Cherokee

Re: Chassis batteries not charging when engine and generator running

Reply #11 –
I was having big issues with my alternator overcharging in the last year
- it would bump up to 15+ volts and I could only pull it down by turning on headlights/foglights, etc.
The combo of replacing the 5 plus year old Optimas and cleaning all connections on the Isolator and coach battery bank returned life to normal and stabilized the output. Looks like I'll get a few more years out of the Hehr Powerline after all!
 
Quote
On 9/16/2010 10:24 AM, Larry Rubin wrote: 
Quote

 There is at least one scenario that would cause the symptom: chassis battery charged by alternator UNLESS the generator is on (and therefore powering the inverter/charger to charge the house battery).
 
If the alternator sense wire is incorrectly installed on the house battery lug of the battery isolator instead of the chassis battery lug, the alternator/regulator would "sense" that the batteries are fully charged when the generator/charger are on since they would be starting to charge the house bank in bulk mode at 14+ VDC. Therefore, the alternator would properly read that the battery was fully charged and
NOT charge.
 
So, the alternator would not be charging either bank and the inverter/charger would only be charging the house bank.
 
Brett Wolfe


Brett - that did it!!!! Thanks so much for figuring this out. I did have to replace the isolator a while ago and the alternator sense wire was zip tied to the wrong battery wire (the house) so of course I installed it with that battery wire on the same isolator lug.
 
So mystery is solved.
 
--------------------------------
 
Now that this is solved, I'm wondering if it would be a good idea to start a new thread to cover the converstion a about the inverter / charger panels. This way, folks would more easily find it.
 
Larry Rubin
2004 U295 38'
 
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Titusville, FL - The Great Outdoors
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