Author Topic: Battery charging via engine  (Read 2755 times)

john brunson

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Battery charging via engine
« on: April 06, 2018, 03:10:49 PM »
1996 Beaver Monterey 36': 

Engine alternator does not charge chassis batteries but pushes coach batteries to approximately 15.2 volts with engine running.  I strongly suspect the isolator that splits the alternator output and prevents discharge of chassis batteries.  We will further troubleshoot that when we return to the coach. It is my understanding that this Cat 3126 alternator has a remote voltage regulator sensor to properly charge batteries.  It appears that the sensor is not getting a proper sample and over charging the coach batteries.  Can someone tell me Where the voltage is sampled  for the alternator?  and how/ where is the output of the alternator adjusted?? If the voltage is sampled on the chassis batteries side of the isolator then that would explain the overcharging.

 I just forked over the $$ for two new 1300 CCA group 31s and i would like to adjust the alternator to charge them no more than 14.1 volts.

Gerald Farris

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Re: Battery charging via engine
« Reply #1 on: April 06, 2018, 05:30:13 PM »
John,
Your coach uses a Duvac design Leece Neville alternator that requires a sense wire to regulate the charge voltage because the battery isolator blocks battery voltage at the output terminal with diodes to allow output but no return path. The sense wire is connected to the chassis batteries only, and if the alternator is not allowed to charge the chassis batteries by a bad cable, connection, or isolator, it has no way to charge at the correct voltage, and therefore, it overcharges trying to get the proper voltage on the sense wire. At bad sense wire will result in overcharging on both battery banks.

As for adjusting the output voltage, some but not all alternators have an adjustable regulator located on the top rear of the alternator. You just turn the slotted shaft to achieve the desired, but you need to fix the chassis battery charging problem first because the regulator can not regulate a charging voltage that it can not sense. If your alternator does not have an adjustable regulator, even Leece Neville has discontinued their production, there were aftermarket ones were still available the last time I checked.

Gerald     

john brunson

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Re: Battery charging via engine
« Reply #2 on: April 06, 2018, 09:43:40 PM »
Gerald,

does the rear of this alternator diagram look accurate?

Gerald Farris

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Re: Battery charging via engine
« Reply #3 on: April 06, 2018, 10:47:14 PM »
John,
It looks accurate, but the sense wire may be tied directly to the chassis batteries, the hot terminal on the starter, or a junction block in the battery bay instead of the isolator. However, it does not matter where the sense wire is connected as long as it reads true chassis battery voltage at all times.

Gerald

john brunson

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Re: Battery charging via engine
« Reply #4 on: April 07, 2018, 02:56:57 PM »
I would imagine the closer to the battery, the more accurate the charge voltage

Gerald Farris

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Re: Battery charging via engine
« Reply #5 on: April 07, 2018, 04:49:06 PM »
John,
Not necessarily, because all the locations that I listed are connected to the chassis batteries with cables that are large enough to ensure no voltage drop when the engine is running. Like the starter location would only have a voltage drop when cranking and the alternator is not charging, but no when the engine is running, and the alternator is charging there would be no voltage drop.

Gerald

john brunson

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Re: Battery charging via engine
« Reply #6 on: April 08, 2018, 04:00:17 AM »
Got to dig into this... it is boiling my coach batteries

Gerald Farris

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Re: Battery charging via engine
« Reply #7 on: April 08, 2018, 04:40:02 AM »
John,
As an emergency repair for a isolator that is open to the chassis batteries (which is what yours sounds like), you can take the chassis battery cable off of the end terminal and move it to the center terminal with the alternator output. Your alternator will then charge your chassis batteries and house batteries correctly until you can replace the isolator. Be very careful to identify which cable is the chassis battery cable and that it has a good connection to the batteries. It would also be a good idea to check the sense wire.

Gerald

Gerald 
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john brunson

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Re: Battery charging via engine
« Reply #8 on: April 09, 2018, 10:20:29 PM »
Gerald,

When I return to the coach Friday, I would like to be equipped with a new isolator.  Do I have a 200 or 250 amp model?  I feel like there is a good probability that my sense wire is functional because the regulator pushes the coach batteries so high; that is to say it appears that the sense wire is reacting as if it sees a chassis battery that is not connected to the alternator output.  If not, then i will just wire the alternator and sense wire directly to the chassis batteries; this should properly charge the chassis batteries and get me home.... or crank the onan and boost as i see the voltage sag......

john

Gerald Farris

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Re: Battery charging via engine
« Reply #9 on: April 09, 2018, 10:49:15 PM »
John,
Your coach came with a 160 amp alternator and a 200 amp battery isolator. There is no reason to install a higher capacity battery isolator unless you increase the output of your alternator.

Gerald

john brunson

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Re: Battery charging via engine
« Reply #10 on: April 19, 2018, 05:44:44 PM »
Problem solved~ corroded but splice on charge wire and charge sense wire to Chassis batteries.