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Old 02-14-2018, 03:17 PM   #1
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Vehicle Alternator Charge of House Batteries

I have a 2017 Compass 24TX (MB Sprinter). I know that the "Store" switch must be on for the vehicle alternator to charge the house batteries while the vehicle is running. I was having issues with the charge of my house batteries, so I wired in a USB charger/voltage meter straight to the house batteries, and I placed it in the side of the cabinet near the coach door. From the driver's seat I can see the voltage of the house batteries at anytime. What have observed is that when the vehicle is running and charging the house batteries, it always seems to be charging at 14.1 -14.2 volts and never lower. Does anyone know if the vehicle alternator current goes through the charge controller to regulate the battery charge?
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Old 02-14-2018, 04:02 PM   #2
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Since the 'charge controller' or converter accepts 120v AC input and outputs 12-14v DC to the batteries - its not something the alternator can feed in to...
Typically charging from alternator is at full voltage - to both chassis and coach batteries - but we all know these RV's are far from 'typical'
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Old 02-14-2018, 06:18 PM   #3
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Realize that the voltage output of the voltage regulator in the alternator is dependent on the current draw. The alternator does not know if the current it supplies is going to the house batteries, chassis batteries, or any DC loads, all it knows is the DC buss is pulling X amount of amps.

So even though you may see 14.2 VDC on the DC buss, most of the supplied current is going to the DC loads needed to run the engine and motorhome. If the batteries are low, they will take more current. As the batteries' voltage increases, the current supplied to the battery decreases,
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Old 02-17-2018, 03:35 PM   #4
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More Battery help?

I keep my house battery on a trickle charge while keeping the house system turned off. The battery charge this morning was 12.44, switched on the house and it dropped immediately to 11.7. Not enough to start the generator by it self and need to boost from the chassis. Is this expected? Seems like an awful lot of draw on the house battery w/ nothing engaged except the CO2/Propane/O3 monitor and clock on the microwave.

Still learning!

Thanks for the feedback.
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Old 02-17-2018, 03:43 PM   #5
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I have the Sprinter chassis as well, and that 14.1 or 14.2 volts you see reflects to some degree the state of your house batteries. I see mine at that same voltage sometimes even a 14.3 volts, while driving, but it always drops down into the mid to low 13 volts as the batteries charge up. Charging from the converter off shore power, I never see 14+ volts, the highest will be 13.7 or 13.8 volts, and drops to 13.2 or so as the batteries charge up.
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Old 02-17-2018, 03:46 PM   #6
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Tn-camper, constantly trickle charging will kill your batteries. Use a smart charger, or battery maintainer that will float your batteries when they reach full charge.
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Old 02-19-2018, 10:46 AM   #7
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Quote:
Originally Posted by tn-camper View Post
I keep my house battery on a trickle charge while keeping the house system turned off. The battery charge this morning was 12.44, switched on the house and it dropped immediately to 11.7. Not enough to start the generator by it self and need to boost from the chassis. Is this expected? Seems like an awful lot of draw on the house battery w/ nothing engaged except the CO2/Propane/O3 monitor and clock on the microwave.

Still learning!

Thanks for the feedback.
If your batteries are that low when charging. You probably should look into getting new batteries. Anything below 13 on a charge is not good. Only more issues will follow.

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Old 04-14-2018, 03:33 PM   #8
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Tn-camper, constantly trickle charging will kill your batteries. Use a smart charger, or battery maintainer that will float your batteries when they reach full charge.


I was just on Amazon looking at battery maintainers. There seem to be several similar looking maintainers/charges. I would appreciate any suggestions as to what type to buy.
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Old 04-14-2018, 08:14 PM   #9
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Originally Posted by dogshowrv View Post
I was just on Amazon looking at battery maintainers. There seem to be several similar looking maintainers/charges. I would appreciate any suggestions as to what type to buy.
For brand name - I've gone with Battery Tender... Used it mostly at home for the car 'left behind' in MI when we wintered in FL.
Worked well for me - charges when needed - floats when full.

Never used anything on the rig - Store is store for me - no significant parasitic drains - can go months without losing charge.
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Old 04-15-2018, 04:53 AM   #10
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Quote:
Originally Posted by Laco View Post
I have the Sprinter chassis as well, and that 14.1 or 14.2 volts you see reflects to some degree the state of your house batteries. I see mine at that same voltage sometimes even a 14.3 volts, while driving, but it always drops down into the mid to low 13 volts as the batteries charge up. Charging from the converter off shore power, I never see 14+ volts, the highest will be 13.7 or 13.8 volts, and drops to 13.2 or so as the batteries charge up.
I recently replaced both of my house batteries and no matter how long they are charged, once I'm drivng, and they are being charged by the alternator, the voltage never goes below 14.1.

I can be in a campground charging for days, but when i disconnect and drive, it will charge at 14.2-14.1 even if if I drive all day.
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Old 04-15-2018, 11:39 AM   #11
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For brand name - I've gone with Battery Tender... Used it mostly at home for the car 'left behind' in MI when we wintered in FL.
Worked well for me - charges when needed - floats when full.

Never used anything on the rig - Store is store for me - no significant parasitic drains - can go months without losing charge.


Thank you. Battery Tender purchase is for chassis battery, not worried about coach batteries but chassis battery only.
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Old 04-15-2018, 11:49 AM   #12
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When you are running the RV the alternator is charging both the cranking battery and house battery(s). Since the batteries are in parallel the alternator senses this combination. There is a slight difference between the house and cranking batteries because of wiring but the alternator provides for most part the equivalent of the lowest battery. For automotive charging systems 14.1 or 14.2 volts is perfectly normal the whole time the engine is running. The other part of the equation that is being overlooked is the amount of current the alternator is generating. This starts out high and tapers off over time.
You typically don't see the voltage this high from the convertor because they are not true chargers. For in depth information check out batteryfaq.org and battery university.
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Old 04-15-2018, 01:47 PM   #13
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Originally Posted by Gladinwj View Post
I recently replaced both of my house batteries and no matter how long they are charged, once I'm drivng, and they are being charged by the alternator, the voltage never goes below 14.1.

I can be in a campground charging for days, but when i disconnect and drive, it will charge at 14.2-14.1 even if if I drive all day.
That does not sound like the regulator(s) work correctly. I think I would start by haveing your new batteries checked and load tested. Its possible one may have a shorted cell or????, which could cause what you are seeing.
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Old 04-15-2018, 04:37 PM   #14
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Originally Posted by scrubjaysnest View Post
When you are running the RV the alternator is charging both the cranking battery and house battery(s).
E-450 Chassis here...
So does anyone know of more powerful alternators, that can be bolted in place of the OEM unit?
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Old 04-15-2018, 07:51 PM   #15
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E-450 Chassis here...
So does anyone know of more powerful alternators, that can be bolted in place of the OEM unit?
It appears you have the 157 amp alternator <https://www.fleet.ford.com/truckbbas/topics/2017/2017_F-350_F-450_F-550_SD_Chassis_Cabs_-_Specs.pdf> . You might try Nations <https://www.nationsstarteralternator.com/High-Amp-Alternators-s/58.htm> but be careful almost every installation requires re-clocking of the alternator plus there are three different mounting ears spacing depending on the chassis VIN
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