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Old 08-31-2012, 12:42 AM   #1
General Disarray
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Default Best way to charge house batteries: Solar or Alternator

I've read a bunch of threads about how to charge house batteries; I'm curious what the advantages of one method over the other might be. I could pick up some solar panels locally and get that going, but I'm leaning toward just upgrading my alternator and charging off that. Seems like the simpler of the two projects. I'm only keeping a 12v 55qt refrigerator going, and maybe a few 12v house lights at this point. I don't boondock, or stay sitting for days on end when I'm traveling with my conversion van. Any reason the extra expense and work for a solar setup might outweigh the alternator route?
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Old 08-31-2012, 12:47 AM   #2
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Upgrade alternator?
How so and why?
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Old 08-31-2012, 12:59 AM   #3
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Default Re: Best way to charge house batteries: Solar or Alternator

Define your loads carefully. Figure out your averge daily draw, and how fast the alternator will recharge relative to how much you drive.

The bottom line with solar is (sort of) this: It is not a panacea, but comes with some real world limitations. Take the name plate rating of the PV, divide that number in half to account for all cumulative system loses, then multiply that number by four to account for the averge hours of good sun you can reasonably expect, per day on average over the course of the year.

So, 200 watts of PV, ( a sort of reasonable number for a Sprinter) will look like this,, 200/2=100*4=400 wattHOURS/day. In the real world, it is ikely to be less, simply because of the limitations of RV installations. For example, RVs seldom have ideal orientation relative to the sun for top production (flat angles, shade, wrong direction etc) and because they are mounted close to the vehicle, they tend to run hotter, and therefore less efficiently. So per Hal's height see 300 WH day. Translate that to AH at 12 volts is somewhere in the 33 AH range. So a 150 amp alternator ( with no other loads) could replace that load in ~20 minutes. In the real world, it won't recharge that fast, but at least that give you the idea.

We live off grid, with a small PV array, and almost never have to run a generator, and I am very happy with that system. That said, in the van, with 225 AH of batteries, we have never had a problem keeping the house batteries charged on a daily basis by driving.

Finally, your fridge is likey to be your biggest challenge. Figure out how much power it uses (in the real world) per day,, and then do or other load calcs. Also remember that a empty fridge will use way more power than a (reasonably) full one.

Good luck,

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Old 08-31-2012, 01:16 AM   #4
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Default Re: Best way to charge house batteries: Solar or Alternator

I upgraded my 90a stock alternator to the150a Bosch back in 05 and added my 4 agms (5 kw-hrs). No trouble with duty cycle load on the alternator. No trouble with the agms with mostly alternator charging and maybe twice monthly shore power top-ups.

My similar sized Engel fridge accounts for 2/3rds of the daily draw. I don't think I'd have less than two kw-hrs of batteries to supply it. The extra batteries allow me to run a 2000w inverter as needed here and there and that eliminated the need for plumbed propane.

Very happy with the lack of need for either solar or genset for our camping style.

Dan
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Old 08-31-2012, 02:00 AM   #5
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Default Re: Best way to charge house batteries: Solar or Alternator

If you don't boondock, solar is just "posh". When I had a Class C RV, I never plugged into the camp power unless I wanted to run a heater or the microwave. Never just to charge the battery.
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Old 08-31-2012, 05:04 AM   #6
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Default Re: Best way to charge house batteries: Solar or Alternator

I love having the solar for the days i get to go camp in the wild and don't want to start the van. Just returned from a long weekend with 8 friends and the fridge was full and cold the whole time. I need to double my house system to two 95AH batteries for a safer margin, but with plenty of sun, no problem. Most of the time living in it i leave the van plugged into shore power with a 1.5 amp charger keeping the battery up and the fridge running on 110V.
Nice to think i don't need to burn any petroleum to run my fridge, music and lights.

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Old 08-31-2012, 03:12 PM   #7
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Default Re: Best way to charge house batteries: Solar or Alternator

I also like the solar panel. Do not have to think about battery charging. When I am not driving the vehicle with refrigerator off, the panel reads 99% SOC in the morning and gets to 100% quickly even on gray days. Never plug into shore power. When traveling with the 80 liter refrigerator running it drops to 92% SOC overnight and gets back to 99 to 100% each day. My 135 watt panel power output about matches the power requirement of the refrigerator. The house battery is a 255 anp-hr 8D. One advantage of a solar panel when controlled by a MPPT 3 stage controller is the ability to do the final bit of charging to 100% SOC without having to run the engine. I would at least have a small panel to maintain a parked van's house battery without having to plug into shore power. I just bought a small 6" x 10" panel with integrated controller for my tractor. You permanently wire to the battery to bring a plug out to a convenient location. Just unplug panel when I use tractor.
The choice may depend on how you use your Sprinter. If you drive it every day then the solar is not as useful. If it sits without being driven between trips, then the solar has advantages. Your posting information does not include your location. Do you live in an area of adequate sunshine?
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Last edited by Graphite Dave; 08-31-2012 at 04:14 PM.
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Old 08-31-2012, 05:59 PM   #8
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Default Re: Best way to charge house batteries: Solar or Alternator

Thanks everyone. I'm just trying to weigh cost vs necissity. We've been plugging the fridge in the cigar lighter, and unplugging it when not rolling. We move around a lot when on trip cuz the van is our house and vehicle. Seems like the fridge never goes long without running the engine again.

I need to get the data off the fridge so I know what draw a non stop running of it will draw. Anyone else get away with running a fridge and lights on just a house battery and alternator? The solar setup is a bit high priced for me, so if I can get away with it I'd love to give the alternator a whirl. Any doing this?
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Old 03-05-2013, 02:16 AM   #9
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Default Re: Best way to charge house batteries: Solar or Alternator

To GeneralDisarray. Unfortunately your requests are being lost in other comments regarding other people's set ups. To answer your question (as per previous pm, but for the benefit of this thread), yes, a Sterling B2b charger will do what you want.
Run +ve and -ve from starter battery to B2B, and +ve and -ve from B2b to house battery. Fuse appropriately at each end. Heavyish cable, particularly from the B2b to house to avoid voltage drop (there's no point in paying for a charger to determine your battery needs 14.6vdc for eg, and only delivering 14.2vdc due to light cables/voltage drop).

If the house battery is inside the van, an agm is a safe option. Keep it simple and get. 12volt one rather than 2x 6volt. Connect a fuse box, and run your loads from there.
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Old 03-05-2013, 02:32 AM   #10
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Default Re: Best way to charge house batteries: Solar or Alternator

Thanks everyone; sooo grateful for the insights.

Just wondering something about charging an AGM (house) off the start battery; what does one need the Sterling battery to battery charger for? Can't I just stick a relay between the starter and house battery, and let it do its thing? What purpose does the charger do when the van's alternator is a charger? Am I missing something?
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