Keep Aux battery in system...or not?

Mendobob

2014 144" WB 4cyl
Insulation is in and now I am trying to figure out if it is worth trying to use the stock Auxiliary battery (95 Ah) in my electrical system. :bash:

Immediate plan: put electric in (planning for future), panels, upper cabinets and fold up bed. Nothing else since I need to haul things in van. For the next year or two my electrical load will have: LED lights, Fan, chargers for phone and PC, and Espar D2 heater - using about 20 Ah/day.

My down the road grand scale plan includes: adding a refrigerator, sink and counters. When I put in the refrigerator my load will increase to a load of about 44Ah/day.

I would most likely add solar panel and system - knowing it is a slippery slope to using more electricity than planned.

So, can I just use the Aux and switch over later without too much difficulty. I typically work off the KISS principle.

thanks for your help!
 

Spike HG

Member
I would never design a system with below listed/attached in the loop BUT since it was already there and time was not moved on with it in play. Planning on doing something when it starts to die/ #s change, it will die 1st, under hood, different type/make, nothing is right but close when new.
If one can get by with only the aux battery for a while till you get a plan, that's a plan.
 

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Midwestdrifter

Engineer In Residence
If you're going to building a power system capable of supporting a decent size fridge you will probably want to put your own batteries in a convenient location. Something around 200 amp hours is usually what people go with. Using the factory AGM battery can be difficult because you need to match it it to the same type of battery and you need to have your your wire runs balanced, which can be difficult with the batteries location. My general suggestion is to not use the factory AGM battery when you install your own auxiliary battery bank later on. For optimal life all batteries in the bank should be matched by type age and size.
 

Terrapin

Member
Hi Mendobob,
I have the factory Aux battery. I use it to charge the house battery bank (375 amp) through a dc to dc charger. The owners manual says you should not pull more than a 40 amp load from the factory aux battery, so I got the 40 amp model. It doesn't make for a really high speed recharge while going down the road, but it does give the house batteries a true 3 stage charge. We typically use about 30~40 amps each day and the system has worked flawlessly for 3 years now.
You might be able to use the factory battery for a couple years until your demands require more and then add a separate independent (house) bank and charge it from the factory aux. At least then when you do add a house bank you won't have to be concerned about matching the house bank type, amps, etc. to the aux battery.

Just an idea. Best of luck. :cheers:
 

Spike HG

Member
Thanks - can you explain why ?
RE:I would never design a system with below listed/attached in the loop .

Not familiar with this battery.

Not really sure on what type, AGM but type, is it like the starter battery, one could easy think it would be because MB states that. Since it is already in play, paid for, free to use, money is part of the #s. Hard to rip out, and not use but seems that it is not a deep cell.

One should have all battery's in the power supply the same, age, type, make if possible to get the most service but there are other factor's that would kill a battery/shorten life.


I do not really know anything about the battery under the hood, did a quick search, found one for sale out of 2015.
 

DieselFumes

2015 4x4 2500 170 Crew
Mendobob, this article might help you with your decision.

Like Spike is saying (I think), the aux battery isn't a true deep cycle battery and so it's not designed to be used quite like a house battery. It'll work for your immediate needs so long as you are driving the van each day, but higher discharge rates could shorten its lifespan. As soon as you get into higher loads though with the fridge, it might not be able to keep up.

The biggest problem is planning ahead so you don't have to do any re-wiring. Once your fan and Espar wiring is in you will not want to ever touch those wires again. If you can set up your distribution panel in a location that you can easily add batteries nearby later on, you should be OK. You'll want those battery wiring runs to be as short as possible.

Some other stuff that might help you with the planning and decision making:
http://sprintervanusa.com/2016/08/07/tapping-in-to-the-sprinter-vans-battery/
http://sprintervanusa.com/2016/08/08/hooking-in-to-the-sprinters-charging-system/
 

Jmolan

Member
I had the same set up, aux. factory battery like the one pictured in the post up above. After fan, fridge, EsparD2, 200W solar and a few extra lights I found I was needed a better source of power. I swapped out the aux. factory "starter" battery for a 105 ah AGM deep cycle. So far so good, also a good battery monitor to see what is going on. It is my hope to be able to "get by" on this simple light set up. If not....
My next idea is to position this big boy I show down below right behind the drivers seat. As I understand it the hook up is under the drivers seat. But I will have to know a lot more before I take this step. It is narrow and tall and would fit, weighs 137lbs!

Screen Shot 2016-10-15 at 1.33.58 PM.png

http://www.batterymart.com/p-pc1800..._QAeNW0cga8cURLb_cet4fF9lcG7Z15REcaAiCM8P8HAQ

PC1800-FT
Made In: U.S.A.
Voltage: 12 Volt
Capacity: 214 Ah
Type: AGM
Length: 22.75"
Width: 4.9"
Height: 12.44"
Cold Cranking Amps: 1300 CCA
Shipping Weight: 137.00Lbs

Additional Specs:

1300 CCA, 1450 MCA, 1600 HCA
1800 Pulse Cranking Amps for 5 Seconds
475 Minute Reserve Capacity
3/8" Stud Terminals
3.3 mOhms Internal Resistance
80 in-lbs Torque
3800A short circuit current
Cycle life @ 77° F 400 at 100% DOD
-40° F to 140° F Temperature Range
Made in the USA
 
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Spike HG

Member
This is what I did to attach to the MB connection point under the seat, near the cut off relay (Isolator relay) that closes with the van running. Fuse is shown and a must. If fuse is over looked, MB has that mistake covered , with an in line fuse that is replaced when the wiring harness is replaced. Fuse is non replaceable, comes with harness. MB fuse is rated for 300amp, would want to have the connectionion point fuse'd smaller than MB 300amper, that's for sure.


https://sprinter-source.com/forums/showpost.php?p=479368&postcount=14


http://www.sprinter-rv.com/wp-content/uploads/2010/09/Aux-battery-retrofit-guideline-NCV3.pdf
 
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Mendobob

2014 144" WB 4cyl
Excellent read - Thanks - looks like I can't use a battery in that space w a higher than 95Ah

It'll work for your immediate needs so long as you are driving the van each day, but higher discharge rates could shorten its lifespan. As soon as you get into higher loads though with the fridge, it might not be able to keep up.
What if I add a second Aux battery - say under passenger seat? Another 95Ah. An AGM? Can these work in tandem? As far as I can tell - I am looking at pretty low amp hrs burned per day...45+-

Would I be wasting my time hooking up solar panels into this set up?

The biggest problem is planning ahead so you don't have to do any re-wiring.
That is the Truth! Especially since I am learning on the fly!
 

Mendobob

2014 144" WB 4cyl
This is what I did to attach to the MB connection point under the seat, near the cut off relay (Isolator relay) that closes with the van running. Fuse is shown and a must. If fuse is over looked, MB has that mistake covered , with an in line fuse that is replaced when the wiring harness is replaced. Fuse is non replaceable, comes with harness. MB fuse is rated for 300amp, would want to have the connectionion point fuse'd smaller than MB 300amper, that's for sure.
Looks like this is for connecting an additional aux battery under the passenger seat?

I have a 2014 - does this guideline cover the 2014 as well?
 

Spike HG

Member
Looks like this is for connecting an additional aux battery under the passenger seat?

I have a 2014 - does this guideline cover the 2014 as well?
Looks like this is for connecting an additional aux battery under the passenger seat?

RE: Looks like this is for connecting an additional aux battery under the passenger seat?

Yes, this is what I connected to, 2016 with the AUX package D28, E36 Cut off relay.
Pic 1 shows two 300 amp disconnect switch’s
Pic 3 shows show’s big blk cable with wht taped end’s, hooked to fuse that I added to MB connection point and to one of the 300 amp switch’s
Pic 4 Shows the grounding point I used. Look @ that point a 17 mm socket fits, that is not a listed MB point, there listed points in Pic 4, 10 mm socket fits. I weight this about the same as adding a AUX battery bigger than the MB 95 AH battery, it’s done every day.

Just looking for a practical way to getter done? To me some posts mean nothing, like using a non-factory listed point as listed in pic 4, I could see a post stating NO NO NO to that point I used, I would not even see it, meaning so what, this may not be the way that someone that DOES NOT work in the electrical field every day see’s a post’s like this. Gotta be tuff.
And then there is the sterling charger, etc.. Let's get your elec system top shelf. Spending more money most likely will get a better system built, but I look for a practical/safe way 1st.



Used this for 2016, thinking things change slow
 

Jackies Dog Grooming

2016 NCV3 144" 4 banger
It would be interesting to find out how big of a Lithium Ion battery I can put in the location of my factory aux battery. I haven't gotten to that point yet, so I haven't researched it much.
 

autostaretx

Erratic Member
It would be interesting to find out how big of a Lithium Ion battery I can put in the location of my factory aux battery. I haven't gotten to that point yet, so I haven't researched it much.
To save us relocating your conversion thread, it'd help a lot if you put your model year (etc) into your signature block (like mine).
((signature block accessible through the "User CP" choice on the forum's top blue-bar set of buttons))

If you know the battery sizing of the factory space (H9?), just looking at LiFEPO4 suppliers with that as a part of the search criteria would probably yield answers.
((i don't recall if LiFePO4 batteries would appreciate the environment they'd be living in under the hood (if an NCV3)))

--dick
 
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Jackies Dog Grooming

2016 NCV3 144" 4 banger
To save us relocating your conversion thread, it'd help a lot if you put your model year (etc) into your signature block (like mine).
((signature block accessible through the "User CP" choice on the forum's top blue-bar set of buttons))

If you know the battery sizing of the factory space (H9?), just looking at LiFEPO4 suppliers with that as a part of the search criteria would probably yield answers.
((i don't recall if LiFePO4 batteries would appreciate the environment they'd be living in under the hood (if an NCV3)))

--dick
Ah yes. It would be helpful if people actually knew what I'm driving, lol. Thanks, Dick. I'll fill in more info now.
 

DieselFumes

2015 4x4 2500 170 Crew
It would be interesting to find out how big of a Lithium Ion battery I can put in the location of my factory aux battery. I haven't gotten to that point yet, so I haven't researched it much.
I wouldn't suggest putting a LiFePo4 under the hood. They don't like being charged in freezing temperatures, and if you went with anything much larger than the stock battery you might need to change out the supply cables for something fatter. That is a long cable run. Better to reserve a space inside the vehicle.

If you insist on doing it, there's a list of lithium battery suppliers that offer drop-in replacements in this article I wrote. You'd probably also want a battery warming pad on a thermostatic controller.
 

DieselFumes

2015 4x4 2500 170 Crew
Excellent read - Thanks - looks like I can't use a battery in that space w a higher than 95Ah
You *can*, and lots of people *do* but it's not clear from Mercedes whether you *should*.

What if I add a second Aux battery - say under passenger seat? Another 95Ah. An AGM? Can these work in tandem? As far as I can tell - I am looking at pretty low amp hrs burned per day...45+-
Re: your amp-hour calculations, you have done the right thing by calculating your daily consumption, but will you drive every day? Do you want a little bit of padding in the calculations so that you can last, say, two days off the battery? It seems to me that you're worried about this question yourself because you're talking about adding more capacity.

If you add another 95Ah battery, you'd be meeting one part of the Mercedes guidelines, because you'd be using batteries that were the same size and the same chemistry. However, the system would "see" your aux batteries in combination as a 190Ah battery, so you haven't magically avoided the issues. Making sure the battery cables were similar lengths (so they charge/discharge in tandem) would be a real pain.

You also have to drive enough hours each day to actually charge the batteries up. Lead-acid batteries have a long absorb cycle. You could find that you're never fully charging your batteries. If they don't get a full charge every month or so, their lifespan will be reduced.

To run thick enough cables between the driver and passenger seat base, it's likely that you'll need to remove both seats and bases so that you can unclip the top on the plastic cable race cover that runs between them. Or run the cables out from the boot under the driver seat, under the van, past the exhaust pipe, and up in to the passenger seat base. You'll then have to route your cables, create a battery tie-down location, and find a way to vent the battery to the outside world (through the floor). It's not clear that you'll actually gain anything by doing that.

If you're going to that hassle, why not do something like a Sterling battery-to-battery charger and install a proper deep cycle battery of a size that's more appropriate?

Would I be wasting my time hooking up solar panels into this set up?
Into the stock aux battery? Maybe. Maybe not. You could use solar to keep your aux battery charging as your fridge depletes it. There's no reason not to, but it's hassle and expense that you could avoid if you are driving frequently enough to keep the battery topped off.

Again, that battery isn't really designed to be deep cycled much. It's up to you to decide whether the solar is likely to add to the depth of discharge (which it would if you feel confident discharging the battery overnight because the solar will recharge it the next day) or not.

As soon as you go to a larger "house" battery, solar starts to make more sense. The more charging you do from solar, the less the alternator has to make up. I'm sure people will shout at me that the alternator is basically free power, but if making it work harder than its design parameters means it burns out faster, then that's not really free. Also, solar works whenever the sun's out, rather than relying on you driving the vehicle. Last I checked, Mendocino's pretty sunny.
 

Jackies Dog Grooming

2016 NCV3 144" 4 banger
^ Good info, Diesel. I figure by the time I understand everything about a battery/solar system to meet my needs, Li-Ion batteries will be less expensive. :thumbup:

Come on Elon, start mass pumping out those Li-Ions out of the giga factory!
 

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