Keep Aux battery in system...or not?

Spike HG

Member
Ok - I've changed the diagram to reflect your suggestions.




Yep - my concern too - it is hard to know what the heck can happen with so many electronic/computer components.:crazy:

thanks for your help
I believe the layout needs tuning, see attached. The cut off relay connects to starter battery shortly after van is running, opens when van is not running.

Do you need under seat connection points, picture's? Not been keeping up, just have time to look @ diagrams, for the most part.
 

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Spike HG

Member
Hi KC - So how do you plan to connect the Aux battery to the House battery? And where does this occur? Off the AUX relay under the Drivers seat (photo taken by Dieselfumes http://sprintervanusa.com/)?

Connection points under seat, bring out to bus/'s, fuse the pos wire, size per wire/load, close to the point, see pic

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

I believe the aux battery could be fused easy, did not do that yet, MB does not install one but. No fuse between the starter battery and aux batt, not a deal breaker, I just moved on?

@or very close to the connection point,a fuse is a must, the white 200 amp semiconductor fuse listed in link
 
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outbound

06/2500/140
i wouldnt be too concerned about draw from the D2, as it's almost negligible;
peaks at appx 11-12amps on the ignition/spin-up phase, which takes just a few mins.
and once the cabin is up to temp, it draws less than 1 amp.

your refrig IS a concern, as they tend to be the largest single draw
but if its a DC unit, employing a danfoss BD35?
you can expect that to use somewhere in the vicinity of 25-60amphours/day,
with a peak draw of appx 4-6amps, upon (warm box) start, settling down to 3 or so while running,
with a ON cycle of appx 1/3 to 1/2 time.

the 5.6cuft one i have takes appx 1-2amps/hour - on avg x 24hours = 25-50ah/day
200w of PV covers it 100% during the summer months, with plenty to spare,
running in ambient temps upwards of 105degF = VERY WELL insulated

but this isnt a typical box, its a GE undercounter unit i converted from 120vac to 12vdc with a BD35,
appears to be a 'designer line' and/or 'competitive replacement' for something like a sub-zero.

as usual, YMMV and just my :2cents:
 

GeorgeRa

2013 Sprinter DIY 144WB, Portland OR
Yes Thats the dilemma. 3 batteries.

Leave Starter alone.

The stock MB Aux battery is under hood already in place. I want to use the Aux just for LED and fan (currently hooked up for that now - so leave that the way it is) and other light loads like USB.

And the Addition - put in a House battery for heavier drains like refrigerator and Espar D2. I would like to be able to charge the the new House battery with solar power for when we are dry camped (and not moving) and the Alternator when the we are driving.
I would suggest to repeat asking yourself why you want to have 3 battery banks and once you reach the final answer ask if this option is worthy its complexity. I am finding myself forgetting how my van was wired by myself and often have to use my up to date electrical diagram, 3 years down the road will you remember which switch to turn on to charge or use a particular battery? To be well informed about the charge state of each bank you will likely end up getting 2 monitors instead of one which is an additional $175.

I purchased my 144" WB van with auxiliary battery under the hood option and added additional battery but, I replaced the MB auxiliary battery with the same battery located inside the van. If I remember correctly I sold the new MB battery for close to $100. Electrically this separation is not an ideal scenario but it works well for me. I am using series two 31 Fullriver 115 Ah so in total have 230 Ah. Batteries are connected with 1/0 cables and are connected to the system at the midpoint between both batteries to simulate closer location. Both batteries are utilizing alternator direct MB connection, 300W of solar and shore power charger.

If I had 170” WB I would most likely just use a large single battery.

George.
 

DieselFumes

2015 4x4 2500 170 Crew
3 years down the road will you remember which switch to turn on to charge or use a particular battery?
George, with MendoBob's proposed system he wouldn't have any physical switches. The factory aux battery would just do its thing in the way Mercedes designed it to. The house battery would do its thing based on the SmartPass cutting in and out as it senses an alternator-provided voltage rather than a starter-battery provided voltage.

The issue is, will it actually work the way it's intended to, especially with the solar charge element of the system.

If he trusts Mercedes' engineers and only runs light loads from the aux battery, he should be fine with just the one monitor on the house battery. Adding a monitor to the aux battery is obviously also worthwhile to know what SOC is, but there's not much that he can do to change that SOC without running the engine.

I'm sitting on the sidelines hoping that MendoBob goes ahead with this system design because it's a really interesting way to combine the aux battery and a third "house" battery. I still believe that the aux battery isn't an ideal option for a conversion van, but in MendoBob's situation and with the unique usage pattern he describes, it could be a viable solution.

On the other hand, I agree that it is adding a lot of complexity where a replacement/alternative battery for the aux battery might simplify things.
 

Spike HG

Member
Voltage only should work well enough for the AUX batt, the BMV 702 can display the house bank voltage/amp's but the other input to display AUX voltage only, no amps. Thinking $20 or so verse the 700, if that was the plan.
 

GeorgeRa

2013 Sprinter DIY 144WB, Portland OR
George, with MendoBob's proposed system he wouldn't have any physical switches. The factory aux battery would just do its thing in the way Mercedes designed it to. The house battery would do its thing based on the SmartPass cutting in and out as it senses an alternator-provided voltage rather than a starter-battery provided voltage.

The issue is, will it actually work the way it's intended to, especially with the solar charge element of the system.

If he trusts Mercedes' engineers and only runs light loads from the aux battery, he should be fine with just the one monitor on the house battery. Adding a monitor to the aux battery is obviously also worthwhile to know what SOC is, but there's not much that he can do to change that SOC without running the engine.

I'm sitting on the sidelines hoping that MendoBob goes ahead with this system design because it's a really interesting way to combine the aux battery and a third "house" battery. I still believe that the aux battery isn't an ideal option for a conversion van, but in MendoBob's situation and with the unique usage pattern he describes, it could be a viable solution.

On the other hand, I agree that it is adding a lot of complexity where a replacement/alternative battery for the aux battery might simplify things.
I agree that there are many ways to do conversiond and we all opt for what’s best for us. I am struggling in this proposal with reasoning except cost reduction. MB auxiliary battery would give about 7 days of lights and house battery about 1 day of a fridge drain, not necessarily a balance system. Having a single bank of 200Ah is much better than 2 x 100 Ah banks wit dedicated loads. With multiple days long camping the auxiliary battery could easily go below 50% SOC without monitoring. With my 230Ah AGMs I have about 3 days in cold weather with the sun blocked. So, a lot depends on the actual use pattern.

George.
 

Mendobob

2014 144" WB 4cyl
Voltage only should work well enough for the AUX batt, the BMV 702 can display the house bank voltage/amp's but the other input to display AUX voltage only, no amps. Thinking $20 or so verse the 700, if that was the plan.


I think your right spike - the. $20 Plan For monitoring voltage on the Aux battery would be fine since we are only talking a total of about 3Ah for all the LEDs that would be hooked up.


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Mendobob

2014 144" WB 4cyl
DieselFumes; If he trusts Mercedes' engineers and only runs light loads from the aux battery said:
Diesel.
I'm. Not sure what you mean trusting MB Engineers. ? - That they have determined that the OEM LED lights will not significantly impact AUX battery load and should work for sometime without charging the MB AUX battery. ?



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DieselFumes

2015 4x4 2500 170 Crew
Diesel.
I'm. Not sure what you mean trusting MB Engineers. ? - That they have determined that the OEM LED lights will not significantly impact AUX battery load and should work for sometime without charging the MB AUX battery. ?
Pretty much, yeah.
 

Spike HG

Member
I think your right spike - the. $20 Plan For monitoring voltage on the Aux battery would be fine since we are only talking a total of about 3Ah for all the LEDs that would be hooked up.


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Hook house up as main battery system, aux as starter/aux/secondary input.

One could set up a visual and audible alarm for a heads up of a low battery issue. Relay can be set up to disable loads, etc.. Relay only 1 amp load.

-In addition to the comprehensive monitoring of the main battery system,
the BMV-702 provides a second monitoring input. This secondary input
has three configurable options, described below.
-3.10.1 Auxiliary battery monitoring
Wiring diagram: see the quick installation guide. Fig 3
This configuration provides basic monitoring of a second battery,
displaying its voltage. This is useful for systems with a separate starter
battery.
-39. Low starter voltage alarm - 702 only
When the auxiliary (e.g. starter battery) voltage falls below this value for more than
10 seconds the alarm will be activated. This is a visual and audible alarm. It does not energize
the relay.
-40. Clear low starter voltage alarm - 702 only
When the auxiliary voltage rises above this value, the alarm is switched off. This value needs
to be greater than or equal to the previous parameter.
 

Mendobob

2014 144" WB 4cyl
Here is the updated version of Aux battery in system diagram per Spikes Suggestions. I did not include the relays between the Starter and Auxiliary batteries since it should already be there (part of MB Aux package).

Anything missing?:thinking:
 

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Mendobob

2014 144" WB 4cyl
I have the CTEK system and am pretty happy with it; about the only thing that would be an improvement is if the MPPT could handle panels higher than 22 volts. Other than that, it's been good so far.


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Hi GS - These CTEK units seem like a good way to go. Are you using it with a OEM Aux battery? And since you say a "CTEK system" - I assume you have the Smart pass with solar too?
 

Mendobob

2014 144" WB 4cyl
I replaced the MB auxiliary battery with the same battery located inside the van. Electrically this separation is not an ideal scenario but it works well for me. I am using series two 31 Fullriver 115 Ah so in total have 230 Ah. Batteries are connected with 1/0 cables and are connected to the system at the midpoint between both batteries to simulate closer location. Both batteries are utilizing alternator direct MB connection, 300W of solar and shore power charger.

George.
Hi George - this sounds pretty simple - and that I like. How do you have both the batteries hooked into the alternator? Would you happen to have a block wiring diagram already posted online in the forum somewhere?

thanks
 

GSWatson

2013 144
Hi Bob - I don't have the aux battery. I have cables to the smartpass coming from the starter battery, as laid out in the diagram you have.

This is my temporary setup; the two Lifeline 6v's are behind them until I get them in a box under the van.




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GeorgeRa

2013 Sprinter DIY 144WB, Portland OR
Hi George - this sounds pretty simple - and that I like. How do you have both the batteries hooked into the alternator? Would you happen to have a block wiring diagram already posted online in the forum somewhere?

thanks
Batteries are connected directly to the MB relay. I have Magnum ME-SBC which needs to be installed at some point. My batteries charging current factory limit is 0.2xC20 = 23A x 2 = 46. If my batteries are heavily discharged the the charging current goes above it so having ME-SBC would limit it to 25-30A. CTEC combo seems perfect, I was not aware of this company during my electrical design. My system is 3 years old and it works great. The dimensions are approximate and the left fuse is closer to the battery.

George.
 

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GSWatson

2013 144
And I found the perfect place to mount the BMV700... Just stays there via friction. I thought I would make a mount, but it's been there three months now. Ah, how the temporary becomes the permanent....



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Mendobob

2014 144" WB 4cyl
And I found the perfect place to mount the BMV700... Just stays there via friction. I thought I would make a mount, but it's been there three months now. Ah, how the temporary becomes the permanent....



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That's a great place for it! Thanks for sharing!
 

Mendobob

2014 144" WB 4cyl
This is my temporary setup; the two Lifeline 6v's are behind them until I get them in a box under the van.
Hi GS, Just Curious - the CTEK manual says the DUAL and Smartpass are designed for 12V. So, if you are using two 6V in series it works fine?
 

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