Building out my system, where/how best to tie B2B in 2019 Sprinter with Aux Battery?

brent.carroll said:

Hi all,

First time poster here. I tried this question over at Sprinter Forums and got little traction. Then, I heard about Will Prowse and this forum!!

Subject line pretty much is it, my aux battery is under the hood. I have been working directly with Victron to spec out my system and I expect components to start rolling in pretty soon (my basic system is 960W solar, 600ah Lithium, 5KW inverter, chargeable by shore power, solar, and well, the alternator I hope). I feel pretty good with just about everything so far (Victron provided a LOT of guidance), but tying into the van electrical is something I am but worried about - I don't want to risk what I perceive as a novice tinkering with a pretty sensitive system.

Any advice would be most appreciated!

~Brent

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ianganderton said:

DC to DC charger needs to come off the battery or pretty close to it

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ianganderton said:

This might be useful https://sprintervanusa.com/2016/08/07/tapping-in-to-the-sprinter-vans-battery/

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CascadeOffGrid said:

The NCV3 with aux. battery option should have a battery isolating relay installed under the drivers seat. There is also a connection point here for running items off of the factory auxiliary battery.

I would strongly recommend against tying into the auxiliary battery system. Mercedes also recommends against tying in more than 100aH of lead acid batteries to this connection point due to potential damage to the alternator.

I would recommend tying directly onto the starter battery with a battery cable to a DC-DC converter to charge your lithium batteries. The NCV3 has a factory terminal fuse block on the battery. I would start there and check if there is an open port on the fuse block. If there is, I would tie a new battery cable onto that point and take that to your DC-DC converter. These factory fuse blocks utilize MIDI fuses.

If you go with a Renogy DC-DC charger, you can tie the turn-on wire to a factory connection point under the drivers seat. There is an "engine running" terminal that will only turn on your DC-DC charger once the engine is running.

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ianganderton said:

If using a DC to DC charger would it be ok to tie into the “under drivers seat” connection? With the charger everything would be rated and controlled to a specific ampage (30 ish depending on the charger).
Is that line fused and if so what with? Wonder what wire runs to it and from where exactly.

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CascadeOffGrid said:

... I don't remember what the body builders manual says but I would not personally put more than a 10amp load on them.

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• engine running (D+) (10A)
• battery direct (25A)
• ignition on (15A)