Advice Needed! Using pre-existing cables on Sprinter for 50A DC-DC Charger with MPPT

[ssanvero]

Hi guys,

I'm just starting my journey with building out a van and getting onto the electrical side of things. This is all quite new to me and I've tried to find as much information online as I could but still feel a bit unsure about my plans of using pre-existing cables in my van. So thought, I'd ask for some help...

So I bought my 2004 Sprinter earlier this year and it used to be a passenger van with a rear air conditioner. The previous owner had left the wire there, which was red and after trawling through the web I'm pretty confident it's the 80 Amp rate wire in the manual below.

So my questions are:

1. Is it as simple as connecting this positive wire directly to my MPPT DC-DC charger and then connecting a negative wire too? Since it is already connected to the car battery, it's rated well above what the charger is rated to draw (50A) and I'll put a 75A fuse.
2. Should there be a leftover negative wire somewhere too from the pre-existing AC setup? I assumed there would be but can't seem to find one anywhere but could be my lack of knowledge on how electrical systems work.
3. If I need to connect my own negative wire then what is the best way to work out what gauge my 80A wire is? I can't see any markings on the actual wire. Would it be okay to connect a different gauge negative wire, as long as it's rated higher than the 50A charger?

Appreciate any feedback!

Thanks guys,
Hans

 

[mikefitz]

Use van body for negative, the vehicle uses the body/chassis frame for a negative from battery and alternator. The controller instructions should specify cable size.
Metric. 16mm square area, AWG 6 would be my guess.
Thicker wire is no problem subject to the size and type of termination on the equipment.

Mike

 

[HRTKD]

I would spend a few more minutes to see if a negative wire is also there. Low amperage off the body/frame is not big deal. Higher amps, maybe not quite as good.

Like mikefitz said above, running a bigger wire for the negative would be just fine. If there is an exposed part of the copper, use a micrometer to figure out the width and you can then back into the area.