Running cables, battery to boot.

[Maker_of_Things]

I have a pre FL 2008 Scout 2.0 tdi.

 

In my previous work car, 2001 Octavia estate, I had a 240v inverter in the boot for charging tool batteries, running power tools on site, and for a small silent compressor. I want to install one in the Scout but can't see an easy route to run a big 25mm welding cable (big to reduce volt drop).

 

Has anyone any tips as to how and where I could get a cable from the battery to the boot without drilling big holes in the body? The inverter will live in the boot cubby on the OS, with a compressor hiding with the CD changer on the NS.

I think I can get the cable out through a grommet where the existing wring exits the spare wheel well to behind the bumper and then route under the car, as I did on the old Octy mk1. Is there a better route through the inside, preferably without removing all of the trim and half the dash?

The cable will need to terminate at the battery but the battery box is so snug over the battery that I don't know if I can terminate there.
There is a bus bar with some big fuses, could I use that? I am thinking of 100A fuse, either on the bus bar or inline on the cable.

Thoughts please?

I'd prefer to install a second battery in the boot, on a split charge, but I don't have space for one.

 

Thank you.

[MikeTheThinker]

6 minutes ago, Maker_of_Things said:

I'd prefer to install a second battery in the boot, on a split charge, but I don't have space for one.

 

How about using two half-size batteries - motorcycle/skidoo etc.  - and putting one in each side pocket, or even mounting one above the other on one pocket?

 

[Maker_of_Things]

4 minutes ago, StickyMicky said:

 

How about using two half-size batteries - motorcycle/skidoo etc.  - and putting one in each side pocket, or even mounting one above the other on one pocket?

 

That would cause more split charging issues as they would discharge into each other. And both spaces will be full of inverter and compressor anyway.
Also with a bit of rethink I am not sure a lead acid battery inside the car is such a good idea anyway, now.

[nige8021]

You could pick up the battery supply from the main terminal on the starter motor and fit an inline fuse to protect the wire running to the boot area

[Maker_of_Things]

5 minutes ago, nige8021 said:

You could pick up the battery supply from the main terminal on the starter motor and fit an inline fuse to protect the wire running to the boot area

Ahh, there's a thought. Cheers.

 

Now still need to figure a route to the boot.

[pikpilot]

Or use one of the spare fuse locations on the battery distribution fuse board. Just make sure the fuse is sized to protect the cable (or smaller), not the load and then, since you have oversized the cables to reduce volt drop, put in individual fuses in the boot area to protect the cable run to each smaller load. This is what you need to do protect against a car fire under fault conditions.

[Maker_of_Things]

Yes. The previous set up had a 100A fuse at the battery end, and a 75A fuse at the inverter. The compressor ran on 240v from the inverter on its own 3A fuse.
 

Do you know what the fuses at the  distribution bus bar are called?

Are they these ones?

https://www.ebay.co.uk/itm/191925440181?var=490999336376&ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649

Cheers.

[pikpilot]

I was thinking of an earlier version when I said bus bar.  I just had a look at my car (2012 face lift) and there are free terminals available on the front face of the fuse box marked as 50A, 80A and ground.

You wire to these from below and then put in similar style fuses to the others in the fuse box in the correct location. You need to test or get a diagram to determine fuse location assigned to these free terminals. 

Please note that the fuse box is unlikely to accept a 25mm welding cable.

 

Take off the cover over the engine bay fuses (see handbook) and see what you think.

 

If you end up taking power directly from the battery, remember that the cable from the battery to the first fuse must be protected mechanically from chafing and vibration as it is electrically unprotected and must not be grounded.

 

It is a common mis-believe that you size the fuse for the end load current. Wrong. You size the fuse to protect the cable (or a smaller fuse). As you go down to a smaller size cable for the final load, it too must be protected by its own smaller fuse. That is why the 12V aux power plug has a fuse in the centre pin (typically 1A or less) to protect the thin cable that goes to your phone etc. If you don't, you could possibly have a 30A+ current setting your phone cable on fire. [I have seen the lightning connectors for Apple products completely burnt away by people just unplugging the cable and putting it in a tray with their keys and coins. And that is at 5V but from a 3A converter]

 

It worries me when I see people running long cables directly from the battery to a relay for lights or to a power amplifier with no fuse at the battery end, only at the load end. It doesn't take much to start a car engine bay fire from a chafed or grounded cable connected directly to the battery.

I will now get off my hobby horse as the information is general and not just for your application, especially as your previous car appeared to follow the rules correctly.

[Maker_of_Things]

That is great advice for those who don't know. 

If I use a fuse box/bus bar terminal then I can bring the 25mm down to fit into a 10mm crimp eye. I have been nosing around in that space, and I don't think going direct to the battery is going to work as the cover is so tight. I wasn't sure if the bus bar would handle another really big load on it, but the starter terminal would be an option I guess.

I still can't find a way to route the cable though, even dropping it under the car and fixing it under the floor.

I can feel a loom grommet in the bulkhead behind the battery but it is in a double wall section so it doesn't come though directly under the dash. I think maybe the loom there goes sideways under the windscreen area to the internal fuse box?

I even thought about up the windscreen A pillar and through the roof lining but I think keeping the cable to the floor would be better.

[J.R.]

Is having a second battery in the boot a real no-no?

 

It would bring several advantages:

 

Easy to cable using a split charge relay, you may not even need to run a cable to the front.

 

You would never risk not starting the vehicle after running your load.

 

No volt drop problems, a safer installation.

[Maker_of_Things]

One issue is the space for a second battery.

The other thing is the battery will need to vent gases while charging. I don't think that is ok inside the cockpit of the car.

If there was space somewhere underneath where I could bolt a battery box it would become a more realistic option. I could have done that on the old car but never got around to it. I never had an occasion where I couldn't restart the engine due to using the inverter but I did have to renew the battery more often though.