So I have various things that I have or will be installing that I want to run of the 2nd battery (laptop, inverter (not for laptop), fridge, work lights) and a few I want to run off the main battery (reversing camera, engine temp sensor)
With the 2nd battery in the engine bay, there's no space to install a fuse block, but I found a way (albeit a little unusual)
I created a platform above the 2nd battery using perspex. It's held in place using the battery holder bolts (2 nuts and washers on each to clamp the perspex) and a bracket bolted at the back of the engine bay using an existing bolt.
I then bolted the fuse block, circuit breaker and fused relays to the platform.
The fuse block is connected to the 2nd battery using 4GA cable and a 60A circuit breaker. I figure I'm never going to need the full 100A capability of the fuse block.
The two fused relays are for accessories powered by the main battery. The relay is triggered by power from the accessory circuit (I actually ran a cable from the back of the cigarette socket for this)
This has been in and working fine for about six weeks. Today I changed all the output leads to go through two plugs (20A), so that if I need to get to the battery, I can easily remove the whole platform - Trip the circuit breaker, disconnect the plugs, loosen the nut nearest the wheel arch, remove the nut nearest the engine, remove the bolt under the windscreen, unbolt the cable at the battery. About a 5 minute job.
Lessons learned.
- Don't by cheap circuit breakers from eBay. They trip ok but when you push the lever to reset it, it will snap off (on the original and the replacement)
- Cheap relay sockets bought from China will not use a consistent colour scheme for their cabling. Three relay holders, three different layouts.
- After you've crimped the connectors and put them in the plug, about half will fall out because you haven't crimped them tightly enough.
- Installers cut corners wherever they can. The circuit breakers screwed to the back of the engine bay don't have covers. The first time I did up the nuts on the battery holder, the end of spanner touched one of them. Hence the electricians tape over them