Saturday, June 3, 2017

Electrical #1 Batteries

It was time to tidy up my makeshift 12v system that had evolved chaotically. I had added a battery to power the autopilot and it was all very untidy.

The first stage of my nice n' tidy electrical install is the battery choice, wiring and mounting. The Tiki is little and doesn't have much space for cluttering up with batteries. I already had one U1 35 amp hour AGM battery that I had chosen for its small size. Going on the convention of only running it down to 50% of charge, this only gave me 18-odd amp hours to work with. Although my power needs are low (autopilot 1 amp/hour; VHF 0.5 amp/hour, + phone and hand-held recharging), 18 amp hours is not enough for extended trips over several days. On the other hand there isn't room on the boat for a big 60 amp hour battery.

2 x 35 amp hour U1 AGMs getting a final charge.

So, I decided on two 35 amp hour batteries wired in parallel, which gives me the same as a big 70 amp hour battery, but in a size that is small enough to fit under the boat's floor boards. The batteries are sealed absorbed glass mat (AGM) so that I don't have to worry about topping up with water, or battery acid in the bilges. I used 8 AWG cable as it is more than large enough to handle the current for my setup (i.e. not required for starting the outboard), and can be assembled using a standard tool and the marine grade ANCOR crimp connections that I use with all my wiring projects (using the 4 AWG cable needed for electric engine starting requires special tools and fittings).

Marine grade heat shrink was used on all connections.

The battery circuit is protected by a MEGA fuse and holder. I was shocked by how much these were at West Marine, so shopped around and got them aftermarket (Del City Online). The fuses were ~$1 each instead of $10.50 at WM, and appear to be exactly the same product.

I knocked up two battery mounting bases from 5/8 marine plywood and gave them two coats of epoxy. The bases were then filleted into the bilges using thickened epoxy. The bases are mounted under the floor in the cabin in the middle of the boat to get the weight away from the stern where they would contribute to stern dragging. The battery hold down straps were pre-installed so that I didn't have to grovel around in the bilges after installing the mounts.

Out of the way under the floor boards and ready for the next step.

The batteries are placed in standard U1 marine boxes and strapped down onto the mounts. The floorboards fit over the boxes with plenty of clearance, and you don't even know they are there - apart from all of the wires emerging which will be dealt with later when I install a distribution panel.

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