Wednesday, 14 November 2012

Tidying up the DC Power Distribution

A while back I installed a pair of switch panels to distribute power from the battery bank to all DC electrical appliances (lights, fridge, fans, etc) in Jim. I chose to use circuit breakers over fuses, partly because they are easier to reset if they blow, and partly because they can easily be used as switches to isolate power to items like water pumps which wouldn't necessarily need their own switch (like lights or fans) but which I may want to isolate at times. Below is how they looked when installed a year or so ago.

 The Victron ESP breaker panels freshly installed

For reasons which I can't really understand, most caravan and motorhome manufacturers still choose to use fuses over circuit breakers, despite AC installers choosing to make the switch more than three decades ago. If you could still buy them, I have no doubt that caravan manufacturers would still use Bakelite switches and rubber wiring. Nevertheless, there are a fair range of circuit breaker panels to chose from, mostly from the world of marine electricals where their use is more common.

I chose to use two 11-way breaker panels from Victron's ESP panel range. I could have used less than 22 circuits, but I would have had to start aggregating various electrical items together in non-intuitive ways. Do the toilet flush, and kitchen extractor fan belong on the same circuit? The Victron panels seem to be less popular than the BEP Marine or Blue Sea Systems panels, despite costing about half that of the BEP Marine panels and about the same as the Blue Sea Systems ones. In my opinion the Victron panels are better looking aesthetically, and I cannot see the alternatives offering anything over the Victron Panels.
When I installed the switch panels, I just wired in the small number of circuits I retained from Jim's orginal electrical installation, and the remaining breakers were left unusused. Below is how the electrical cabinet looked when largely empty; the bus bars for the newly installed panels are on the top right.

The empty electrical cupboard. With Blue Sea Systems bus bars for the negatives, and Victron ESP panels for DC positive overcurrent protection

Given that I am now begining to install some electrical appliances, I thought it was about time I labelled up each circuit on the panels, and worked out what breaker rating each circuit would require.

Tuesday, 13 November 2012

Solar Install

I haven't found much time to work on Jim recently. With the sun down by about 4pm I don't get any daylight during the week, and unless I'm up at dawn I only get about six hours on Saturday and Sunday. Despite this, I've managed to make some progress on the installation of the solar panels.

5 BLD Solar 100w solar panels installed on the Brownchurch roof rack

The first thing I had to do was run the cabling under the roof rack. The cables are fixed to the steel using rubber line P-clips; all available steelwork is occupied with solar panels at the back end of the rack, and so to ensure that the solar panels can sit flush in the frames, all of the clips had to be fixed using countersunk rivets. This task involved drilling about 70 5mm holes in the steel roof rack, countersinking each hole, painting each hole to protect the exposed steel, and then riveting a p-clip in each hole. As well as testing my patience, my cordless drill batteries committed suicide, I snapped two drill bits, and my riveter declared war on my hand.
A stainless steel, rubber lined P-clip holding the 4mm solar cable to the roof rack

Countersunk rivets holding the P-clips to the roof rack, zinc rich paint protects the holes drilled in the galvanised steel

Stainless P-clips support the 4mm solar cable every 20cm along the roof rack

I toyed with the idea of using conduit, but decided it was unnecessary. The solar cable is double insulated, and is fairly protected being 3.5m off the ground, in the 80mm gap between the roof of the truck and the underside of the roof rack. I've clipped the cable every 20cm, and have wrapped it in cloth tape where is likely to chafe.

Four cables were run across the rack (two positive and two negative), to allow me to run two parallel strings of solar panels, each with four 100w panels in series. Three of the eight panels are likely to be in shade for some of the day as the adjacent awning sticks up a fair way. You can see the potential shading issues with the panels on the right of the rack in the picture at the the beginning of this post.

To give me a better chance of getting a good charge into the batteries I have wired the three partially shaded panels into one string of four panels, and the the remaining unshaded panels into another string. The Morningstar MPPT regulator I am using only has one set of panel inputs (as most off-grid regulators do) and so i am parallelling the two stings together. I am not knowledgeable enough on solar wiring to understand the impact this situation will have on the charge current and voltage, and the ability of the MPPT regulator to track the optimal power point properly, over two strings in differing light conditions. Can anyone reading enlighten me?