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December 2nd

Building Blocks of a Monitored Electrical System

Posted by // December 2, 2012 // COMMENT (0 Comments)

Boats and Gear

After months in the dark, I’m finally starting to get some lights turned on. On the boat, that is. Although I’ve had the bare bones in place for a while I’m just now getting into the wiring in earnest. It’s tricky and often frustrating work but it is immensely satisfying to finally have things like lights and A/C outlets. Actually, I’m sitting on the boat as I write this.

The not-so-basic building block of my electrical system is a panel from Blue Sea. It was a gift from my father and is the single most expensive and technically advanced piece of equipment on the boat. It’s also enormous,.a 14”x14” block of no less then thirty breakers and switches which takes up the entire starboard side of the bulkhead. He got  it for me in the early days of the boat project, long before I realized what I had gotten myself into and though I tried to sound grateful I was actually appalled when I saw it. It seemed like such a ridiculous thing to put on a little boat. Since then I’ve slowly come around. I’ve still yet to use more than half the breakers but the panel itself is very well designed and the monitoring system so useful that I’m beginning to overlook its gargantuan size.

The Electrical Panel

On the DC side the panel is fairly simple. There is a pair of three way switches, one each for the house and cranking battery and on the house side power is led from the switch to a pair of busbars which are wired to two rows of circuit breakers.

One DC busbar and its row of circuits

 All this wiring was already done when I received the panel, along with a bunch of more complicated stuff which has to do with the systems monitoring. To hook the panel up we built a frame and installed it into what was once a galley cupboard. Behind it we placed a DC negative busbar and two A/C busbars for neutral and ground wires.

The DC Negative Busbar
And dual A/C busbars. The green wires are ground and the white neutral, the hot wires go directly to the panel


For my first few circuits all I had to do was run the battery cables to the main switch and the negative busbar and wire up individual circuits. Circuits are wired with the negative wire to the negative busbar and positive to the appropriate circuit breaker, and that’s about it. For the first couple months I had only two breakers on- the bilge pump and the tri-color, As long as the boat wouldn’t sink and I could go sailing, I was happy! The A/C side of the panel is a bit more complicated and I won’t go into that now as I’m not sure I understand it well enough yet to write about it.

DC Circuits

My Blue Sea panel has a couple really neat features for individual circuits, particularly the bilge pump. There are two switches for the bilge pump, an on/off switch for the circuit and a manual on switch for the pump itself. The breaker has an ingenious design which makes it virtually impossible to switch it off accidentally and the rocker switch for manual pumping cannot be left on. This circuit is also pre-wired to the systems monitor so that it can keep track of how often and how long the pump is cycling, and I believe I could program various alarms in there if I wanted to.

Note protected switches on bilge and alarm circuits

Really though I’ve done very little with this systems monitor, I expect at some point I will use more of the features but at the moment I’ve got bigger things to work on. I didn’t even have the monitor hooked up at all until a few weeks ago. I kept putting it off out of a fear it would be quite complex but in the act I was pleasantly surprised to find it quite straightforward. The heart of the systems monitor is a DC shunt, a solid-state (see below) device that goes in the negative circuit of the house battery and allows for measurement of the amperage going through the circuit. With a little user-inputted background information, mainly the number and size of batteries, the systems monitor uses this amperage measurement to keep track of the number of amp-hours remaining in the battery (ie. their state of charge). It also keeps track of metrics such as how many times the battery has been cycled and can be hooked up to sensors for keeping track of things like battery temperature and the amount remaining in various tanks.

The DC shunt. The small yellow wires run to the systems monitor

The tank monitoring stuff I haven’t gotten into yet, and likely never will but the battery metrics have already proved invaluable. The batteries I’m using are a pair of Odyssey AGM deep-cycles which my father rescued and resuscitated for me. After a couple months of use the house bank was once again in quite bad shape, operating at about 35% of its capacity. With the systems monitoring hooked up to tell us what was going on and an external charger on hand we were able to resuscitate the battery a second time and to figure out that it had gone on the fritz because it wasn’t being fully recharged. For now, it’s working well again.

The Blue Sea systems monitor provides plenty of useful information on battery sta

In addition to the systems monitor and batteries the third major component of my electrical system is a Xantrex Inverter/Charger. This is tucked safely in the top corner of the port cockpit locker and wired in two separate circuits to the A/C and DC sides of my electrical panel.

Inverter/Charger on its shelf. Ventilation is important as it can produce a good deal of heat

On the A/C side power is coming from the shorepower inlet direct to a breaker on the panel and then back to the inverter and again to the panel. The DC wiring is simpler, going straight from the inverter to the house battery, passing through the shunt on the way. When I’m plugged into shorepower the inverter charges the house battery as needed (I can charge the cranking battery as well by paralleling the batteries using my panel switches, but this is rarely necessary) and when the battery is fully charged it goes into standby mode.

On the A/C side when plugged in it remains in pass-thru mode, funneling shore power directly to the panel. Unplugged from shorepower I leave it off unless I need to run an A/C load. This puts it in inverter mode where it pulls power from the house battery, converts it to A/C, and passes it to the A/C bus and on to my plugs.

The inverter/charger is wired through the shunt so that all the DC loads register on the systems monitor, both the current it sends to the batteries when charging them and the load it draws when using them to produce A/C power. The systems monitor should also be monitoring the A/C loads via a separate Hall effect sensor (basically an A/C shunt) but I haven’t got this working yet. Knowing amperage on the A/C side is far less important than the DC so this is still a fairly low priority.

Having trouble keeping track of all this? I certainly am… Here’s a (very) simplified wiring diagram. I’ve left out some things like the battery paralleling circuits and systems monitor circuits, and A/C circuits are drawn in a rather inaccurate way that electrical engineers will probably find infuriating. This in order to unclutter things, certainly not because I don’t know what the hell is going on in there, OK? Click to enlarge.

I’m not much good at these, but you get the idea

With these three things- my batteries, electrical panel/systems monitor and inverter/charger I have everything I need (well, quite a bit more than I need, actually) to power the boat, keep track of the state of the batteries, and to keep them charged. This last is contingent on regular access to shore power, missing from my system is a charging source that doesn’t require being plugged in. I can charge the batteries via the alternator on my inboard Yanmar but I’m loath to do so. Instead, I plan to install a couple good-sized solar panels whenever I can find a good deal. For now I’m usually at the dock where I can drain all the power I want – recent power-hungry (A/C) acquisitions include a space heater to get ready for winter, a tiny, boat-sized electric crockpot and a rice cooker to match. Plus I’ve got light to read by. Things are getting positively cozy.

Edit: I have been corrected on a couple small points:
The shunt is not a ‘solid state device’- I probably should have known better as I got this, apparently inaccurately, from somewhere else without really understanding its meaning! The shunt actually a finely calibrated resistor. A shunt (in this usage) creates a minute voltage drop that is in direct proportion to the amperage flowing through it. This voltage drop is small enough to be negligible to the system but large enough that it can be measured by a finely-tuned millivoltmeter in the systems monitor,  giving an accurate measurement of the total amps flowing in or out of the batteries.

I neglected to mention that the A/C busbars should, and will eventually be, covered.

Xantrax has been corrected to Xantrex

Lots to learn!

This article was syndicated from Safe At Harbour But Meant For The Sea: DIY Sailing with Paul Calder

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