DC Panel Upgrade

Project date: 2003



The first question is, "what does this consist of"? This upgrade consists of adding two switches and two meters to the cabin. I could not find a suitable place to put these, so I decided to replace the current DC switch panel in the cabin with the upgraded panel. The area to be upgraded, and the panel to be replaced are shown here. I will be replacing this 4 switch panel with a 6 switch panel with AC and DC voltmeters.

The second question is, "why is this necessary"? The first problem I have is I need a location for a switch to switch the stereo rear berth amplifier on and off. The second add-on switch is to switch a DC meter between the two batteries. And, both a DC and AC meter is to be installed.

The AC meter is the most straight-forward, so I will cover that one first. When you go to different marinas, the AC shorepower connection is sometimes not known. It would be nice to see the AC voltage to be sure it is between 110VAC and 120VAC - the nominal voltage range. Any voltage lower than 110VAC could be classified as a "brown out" condition, and could damage air conditioners, refrigerators, and other electronic equipment that is powered by the AC line. Therefore, it is nice to be able to "see" the voltage while at different marinas.

 

 

By proper use of a DC Voltmeter, you can get a pretty good idea of the state of charge in the batteries. There is a trick to how this works. While there is some disagreement between experts on this method, it is better than having no method at all. The idea is that under no-load or open-circuit conditions, a Lead Acid battery will show a certain voltage that can be intrepreted as to its state of charge. In other words, a battery will have a voltage that changes, depending on the state of charge, but it can only accurately be measured in an open circuit (nothing connected to it). Also, the longer the battery is left in an open-circuit condition, the more accurate the reading. Different batteries have different voltages that indicate a full charge, so check with the manufacturer of your particular battery type for these values.

State of ChargeWet CellGell CellAGM
100%12.6VDC12.85VDC12.8VDC
75%12.4VDC12.65VDC12.6VDC
50%12.2VDC12.35VDC12.3VDC
25%12.0VDC12.00VDC12.0VDC
0%11.8VDC11.8VDC11.8VDC

The requirement to measure the batteries under no-load conditions require some planning on wiring the DC meter. I plan on using a switch to allow switching from battery 1 to battery 2. If I wire directly to the batteries, then I can turn off the main DC breaker and battery switches in the boat, which turns power off to everything, except the bilge. Then wait 20 minutes and make a test reading. To make sure the reading is not skewed, I also turn off the battery charger using the AC breaker.

I decided on using a switch that has three positions. One, the starting battery, two, the house battery, and three, off. The off position is required, since leaving the switch in either battery position keeps the voltmeter connected to one of the batteries. While not a significant load, it might affect the "at rest" period when attempting to measure open circuit conditions. Draining the batteries with the meter is of no concern, due to the low current being fed to the meter.

The switches used in this boat are Carling Switch Contura III series switches. I was able to find a 3 pole switch that I will wire directly to each battery.

Now that I have the design layed out, I need to come up with a panel to mount everything in. I found a small fabrication shop that specializes in anodized panels, and they made a mounting panel to the specifications shown below. The shop even lettered the panel for me. This is going to make the project look professionally done.

Here is the panel after it was finished by the fabricator, Williams & Sons (Web Site), anodized and lettered to my specifications.

Fortunately the old panel came out really easy, and had its own connector. I need to transfer the switches and connector to the new panel. During the transfer process, essentially every wire had to be removed from the switches, so a means of identifying the individual wires was in order.

If there was ever a need to "measure twice-cut once", this is it, although its more appropriate as as "think-twice, cut-once". I "blue-taped" the are to be cut out to receive the new electrical panel. I made a template of the switch panel, then put the template on the area to be cut, then marked over the tape. This prevents marring, plus provides some degree of protection when using the cutter.

Yeow!, not too straight. Well, it is not really that easy to make the cut. Good thing it won't show. I used a spiral cutter for this, and regardless of what the commercials show, are quite difficult to use freehand, so be very careful here.

The next order of business is to disconnect AC power and remove the breaker panel. This panel is a rather nice in that it has a plug in wiring harness. The connectors are all different orientations, so it is impossible to get the wires plugged in wrong. However, it is still a good idea to mark everything as it is dissassembled. Here is where I connected the AC meter, and I also added a 1/2 amp fuse to keep everything safe.

Here are the sensing line connections for reading the Starting and House batteries from the DC meter. You can see one of the yellow waterproof fuse holders on the wire. These also have 1/2 amp fuses for safety, since they are always live.

US Coast Guard regulation, 33CFR183.4605(a), Subpart I, requires that all conductors connected to a battery be over-current protected within 72 inches of the battery. As I have repeated over and over, when you do a project on a boat, there are specific federal laws that regulate what must be done, especially with the electrical and engine/fuel systems. Anyone attempting these projects must know the provisions of 33CFR183.

You can download 33CFR183 or the phamplet "The Boat Builder's Handbook" from the USCG's web site. The handbook implements the regulation, and is a bit easier to read.

The last step was to wire in the Stereo Amplifier, screw the panel in, then reassemble everything. Let me tell you, I had a real messy looking boat for awhile, with panels dangling in air, hanging by wires, tools everywhere. But, there was an orgainzation to the mess, and the final product is really pleasing.

 


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