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Good Decisions Require Good Info from Ammeters

What started as a relatively simple project, adding a third, independent battery bank for house loads on Wired, has so far resulted in the addition of new voltage meters, replacement of a good deal of the cabling in the primary circuits and a small amount of general housekeeping in the main panel.

Before actually tackling the addition of the new bank we've decided to take on one additional small project. Although the new Blue Seas voltage meters function perfectly and provide accurate real time information on battery condition, they do not monitor amperage so we're going to go ahead and install a new ammeter as well. After all, there is no such thing as too much information and since we will have a brief opportunity to log this info before we install our new bank it will be valuable in determining our requirements for amp/hour capacity.

Projects like installing an ammeter can expose you to high current. You must have an understanding of how electricity functions and exercise safe work habits. If possible you should begin by removing the cables from the negative post of EVERY battery bank and if applicable, by unplugging the AC shore power cord and/or shutting down the generator. This project is within the capability of a good DIYer, but if you're unsure, do the right thing and call a professional marine electrician.

Ammeters work by measuring the current flowing through a circuit. Modern ammeters employ a shunt installed in the circuit being monitored. The shunt can be located anywhere in the positive side of the circuit. Two small gauge conductors run between either side of the shunt and a display meter. The display can be mounted in any convenient dry location even one well away from the circuit being monitored.

Make sure when purchasing an ammeter that it is sized to exceed the maximum current that will flow through the circuit. The shunt will act as a fuse and blow if the current exceeds the allowable capacity rendering the circuit dead. This can be dangerous if you lose power at the wrong time. In any event you will be out the cost of the shunt, the lions' share of your investment.

In our case the main panel is becoming congested. I chose to mount the shunt outside of the panel, closer to the battery bank. Knowing that ultimately our intention is to reconfigure our house system, it made sense to make some changes at this stage. Since I had a piece of primary cable left over from my last project, I decided to run it from the panel towards the proposed location of the new bank and see where it landed.

Good luck prevailed when the cable end landed in a dry location between two the existing battery banks.

For reasons I don't completely understand the engineers at Hatteras had installed a master switch for the house supply fed from the supply post on the port engine master switch. I eliminated the jumper between these switches and connected the new cable directly to the supply side of house switch. The other end I connected to one side of the shunt. I installed a short (temporary) cable from the other end of the shunt to one of the existing banks. This cable will be replaced with one leading to the new bank when it is installed.

After mounting the shunt the next step was to mount the display. There was room next to our voltage meters so the decision was simple. One conductor connects to each of the small terminals on the shunt and to the corresponding terminals on the back of the display. As always, the longer the run is the larger the required awg. I used a length of 14/2 Anchor Boat Cable supported neatly alongside the primary cable.

(Neatness counts, make sure your crimps are tight. Rings are always preferred to forks and don't skimp on ties. Unsupported wires are prone to chafe, wear and stress.) Both conductors are "hot." Be careful not to accidently ground them and do not mistakenly connect them to the large terminals or your meter will be destroyed.

After tightening the connections and mounting the display it is time to reconnect the negative conductors. Make sure all loads are turned off. This will eliminate sparking as you connect the cables. Take a moment at this time to ensure that the posts are clean and the clamps are in good condition.

Presto! Your new ammeter is up and running. If you're like me, you might be surprised to find out just how much electricity you are consuming. In my case I found that the "instant on" features in our 12 volt TV(s) and stereos plus the wireless modem were consuming almost 2amps, 24 hrs a day! Good info to have and another job to add to the list.

Peter Patterson is a Canadian Coast Guard certificated Master and an ABYC certified marine technician. He is a former Canadian Yachting Association Instructor/Evaluator and powerboat instructor. Currently he is on trickle charge while he re-invents himself.

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