This is going to be a long post, because I want to try to get all of the relevant facts out in front of the experts and, to be honest, I am not really sure which facts are relevant. The short description is that when my air conditioning
units come on, the shorepower voltage drops and, if the conditions are right (or wrong, depending on your viewpoint), the air conditioning
unit breaker opens and shuts down the air conditioner.
Now for all of the facts. The boat is a 1978 Morgan
. We are currently located on the James River, near Richmond, VA. We are about a mile downriver from a coal-fired power plant. When the tide is going out, the outflow from the power plant causes the river water, measured at my speed knot
meter, to be between 89.5 F and 90.5 F. When the tide changes, the river temperature runs between 84.5 F and 88.5 F.
We have a forward air conditioning unit - a Dometic 16K BTU unit purchased and professionally installd last summer. We have an after air conditionig unit - a Mermaid 12K BTU unit purchased 5 years ago and professionally reinstalled last summer.
The marina we are in is more than 30 years old and has seen very little maintenance
. We are at the T-head furthest from the electrical
connection to the main. Our electrical
connections appear to have been installed by amateurs, and most of the other connections for the slips between me and the fuse panels
and meters appear to be similarly installed. The current
owner of the marina is not amenable to making any upgrades and barely covers the cost of maintenance
Originally, the boat had a single
30 amp shorepower connection. About two years ago, in anticipation of adding the second air conditioning unit forward, I installed a second 30 amp line. I then built a single
A/C power control station, using two 7 breaker Blue Sea panels
and a Blue Sea digital A/C multimeter. In order to monitor
both lines from a single multimeter, there is a switch that transfers from one line to the other. The multi-meter reads A/C voltage, frequency, and amperage and calculates wattage. However, the amperage is measured by using coils that one side of each A/C input is run through and the magnetic flux from one tends to interfere with the other, causing the amperage and the wattage to read inaccurately unless one line is completely shut down.
My original intent was to put both air conditioning units on one power panel and all other A/C loads on the other power panel. This would allow me to run one shorepower cable when I did not need A/C or heat and only run the second line when needed. This worked when I was in the marina where I had the air conditioning units installed and in a marina where I stayed overnight when returning to my home port.
However, as soon as I got to the home port and plugged in the second shorepower line, breakers started tripping. In order to work around the problem, I transfered the aft A/C unit to the "house" panel and left the forward A/C unit on the second line.
Here is where we get to the actual problem. When I connect both shore pwer cables
, but before I turn on the air conditioning units, I will tend to have an A/C voltage of, for example, 115 volts on one line and 114 volts on the other line. When I turn on the after unit, the A/C voltage on that line will drop between 5 and 7 volts, depending on things like the water temperature, how clean the raw water
strainer is and what the starting temperature on the boat is. When I turn on the forward unit, the A/C voltage will drop between 6 and 10 volts, again depending.
Usually, if the voltage starts high and doesn't drop very far (in the spring and fall), the systems run OK. But, when the temperature is high and the starting voltage is low (in the summer), I can't keep the units running. The individual breakers (15 amp) trip, dropping the units off-line. Sometimes, it will happen once or twice, and then run OK, other times - like today - I can't keep them running for more than five or ten minutes.
So, here are my questions. First off, is it normal for a large internal load to drop the A/C shorepower voltage on the boat, or do I have a problem with my connections, my shorepower lines or something else? I have retraced all of the connections on the boat and they appear to be solid and tight. One shorepower line came with the boat when I bought it five years ago, the other is about four years old. I have used an emery board to clean up the male connections on the pier side end of the cable, but I have not been able to clean the male ends at the boat connection and obviously, can't clean the female ends of the cable or the pier connector. Is there something else I should be checking?
Is the problem that I should be using 20 amp breakers rather than 15? The Dometic spec sheet indicates that the fully loaded cooling amperage should be a little more than 10 amps at 115 volts and the sea water pump is another 2 amps. The Mermaid spec sheet indicates that its cooling amperage is about 9.5 amps, with a pump running about 2 amps. It seems that this would be close to the amperage of the breaker. Does A/C power work the same as D/C power, where a decrease in voltage for a given load would result in an increase in amperage to compensate?
The Mermaid has a high pressure trip on it if the sea water simply cannot cool the unit - flow is too low or temperature is too high. This has tripped occasionally, but the breaker opening occurs much more frequently now. The documentation
for the Dometic unit indicates that it will become "less efficient" if the sea water temperature is over 90 F, but it doesn't say anything about it tripping off line.
I am looking at moving my boat to another marina, closer to the Chesapeake Bay
, where the water temperature would be cooler for the next month or two, but if the voltage issue continues, I am not sure if it is worth it. The new marina has only a few boats on the electrical branch I would be on, but the wiring
is of a similar age to the current
marina. The owners at the new marina appear to be much more amenable to upgrades, but they are on their own schedule.
I am pretty good dealing with the D/C power system, but the A/C system sometimes strikes me as PFM. I know that when I lived in a house, I never felt the need to check the incoming voltage, so I don't know if this happens normally, or if it just happens in this situation. I guess I assumed that if there was 115 volts at the power plant, and more loads came on line across the system, they would keep upping the generator
output to compensate, but that doesn't seem likely now.
Bottom line - is there anything I can do about this, or do I just have to suck it up and know that the loads will drop the voltage and that's all I can do?