Decreasing A/C Voltage When A/C Comes On

[sdowney717]

How well insulated are your suction lines? I doubled up the insulation getting some pipe insulation foam tubes from the HD store. It seems to have improved the cooling. Returning cold freon back to the compressor is good as it keeps the system cooler.

I use an Attwood 12v DC bait well pump for the cooling water flow. I get 5 gal per minute from the little 750gph pump measured at the boat outlet.
And the outlet really is one hose size smaller the the 3/4 hoses I use.
Simply use a relay to switch 120v AC to 12vdc for the pump.

I cleaned the heat exchanger using the hoses and muriatic acid from the HD store. It is made for pools and spas to adjust the PH.
I diluted it 50% with water and two funnels in the hoses. It came out nice and clean and getting decent lower discharge temp at the outlet since the cleaning.

Does it matter which way the cooling water flows inside the heat exchanger on the cruise air condenser? Mine is backwards. The hoses naturally fit better and shorter with the in and out reversed.

[sailorchic34]

Heres a link to some larger pumps"

Marine Pumps by March and CalPump

The LC5CP-MD is 900 gph would work. I would put that in and if need be add a ball valve on the discharge to throttle the flow a little, if needed. Do the bucket flow test first though as I'm betting it will be around 500-550 gph when installed.

I looked at the 630 gph pump from the other manufacturer,further down the page, but I do not think that will get you there. The pumps are rated at one foot of head so pretty much open flow.

You can look at the flow chart tables and see that the flow rate drops off quite a bit with more head loss. If you have 3/4" diameter hose, you probably have about a 11 feet total head based on heat exchanger pressure drop, length of run and vertical lift. Could be more, but not much less. 5/8" hose (that inside diameter btw) would have about 15.5 feet pressure drop for your installation.

The second pump in series might work for you to. I'm not a big fan of pumps in series as one pump effects the other. but a second pump inline in series would fix the problem. Of course you have a second pump to fail now too.

Pumps in parallel might work, but you need check valves in each discharge and I would be worried about the check valves fouling. Simple is nice.

[DotDun]

As others have said, if the hose is less than 3/4" at those lengths your pump may not be able to deliver enough water. The difference between 1/2 & 3/4 is ~60% more in gpm flow (at the same pressure).

If the heat exchanger is dirty, use phosphoric acid to clean. Barnacle Buster is good stuff, packaged/marketed for just this purpose. You can buy phosphoric acid cheaper at auto paint supply store, but then you have to figure out how to dilute, etc. If you could build a re-circulate pump (5gal bucket and spare bilge pump) and circulate Barnacle Buster through the system for an hour, you'd be assured of a clean heat exchanger.

I use Cal 580gph pumps and on one of my units there is at least 18' of 3/4" hose. The pump is in the bilge and the AC unit is on the bridge deck ~4' higher than the pump. It works fine, even in 90 degree water. Water temp is less important than water flow, high water temp will expose the problem of low water flow.

[GordMay]

Originally Posted by DotDun

... The difference between 1/2 & 3/4 is ~60% more in gpm flow (at the same pressure) ...

Since (3/4 ÷ ½) squared = 2.25; a 3/4" hose will have 225% the capacity of a ½" hose.

[DotDun]

Originally Posted by GordMay

Since (3/4 ÷ ½) squared = 2.25; a 3/4" hose will have 225% the capacity of a ½" hose.

Pump capacity counts also. Go the other direction, a pump designed to fill a 3/4" hose certainly can't fill a 1.5" hose.

I can't recreate the calculations now (it's been a while), but from what I remember, a 500gph bilge pump will send ~8gpm thru a 3/4" hose and ~5gpm thru a 1/2" hose.

[sailorchic34]

Hum... Well any centrifugal will pump a range of flows. The pump rating on smaller pumps (IE pumps like you have onboard) are listed at full flow, either 0 or 1 foot of head. At the other end of the curve you have max head and zero flow.

A pump will work anywhere along that curve, and will balance, output HP with actual head and flow the GPH at that point on the curve..

So a 500 gph pump might flow 8.5 gpm on a 3/4" of say 4 feet in length, or say 2 gpm at 19 feet of length. That same pump with 1/2" hose could also flow 8.5 gallons but maybe the hose is only 2' long. More friction loss, less flow rate. The number are just estimates BTW as each pump has it's own flow curve.

Plus the number and types of fittings and valves make a difference. With hose, you have an insert fittings, that really adds pressure drop. This as the insert fitting may be roughly 1/2" bore on a 3/4" hose. So that has a large effect on flow rate too. Each elbow, valve, strainer, etc add pressure drop.

It why in real life a 500 gph pump will never put out 500 gph when installed in a boat. If your lucky it will be about 1/2 that to maybe 2/3 of rated capacity.

The type of hose or pipe makes a difference too. Corrugated hose has very high pressure drop per foot. If I remember correctly, normal smooth bore hose has roughly twice the friction loss as solid pipe. Copper flows better then steel in the same pipe size, which of course they are not exactly the same diameter. Plastic pipe PVC, PB, PP, PE generally have the best flow coefficients.

BTW You could in theory hook a 500 gph pump up to a 24" pipe and it will pump 8.5 gpm. It's just going to take a bit of time. to fill the pipe. Oh there would be some laminar flow issues, but it would move water.... very sloooowly..

I see eyes glazing over so I'll stop here..

[CaptFrankM]

OK, new data (sorta):

We have moved temporarily to another marine in Urabanna, Virginia. Water temperature is not significantly different. However, upon arrival, the first thing I did wass flush both units with the (much) higher pressure dock water here.

When I flushed the foreward unit, I operated the valves from the boat, so I did not see what came out of the line when I flushed it. However, when I flushed the after unit, i was on the pier for the flush. I'd love to say this was foresight, but actually, I was being lazy. I had turned off the water on the pier before moving the house from the fforward to the after unit and didn't feel like going up, turning it on and then adjusting the valves on the boat). Bottom line - when I turned on the water on the pier, there was a second or two of hissing and bubbling, with a trickle of water. Then, there was a plug of mud that came flying out the discharge thru hull. Literally a two second flow of what can only be described as mud. When it hit the water next to the boat, it spread out and sank! After a five minute flush, the water was running clear and cold.

I stopped the flush, started the unit and got at least twice as much flow out as I have seen in a year. This was after flushing the system using the water at the old marina last week.

In addition, the voltage here when I pulled in and before I put any loads on the system was running about 120 volts. The forward line with the A/C fully loaded is 118.8 volts and the after line with the A/C fully loaded, all normal house loads and the battery charge in Bulk is running 116.9 volts.

A cheap marina may cost more in the long run.

[twistedtree]

That's great news, and I think confirms there were two problems:

- Obstruction in your lines

- Poor dockside connection and wiring at the other marina.

[svBeBe]

Originally Posted by CaptFrankM

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 452 ketch. 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?

I had to explain to my grandkids why this was happening to us at a certain town quay here in Turkey a few weeks ago.

Think of Voltage as water pressure. If the supply line is not big enough and you are near the end of the line with other connections before yours, you will see the voltage (pressure) drop when you start using it...you will also see it drop when others in line before you use more. I went on to explain Amps as the amount of water that is actually flowing through your line at that time. When you have the problem you described, as your Amps increase, your Volts will decrease.

Regarding sea water temperature, it has a direct impact on how much your compressor runs and your cooling efficiency, so in your situation when your compressor is running more because of a change in water temperature, you will have more of a problem.

From what I have read in your posting, I do not believe there is a significant problem on-board, but rather the problem exists at your marina, which you state has not been maintained in 30 years. For instance, it was very rare to have anything near the amp loads we have now as compared to 30 years ago. The number is probably something like 10 times more amps needed as compared to 30 years ago.

Bill

[CaptFrankM]

After a week in Urbanna, I can safely say that the air conditioning units are working fine. After flushing both units when we came in, both units have run perfectly - well, except for one time when the forward A/C tripped off during a thunderstorm. Apparently, we brought the bad weahter with us, since Urbanna lost power for the first time this year, four days after we came into port!

I am still considering upsizing the output lines for the aft unit, but will hold off on doing that and changing the breakers to 20 amps until the fall.

Thanks, everyone, for your input.

[DeepFrz]

Great news that you found the problem(s).

[chala]

Originally Posted by CaptFrankM

changing the breakers to 20 amps until the fall.

I would not bother too much about changing the breakers, the originals one’s seems to have done a good job of indicating that something was wrong and in the same time protecting the equipment.