Decreasing A/C Voltage When A/C Comes On

[CarlF]

I would guess you have the circuit breakers right on the edge of tripping. The lower the voltage the higher the amp draw from those compressors. Remember, it could be another boat in the marina that's also dragging the voltage down. Does a breaker ever blow when you are running only one cord/one air conditioner?

One thing to check is to make sure your two 30 amp cords are plugged into outlets that are on opposite phases of the marina supply. Try the 2nd cord in different outlets to see if another works fine (because it is on the other phase). If the marina was badly wired, there may be much more load on one phase than the other. Or several boats may be using 30 amp adapters in 50amp outlets - and all drawing from the same phase.

If all the wiring in the boat along the air conditioner circuit is 12 gauge or heavier, swapping to to 20 amp breakers would be worth a try.

I also never run my 30 amp cords much above 20 amps on a continuous basis. The fire risk is just too significant.

Carl

[Snore]

Frank where are you taking the readings?

Since you stated the problem did not occur at the other marinas, it would seem prudent to take the readings at the marina's receptacle. Taking the readings at the breaker panel are impact by your wire and connectors.

Bill

[DotDun]

Your 50' 30amp shore power cord wil contribute a 2 volt drop when running @ 20a. Remember, voltage drop is accumulative, hence if the wire on the dock is too small, it will affect you dramatically. Use the voltage drop calculator at:

Genuinedealz - Technical - Calculators

you'll see that 300' of 10awg wire running 20a will contribute 12v of drop.

I'm with Bill, the marina has a wiring problem.

Also, remember that as voltage drops, current draw will go up.

IMO, if the water temperature was the problem (by increased head pressure and causing the breaker to trip), the system is designed way too close to the limits.

[CaptFrankM]

OK, I have just returned from the boat. I replaced the older of the two shore power cables with a brand new Marinco EEL cord - still 50 foot, still 30 amp. I took a reading on the old cable and then replaced it and took a reading on the new one. The difference was 0.2 volts, which I think would be within the margin of measurement error. I will keep the old cable as a back up, in case anything happens to one of the "primary cables."

I also checked the wiring size on the boat itself. The wiring from each shore power connection to the AC power panel is 10 gage, the wiring from the power panel to any load is 12 gage.

Finally, the river water temperature has dropped to 86.4 degrees - apparently, the load on the coal-fired plant has been reduced, so it is having less of an effect on the river temperature. Since the temperature has dropped, both the forward and the aft A/C units have run without a hitch, even though I still have the same voltages at the power panel.

I appreciate all of the comments about the problem being in the marina and I agree that it is contributing to the problem, but there really isn't anthing I can do about it. People who the current owner considers "troublemakers" tend to get asked to leave. Since this is the only marina that a deep draft sailboat can get into and live aboard upriver from the Chesapeake Bay on the James, I can't afford to make waves for another year. I can afford to move out of the marina for a month or so, so that will be my immediate plan.

I also appreciate the input regarding the interaction between voltage and amperage. I knew that to be true with DC loads and I suspected that it was true on AC loads, but I am glad to get it confirmed. I particularly like the idea of running a generator to power the air conditioning units, since the voltage would be "cleaner" but I have a feeling that neither my neighbors nor my wallet would like it.

[twistedtree]

With #12 wire running from your breaker panel to the AC units, you could swap the 15A breakers for 20A without rewiring.

[chala]

Originally Posted by btrayfors

I certainly agree with that. As I said above, "Just as a matter of good practice, you should not run the 30A power cords or the circuit breakers anywhere near their ratings on a continuous basis."

As Sailmonkey said, with a LRA of 60A, a 15A circuit breaker isn't likely to cut it, especially if there are other loads on the circuit.

Bill

Originally Posted by chala

Valuable information Gord
Further more Extemp.
Some Standards accept 1.05 time the full load current as acceptable and the thermal protection should not trip. This is 1.85 Amps * 1.05 = 1.94A. Assuming that your Ampmeter read true, your reading is 1.95A.
I would assume that your motor is protected by a thermal overload, if not be careful; there is no need to burn the place down.
The above Standards also state that at 1.2 times the full load current, the thermal overload should trip in about 15 minutes.

Originally Posted by CaptFrankM

Line 2 - no load. 115.8 volts, 0 amps.
Line 2 - forward A/C running. 110.7 volts, 11.9 amps.

Line 1 - no load. 115.5 volts, 0 amps.
Line 1 - aft A/C running only. 108.6 volts, 13 amps.
Line 2 - aft A/C and Battery Charger running. 105.3 volts, 20.1 amps.

Where were the readings taken, at the breakers or at the air/cond units?

[CaptFrankM]

All of the readings were taken at the Blue Sea multimeter at the AC power panel. I have, in the past, taken readings at both A/C units and found there to be a 1 to 1.5 volt difference between the power panel reading and the reading at the units, which I attributed to the length of the cables and the quality of my connections. In addition, I have checked the multimeter on the panel against my handheld digital multimeter and found a small difference.

I have tried to get readings at the power connections on the pier, but short of building a something that plugs into the connection and has bare wires to connect a multimeter to, I am not happy with the readings. It's always tricky to get a good connection and, althought I have opened up the fuse panel and taken readings off the busses in there, I get very unhappy standing on a pier with a live power panel open. I think it affects the quality of my readings

[DeepFrz]

Have you had any further problems?

[CaptFrankM]

We have been running with just the A/C unit and house loads on, the battery charger and water heater off. Yesterday evening, my wife turned off the A/C to turn on the water heater for showers.

In about a half hour, the temperature in the aft cabin went from 75 to 80. When we turned the A/C back on, it ran for about half an hour, then the compressor shut down on high pressure (river water temp 85 F). I cleaned the water filter, removed the air filter temporarily and removed the door to the closet that the A/C sits in to try to get as much air flow as possible. We reset the compressor trip and it ran for an hour, cooling back down to 76 F. Then it tripped out again. I reset it and it ran for about 90 minutes, cooling down to 72F. I reset it a third time and it ran through the night.

About 10:00 PM, I started the battery charger and it ran through the night, too. This morning, with the A/C cycling and the battery charger in float, I had 120 volts, so I turned on the water heater. I'll let that run for a couple of hours, then take it out again.

Hopefully, juggling loads will get us to the weekend. By the way, all of the trips this time were in the compressor high pressure circuit. The water coming out of the sea water overboard thru hull is hot to the touch.

[sailorchic34]

85 degree river temperature, should not be causing the problem. In general water source heat pumps, which marine AC units really are, work fine up to about 95 degree inlet water temperature.

Have you measured your discharge water flow (with a bucket) and temperature. With 85 degree inlet water, you should have 5 to 10 degree rise on the discharge. So no more then 95 degree discharge water.

If its 98-100 degrees, your water flow rate is low. If it's only a few degrees different then the inlet temperature then the condenser water heat exchanger might be limed up a bit. You could use phosphoric acid with inlet and outlet hose up to hold the acid in the heat exchanger , Hold for 10 minutes and flush. You can get phosphoric acid at hardware stores, generally in the paint department...

If the temperature is high then the water pump is not up to capacity or has a partly clogged inlet. That it ran better after the sea strainer was cleaned, says maybe a water flow issue on the condenser side.

[CaptFrankM]

I have not measured the flow rate on the after unit since I had the system professionally reinstalled. It had originally been installed by a previous owner, who was one of "those" guys - the type who, if he has no suitable electrical wire, clips both ends off of an extension cord and keeps on going.

Part of the problem with the aft unit was that the inlet to the unit is nice and short - about three feet to the strainer and then three feet to the pump and three feet to the unit. The pump itself is just at the waterline and the unit is mounted about two feet above that, so the vertical lift is well within limits. However, the outlet is about 20 feet, because the P O ran it to the transom, and the only possible place to move it would still require a minimum of 10 feet.

The pump itself is a March liquid cooled 500 gph unit. The Mermaid people say that the pump should produce a flow rate of no more than 550 GPH. Given the resistance of the of that outlet tubing, I know that I am not getting the full 500, but I should be getting at least 400 gph.

When I had the system re-installed, I had a flsuhing port installed between the strainer and the pump, with a valve between the flusing port and the pump. Whenever the high pressure trip happens, or once a month, or after really heavy rains up river, I will back flush the strainer and raw water thru hull, but I have not flushed the system itself recently. I will give that a try tonight and see if it helps. Then I can try a phosphoric acid flush, although that seems like a pretty major evolution.

Should I mix the acid in a bucket and use the pump to suck it in, or fit a funnel to the inlet house and try to pour it in? Is this stuff nastier than muriatic acid?

[sailorchic34]

OK... Hold up on the acid flush..

23 feet total of hose is a lot of hose for a small marsh pump. The marsh pump only develops 19 feet of head total on a good day. That could be it right there. Two options, well really about 4, but keeping it simple.

First hose has a lot more friction loss then pipe, So maybe change out the hose to pipe where there are long straight pieces. If possible.

Second option; install hose one or two pipe sizes larger. I assuming you have 3/4" hose (1/2" hose would be way bad), which would be OK for 5' at 8 gpm. But for a 20 foot run I would upsize it one or two sizes. That will in effect reduce friction head which will increase flow rate. Really for 20' I would run at least 1" hose /pipe.

Third option, install the next size up pump, say 600 gpm. I say this, because with a 23' hose run your probably only getting 300 ish gph from that 500 gph pump, so your not getting the heat rejection that you need.

So putting in a 600 gph or even 650 gph might get you closer to the 500 gpm you really want with the warm water.

Four, punch another hole in the boat close to the AC unit and dump the water there...


Oh you can use a bucket to catch the water for say 15 seconds. Then weight the bucket of water. Toss the water out and weight the bucket empty. Subtract the bucket weight from the bucket with water weight. Then divide by 8.55 to get gallons per 15 seconds. Then multiply by 240 to get the gallons per hour.

If your boat sits in fresh water, divide the water weight by 8.33

[CaptFrankM]

Looking at your four options:

There is only one spot where I might be able to replace the tubing with pipe and that is only for about four feet. I may come back to that, but it doesn't look like it would make a lot of difference at this point.

Upsizing the hose is a better possibility, even if I only cut into the line and replace ten or twelve feet of it (there are several places where structural issues restrict the hose to the current size).

Upsizing the pump is something I have looked at several times, but I can't find a pump in the 600-700 gph range. There is a Cal pump that is rated at 580 GPH, but then everything seems to jump to 1,000 GPH or greater. Since the documentation is very specific about not exceeding 550 GPH, I don't figure I can go that high (unless I throttle the flow somehow). I would really appreciate any suggestions - from anyone. Really!

As for punching another hole, I would do that if I could, but the A/C unit is just off the centerline to port (next to the mizzen mast), so that any run would have to go under the cabin sole. The current run is the only easy one. It's impossible to go to port because the cabin sole touches the hull on its outboard side, meaning I'd have to expose the hose (there is an electrical wire that does just that and requires a cover to protect it). To go to starboard, I would have to pull up the toilet in the aft head to get to the deck underneath. Really, for as much as a PITA as it is, the lead out aft is really the only one that works without rebuilding the aft cabin.

[chala]

Originally Posted by sailorchic34

Have you measured your discharge water ………. temperature. With 85 degree inlet water, you should have 5 to 10 degree rise on the discharge. So no more then 95 degree discharge water.

If the temperature was higher than the above quoted I would try if it was a simple thing to do, to temporarily remove and reinstall and use the pump of the other unit in series with the original pump, somewhere in the discharge line where it is easy, preferably 1/3 to ½ the distance from the original pump and see if it make a difference in flow, temperature. To adjust the flow it should be possible to throttle the discharge line.

[chala]

Originally Posted by GordMay

Operating a motor at the "outer limits", either high or low, of its Voltage requirements (Voltage tolerance band) reduces its efficiency and can cause premature failure.

From WEG Electric Motor Manual.