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Old 06-28-2020, 09:18 AM   #1
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Low Voltage AC Issue

I have a Beneteau ST 34 and we moved to a new marina this year. We have 2 Cruisair Qht systems and on the AC unit in the main salon, Im getting a LO AC error which the manual indicates operating voltage remained below an acceptable limit for 3 minutes or more (100V for a 115V system). It shuts the system down if this error occurs. I can cycle through on / off and will come back on but if its a hotter day, it will shutdown within 5 minutes or so. Ive tried 3 different shore power receptacles and 2 different shore power cords and they all produce the same result. I can watch the volt meter display in the boat and prior to the AC coming on, it runs from 116 - 111. As soon as the AC kicks in, the voltage drops to just above 100 and then eventually drops below 100 triggering the shutdown. Were running AC while on the boat at about 75ish. When we leave the boat, were setting at 80. Normally when we come back to the boat after a week, the AC in the salon is shutdown - AC in bedroom i has no issues. Im no electrician or AC guy, but I though Id throw it out to the group prior to calling for professional assistance. Thanks.
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Old 06-28-2020, 09:54 AM   #2
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Check the voltage at the marinas power post. If its low there then it their issue.
Ive been to marinas that barely make 100.
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Old 06-28-2020, 10:47 AM   #3
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As jleonard notes above, first check the voltage at the power pedestal. Disconnect your shore power cord from your boat and measure the voltage at the female end of the cord. With no current flowing, the voltage you measure at the end of the 30' cord will be the same as at the pedestal.

A better way is to make sure both A/Cs are running (turn the thermostats down temporarily) and see if you can get inside the pedestal to measure the voltage while it powers your A/Cs. The current draw by the A/Cs may make a difference from the measurement with no current being drawn.

Also after running both A/Cs for ten minutes, feel the shore power cord connectors at both ends for a hot spot which is a sure indication of a voltage drop there.

At the end of the day, running two 16,000 btu A/Cs off of one 30 amp shore power supply is marginal, good voltage or not. I bet you are drawing at least 25 amps when both are running.

But perhaps your boat's internal wiring is contributing to the voltage drop. If you can confirm decent voltage at the power pedestal while the A/Cs are running (110V or greater) then measure the voltage to the main AC breaker on your power panel and work your way to the breakers supplying the A/C units to see if there is a drop.

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Old 06-28-2020, 11:35 AM   #4
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What David said
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Old 06-28-2020, 11:51 AM   #5
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Like jLeonard, my first suspicion is the marina's shore power. I have a Dometic/CruiseAir Air Conditioner and experienced a situation exactly like you described. Troubleshooting was frustratingly difficult, as invariably, when I measured the voltage at the pedestal, it was good. Turns out that the marina's power was not sufficient nor stable.



A short term workaround could be to set your inverter on "power assist", if you have such a system. This would smooth over the low-voltage situations. I wouldn't want to do this for weeks at a time while not at the boat however. Not sure I fully appreciate why you want to run the A/C at all while you are away from the boat long term??



Also, you might want to check where you store your excess shore power cable when running these heavy loads. If you keep it all neat and tightly COILED up in a storage compartment, you might find it to be fairly hot. Not good!
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Old 06-28-2020, 12:42 PM   #6
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If you turn off the bedroom AC will the Saloon continue to run or does it still draw down the voltage to 100v and then kick off?

Voltage drop is most likely a function of undersized wires or bad connection due to loose connection or corrosion. Since you have already tried several pedestals and shore cords I would be looking at the boats shore power receptacle for any signs of loose wires or corrosion.
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Old 06-28-2020, 01:09 PM   #7
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Quote:
Originally Posted by Clemson101 View Post
I have a Beneteau ST 34 and we moved to a new marina this year. We have 2 Cruisair Qht systems and on the AC unit in the main salon, I’m getting a LO AC error which the manual indicates “operating voltage remained below an acceptable limit for 3 minutes or more (100V for a 115V system).” It shuts the system down if this error occurs. I can cycle through on / off and will come back on but if it’s a hotter day, it will shutdown within 5 minutes or so. I’ve tried 3 different shore power receptacles and 2 different shore power cords and they all produce the same result. I can watch the volt meter display in the boat and prior to the AC coming on, it runs from 116 - 111. As soon as the AC kicks in, the voltage drops to just above 100 and then eventually drops below 100 triggering the shutdown. We’re running AC while on the boat at about 75’ish. When we leave the boat, we’re setting at 80. Normally when we come back to the boat after a week, the AC in the salon is shutdown - AC in bedroom i has no issues. I’m no electrician or AC guy, but I though I’d throw it out to the group prior to calling for professional assistance. Thanks.
I have surveyed many Euro built boats using Euro wiring standards. i.e. 240 volts. When exported to NA they simply changed the connections and left the 240 conductors in place ...... their conductors are simply not up to what the systems were asking them to do. Many (recognizing the issue) simply change the main breaker to a 40amp breaker. No not the one on the panel, the often hidden one close to the shore power inlet.

240volts can get a way with much thinner conductors .... drop the voltage to 120 and the current goes way up. These conductors do not meet ABYC Standards for 120 but they've been doing this for decades. I am amazed that they get away with importing these boats like this.
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Old 07-12-2020, 10:53 AM   #8
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Thanks boatpoker. There are 2 breakers near the shore power outlets. Is this a simple fix or is it something I should have a marine electrician survey and determine any course of action based on your experience? Thanks for the explanation.
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Old 05-07-2021, 10:08 AM   #9
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AC Voltmeter Reads 100V

My AC voltmeter that monitors input AC volts on one of my two 30A power inputs has always read low (100V) since I purchased the boat. There is a note taped to the back of the meter by a PO that says "reads low". I measured the input power and it is 120V. Tried adjusting meter dial but adjustment doesn't work.

I'd like to replace it with a new meter but it is tough finding one that matches it's partner on the other power leg. The front of the meter says SO.65, Class 2.5. I've seen a few that might work but show SO.45. Does anyone know what this SO label means?

The meter brand on it looks like "Brother" and the other says V.D.O. and those brands are likely obsolete since my Jefferson is 33 years old. Both are 0-300VAC.

Any ideas on possible sources for this meter?

Thanks!
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Old 05-07-2021, 10:11 AM   #10
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Pictures didn't post. Here they are.
Attached Thumbnails
20210505_162603_resized.jpg   20210505_162549_resized.jpg  
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Old 05-10-2021, 06:31 AM   #11
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USA 240 volt power comes from 2 - 120v lines. One red, one black wired

IF when the marina was first wired, it is possible that to wire 120V outlets too many of one red or black legs was selected.

If by chance 75% of the 120v is pulled from one leg , it will always suffer from low voltage.
This is common in RV parks too.

The simple solution is a 240V plug with 2-120V sockets , one for each leg , use the highest voltage leg for the air cond.
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Old 05-10-2021, 09:07 AM   #12
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Thanks for responding FF. I think it is a bad meter. It always reads low - in at least 5 different marinas and regardless of load. I am having a difficult time finding a replacement that looks the same as its counterpart on the other leg. Was hoping someone might know of a source or be able to explain what SO65/SO45 m3eans.
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Old 05-10-2021, 10:56 AM   #13
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There should be an adjustment screw on the meter.
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Old 05-10-2021, 10:58 AM   #14
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Tried the adjustment - doesn't work.
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Old 05-10-2021, 11:47 AM   #15
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Ditch both of those obsolete meters and go digital for a more precise reading.
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Old 05-11-2021, 05:51 AM   #16
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At least swap the meters to see if its the meter or the wiring.
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Old 05-11-2021, 06:37 AM   #17
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I do believe VDO is still in business.
Just my personal shabby opinion, I like analog meters. I can put a piece of tape on the meter for the high reading. Also realize on an analog gauge, the normal operating range is in the center 2/3 of the gauge. I can tell at a glance if I might be having trouble.

Get your multi meter out and read across the current meter.

It reads low both on shore power and generator power???
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Old 05-11-2021, 07:59 AM   #18
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Thanks OldDan. I like the analog meters too for the same reason. Maybe it's my age <LOL>! I also prefer analog clocks. Anyway, VDO is definitely still in business but they don't make a matching AC voltmeter. I'll check with my multimeter. The reading is low on shore and generator power.
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Old 05-11-2021, 09:12 AM   #19
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There are meters that look just like those on Wish and Alibaba.
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Old 05-11-2021, 09:41 AM   #20
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Originally Posted by boatpoker View Post
I have surveyed many Euro built boats using Euro wiring standards. i.e. 240 volts. When exported to NA they simply changed the connections and left the 240 conductors in place ...... their conductors are simply not up to what the systems were asking them to do. Many (recognizing the issue) simply change the main breaker to a 40amp breaker. No not the one on the panel, the often hidden one close to the shore power inlet.

240volts can get a way with much thinner conductors .... drop the voltage to 120 and the current goes way up. These conductors do not meet ABYC Standards for 120 but they've been doing this for decades. I am amazed that they get away with importing these boats like this.
Excellent info from a pro Im guessing. Its not the first or only time that ABYC standards are ignored by offshore and domestic builders. Problem is these standards are often treated as suggestions only, and many are frequently not legally enforced cause they are not legally binding
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