Low Shore Power Voltage with Load

[Vincentc]

Yesterday I replaced the shore power breakers and shore power receptacles (30amp) and when I tested my installation I found the following readings on the air conditioner panel voltmeter and watt meter:
no load- 112v 1000w
fan/water pump 110v 1000w
fwd compressor 104v
aft compressor 103v
fwd & aft comp 96v 3200w

This is dual 30 amp service.
The Ship Service volt meter shows 115v with just the refrigerator load. I did not check the ship service with a load.

This is the first time I noticed low voltage at the dock, but cannot say I've ever carefully checked it.

I guess my first step shoul be to plug the AC into the receptacle used for the Ship Service and see if anything changes.

Any insight on likely causes and testing methods will be appreciated. Obviously the watt meter for the air conditioner service has a problem, but the voltmeter appears to be accurate.
Thanks

 

[SeaEric]

If you're looking at the Hatt OEM analog meters, you may be surprised by how inaccurate they are. I just went through this on my 41 TC. I installed Blue Sea digital meters that will display hertz, volts, amps and watts. They have been wired to the panels so that they will display data from either the shore power or the genset power sources.

What I thought was a big electrical problem based upon the analog meter info turned out not to be a problem once I had accurate info.

 

[Vincentc]

Eric,
Your comments are appealing to me. I would appreciate your posting a photo of you installation and perhaps a model number on the digital meter.
Thanks

 

[Pascal]

Blue Seas AC multmeter 8247
In the meantime check your readings with a handheld. While the old panel mounted Vmeter may be inaccurate that is a big drop Make sure everything is tight and clean

 

[Boatsb]

What is the voltage at the pedestal and the cord end? If there is a 1000 watt load ( that's almost 10 amps) with nothing on you have a problem somewhere. It could be a bad meter or some stray current. Using real meters you need to measure the voltage, frequency and amperage before you find the problem. The meters on the boat are old and never were very accurate. They are for reference not measurement.

 

[MikeP]

Agree with others re checking voltage with a multimeter.

Re the oem volt gauges - it's worth checking that the "0" position of the needle is actually at zero with no power applied to the panel. There is a small screw that controls the zero point. If your meter needle doesn't rest at "0" with no power applied, it won't indicate correct voltage. I have three of the oem meters that all used to read different voltages and different then the multimeter. I noticed that all the needles rested at a different point with no power. After zeroing the meters they now agree with the multimeter - at least within what I can interpolate between the oem meter indices.

But I totally agree that the gauges Eric installed are really neat and easy to see. The old meters are difficult to see, even if you can get them to read accurately.

 

[Boatnut]

Vincent,

What you may have is a very common problem. We see this all the time especially when in the Carribean. At 115v you are already on the low side. General specifications are 120v plus or minus 10%. The most common cause of this problem is the branch circuit you are connected to is already at maximim load, and your load tips the scale. When a circuit is sitting at maximum load, the point when the voltage drops severly is more like an avalanch than a glacier.

Some other causes could be poor connection on the shore power circuit, either onboard or ship side. Wiring too small for the load.

This situation occurs often in marinas when there are a lot of boats using power. As the people go home typically on Sunday the voltage will come back up and the problem goes away, until the next big crownd arrives. Needless to say in the heavy useage arena, it's the marinas responsibilty to correct the problem (good luck trying to get them to correct it).

As for meters, being some of us use them daily, Fluke is IMO the best meter you can buy. I am quite sure I saw a marine version on there web site. The are very rugged and will outlast most other meters 2 or 3 to 1, and there price to repair them is quite reasonable. The case option is a wise investment.

I hope this helps.

 

[Boatnut]

Agree with others re checking voltage with a multimeter.

Re the oem volt gauges - it's worth checking that the "0" position of the needle is actually at zero with no power applied to the panel. There is a small screw that controls the zero point. If your meter needle doesn't rest at "0" with no power applied, it won't indicate correct voltage. I have three of the oem meters that all used to read different voltages and different then the multimeter. I noticed that all the needles rested at a different point with no power. After zeroing the meters they now agree with the multimeter - at least within what I can interpolate between the oem meter indices.

But I totally agree that the gauges Eric installed are really neat and easy to see. The old meters are difficult to see, even if you can get them to read accurately.

I agree with the zero calibration as mentioned; however the most accurate way may be to measure the voltage with an accurate meter and use the zero adjustment to calibrate the OEM meter to match the more accurate number found on you hand held.

 

[spcoolin]

Vincent,

What you may have is a very common problem. We see this all the time especially when in the Carribean. At 115v you are already on the low side. General specifications are 120v plus or minus 10%. The most common cause of this problem is the branch circuit you are connected to is already at maximim load, and your load tips the scale. When a circuit is sitting at maximum load, the point when the voltage drops severly is more like an avalanch than a glacier.

Some other causes could be poor connection on the shore power circuit, either onboard or ship side. Wiring too small for the load.

This situation occurs often in marinas when there are a lot of boats using power. As the people go home typically on Sunday the voltage will come back up and the problem goes away, until the next big crownd arrives. Needless to say in the heavy useage arena, it's the marinas responsibilty to correct the problem (good luck trying to get them to correct it).

As for meters, being some of us use them daily, Fluke is IMO the best meter you can buy. I am quite sure I saw a marine version on there web site. The are very rugged and will outlast most other meters 2 or 3 to 1, and there price to repair them is quite reasonable. The case option is a wise investment.

I hope this helps.

I agree with the zero calibration as mentioned; however the most accurate way may be to measure the voltage with an accurate meter and use the zero adjustment to calibrate the OEM meter to match the more accurate number found on you hand held.

X2 on both posts...Couldn't have said it better

Steve~

 

[SeaEric]

Can't say enough good about the Blue Sea meters. I will post a photo tomorrow when I get to the boat again. Mike P saw the install. Pascal was the guy who made the suggestion to add these. It was money well spent. If I recall, parts and pro install was just under $800. for 2 meters, one for the house service and one for the AC service.

FWIW, My original 1966 AC units (still working perfectly) draw almost EXACTLY the wattage (as measured by the new digital meters) that my 1966 Hatteras owner's manual says that they will draw. The original analog meters said something way different on watts and voltage under load.

Pics tomorrow.

 

[Boatnut]

Vincent,

What you may have is a very common problem. We see this all the time especially when in the Carribean. At 115v you are already on the low side. General specifications are 120v plus or minus 10%. The most common cause of this problem is the branch circuit you are connected to is already at maximim load, and your load tips the scale. When a circuit is sitting at maximum load, the point when the voltage drops severly is more like an avalanch than a glacier.

Some other causes could be poor connection on the shore power circuit, either onboard or ship side. Wiring too small for the load.

This situation occurs often in marinas when there are a lot of boats using power. As the people go home typically on Sunday the voltage will come back up and the problem goes away, until the next big crownd arrives. Needless to say in the heavy useage arena, it's the marinas responsibilty to correct the problem (good luck trying to get them to correct it).

As for meters, being some of us use them daily, Fluke is IMO the best meter you can buy. I am quite sure I saw a marine version on there web site. The are very rugged and will outlast most other meters 2 or 3 to 1, and there price to repair them is quite reasonable. The case option is a wise investment.

I hope this helps.

I guess I better appologize, as I misunderstood pascal's comment about he Blue Seas meters thinking it was a test meter. I honestly had no idea that replacing the OEM meters would be a solution to a possible low voltage problem.

 

[Vincentc]

We went for a dinner boat ride yesterday

and the time I would have used to further test the voltage question was spent cleaning up the boat.

While we were out I did notice that the air conditioner volt meter read almost as low when we were running off of the generator.

Regards

 

[TopHattandTails]

Vincent- forget about the house meters. All they tell you is whether or not you have power to the boat. Tong an electrical outlet, the end of the dock cord, then pedestal. That will tell you what your dealing with.

 

[MikeP]

Well, the problem MIGHT simply be the house meters being bad/no longer calibrated. If everything is running fine and there are no actual symptoms of low power, then perhaps there IS no actual power problem. As noted, a multimeter reading in the various places should quickly identify the issue - meters OR power and if power, whether it's marina voltage being supplied or a boat issue.

Note that pedestal (marina) voltage may vary based on how many folks are in the marina operating things on their boats. So do all the checks in the same time frame.

Good Luck and let us know.

(Eric's new meters ARE pretty slick!)

 

[Vincentc]

It may just be the volt meter.
I tested both shore power lines at the "Smart Plugs" and they each indicated 123.8v on the multimeter. Inside the boat, the ship service meter was at 124v and the air conditioner box showed only 114v.

The air conditioner electric box and meters are hidden away inside the closet next to the steps leading down to the aft cabin and the meters are difficult to and seldom read. Assuming it is worthwhile to know voltage and amperage, I will probably put a couple of analog meters on the saloon bulkhead just outside of the steps and on the back side of the existing closet electrical box.

The digital multi meter looks very nice and $210 at Defender is not bad, but for less than half that I can buy both an analog volt and amp meter, and have a more "traditional" look.

Thanks for the advice,

 

[SeaEric]

Here are my new meters. Display is set to voltage.

 

[daniel r morrison]

different voltages down stream can mean resistance ( corrosion) in the wiring or connection points. as for your incomming voltage it is not uncommon if you are at the end of a long dock to show 120v with no load and much less as you increase the load. voltage drop can be considerable with long 120v branch circuits and too small of conductors

 

[Vincentc]

Eric,
Thanks for the picture. Good looking and much more practical installation. The current meters are difficult to view, yours is a lot better. The local electronics store had the Blue Sea analog meters but not the volt meters, so I ordered them from Defender. While I was at the store, I bought a pair of DC volt meters to put next to my direct oil and water gauges. The Hatteras volt meter reads about a volt too low.

When I said I tested voltage at the Smart plug that is the plug that connects to the shore power inlet on the boat. I think everything is OK but it will be nice to check things without contortions.

 

[SeaEric]

To reiterate, my 2 new digital meters are connected to the 2 electric panels so that they display both shore and gen info, depending upon which power source is in use. Its amazing how far off the old OEM analog meters are. I'm very pleased that I no longer have "electrical load anxiety" based upon what I now know to be their incorrect readings.

 

[Vincentc]

I have mounted, but not yet connected by new Blue Sea analog AC gauges. The old gauges gave false readings and are not very accessible. I have to genuflect in front of the stairway to read the gauges in the panel under the stairs:

And the gauges for the air conditioner are hidden in the closet outside of the stairway to the aft cabin.

I put the gauges for the air conditioner on the bulkhead just forward of that electrical box:

and put the gauges for the Ship Service on the wall just inside of that electrical panel below the aft cabin air conditioner control.

The runs from the gauges to the respective panels is less than 2 feet and the gauges are now positioned where I can look at them standing up and without going into the hanging closet.

Since the DC volt meters on the ship service panel are also difficult to read and about 2 volts off, I purchased 2 new DC volt meters and an ammeter to monitor DC useage and am mounting them below the tank tender and direct engine gauges all located on the bulkhead between the Saloon and dinette.

I does look like the ammeter is a little crooked. Not sure how that happened.

It may not be as nice as Eric's digital gauges, but wedding funding got priority over the boat.

If anyone is inspired to copy my efforts, please note that the gauges just below the Cruiseair control lie next to a rather large wiring harness inside of the closet. Be very careful where you drill.

Regards,