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Old 03-05-2016, 09:21   #1
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Low Shorepower voltage with increased load?

Our boat was built for the Asia/Europe market, and is set up for 230v, 50cps power. We have cruised Asia for 10+ years, and Europe for 3 years, with no shore power issues. We've sailed to the Caribbean, and have run into a confusing situation when plugged into a US marina (Puerto Rico, or US Virgin Islands). As all my motors are both 50/60cps tolerant, and resistive loads do not care what the frequency is(elect stove, water heater, etc) I bought a step-up transformer, plugged into the 120v power pole, and thought all would be well. But as I load the system, my voltage drops down significantly. At a small load 2-3 amps I show 240vAC on my boat power dist panel. But at 6-8 amps load, I show a 210-220vAC reading. And at 12-13 amps I read 200-210 volts. And if a motor kicks in, the amperage jumps to 16 or so, but the voltage drops to 170-180 vAC. And, of course, the AC motor(aircon, etc) trips off for low voltage! All the boat equipment is the same as it was in Europe. My 110v power cord is a standard, manufactured 30amp cordset, the transformer is rated for 10,000 watts, and the power cord from the transformer to the boat inlet is the same one I've used in Europe for 3 years without issue....and routinely loaded it up to 16-18amps. Further, I've never popped the c/b on the marina power pole. As long as I keep my load below 3600 watts(30 amps at 120v) there should not be an issue.....except 170-180 volts is unacceptable to my 230v motors! and if I run my on-board genset, there are no issues at all. I do not have a clue what is wrong or where to look for the issue here.....I need help!
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Old 03-05-2016, 10:11   #2
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Re: Low Shorepower voltage with increased load??

Ah, Voltage drop in wiring. Always fun. Part of the issue is a 110V shore power cord (made in china for the most part) are not really rated for 30 amps continuous load. It's rated for 30 amps at intermittent load. Then the voltage drop that was barely acceptable at 30 amps multiples via the step up transformer.

It could also be that the dock wiring might be sub-standard. If your pulling 16 amps at 230V, your already at 32 amps on the 30 amp shore cable. That would pop a 30 amp breaker, or rather it should.

You think about buying a 50 amp shore cable and a 50 amp/30 amp adapter. The 50 amp cable would have less voltage drop and would most likely solve the voltage drop issues.
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Old 03-05-2016, 11:44   #3
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Re: Low Shorepower voltage with increased load??

What she said.


Wiring designed for 220VAC systems will be half the ampacity of wiring that can carry the same wattage at 110/120VAC. So you'd literally need to rewire the boat with heavier gauge wiring all the way, in order to compensate for the voltage drop in the thinner wiring originally used in the 220VAC system.


It might actually be easier to just make a couple of new runs for 110/120VAC, complete with the right bits all the way. Or (electricians, please leave the room or cover your eyes) if your use is really just occasional...really conservative and careful use of a heavy extension cord, to be disconnected when no one is around to keep an eye on it.
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Old 03-05-2016, 11:45   #4
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Re: Low Shorepower voltage with increased load??

The transformer is likely the cause of much of the voltage drop. Measure the primary and secondary voltage at various loads. That will tell a lot.

Don't forget that the current on the 110V primary is twice the 220V secondary.
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Old 03-05-2016, 13:05   #5
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Re: Low Shorepower voltage with increased load??

Quote:
Originally Posted by hellosailor View Post
What she said.


Wiring designed for 220VAC systems will be half the ampacity of wiring that can carry the same wattage at 110/120VAC. So you'd literally need to rewire the boat with heavier gauge wiring all the way, in order to compensate for the voltage drop in the thinner wiring originally used in the 220VAC system.


It might actually be easier to just make a couple of new runs for 110/120VAC, complete with the right bits all the way. Or (electricians, please leave the room or cover your eyes) if your use is really just occasional...really conservative and careful use of a heavy extension cord, to be disconnected when no one is around to keep an eye on it.

I believe you meant to say: Wiring designed for 220VAC systems will carry the same maximum ampacity at 110/120VAC which results in half the wattage.

The way I interpreted the OP is he is using the same wiring and voltage that he used in Europe. He simply is plugging his EU shorepower cord into the secondary of a 120/240V autotransformer with it's primary plugged into a 120V/30A dock. Hence, it's not a wiring problem from the EU shorepower into the boat.

It's either:
- The transformer - unlikely if it's rated at 10KVA (assuming the OP meant KVA vs. watts)
- The 120V/30A shorepower cable
- The dock wiring.

My suspicions start at the bottom of the list and go up.
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Old 03-05-2016, 13:14   #6
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Re: Low Shorepower voltage with increased load??

Dun--good post.
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Old 03-05-2016, 13:23   #7
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Re: Low Shorepower voltage with increased load?

I would put the transformer on the dock with a very short cord (1 meter). This reduces the voltage drop over the double-the-current-part of the system to a minimum

Just cut up the shore power cord to make a small one. Buy some connectors so you can make any cord length.
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Old 03-05-2016, 14:06   #8
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Re: Low Shorepower voltage with increased load?

DotDun....you are exactly correct. The boat was originally wired for a 230v, 3-wire, 50cps system, and it continues to work well. I have no intention nor plan to rewire the boat or to convert it to a 110v system. And yes, I'm using my European shore-power cord between the transformer secondary and the boat power inlt. And the 120v shore power cord is a very popular brand, as it was manufactured and without alteration. And if the marina dock power was that bad, other boaters would have also complained...and they haven't that I'm aware of. So the only logical explanation I can come up with is an issue with the transformer. But at a rated capacity of 10,000 watts(not Volt-amps, but close for this purpose) it should be operating well below its rating. Can anyone explain to me how a transformer, working at about 1/3 its rated capacity, cause such a reduction in output Voltage? I just don't get it? Also, FWIW, I added a pie fan to the transformer to help keep it cool. And even without the fan, wire and coil operating temps were almost ambient....a little warm, but certainly not elevated or hot.
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Old 03-05-2016, 14:11   #9
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Re: Low Shorepower voltage with increased load?

Sailorchic34...your idea may be the best I've heard yet! The 50amp shorepower cord is big, and spendy...but that should eliminate that possible issue. Thanks for the idea!
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Old 03-05-2016, 14:14   #10
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Re: Low Shorepower voltage with increased load?

Quote:
Originally Posted by sailcrazy View Post
DotDun....you are exactly correct. The boat was originally wired for a 230v, 3-wire, 50cps system, and it continues to work well. I have no intention nor plan to rewire the boat or to convert it to a 110v system. And yes, I'm using my European shore-power cord between the transformer secondary and the boat power inlt. And the 120v shore power cord is a very popular brand, as it was manufactured and without alteration. And if the marina dock power was that bad, other boaters would have also complained...and they haven't that I'm aware of. So the only logical explanation I can come up with is an issue with the transformer. But at a rated capacity of 10,000 watts(not Volt-amps, but close for this purpose) it should be operating well below its rating. Can anyone explain to me how a transformer, working at about 1/3 its rated capacity, cause such a reduction in output Voltage? I just don't get it? Also, FWIW, I added a pie fan to the transformer to help keep it cool. And even without the fan, wire and coil operating temps were almost ambient....a little warm, but certainly not elevated or hot.
No, you have it wrong. The longer the circuit, the more losses you get. Where you normally have a 230V shorepower cord, you now have an extra transformer plus an extra 110V shorepower cord. This is why I recommend to shorten the circuit as much as possible, and to do this where the current is highest, i.e. at the 110V part, where losses are highest.
The transformer can have issues as well, but you need to do the recommended measurements described above by another member to research that.
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Old 03-05-2016, 16:26   #11
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Re: Low Shorepower voltage with increased load?

Jedi's right.
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Old 04-05-2016, 04:02   #12
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Re: Low Shorepower voltage with increased load?

Don't guess, measure. Get a volt meter (or someone who knows how to use one) and measure the following with the boat operating at some significant load.

1) shore box voltage
2) transformer primary
3) transformer secondary
4) voltage at output of main breaker at distribution panel
5) voltage at a 220V convenience outlet

Report back these 5 numbers and we can most likely tell you where the problem is. Everything else is just guessing.

Transformers are notorious for having useless power ratings. Unless they also specify impedance at 60Hz you can't tell anything about their regulation. Can you post all the specifications of the transformer or a data sheet?
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Old 04-05-2016, 05:14   #13
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Re: Low Shorepower voltage with increased load?

Wow do we have a bunch of smarty elec' gurus here!

Everybody has made awesome suggestions...

I would start with Dan's 5 item list to narrow it down... Another idea is to make up some long leads for your multimeter and check voltage drops of each line, connection point/component to connection point/component....

You're not going to get the "exact" voltage drop, but it will be scalable relative...

Do Dan's list first!
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Old 04-05-2016, 06:34   #14
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Re: Low Shorepower voltage with increased load?

Quote:
Originally Posted by HappyMdRSailor View Post
Wow do we have a bunch of smarty elec' gurus here!

Everybody has made awesome suggestions...

I would start with Dan's 5 item list to narrow it down... Another idea is to make up some long leads for your multimeter and check voltage drops of each line, connection point/component to connection point/component....

You're not going to get the "exact" voltage drop, but it will be scalable relative...

Do Dan's list first!
+1 with one additional twist. Please report measured voltages, in all locations suggested by Dan, at:

- idle (no load),
- small load (2-3 Amperes),
- medium load (6-8 Amperes),
- high load (approx. 15 Amperes).

You already did some of that:
Quote:
Originally Posted by sailcrazy
At a small load 2-3 amps I show 240vAC on my boat power dist panel. But at 6-8 amps load, I show a 210-220vAC reading. And at 12-13 amps I read 200-210 volts.
so it is only a matter of repeating that and taking additional measurements at places suggested by Dan.
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Old 04-05-2016, 07:04   #15
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Re: Low Shorepower voltage with increased load?

Dan and mrm....unfortunately, we just put the boat up on the hard in Puerto Rico for the summer/hurricane season, and we're now back at our home in MN; getting some additional readings will not be possible until we return in Nov. The amp and voltage readings I did post came from the boat's elect dist panel meters, which measures power at the entrance to the dist panel. The transformer is an "ebay special", and likely made in China. I deliberately bought the 10,000 watt size to have plenty of capacity for motor startup(watermaker 1.5hp, refer 3/4hp, and 2 aircons) and to ensure it would not need to run near capacity. As the amperage load is increased it does emit a louder and louder noise, but I just assumed that was due to a not-so-secure mount or case.....I did not think the transformer could reduce the voltage to such a degree (and I don't understand electrically how it could). Increase the amperage draw-yes (bad connections, to small conductor size, to small a wire in the windings, etc), but that should not effect a voltage drop at increased load. Remember, at a small load(2-4 amps) I'm showing 240v at the panel; its only as the amp load increases the voltage drops. And the rest of the system(except the 110 shorepower cordset) is exactly the same as we've been using for the past several years...without issue.
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