Low Shorepower voltage with increased load?

[GordMay]

Voltage regulation is the measure of how well a power transformer can maintain constant secondary voltage given a constant primary voltage and wide variance in load current.
The lower the percentage (closer to zero), the more stable the secondary voltage, and the better the regulation it will provide.

ie: A transformer with a nominal output voltage of 240 VAC and a Voltage Regulation of 5% has an output voltage of 240 VAC at no-load, and (240 VAC – 5%) at full load – hence the transformer output voltage will be 228 VAC at full load.

Transformer Impedance and Voltage Regulation are closely related.

[tinkrman69]

Originally Posted by sailcrazy

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.

The voltage drop will increase with load increase. Which usually means wiring...too small or old. Sailorchic's post is the best I've seen so far. Other than checking the voltage drop at each connection the one new component...the 110v cable...would more than likely be the culprit.

a step up transformer consumes a lot of amperage, just to step the voltage up, not to mention what is being consumed on the boat. the increased noise in the transformer, with increased load is normal. with the higher load it has to work harder, the coils will vibrate more. and frequency does affect static loads...burners...too high a frequency..cycles..will cause faster oxidation in the element, the same kind of oxidation that happens in wires, lower cycles will cause it to heat slower...albeit..;minuscule in both
scenarios.

altho 3 years isn't that old for the existing 230v cord I'd check it any way as the ends may have corroded, causing the drop. the wiring on docks are notorious for brown outs. see to it the voltage drop isn't at the pole. a new cable may solve your issue, but depending on the source...the dock/pole...it may not.

[Terra Nova]

Sounds like it is the crappy transformer.

[captstu]

I'm missing something - why not use the marina's 240V 50 A power to run your boat - depending on your devices, you might not need any transformer.

[unclemack]

I'm in the UK, on 240V shore power with a standard 2.5 sq.mm x 25 metre cable from the yard post. Boat has 2.5sq.mm cable too.

Shore power goes through a cheap plug-in power monitor for convenience, a Tektronix THS720A confirmed that the monitor was acceptably accurate.

I see 240V at low current draw but 230V @ 11A using a 2.8kW kettle. Turn on a 1.8kW heater at the same time and voltage drops to 224 @ 20A.
All approximate.

In my limited experience this is perfectly normal in a marina when you're some distance from the service transformer.
My neighbours and I were cursed for months by a faulty marina 3-phase distribution panel breaker. I learned then that they were completely unaware of their own similar voltage drops.

Is it possible that you didn't start monitoring your voltmeter until problems began and so were unaware of these "normal" voltage drops?

+1 on the DVM measurements btw but access for probes won't be all that easy.

Infra-red thermometers are cheap and are incredibly useful for many things on board. First thing I did with my new-to-me old boat was scan the engine & some other things to establish normal temperature values.

Scanning all the way from power pole to appliances can be done very quickly - bad connections, overloaded cables, transformers etc. all can cause temperatures to rise significantly.
Might save yourself some time.

[socaldmax]

Originally Posted by sailcrazy

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!

I'm not saying that the shore power cord isn't the problem, but since none of us are there and there are a few pieces of the puzzle in line between the pedestal and your main breaker, I'd suggest using an IR temp. gun to check the connections at the pedestal, in and out on the transformer, at the boat, etc. to determine exactly where the voltage drop is occurring.

More than likely that might be the culprit, but I just hate throwing money at problems without any evidence of what the problem really is. I used to fail students for "easter egging" rather than logical troubleshooting, so it would be very hypocritical of me to suggest doing that these days. I've got an IR temp. gun I bought for under $30 and it has been very useful, I use it for a lot of things, from cooking to determining if my radiator is functioning normally.

[Cadence]

Originally Posted by sailorchic34

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.

It might pay for him to sneak a peek, if he can access it at the dock, to see if the drop is his cable or the marina's inadequate wiring. May save a nickel or two. No point in upgrading if the drop is before it even gets to him Although I think he did indicate more than one marina and not in an area one would expect a half assed marina.

[mrm]

Originally Posted by sailcrazy

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.

That is a pity as without those measurements we can only speculate, but...

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)

Easily enough. If the core cross section is too small it will start to work in the non linear range and finally saturate.

Please have a look at a reputable transformer manufacturer, locate their 10 kVA model (click 'sketch and table with dimensions' in the link below) and compare size and more importantly weight to what you have. If there are significant differences, it is quite possible that your transformer is the culprit. The loud noise you mention suggests the same and certainly indicates a sloppy design / manufacture.

single phase power transformers with power between 2,0 100kVA