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Old 06-19-2013, 10:30 AM   #1
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More amps wanted

My wife and I live aboard and most of the time we manage our shore power loads with infrequent circuit breaker trips. Our Taiwanese trawler has the standard 2-30A 125V shore power cables. One cable provides 30 amps to the air conditioning and one provides 30 amps to the rest of the boat electrical systems. We have a ship shore switch and a 8KW generator wired for 125V.

I am contemplating another air conditioner and would like to have more amperage for the rest of the boat.

Going to 50 amp 250Volt is not practical and I would have to rewire the generator and change too many devices and upgrade too much wire.

But I am considering two 50 amp 125volt shore cables from a 50 amp 125/250 Y. I would change the inlet fittings and up the wire size to the ship shore switch. I would change my 2 main breakers from 30 amp to 50 amps and up size the connecting wires from the ship shore switch.

My estimate for new Y adapter, cables, inlets, wire and breakers is about $1200. For this I would have 100 amps on board instead of 60 and I might have to manage load when on generator.

Any comments? Sanity check please?
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Old 06-19-2013, 11:12 AM   #2
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You've currently got 30 amps available to run air conditioners. Does your existing air conditioner use all of that? Maybe there is already enough capacity to run the additional AC that you want to add.
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Old 06-19-2013, 11:50 AM   #3
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You have almost an identical setup to me and I have tow A/Cs.
SO I agree with HopCar, as you should be able to add one a/c to your existing setup.

The other question I would have is many marinas will only give you one 50 amp circuit or 2 30's. So it seems to me you run the risk of actually lowering your capacity.
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Old 06-19-2013, 12:42 PM   #4
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Originally Posted by obthomas View Post
My wife and I live aboard and most of the time we manage our shore power loads with infrequent circuit breaker trips. Our Taiwanese trawler has the standard 2-30A 125V shore power cables. One cable provides 30 amps to the air conditioning and one provides 30 amps to the rest of the boat electrical systems. We have a ship shore switch and a 8KW generator wired for 125V.

I am contemplating another air conditioner and would like to have more amperage for the rest of the boat.

Going to 50 amp 250Volt is not practical and I would have to rewire the generator and change too many devices and upgrade too much wire.

But I am considering two 50 amp 125volt shore cables from a 50 amp 125/250 Y. I would change the inlet fittings and up the wire size to the ship shore switch. I would change my 2 main breakers from 30 amp to 50 amps and up size the connecting wires from the ship shore switch.

My estimate for new Y adapter, cables, inlets, wire and breakers is about $1200. For this I would have 100 amps on board instead of 60 and I might have to manage load when on generator.

Any comments? Sanity check please?
I want to upgrade too...but I am going to go with a 125/250 service with this panel added...

3310 - AC 12 Positions w/Shore/Gen. Mains and Meters
Power Distribution Panels


You can do it your way but you have to assume the buss bars on your existing panels can handle 50amp.

I prefer the one wire and no splitter unless I get a smart y to supply with 2-30s.

I doubt you would have to do much with your genset...mine is just jumpered across 2 30 panels..you could do the same with 2 50's.

Either way you have 100 amps to work with...

But also agree with HopCar..30 amps on one circuit will power 32000BTUs of AC...plenty for up to a 45 trawler even in Florida.
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Old 06-19-2013, 12:49 PM   #5
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The limiting factor is usually the dock power wiring and amps availible. Not so much the boat. How much dock amps do you have?

We decide to eliminate/convert as much AC power stuff as possible to DC propane and/or do with out. The Eagle is 58 ft, has four AC on 50 amps. So you should have enough AMPS to add another AC?
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Old 06-19-2013, 12:52 PM   #6
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I have had a similar situation in the past. I wanted to add another A/C. So i added a second 30 amp service for the new unit, and split off some of the other loads so that there would no longer have to be any load shedding. It worked great. I could run it on 2-30s or 1-50 (with a splitter).
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Old 06-19-2013, 12:55 PM   #7
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The limiting factor is usually the dock power wiring and amps availible. Not so much the boat. How much dock amps do you have?

We decide to eliminate/convert as much AC power stuff as possible to DC propane and/or do with out. The Eagle is 58 ft, has four AC on 50 amps. So you should have enough AMPS to add another AC?
Depends on the marinas you frequent.

Most of the AICW has marinas that offer 50A 125/250 on every post where transients are assigned. Some ONLY offer 125/250 shore power. 50A 125/250 is a huge jump over 2-30's like the OP has.

Of course like was posted, if he only has 1 AC on the second 30 amp service...adding another AC usually isn't a problem...especially with the newer AC amp draws.
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Old 06-19-2013, 05:30 PM   #8
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We have two 30amp cables coming in. One feeds the AC panel which also powers one A/C unit and the other one just powers the second A/C unit. Works just fine and if we tie up where there is only one 30amp service we still can run one A/C unit.

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Old 06-19-2013, 06:32 PM   #9
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Same here one 30A for a dedicated 16K BTU heat A/C and the other 30 A for ships service and an another 12K BTU Heat A/C unit. Even toasting bread and making coffee we are fine.
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Old 06-19-2013, 06:45 PM   #10
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I have one 16000 unit and.one 12000btu. Ac units on one 30 amp circut
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Old 06-19-2013, 09:26 PM   #11
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I have one 16000 unit and.one 12000btu. Ac units on one 30 amp circut
more typical setup...

for those that want to power at least one ac if only one 30 amp outlet available, easy enough to add a cb to your main panel to feed the second panel.
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Old 06-19-2013, 11:08 PM   #12
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Would it help to use soft start units to drop the start loads of the AC compressors? .. that seems to be the killer of 30amp marine services. The soft starts also have a side benefit of added compressor life,
We use them on larger compressor loads and they seem to make a difference.

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Old 06-20-2013, 04:41 AM   #13
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To throw up a different idea: much of your amp demand is momentary, coming from the start-up of the a/c compressors. Why not invest in a good quality inverter of the type that "parallels" with shorepower? (Victron & MasterVolt both make excellent versions). These will supplement your shorepower with a burst of energy from the House bank to assist with a/c start-up...and when loads stabilize, will put the energy back into the House bank. You can also reduce start-up compressor loads by using the SmartStart device from Dometic: a 65% reduction in start-up amp draw.
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Old 06-20-2013, 06:34 AM   #14
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A different more efficient solution might work for you.

Load shedding.

This is the installation of a simple relay to automatically allow the loads to have a priority.

EG , when one air cond is on, a HW heater on that leg would be disabled.

As many power demands can be stacked , the HW can wait a few min , as can the fridge, or ice maker, load control is simply a matter of choice.

This keeps your small noisemaker , and allows cruising to older marinas that only have historic modest power.
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Old 06-20-2013, 07:21 AM   #15
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Would it help to use soft start units to drop the start loads of the AC compressors? ..
Unequivocally correct. Even better if you want to get high tech is to use a variable frequency drive (VFD) on the compressor and match power to demand.

The most efficient and least power consuming units use a variable speed compressor drive. They are quiet, virtually eliminate starting current issues and really do cut down on electrical power use. I have spec'd them on boats that had electrical demand issues created by the a/c system and had great success. It is becoming rare to see a new boat that doesn't use them.
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Old 06-20-2013, 09:02 AM   #16
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"The most efficient and least power consuming units use a variable speed compressor drive."

Are these different from the Mutsubishi "mini split" heat pumps that use an inverter to power the units?

The mini splits are mostly made for dirt houses so not much is made for 15A with 120V.

Any source for an RV , air cooled unit? With a remote for the interior?
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Old 06-20-2013, 09:45 AM   #17
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Are these different from the Mutsubishi "mini split" heat pumps that use an inverter to power the units?
I haven't dug all that deeply into the mini-splits other than installing several Daikin units on a couple of houses we own. When the say inverter they mean a variable frequency drive that takes utility standard power, converts it to DC, then reconstitutes it at the frequency demanded by the control system for the compressor and fans. So, I am willing to assume they are virtually identical, in function at least.

Quote:
The mini splits are mostly made for dirt houses so not much is made for 15A with 120V.

Any source for an RV , air cooled unit? With a remote for the interior?
I don't know of any 120V off the shelf units, all the ones I have had experience with are either 240 or 380V 3 PH systems. I do know that Fuji makes a 120V VFD but it is fairly low power at around 4 or 5 amps.

If you are an adventurous sort and have a 120V/15A unit lying around and have about $250 to play with, it might be worth inserting that Fuji unit in line with the compressor and use a thermostat or suction pressure as a control input. How many amps does the compressor draw on the RV unit? Another option might be to control the evaporator fan only and let the system head pressure controller handle the compressor through one of the "intelli-start" devices that the off-the-grid folks use. I can't say anything about how cost effective it might be but it is certainly worth looking into.
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Old 06-20-2013, 11:47 AM   #18
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... let the system head pressure controller handle the compressor through one of the "intelli-start" devices that the off-the-grid folks use.

Oops, typing faster than thinking ... that should be suction pressure.
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Old 06-20-2013, 08:30 PM   #19
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I have 3 AC's running off a 30A leg. I plug into a 50 amp socket and use a Y splitter to 2 30A cables that connect to the 2 30A connectors on the hull.

I have a 16,500 BTU, and 2 6500 BTU units. All three crank pretty close together and cycle on and off without problem all the time. We are full time liveaboards in FL....
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Old 06-21-2013, 10:15 AM   #20
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WOW, Thanks for all the replies. I feel like I hit a subject that has a lot of interest.

For the record, I have two AC units on one of my 30 amp shore cords. I replaced them last year and they are soft start and efficient. Actually it is the heat that is the highest load My larger 16.5K BTU unit draws about 19 amps, my smaller 9K BTU unit draws about 10 amps in heat mode. I want another air conditioner because while the two units are enough most of the time they are not enough in the evening after the engines have run all day.

Of the previous posts, all appreciated and considered I find the load shedding relay as the most intriguing. I am now contemplating a combination of 50 amp 125 shore cords and a load shedding relay as well.
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