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Old 09-01-2017, 04:24 PM   #1
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50amp to 30amp adapter and air conditioning

Probably a stupid question, but if I use an adapter to convert 30amp outlet at dock to 50amp outlet on my boat, how would I tell of my air conditioning should work?

And is that what you normally do with a 50amp boat at a slip with 30amp?

Thanks,
Mike
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Old 09-01-2017, 04:54 PM   #2
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Your boat almost certainly has a 120/240V, 50A shore power inlet. If your slip has no 50A power, the way to get power to your boat is to use a dual 30 amp male adapter with a 120/240, 50 amp female that plugs into your boat. Each 30 amp supply must be on separate legs for this to work and the Marinco Y adapters check for this.

If you only have a single 30A supply at the dock or they are both on the same leg, then you can use a 30A to 120/240, 50A adapter (if they make such things, or use one side of the Y adapter). But only one half of your panel will be powered.

Your panel is split into two 120V legs, each powered by separate legs of the 120/240 service. Whether your air conditioners will work on a single leg depends on how big they are and which leg supplies them. Ordinarily a single 30A supply will only power one A/C.

I know this has been a little confusing, but it is all dependent on how your boat is configured and what kind of shore power you have available.

If by chance your boat has a single phase 120V, 50A connector (unusual), then you just use a 50/30A adapter but the 30A supply will probably not run more than one A/C without tripping the breaker.

David
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Old 09-01-2017, 07:51 PM   #3
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My boat has a 50/120 panel and inlet. Yeah, it is a bit unusual. Conveniently, my home slip happens to have a 50/120 power outlet.

You can get 30/120 to 50/120 adapters if your boat is like mine. The Y adapter that David mentioned will allow you to get one of your panels running if you have a 50/240 boat and only a 30 amp pedestal.

Typically, you will have some instrument in your electrical system that shows you how much current you are drawing. With 30 amp power, you just want to keep eye on that to monitor your use to keep you from going over the 30amps.
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Old 09-01-2017, 11:03 PM   #4
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I know I have the A/C on one panel and other stuff on another. Boat has the newer 50amp, not the older more rare one. So sounds like I should invest in a Y adapter for two 30amp to one 50. And not waste time on the single adapter since I can use one half of the Y?
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Old 09-01-2017, 11:08 PM   #5
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I know I have the A/C on one panel and other stuff on another. Boat has the newer 50amp, not the older more rare one. So sounds like I should invest in a Y adapter for two 30amp to one 50. And not waste time on the single adapter since I can use one half of the Y?
Unless you will just be staying at one marina you will run into situations were you need both. You cannot use one half of the Y in situations were you have only one 30 amp post (or two posts on the same leg). In those situations to have power you need the 30 amp to 50 amp adapter.
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Old 09-01-2017, 11:10 PM   #6
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Unless you will just be staying at one marina you will run into situations were you need both. You cannot use one half of the Y in situations were you have only one 30 amp post (or two posts on the same leg). In those situations to have power you need the 30 amp to 50 amp adapter.


Got it! Very helpful, thanks!
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Old 09-02-2017, 08:08 AM   #7
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If you plan to cruise, you should invest in whatever adapters you may need at different marinas. There's a good chance you'll be given a slip with only 30 amp receptacles. You should ask for whatever your boat needs but that won't always be available.
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Old 09-02-2017, 08:14 AM   #8
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IF you use a Y to split the 240V into (2) 120V legs , check the voltage on either leg as the one with the most consumers will have the lowest voltage.

A higher voltage will allow your air cond to last longer and start easier..
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Old 09-02-2017, 10:26 AM   #9
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We have a 50A, 120/240v power. We have used a 30a (shore) by 50a (boat) adapter made by Marinco when we were at a slip without 50a power. It worked fine for aircon (2 of 3 units at one time). The only concern we had was making sure we stayed under 30 amps. With the reverse Y adapter, you must connect both 30 amp ends to the dock and they must be on opposite phases. For the dire fe in price, we just went with the single 30/50 adapter and monitor amp loads. However, we have rarely needed it in the Great Lakes.
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Old 09-02-2017, 11:34 AM   #10
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It is possible to run two AC units off 30 amps but you are pushing it. I would suggest turning off all other AC equipment while running both units. In particular, turn off hot water heater, battery charger and any fans. Also you may want to run the refrigerator on 12V while you are cooling the boat with two ACs. Once the boat is comfortable, you should go back to one AC.
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Old 09-02-2017, 11:56 AM   #11
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It is possible to run two AC units off 30 amps but you are pushing it. I would suggest turning off all other AC equipment while running both units. In particular, turn off hot water heater, battery charger and any fans. Also you may want to run the refrigerator on 12V while you are cooling the boat with two ACs. Once the boat is comfortable, you should go back to one AC.
It depends on the size of the air conditioner or more importantly, how much current they draw. I have a single 18,000 BTU unit and sometimes trip the master breaker if I use the microwave for more than a few seconds.
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Old 09-02-2017, 12:05 PM   #12
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It is possible to run two AC units off 30 amps but you are pushing it. I would suggest turning off all other AC equipment while running both units. In particular, turn off hot water heater, battery charger and any fans. Also you may want to run the refrigerator on 12V while you are cooling the boat with two ACs. Once the boat is comfortable, you should go back to one AC.
We do balance the loads, as you recommended. Fridge is on 12v. We have a raised pilot house and run the upper a/c first, letting the cool air flow downhill to the rest. This only happened at one Marina where we were placed on a T-head.

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Old 09-02-2017, 01:00 PM   #13
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A few things to add.....

There are a couple of ways to confirm whether your HVAC is 240V or 120V. On a newer boat like yours I would expect 240, but you never know. First check is to look at the breakers. If they are tandem breakers (two switches with a bar connecting them so they switch together), then it's 240V. The other is to go look at the name plate on one of the compressors.

If you go the route of a 2x 30A combiner to create 240V for a 50A plug, which I expect you will, be sure to also buy at least one 25' or 50' 30A extension cord. The two 30A plugs on the combiner are short - maybe 3' each - and quite frequently you will find the two 30A outlets that you need are spaced much further apart than that.

Last, there is yet another way to get 240V service from a 30A dock socket, and that's with a transformer. I know a number of people who have luggable boost transformers to bump 208V up to 240V. But there is no reason you can't do the same thing to convert from 120V to 120/240V. The plus side is that you only need a single 30A outlet. The down side is that you will be restricted to the power of a single 30A outlet, so about 3500W. With a dual 30A to 240V combiner you get the power of two 30A outlets, so about 7kw. That all compares to the approx 12kw you get from a 50A outlet.
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Old 09-03-2017, 07:40 AM   #14
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Power lacking folks can find a setup at a RV store that will operate 2 air cond , one at a time, switching back and forth every so often.
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Old 09-03-2017, 08:02 AM   #15
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Air conditioners draw far more current when starting than when just running. Mine (18000 BTU) draws maybe 25 amps for a few seconds when it starts and perhaps 18 amps when running (rough guesses). If you have two and you turn them both on at the same time, the surge could trip the main breaker or dock breaker. If you turn one on, wait a few minutes and turn the other on, you might be OK.

Boat and dock breakers will typically handle an overload for a short time before tripping.

Remember though, that the thermostat cycles them on and off to meet the temperature you have selected so at some point they might both cycle on at the same time and trip the breaker.
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Old 09-03-2017, 08:52 AM   #16
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Understanding if the ship's inlet is 240 volt, and what the voltage the AC's are would help eveyone give a better answer. If the ship service is 240v, strongly recommend a "Smart Y" adapter, which when used to with 2 30A 120 outlets (assuming they are out of phase, which you will safely find out when connected) gives you 30amps of 240 service,
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Old 09-03-2017, 10:34 AM   #17
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I'll check the labels on the hvac. In the meantime, my boat's power inlet, which is 50a 125/250V, has this placard above it. I must admit, the electrical aspect of the boat is probably where I'm least knowledgeable at this point. Name:  IMG_9318.JPG
Views: 143
Size:  85.9 KB

By the way, I wasn't even able to connect to shore power because my 50amp cord wouldn't fit into the 50amp outlet on the dock. The female outlet at the dock had 3 slots, two of them straight and one of them has a little curve at the end. My cord has one straight male prong and two with a curve at the end. I'm thinking the one at the dock is the older 50amp type?

Thanks!
Mike
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Old 09-03-2017, 10:56 AM   #18
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By the way, here is the male end of my cord and the female outlet on the dock. Name:  IMG_9336.JPG
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Size:  74.6 KBName:  IMG_9320.JPG
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Size:  90.0 KB

As you can see, they don't seem to be compatible. I'm assuming one is 50a 125v and the other is the newer 50a 125/250v?

If so, is there an adapter available. Google search wasn't my friend in this case.

Thx.
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Old 09-03-2017, 11:04 AM   #19
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You are right. You 50-125/250. The dock is 50-125. Yes there is an adapter available.
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Old 09-03-2017, 11:05 AM   #20
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I'll check the labels on the hvac. In the meantime, my boat's power inlet, which is 50a 125/250V, has this placard above it. I must admit, the electrical aspect of the boat is probably where I'm least knowledgeable at this point. Attachment 68264

By the way, I wasn't even able to connect to shore power because my 50amp cord wouldn't fit into the 50amp outlet on the dock. The female outlet at the dock had 3 slots, two of them straight and one of them has a little curve at the end. My cord has one straight male prong and two with a curve at the end. I'm thinking the one at the dock is the older 50amp type?

Thanks!
Mike
OK, your boat plug with wings on two of the prongs is a 50A 120/240V plug, and is the most common type of 50A shore power connection.

Your dock with a wing on only one prong is 50A 120V. There is probably a 30A 120V outlet on the same or nearby dock box.

It sounds like you will need to get a reverse Y that takes two 30A 120V dock outlets and converts it to a single 50A 120/240 receptacle that you can plug your boat cord into. You will need two 30A receptacles. The only caveat is that you will be limited to 30A of shore power draw, not 50A. And a heads up.... the Reverse Y adapters are expensive. Figure around $700.
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