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Old 05-27-2022, 11:18 PM   #1
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soft start for marine AC

I have absolutely no knowledge of marine AC systems. I have 3 ac units on the boat each is 16,000 btu, all 3 units are on a separate 30 amp AC circuit, This air conditioner circuit has a 30 amp main breaker and each ac unit has a its own 20 amp breaker. The issue is when one of ac units turns on the current draw is large enough to trip the main breaker. This started out as it would trip it occasionally but now it tripping the main breaker all the time, even if it is the only ac unit energized. The ammeter shows about 40 amps of draw when the breaker trips.... Will a soft start unit solve this issue or is it just a band aid should i just replace the entire unit? Thanks
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Old 05-28-2022, 01:28 AM   #2
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Hmmm do you mean to say all three units have there own 20 amp breaker and all are on the same 30 amp service? If so All three units running at the same time would draw over 30amps, which would flip the main 30 amp circuit breaker, also any two units starting at the same time would again pull more than 30 amps and again also trip the circuit. At no time can you pull more than 30amps all together without tripping the main breaker if all you have is a 30 amp service, you may have been able to get away with it for a little with all brand new air con units but as they get older they will draw more amps just running just the way it is, nothing wrong or broken there. Soft start would fix the two units tripping the breaker when starting up together, but will not fix you running 3 units at the same time. Kinda an odd setup and don’t know many marine electricians that would ever consider setting it up like that because 1 30 amp service is just not big enough for running 3 16000btu units, and you are lucky your breaker is tripping, if it wasn’t you would be headed quickly towards a fire. You should pull one of the ac units off that 30 amp service and put it on your house load, also find a couple lower draw things on the house load and maybe put it on the air con service to distribute the load a bit better, that is if you have the extra amps not being currently used. Really don’t want to tax a 30 amp breaker to the full 30 amps 100% of the time. I try to aim for around 25 amps constant draw for my max. Other option would be upgrade to 50 amp 240v service. That would Definitly be enough to power 3 16000btu units as well as a rather large house load, like if you had a full electric galley. If you have a full electric galley now you would more than likely not be able to cook, and have that ac unit running while at the same time if you did pull one of those ac units to the house load.
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Old 05-28-2022, 05:01 AM   #3
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I have absolutely no knowledge of marine AC systems. I have 3 ac units on the boat each is 16,000 btu, all 3 units are on a separate 30 amp AC circuit, This air conditioner circuit has a 30 amp main breaker and each ac unit has a its own 20 amp breaker. The issue is when one of ac units turns on the current draw is large enough to trip the main breaker. This started out as it would trip it occasionally but now it tripping the main breaker all the time, even if it is the only ac unit energized. The ammeter shows about 40 amps of draw when the breaker trips.... Will a soft start unit solve this issue or is it just a band aid should i just replace the entire unit? Thanks
A lot depends on model and age of the AC units. Older piston model compressors draw more running amps. Newer rotary compressors draw less and require less on start up.

Regardless, you won't be able to run all three, ever on 30 amps. With a soft start you might get 2 running, but there's an equal chance the main breaker will heat up and trip after 10 or 15 minutes. All this is predicated on having pristine connections between your boat and power cord, your power cord and the power pedestal on the dock, and not being at the end of the dock with low voltage during peak season.

As previously mentioned, converting to 50 amp 240 volt power service would be a much better solution.

Ted
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Old 05-28-2022, 09:52 AM   #4
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Don't equate the breaker ratings with the AC unit's running load.


Also, breakers have different trip profiles, in terms of magnitude and duration of overload before they trip.


Will any one of the AC units trip the 30A breaker on startup? If so, then it's most likely the 30A breaker, not a degraded AC unit. If only one AC units trips the 30A breaker, then I'd consider the AC unit as a possible source of the problem. But since it trips the 30A breaker, and not it's individual 20A breaker, I think it's very likely just a bad 30A breaker.
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Old 05-28-2022, 10:48 AM   #5
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I agree with T.T.

Circuit breakers can age out. THere are springs and levers inside. Yes, I've had them apart.

THe springs weaken over time but mostly from previous trips.

Look into a type that has a better current/time profile. You may not have a choice here depending upon what the mounting situation is but ask.

If the circuit is simply overloaded then it will still trip. If the overload is of a short enough time then the C.B. will allow it.

There are also hard starting kits which are basically a larger start capacitor which gives the motor a bigger , quicker boost so the high start current is reduce more quickly. Common in the RV side when the owner is trying to start an AC on a small generator which cannot handle the high starting current.
Once the AC is running the gen can handle the load. Ask about those also.

A timer may also help so only one can start at a time and run for a short time before allowing the next to start.

However, from what you have said the supply will not handle all three without causing trouble.
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Old 05-28-2022, 11:48 AM   #6
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Let me expand a bit on the idea of converting to 50A/240V service.

I suspect you already have 50A/240V and one leg is supplying power to your A/Cs, but it is limited by a 30A main breaker. It would be very easy just to upgrade that breaker to 50A assuming it is part of a circuit breaker panel and all three of the 20A A/C breakers are fed through a buss. Otherwise you may need to upgrade the wiring to safely allow 50A.

In any case that is much easier and less costly than adding three soft start kits to your A/Cs.

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Old 05-28-2022, 01:17 PM   #7
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I just read my initial post and it wasn't very clear. A little more info. The boats shore power is 50amp 120. this 50 amps is split into two separate main circuits one for AC and heat and the other for everything else. I don't run more then two ac units at the same time and I could do this for the first few years of owning the boat without any issues. Starting last year, one of the AC units occasionally would draw excessive current on start up (locked rotor amperage) now it does it all the time. I'm not an AC guy so I don't know if there is a "dump valve" on the compressor that failed.
The two other AC units can both be run at the same time without issue, it's the third unit that I question the excessive start up current draw, hence the question of has anyone any experience with using a softstart or just replace the entire unit its 20 years old. Thanks
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Old 05-28-2022, 02:54 PM   #8
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You say your shore power is 50A 120 but it almost certainly is 50A/240/120. The 120V is obtained from each of the two legs to neutral. 240V which you don't use is obtained from the two legs. So you have two 50A 120V circuits inside the boat, one feeding the three A/Cs and the other feeding everything else.

For some reason you have a main 30A breaker on the one feeding the A/Cs. Like I said in an earlier post you could probably just replace the 30A breaker with a 50A and it would be safe and wouldn't trip.

But having said all of that, it does sound like you have a problem with one of your A/Cs. It would first replace its starting capacitor and see if that doesn't solve it. They are cheap and easy to replace.

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Old 05-28-2022, 03:12 PM   #9
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Take a look at your shore power plug and note the configuration and markings.
Is the second leg / breaker for everything else 30A or 20A? I seriously doubt a boat mfg would split a 50A 120V and connect it to 2 - 30A breakers... that would / could overload the pedestal on a regular basis.
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Old 05-28-2022, 03:30 PM   #10
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Replace the 20 year old unit. It's almost guaranteed to be a piston compressor.

Ted
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Old 05-28-2022, 03:47 PM   #11
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my AT is a 30amp boat. I have 2 A/C. I have a 5amp breaker for the A/C circulating pump, a 15amp breaker for the 12K BTU A/C and 30amp breaker for the 30k BTU A/C. I have replaced all 3 of the breakers and a soft start on each A/C plants. I can run the two A/C w/o a problem.
Because I have only 30amp boat and electric stove, washer/dryer and a microwave.... I know how close I am to triping the main house breaker. I put a 2nd amp meter in the galley. I have proudly learned 'the 30amp dance.' I can shed loads to keep from tripping the main house battery.
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Old 05-28-2022, 05:20 PM   #12
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You say your shore power is 50A 120 but it almost certainly is 50A/240/120. The 120V is obtained from each of the two legs to neutral. 240V which you don't use is obtained from the two legs. So you have two 50A 120V circuits inside the boat, one feeding the three A/Cs and the other feeding everything else.

For some reason you have a main 30A breaker on the one feeding the A/Cs. Like I said in an earlier post you could probably just replace the 30A breaker with a 50A and it would be safe and wouldn't trip.

But having said all of that, it does sound like you have a problem with one of your A/Cs. It would first replace its starting capacitor and see if that doesn't solve it. They are cheap and easy to replace.

David

The AC was added by the PO, this is an NW boat and came from the factory with the 30 amp circuit just for some built in resistance type heaters. When the AC was added they installed a few breakers in the existing heat circuit. Our marina doesn't have 220/240 just 120


The boats that came with factory AC had 50 amp breakers and a larger genset.



I can replace the start capacitor but was hoping someone had some experience using the softstart device. Running 2 out of the three ac units the current draw is in the low to mid 20s.
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Old 05-28-2022, 06:36 PM   #13
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Replace the 20 year old unit. It's almost guaranteed to be a piston compressor.

Ted
When you replace the unit (Dometic), install a soft start system.

I did this 2 years ago when I replaced my aft compressor. Easy on the generator now.
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Old 05-28-2022, 07:02 PM   #14
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I would start by replacing the 30A breaker. The fact that it trips, and not the 20A, is a pretty clear indicator that it's toast, so no matter what I'd do this first.


Next if it still fails, I'd probably get someone to check out the AC unit. It's drawing more current to start up than it's twins, so something is amiss with it. I don't know enough about HVAC system to know if a low refrigerant charge can increase the startup current, for example. In the end, it might be time to replace the AC unit.


Given both of the above, I think adding a soft start is just covering up the problem, and is very much the wrong thing to do - at least at this stage. At a minimum I'd want to understand why this one HVAC is drawing more on startup than the others, because that's the fundamental problem.


If you do end up replacing the HVAC unit, then I think the earlier suggestion to replace with one that includes software is a great idea. Just don't use a soft start to sweep a clear malfunction under the table. Use it as a way to improve on an otherwise correctly working system.
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Old 05-28-2022, 07:28 PM   #15
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Many years ago I wanted to run the little 5000 btu AC on my boat with a Honda 2000 watt portable generator. The total running draw of the AC and pump was about 650 watts. It didnít work.

The starting load was about 3000 watts. On a piston compressor if you look on the tag for the LRA (Locked Rotor Amps) number, that is your starting load in amps.

I installed a cheap Supco Hard Start Capacitor and it completely solved the problem. In fact I was able to start and run the AC on just a 1000 watt generator.

The installation was very easy as well.
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Old 05-28-2022, 09:04 PM   #16
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Many years ago I wanted to run the little 5000 btu AC on my boat with a Honda 2000 watt portable generator. The total running draw of the AC and pump was about 650 watts. It didnít work.

The starting load was about 3000 watts. On a piston compressor if you look on the tag for the LRA (Locked Rotor Amps) number, that is your starting load in amps.

I installed a cheap Supco Hard Start Capacitor and it completely solved the problem. In fact I was able to start and run the AC on just a 1000 watt generator.

The installation was very easy as well.
I have those on all 3 of my AC units. Definitely easier on the generator.

Ted
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Old 05-28-2022, 10:12 PM   #17
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So... the basic Supco capacitor is around $11. The MicroAir EasyStart is around $300. They do not appear to be wired the same. What's the difference?

https://www.microair.net/products/ea...r-conditioners

https://www.supplyhouse.com/Supco-SP...crease-90-277V

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Old 05-29-2022, 05:19 AM   #18
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So... the basic Supco capacitor is around $11. The MicroAir EasyStart is around $300. They do not appear to be wired the same. What's the difference?

https://www.microair.net/products/ea...r-conditioners

https://www.supplyhouse.com/Supco-SP...crease-90-277V

Peter
My understanding is that the Supco is only an added capacitor (stored energy) to supplement the AC's one, for some extra umph.

Ted
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Old 05-29-2022, 08:55 AM   #19
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First check and probably replace your existing capicators.
Plenty of youtube videos on how to diagnose. They do degrade over time before failing.
Second to answer your original question. A good soft start isnt cheap but it is a good investment. They are more than just an added capicator. It incorporates a logic board and really lessens the initial starting load surge. It is an add on for new units so buy it now and it will outlast the existing unit. Also as said above there are differences in breakers. A ACR rated breaker will hold longer than a fast trip and yes they also degrade over time and repeated tripping.
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Old 05-29-2022, 09:42 AM   #20
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I added soft starts on my A/C units some years back and made it much easier on my genset. Well worth doing even if you do the other suggestions.
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