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Old 19-11-2007, 18:51   #1
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Aircon from Inverter from Batter Charger

I'm designing a boat to be used on Euro and US shorepower. I like the Mastervolt battery charger that accepts shore power at 120/60 and 240/50. If I use that to power an inverter, is it safe to run the battery charger and inverter all the time to power all the AC devices?

Is there a reason not to power a 16,000 BTU aircon from a Battery Charger -> Inverter -> Aircon?

Both the charger and the inverter have the wattage to support this with 2x room to spare.

Wouldn't this design be safer, since the power only comes in directly to the battery charger?

Wouldn't it be more robust since the inverter would take power from the batteries if there wasn't quite enough power from shore?

What am I missing?
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Old 19-11-2007, 18:58   #2
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Most HVAC compressors will require up to 5xA to start then drop down to running A.
16,000BTU is just too much for an inverter and battery bank. Well, unless you're sailing a 72'er
I've successfully run a 5000BTU HVAC on a 800Ah battery bank for 6 hrs before recharging.
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Old 19-11-2007, 19:06   #3
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Most HVAC compressors will require up to 5xA to start then drop down to running A.
16,000BTU is just too much for an inverter and battery bank. Well, unless you're sailing a 72'er
I've successfully run a 5000BTU HVAC on a 800Ah battery bank for 6 hrs before recharging.
The literature (if you believe it) suggests that startup amperage is 1.8X normal. I do think I can run the 5000BTU unit off of the inverter and battery bank with a 600Amp 24V house bank. The literature say's I need 240Amps for 8 hours.
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Old 19-11-2007, 19:42   #4
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A/C on Inverter

I have used a small mains powered A/C ok from the ships inverter I would only go for a pure sine wave type & I would go for an inverter type oF A/C & yes to running off the batteries with a good charger.It keeps all simple. The masterVolt units are very good.

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Old 20-11-2007, 03:05   #5
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1. If I use that to power an inverter, is it safe to run the battery charger and inverter all the time to power all the AC devices?
Is there a reason not to power a 16,000 BTU aircon from a Battery Charger -> Inverter -> Aircon?

2. Wouldn't this design be safer, since the power only comes in directly to the battery charger?

3. Wouldn't it be more robust since the inverter would take power from the batteries if there wasn't quite enough power from shore?
1. I would NOT utilize the Charger-Battery-Inverter system to power the Alternating Current (A/C) loads when A/C Shore Power is available. I would power the A/C loads directly from Shore Power, when available - reserving the Inverter for those occasions when utility A/C power is unavailable.

2. Each additional device in a power supply circuit represents an additional point of failure, and decreases efficiency. A more direct supply is simpler, more efficient, and safer.

3. It’s unlikely that any practical Battery-Inverter combination will be more robust than most utility-supplied Shore power supplies.
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Old 20-11-2007, 11:48   #6
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An upcoming Mastervolt solution

I agree with Gord. In general the alternative energy (off grid) market uses 48V and higher to successfully drive high power inverters that handle such devices as airconditioners, washers and dryers.

Mastervolt has a high-frequency "switcher" design to provide an isolation transformer function between shore and ship. So far they address the Euro market and have not released a "30A" unit for the US market due to ABYC internal squabling as to what constitutes a safe isolation design. This Mastervolt design is the way of the future.

I'm not sure if their product is a true "cycloconverter". A cycloconverter is capable of converting a range of input voltages and frequencies into other voltages and frequencies thereby addressing a conversion between the Euro and US voltages and frequencies or vice-versa.
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Old 20-11-2007, 12:48   #7
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In addition to the above considerations, many of the contemporary marine A/C systems employ a soft-start power curve which can sometimes confuse the specs people quote regarding start current draw and which are more appropriate in any power sensitive system.
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Old 20-11-2007, 13:09   #8
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Disagree, all it takes it the power cord to be unplugged and the shore power is down, or marina guy to turn off the wrong plug etc.

Inverters can be purchased to use shore power, if available and revert to battery power has required. This provides additional secrurity in the event of loss of shore power not the reverse.

This type of system is often called an UPS (uniterruptable power supply), and is typical of most critical inductrial systems.

The only dilemma is how to deal with the various shore power supplies, seems to me a transformer solves all of the issues.

50 to 60 Hz will only be critical when reducing the frequency, the answer is to purchase all motor systems to operate on 50 hz base, they will have more power and run cooler when run on 60hz.
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Old 20-11-2007, 13:28   #9
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... This type of system is often called an UPS (uniterruptable power supply), and is typical of most critical inductrial systems...
I just (Monday) supervised the commissioning an Uninterruptible Power Supply for a police communications centre. The 500VDC Battery Bank consists of two ten foot rows of closely coupled batteries, 6 feet high. The AC Utility supply is backed up by a 250 kW Generator. I’d guess the batteries might weigh about 1,000#, or more.
I wouldn’t compare a boat’s practical Battery-Inverter system with an Industrial UPS System.
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Old 20-11-2007, 13:43   #10
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So you think it takes 1000lbs of batteries to supply a small air conditioner with power.

5000 Bt/hr unit should draw about 40 amps at 12 V with a duty cycle of 50%.

So for and overnight run, I would need about 40amps*12hr/2 =240 amp hours, a nice 500 amphr battery pack should be fine, with some left over for the fridge as well.

Don't think this takes 1000 of lbs to make happen.

Glad your not sizing our systems, the inverter would weigh oh maybe 10 lbs.

Hey remember the battery is back-up worst case the power is cut after 12 hours on low battery voltage, and you say the shore power is more any way reliable.

Unless one installs a system to turn on the genset. (Iwouldn't other would).

Still not thousands of lbs.
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Old 20-11-2007, 14:21   #11
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A/C

Ok different sollutions for different boats. Not all are the same. I reasoned it was best to have a stand alone battery charger & inverter for redunancy. It is more cost effective to replace one at a time & you can work arround one being U/S at a time. The MaserVolt charger is able to run the boat without the batteries being connected. ie a very stable DC power supply if necessary. The use of the inverter to provide primary AC power is fine & who is to say using it will cause more failures. The electronic design & the board construction of mine is such as I am happy to use both of them every day. Power requirments for a Air Con is not too bad if it is only for those days when there is no sea breaze & hi humid conditions & if the temp is set to cut ot at say 23 Deg C then all that is left running if the fans. So cooling for say 3-4 hrs at night. The use of the sine wave inverter gets around applicances which references the mains frequency for timing such as soe micro wave ovens, bread makers etc. I am trying to use the sun to input 2000watts a day & not have any connection to shore power.
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Old 20-11-2007, 14:46   #12
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1.So you think it takes 1000lbs of batteries to supply a small air conditioner with power…
2. Hey remember the battery is back-up worst case the power is cut after 12 hours on low battery voltage...
1. No I don’t think it takes 1000lbs of batteries to supply a small marine air conditioner. It was jscott who raised the issue of Industrial UPS systems. I merely described one, with which I have recent experience.

2. No, BlueRapcity was proposing the Battery-Inverter System be an On-Line UPS, not a “Stand-By” system.
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Old 20-11-2007, 15:02   #13
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I must be missing something too. I see nothing wrong with your plan. You are not looking to power your a/c in the absence of shore power. You do, however, need to account for a possible loss of shore power. You would want most systems to shut off (especially the a/c). You should probably consult an electrical engineer about the best way to parallel the wiring. I would like to avoid running amperage through the batteries on the way to the inverter.

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Old 20-11-2007, 16:21   #14
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Nigel Calder discusses at length in his book Boatowners Electrical and Mechanical Manual exactly what you are talking about.

See the sections on "The Inverter Based Boat" or such. DC generator, battery bank, inverter and variable speed compressors for refrig an A/C. If think if you designed a complete system where everything was chosen to integrate into this strategy it could work very well. I am looking at doing this when we are refitting out boat.


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Old 20-11-2007, 19:21   #15
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We'll now I'm still confused which is where I started.

My previous boat had a full blown power converter. It would take any power and any frequency. The problem was that it weighed over 100 lbs. In addition, I fried one of the computer boards because it got too hot. If I can use the Battery Charger - Inverter to power all my 120 AC needs I would be creating a poor mans frequency and voltage power converter. All based on the ability of the Mastervolt Battery Charger taking in any power and frequency. I suspect the loss in wattage would be significant (20%) but with the battery back during startup load and such it "might" be more forgiving with poor quality shore power.

Two of the design constraints I'm working with are not having a genset and using 2 very high power alternators that could potentially drive the big aircon form the alternators. 2 Mastervolt 110V 24V alternators.

I'll try to talk with Mastervolt about this at some point but since nobody is doing it now, I still suspect it's a bad idea.

This is what happens when computer guys start designing boat systems...
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