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The inverter chargers seem pretty expensive for a small battery bank on a 27 foot boat. Seems to me separate charger and inverter make more sense as if one goes down the other is not necessarily down. Also seems it might be easier to design as system with solar/wind/generator with separate components. If you have an existing charger that you are happy with just figure out the amount of electrical use you need and get a stand alone inverter. You may be better off just using 12 volts, most AC stuff that you need an inverter for will pull lots of juice. A small inverter for a TV makes sense, less so for cooking devices and computers. You can get 12 volt chargers for laptops and what not.

What are you trying to power that requires 120(or 220 in Europe) volts?
 

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Discussion Starter · #3 ·
Thanks for your help I need to power a CPAP breathing machine for sleep apnea as well I would like to power a small 1000 watt microwave and a fan that is about It I am located in the Great Lakes basin in Ontario Canada I have to large deep cycle marine batteries. I haven't purchased a charger and or inverter yet. Be interested in your thoughts.

David
 

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Keep in mind that the wattage listed as cooking power of a microwave is not the AC power it uses. A 700 watt microwave consumes about 1150 watts AC. They also work a lot better with a pure sine wave inverter. Most inverter/chargers are not pure sine wave in the more affordable category.

An inverter output of 1150 watts requires about 115 amps DC.
 

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Charger only, no inverter at this time.

If I was to install an inverter to run a microwave it would be a 2000 watt sine wave.

One other issue is that an inverter needs a large battery bank if it is expected to run a high current item like a microwave, even for only a few minutes. If the battery bank is too small the voltage will drop quickly and the inverter will shut down. I recently replaced the house bank on a boat for this reason. The 2000 watt sine wave inverter pulled the voltage of a bank of 2 group 27 batteries down enough to cut out after only a minute or two when running a coffeemaker. The replacement battery bank was 4 golf cart batteries totaling 484 AH solved the problem.
 

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Thanks for your help I need to power a CPAP breathing machine for sleep apnea as well I would like to power a small 1000 watt microwave and a fan that is about It I am located in the Great Lakes basin in Ontario Canada I have to large deep cycle marine batteries. I haven't purchased a charger and or inverter yet. Be interested in your thoughts.

David
Fans such as Hella, Caframo & cheap truckers fans can be run on 12V DC. They draw multiples less current than a home fan run through an inverter.

Many CPAP's can also be run on DC but you may need to get a bit creative. If not a small pure sine inverter dedicated to only the CPAP would be the most efficient..

Inverting is inefficient and with two small batteries keeping your devices running off DC will use far less energy.

We have an Emerson 700W microwave. It draws a measured 1190W at 119V!

1190W at 11.5V = 103.5A X 1.20 (for approx inverter inefficiency) = 124.2A

This equates to a 70% increase in consumed wattage than most would ever assume. Apply the same 70% increase in consumed wattage, with a 1000W microwave vs. a 700W, and you are burning approx 1700W!!

1700W at 11.5V = 148A X 1.20 (for approx inverter inefficiency) = 178A

124A for a 700W Microwave!!! :eek::eek::eek:

178A for a 1000W Microwave!!! :eek::eek::eek:

If the battery voltage sags to 10.7V you are now at approx 133A just on a 700W "rated" microwave.....

Battery temperature, battery type and the Peukerts constant will also dictate how long the bank can support a 100+A load before dropping out the inverter on low voltage at 10.5V or so....

Keep in mind that even a 3% voltage drop equates to the inverter dropping out at a terminal voltage of approx 10.8V and the wire voltage drop does not include terminals, fuses, terminations or switches... This means an inverter sized for a wire drop of 3% could in actuality drop out at 11V or more as installed.....

With short term microwave use most good sized flooded deep cycle house banks can easily survive this load for the duration the microwave is run, if they are healthy. If they are sulfated and not healthy, or not large enough, you'll know it pretty quickly.

I would suggest learning to use the stove/oven, if equipped, and looking to DC solutions for the rest.....
 

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Here's a real-life example from a friend of mine:

He had a 3-battery setup, 1 starting and 2 house.
900w microwave.

His wife tried to microwave 2 baked potatoes for 10 minutes and totally killed a healthy house bank.
Let's figure a 160A real world load for a 900W microwave..

If you have two 90Ah group 27's (guessing) with a Peukert of 1.27, the Peukert corrected load the battery sees (at 75-80F) would be roughly 370A yielding a theoretical 81 Ah's total. If the temperature of the batteries is below 75-80F you will have even less usable capacity..

Course we also have voltage drop to contend with so it stands to reason that two G-27 batteries would not survive a 168A (370A Peukert corrected) load for more than a few minutes before the inverter tapped out on low voltage....

That said I very often use a now 8 year old group 31 flooded DC battery in boat yards where running a 300' extension cord is simply not worth it. I use this G-31 battery in conjunction with a 2000W inverter to power my Milwaukee heat gun.

With this portable power pack I can do enough dual wall heat shrinks to re-wire a typical cruising boat battery bank. The key is these are short duration shrinks, under two minutes, and the battery is then allowed to recover/rest. I then bring it home and charge it at 14.8V until current falls below .3% of initial Ah capacity. If I pushed it much beyond 2 - 2.5 minutes the voltage would likely tap out. The battery has served a long hard life and her voltage drops a bit faster now days...... Also I am running less than 16" of 2/0 wire for very minimal voltage drop, something most installations on boats simply can't do........
 

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Discussion Starter · #10 ·
Well, I guess shore power is the only way to work the microwave/cpap issue. I have an alcohol stove I will have to get savvy with. So much for the inverter,,, The batteries I have are two new G 27's so I don't want to cook them,, Shore power and a charger is what I am going to get. Thanks for all of your help!!!! I am totally confused and afraid of boat power,,,, lmao

David
 

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I spent a week on sailboat with a guy using a CPAP. He used a small dedicated inverter that plugged into a 12V receptacle. Actually he used two inverters, because the first one started smoking and quit working. He had the foresight (or something) to bring a spare inverter and it seemed to work OK - no dead batteries at dawn or anything. How much power does the CPAP require?
 

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i put a 1000 wtt xantrex charger invertor into my ericson--i loved it.
want to install a 2000 wtt into this boat---problem is they are pricey, so iam waiting....

there is not enough battery power under the sun for microwave and espresso machnes while solar powered,unless you have entire topsides solar and a few dozen batteris for storage. good luck.
there are folks out here cruising with cpap machines--- they seem to be successfully usng their electrical systems without too many fails...
 

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I also use small inverters from the 12V receptacle. These units give up working very easily so you must always have a spare. I use them because I am in the transfer business and most boas do not have inverters. If you need inferters make sure you have high capacity ones and select full sine inverters, the others cause more problems than they solve.
 

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Maine Sail just throws out these numbers - I have to sit down and really think to understand them. BTW, Main is generally correct!

You mentioned you were getting confused by boat electrics - this is a pretty good basic book
Sailboat Electrics Simplified: Don Casey: 0639785800361: Amazon.com: [email protected]@[email protected]@http://ecx.images-amazon.com/images/I/[email protected]@[email protected]@516KsML1v1L
And Google if your friend as you dig deeper.

I think you got the answer to your original question - inverters are useful, but are very power-hungry. Go 12v if you can; where possible use AC when you are connected to shore.
 
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