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Question on Shorepower?

Old 08-27-2003, 11:50 AM
Join Date: Oct 2000
Location: Knoxville,TN, USA
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Default Question on shorepower

There are many additional things to consider or be aware of for what you are considering even beyond what has been discussed on this thread.

Here's what I consider when calculating invertor installation.

An invertor consumes a small amount of power just being attached to your batteries even with no load attached. Enough to make a substantial drain to a small, less than very strong battery system overnight. This unless you physically turn it off so that DC is disconnected from the invertor.

Invertors are less than 100% efficient in conversion from 12VDC to 115VAC. 90% efficiency might be considered avarage. That means for every 100 watts of power you draw from batteries only 90 watts is available. That is parasitic loss.

When converting from 12VDC to 115VAC, you lose efficiency. Wire the DC input to your invertor with wire rated for the DC ( battery ) draw not the AC. Use marine grade wire that is fine stranded and is also tinned to help prevent corrosion. These DC connections are very high amperage and deserve extra consideration at every crimp, lug, screw or connection of any type.

I have found the best way to use an invertor is to use four or eight 6 volt golf cart batteries wired series parallel. This gives high current and long lasting power. This is not what everyone wants to hear but in reality the batteries in your boat are in no way capable of providing substantial inverted 115VAC for any period of time.

Also consider that different invertors have different waveform outputs. Some AC devices require more pure sinusoidal waveforms. Most less expensive invertors provide squarewave outputs. This is adequate for many things but not all. Electric motors and incandescent lighting run fine on square wave or synthesized sine wave.

An invertor load will draw down your boat batteries in a hurry. If you have standard alternators you will run them very hard to even think of recharging in a reasonable time. A standsard 60-65 amp alternator will require a few hours to get your battery(s) back to a reasonable level. And, you can't do that at idle. Your alternator will require around 2500 RPM to provide a reasonable charge rate. To really make your system reliable and strong install 130 amp alternators.
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Old 08-27-2003, 07:01 PM
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Well, that kinda brings everything into perspective!!

Who knows where to find a good deal on a Used or Rebuilt or Reman. Generator??

I looked up that site and I'll call them to see if they have any used ones. It looks like a new one runs about $4750.00 (I wonder if that comes with everything I need or if that's just the start?) This is a fixer upper so Used is the way I would like to go!!
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Old 08-27-2003, 09:14 PM
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A 6500 Btu AC will pull around 8 amps running plus an amp for the water pump. This means 9 amps at 120 volts = 1080watts. Divide 1080 by 12 volts and you will need the batteries to supply 90 AMPS. Figure a loss of 10% thru efficiency drop thru the inverter and you are knocking on a 100 AMP drain on your batteries whenever the compressor is running.

So, you have a 100AMP drain from the AC. Your 12v fridge pulls 4 or 5 amps. Your Stereo (150 watt normal decent system) will pull at least 10 amps at normal listening levels. You will also have some 12 volt lighting on in the cabin I'd expect. This totals up to a 125 AMP drain on the batteries when the AC is running in cool mode. If it is hot outside and you leave the cabin door open as we usually do, then the AC will run 75% of the time if not continuously. For benefit of this situation, let's figure that over an entire 8 hour day at anchorage, you will average a 90 AMP drain.

One Group 31 battery will provide around 90 amp hours of power. This means that for each Group 31 battery, you can run your setup for one hour. Each Grp 31 battery weighs around 45 pounds.

8 hours of runtime will require 8 group 31 batteries (360 pounds of weight). Remember that these batteries are SEPARATE from your starter batteries, else you will have no juice left to start the motors after 8 hours.

Saturday night, when you dock the boat, you had better have a 100 AMP charger hooked up all night long, or else you will still have dead batteries come Sunday when your friends are dropping their anchors. 800 Amp-hours of batteries won't recharge from fully dead to firecrackers in just a couple of hours...

As far as swimming off the stern, put the Honda on the nose on a little rubber welcome mat.

And someone mentioned putting a portable genset in the engine room. Nope. Only for storage, and even then, only if you close the fuel cock and close the fuel tank vent. DO NOT run a portable genset in a marine engine compartment.

Hope you have gotten some helpful answers on this thread.
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Old 08-27-2003, 09:59 PM
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For those raftup/anchor periods where cuddy time is necessary for the family..... and a separate larger cooler stocked with ice which may include some beverages of choice.....Screw all the gizmo's when you're trying to enjoy a good raftup and a good stereo system.....Just another out of the box alternative....
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Old 08-28-2003, 09:38 AM
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Location: ST. Louis, MO, USA
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That site was for new gensets. Check out boat trader for used. You can usually find working used units under 6 kW for around $2K. You'll need a $200 transfer swictch, thru hull, strainer, exhaust muffler, & misc hardware(another few hundered). The good news is that the units are pretty much self contained with auto shutoff and simple wiring to hook up.
mcollinstn has it about right. But you may need even more than 8. Startup amperage can be 2-3 times the normal running current on the AC units.
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Old 08-28-2003, 10:55 AM
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Thanks Guy's,
I think I'll get by for the rest of this season and start looking for a good used Genset that I could install over the Winter!!

If anyone here's of one please let me know!!!

Thanks again!!
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