mg2006,
Here is the secret which you have some of the information already. As I stated the number was not real accurate, more of a guess-timate. Ok you know if you have watts and you divide by volts you get amps.
1000/120=8.3 amps or 1000/12=83.3 so where is the 6.7 amps
That was easy! So where is the 6.7 amps. That comes in several forms, line loss, efficiency factor, planning on inductive resistive loading. I didn't or better couldn't really figure the real numbers because I did not have the actual specs of distance between the battery and inverter, inverter efficientcy, size wire, temperature, type of inductive loading at startup, and if the heater unit would be pure resistive load or combination of resitive and inductive load.
So the 6.7 amps was a guess based on other installations.
So why are these losses important. Well a small difference in voltage equals a large difference in current. Lets say we have 11 volts DC at the Inverter, due line loss, not to crazy!
1000/11=90.9 amps.
Now since we all know inverters are not 100% efficent, more like 90%, so to produce 1000 watts at 120 volts you need to put in 1100 watts at DC volts.
1100/11=100 amps
You are getting the idea! of course this is all theoretical due to the lack of ture specifications. But here I have only touch two of the losses, line loss and effieciency
Look at my post under electrical and electronics forum shore power question. The same thing happens with your shore power, line loss.
When figuring out your power requirements there is also a duty cycle to consider. In the case of the heater I used 100%. Let's think of a 1000 watt microwave. You run the microwave 4 times a day for a total of 10 minutes.
Using the same process! 1100w/11v=100a however for only 10 minutes.
So 10 minutes is one sixth of an hour, hence you would use 16.6 amp minutes or .6 amp hours per day. Big difference! So a 75 amp hour battery would handle that just find.
The thing you need to do is to make a list of the options and duty cycle. Looks like this working on a 24 hour day.
Loads.........A standby....StandbyHours......High A....High A Hours....AHR Day
Instruments......0.............0......................0.5..............10................5.0
GPS.................0.............0......................0.5..............10................5.0
DGPS...............0.............0......................0.5..............10................5.0
Radar.............2.3............4......................3.9..............2.0..............16.8
VHF................0.8............8......................5.0..............0.2...............7.2
Autopilot.........0.1............8......................5.0..............1.5...............8.3
Engines.............0............0......................30.0............2.0...............60.0
Cabin lights.......0............0.......................5.0.............3.0...............15.0
Navigation.........0............0.......................1.0.............3.0................3.0
Anchor lights......0............0.......................1.0.............8.0................8.0
Batt monitor.....0.1..........24........................0................0.................2.4
Bilge pumps.......0............0.........................0...............0....................0
Waste water.......0............0.........................0...............0....................0
Windless............0............0.......................70.0............0.1...............2.4
Blowers..............0............0.......................4.0.............4.0...............12.0
CO2 detector......0.1........24........................0...............0..................2.4
Washdown Pump.0............0........................12..............0...................0
Freshwater Pump0............0........................12.............1.0...............12.0
...................................................................Total Amp Hours.......164.5
Hope this helps!
Mike -
