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Old 03-07-2009, 07:50   #16
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There are inexpensive (<$20usd) DC/DC converters available to power laptops and other equipment straight from ship's batteries that supply constant voltage from the varying source of the house banks.

The problem with the Macbook Pro is the specialized magnetic power adapter end (which is brilliant in itself, but not for this application). You would need to cut this end off of your power adapter (or get another one), determine which wires hook where and splice it onto the DC/DC converter output. Not difficult, but not pretty.

Mark
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Old 03-07-2009, 09:41   #17
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Post Inverter load calculations

For a rule of thumb just realize that the products of voltage times current at each voltage are equal for any transformer.

Easier said...the amps at 12 volts will be 10 times the amps at 120 volts. So a hair dryer using 15 amps at 120 volts will use 150 amps at 12 volts. If it is used for 12 minutes (1/3 hour) it will consume 50 amp hours.

If you want to add a refinement, divide by the conversion efficiency of your inverter. Mine is 89%. So the actual amps are 168.

Hope this helps. (And that's a pretty decent load.) You will need at 2 kw (or 2000 watt) inverter as amps times volts = watts

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Old 03-07-2009, 10:46   #18
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yea, dont forget the inefficiency of the invertor, said to be 10-20%. By the time you figure the amps drawn, the inefficency, and the in ability of batteries to accept a high rate of recharge for long periods of time... that hairdryer is pretty costly in amps!
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Old 03-07-2009, 12:31   #19
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The best plan is to only let your wife use the hair dryer when the engine is running.
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Old 03-07-2009, 13:02   #20
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What an educational thread!

I may no longer be "running on empty" when it comes to understanding Electrical topics, however I'm still "a work in progress", and this area of inverters is new to me. Coincidently I'm installing a 2000 watt Mastervolt Combi (100amp/2000 watts)......
However everything down under is at 230-240V AC.

Could someone address the issues and concepts presented in this thread to my 230-240V down-under circumstances?

For example:

@ 80% efficiency will that mean I will "frying/excesively draining" something if I use a 1600-1800 watt @ 230-240V water kettle, and if not how long can I use it?

As the inverter is a full sine wave, how long can I charge my PC without "frying/excesively draining" something?

Other pertintent data, consideratons, etc. I should be aware of/keep in mind would also be appreciated.

BTW, my House Bank will be 900 A/hrs (12V DC) ... which means, as I understand it, 80%-50% capacity (30%) means I will have ~270 A/hrs to work with.

Gracias in advance.
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Old 03-07-2009, 17:55   #21
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Apple makes a 12V DC adapter for laptops that plugs in to a cigarette lighter. Its for use in autos that should work just fine for you. See your nearest Apple store.

Good luck

Joe S
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Old 03-07-2009, 18:00   #22
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Thanks!
Will definitely try.
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Old 03-07-2009, 19:35   #23
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Blue Soverign, your 1600 watt kettle will pull about 160 amps from the batteries, and should take a little under 4 minutes to bring a liter of water to the boil, which should take about 10 amp-hours out of your battery bank, but in reality will take 15 amp-hours out of the bank due to the relatively high current and Peukert's Law. Note that using an 800 watt kettle would take 8 minutes, but only take consume about 12amp-hours. No worries, but somehow you need to put the amp- hours back into the batteries.
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Old 03-07-2009, 19:45   #24
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What an educational thread!

I may no longer be "running on empty" when it comes to understanding Electrical topics, however I'm still "a work in progress", and this area of inverters is new to me. Coincidently I'm installing a 2000 watt Mastervolt Combi (100amp/2000 watts)......
However everything down under is at 230-240V AC.

Could someone address the issues and concepts presented in this thread to my 230-240V down-under circumstances?

For example:

@ 80% efficiency will that mean I will "frying/excesively draining" something if I use a 1600-1800 watt @ 230-240V water kettle, and if not how long can I use it?

As the inverter is a full sine wave, how long can I charge my PC without "frying/excesively draining" something?

Other pertintent data, consideratons, etc. I should be aware of/keep in mind would also be appreciated.

BTW, my House Bank will be 900 A/hrs (12V DC) ... which means, as I understand it, 80%-50% capacity (30%) means I will have ~270 A/hrs to work with.

Gracias in advance.
Plug your labtop in just as you do in your house. The only problem would be the invertor uses power even when no load is on it. Check the literature.

Don’t forget Peukerts coefficient. That electric coffee kettle is going to use more AHrs than amps X Hrs suggest. The invertor efficiency has nothing to do with Peukerts coefficient.
I am assuming 24 volts 450 AmpHr battery. 20 hr rate is 22.5 amps
A 1700 watt kettle/ 24 volts = 71 amps. Assume invertor efficiency of 85% yields 84
Amps.
That is 3.7 times the 20 hr rate. At that rate the usable capacity of your battery bank is 75%. Your battery bank would be downrated to 337 AmpHr from 450 AmpHrs.. If you were to use 30% of your battery capacity you would have 100 Amphr to play with, at a 84 amp draw a little over an hour.
This is where it gets scary. When you recharge that battery bank the Peukert Effect rears up again and bites you. An 80 amp output from the alternator means 60 amps stored in the battery. So for every hour you use the kettle you need to charge for almost 2 hours. It will actually be longer as the charge rate will drop.
Using your battery bank in the 50% to 80% range is bad news for longevity.
Why in the world would you use an electric kettle on an invertor I couldn’t even begin to guess. Use propane.
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Old 03-07-2009, 21:28   #25
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Lightbulb

And leave the hair dryer at home !!
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Old 04-07-2009, 09:23   #26
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Inverters

Just to chime in once more, we have separate (rather than the combi-that's a personal choice) Mastervolt charger (80 amp) and inverter (2 KW) and the Mastervolt MICC controller. I think they are great and can recommend them.

Steve
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Old 04-07-2009, 10:17   #27
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Apple makes a 12V DC adapter for laptops that plugs in to a cigarette lighter. Its for use in autos that should work just fine for you. See your nearest Apple store.
Unfortunately, what Apple sells is an airline adapter. It doesn't work on 12V cigarette lighters and Apple has a warning about this. The Macbook Pro runs on 18.5V, so you will need to modify a DC/DC converter with a magsafe tip.

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Old 04-07-2009, 10:20   #28
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Re: Computer charging

I'm curious, doesnt the laptop charger unit convert 120 volt ac to 12 volt or another similar DC voltage? doesnt that get rid of the square wave or other issues in the process??
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Old 04-07-2009, 17:38   #29
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Yes it converts it to a lower voltage. The problem is it may not be the correct voltage and/or the charge regulator may not "see" the right voltage which may cause overcharging of the lithium ion battery in the computer thereby slowly ruining it which I have done to 3 battery packs before I learned not to charge them with my 2500 watt Heart Interphase invertor.
Now I use a 600 watt pure sine wave invertor.
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Old 04-07-2009, 17:50   #30
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Paolo,

There was another thread on here a while back where someone else was powering their ibook direct from the battery with no problem.

I would think that (assuming you could maintain proper voltage and properly conditioned signal) that this method would be favourable as the power adapter on most computers and especially on macbooks loses a tremendous amount of power to heat while converting from 110/220 to DC.
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