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Old 04-07-2009, 17:03   #31
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I just found this on google. It's a 12v DC-DC power adapter for mac laptops:

HyperMac Introduces World's First DC Car Charger For All Apple MacBook Models - Sanho Corporation -

(and sales page)
HyperMac Pure DC Car Charger for MacBook

For simple straight up 12v DC devices I don't see why you couldn't build your own, but for a computer that is a big investment to be taking a chance on dirty power.


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Old 04-07-2009, 17:04   #32

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Originally Posted by mesquaukee View Post
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.

Donít 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
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 couldnít even begin to guess. Use propane.
Thanks for this, it's genuinely appreciated.

You have just re-affirmed what my electronics advisor down here told me just this weekend: Best use the kettle only when you run the Genset in the morning and evenings to charge up your batteries!

Regarding you propane comment, I'm looking for 4.5kg alloy tanks (very light) to replace my 3kg steel (?) tanks. They use to sell them down here, but now only 5kgs are available. Even 4.5Kg was going to be "stretch", with 4kg tanks known to work. Two 4.5kg tanks would increase my propane capacity by 50% over my two 3kg tanks.

Any ideas? (probably should start a different thread for this query)

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Old 04-07-2009, 21:04   #33
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colemj--Mark, Thanks for correcting my inadvertent error. I thought I knew something that I didn't. My bad.

Joe S
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Old 05-07-2009, 08:02   #34
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Hi Joe,

Looks like we are now both incorrect! The post above lists an actual DC/DC converter for the Macbook that is new on the market (taking pre-orders). However, it costs $150!

I just bought a DC/DC converter for a toughbook display for $18. I am thinking of buying another one, cutting the magsafe adapter off of my current powerbrick cord and installing a standard connection jack on both ends. That way I can plug it into the brick, or into the converter.

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Old 05-07-2009, 08:26   #35
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It couldn't hurt to send an email over to your manufacturer's engineering department to verify the exact electrical input your electronics need before just plugging in. Could be you need a very specific (say 13.7 or something) voltage with a given polarity and amperage and such. Not that that should be too hard to do, but could be better to ask before frying a computer.

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Old 29-01-2014, 10:43   #36
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Re: Use of Inverters

A couple of years ago I bought an inverter from a Chinese website called it worked very well so I went back to buy a Tablet from them.
It arrived by DHL but was defective on arrival, I posted It back and they sent another older defective model as a replacement.
I've been fighting with them to replace the Tablet or refund my money and they just ignore my phone calls and e mails.
I've been caught and I post this as a warning to others, please pass it around.
If you send me a message I will give you a good Chinese site for Iphones Pads Tablets etc I've used since with no problems.
I hope this helps you from getting ripped off.
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Old 29-01-2014, 11:18   #37
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Re: Use of Inverters

I buy a few items from time to time from one of China's best importers, Harbor Freight! Some of the unbelievably high priced commercial stuff we buy in UK or America is cheap priced stuff and is actually not so bad. China has come a long way. But.............I have also bought West Marine (china) Aruba binoculars for top price only to experience a total RIP-OFF and should never have been offered....In general, ask......Some things we used to know as quality are now CHINA junk, and to YOU rubbish.....Things have changed....ask before buying for your boat.

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