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Old 07-18-2018, 12:45 PM   #1
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Default Low power draw laptops that can run on direct 12v

What are you guys using.

I've seen a few guys running a laptop hooked directly to a 12v socket with the original cable\power brick sitting on the floor disconnected. The power brick was 12v. He made his own cable, and said it's been working fine for years.

I'm going to need a low power machine with a lot of spare battery capacity shortly and was doing some shopping, but thought I'd see what you guys are doing.

PS I'm no longer a power user, I don't game or do any video editing. 99% it's just emails, recipes, to do lists, browsing and maybe the occasional movie in bed.
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Old 07-18-2018, 01:10 PM   #2
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We just went through a similar routine, but we had been running on 12v for a long time. I don't know if there are any native 12v computers around any more, as what we found were all higher.


What we did find was that there was really now reason to use the 12v power to run or recharge the computer. With native 12v you should still use a voltage stabilizer and at high DC voltages, you need to use a 12 to whatever DC voltage adapter. When I tested the new 12v to 19.5v adapter that we got for the new computer, it actually used as much power as running an inverter and the normal AC brick that came with the computer. Using a small higher efficiency inverter should make it use less than the 12v converter setup.



Details of what we found here


http://www.classbforum.com/forums/f2...ters-7727.html
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Old 07-18-2018, 01:34 PM   #3
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.

Understand the inner workings of a voltage step-up "black box".

To step up from 12v DC to 18v DC,
the most common method is to
feed the 12v DC through an inverter circuit to turn it into AC,
then convert the AC to 18v DC.

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Old 07-18-2018, 02:04 PM   #4
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You can get laptop-specific 12VDC power adaptors on eBay very cheaply. They are available for most popular laptops. But, I agree with Booster: in this and many other areas, it is starting to look like going native 12V isn't worth the effort vis just using small inverters.

If I were doing a new van today, I would consider doing the opposite of what I did last time: I would push as much as possible to 120VAC and put my effort into a set of efficient inverters. LED lighting is a likely exception.
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Old 07-18-2018, 02:22 PM   #5
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Quote:
Originally Posted by avanti View Post
You can get laptop-specific 12VDC power adaptors on eBay very cheaply. They are available for most popular laptops. But, I agree with Booster: in this and many other areas, it is starting to look like going native 12V isn't worth the effort vis just using small inverters.

If I were doing a new van today, I would consider doing the opposite of what I did last time: I would push as much as possible to 120VAC and put my effort into a set of efficient inverters. LED lighting is a likely exception.
And at this point Avanti, what about the compressor refer?

Thanks.

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Old 07-18-2018, 02:56 PM   #6
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And at this point Avanti, what about the compressor refer?
Actually, the recently-reported successes of folks who have been trying out modern high-efficiency 120VAC fridges is the thing that got my attention in this area. I have long assumed that native 12VDC compressors would be vastly more efficient (both in fridges and A/Cs). But, apparently, it ain't necessarily so.

I would still look carefully before deciding, but 120VAC with a well-matched inverter now has my attention.
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Old 07-18-2018, 03:07 PM   #7
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Actually, the recently-reported successes of folks who have been trying out modern high-efficiency 120VAC fridges is the thing that got my attention in this area. I have long assumed that native 12VDC compressors would be vastly more efficient (both in fridges and A/Cs). But, apparently, it ain't necessarily so.

I would still look carefully before deciding, but 120VAC with a well-matched inverter now has my attention.

Definitely something to look closely at if the need for a new frig arises. The Danfoss has multiple speeds available as well as computer controlled speeds for efficiency. It is likely they are using an AC frequency converter for that purpose, so they probably already are AC based motors in the refrigeration unit.


Durability would probably be the biggest issue.
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Old 07-18-2018, 04:33 PM   #8
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It is likely they are using an AC frequency converter for that purpose, so they probably already are AC based motors in the refrigeration unit.
Yes. IIRC all fully-sealed compressors use synchronous multi-phase AC motors in order to avoid having to have brushes sealed inside. They therefore have fairly fancy controllers.
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Old 07-18-2018, 07:15 PM   #9
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I actually just completed our "AC charging station" a couple of days ago.




We have another of the same inverter in the video cabinet.





I really like the little Samlex 120 watt PSW inverters as they a very small, high quality, and seem to be very reliable. They run at about .3 amps idle, but we shut ours off with separate power switches anyway. The downside of them is the single two prong plug on them and no built in on/off switch.


Both of ours have had the two prong outlet removed and a power strip direct wired into the unit. A small piece of fiberglass sheet epoxied in place fills in the missing plug are and holds the cord grommet. It works nice this way because you can bond neutral and ground together when you put in the cord, and that is how standalone inverters should be wired.


Attached Images
File Type: jpg Samlex cord attached.jpg (113.7 KB, 152 views)
File Type: jpg AC charging station.jpg (191.3 KB, 150 views)
File Type: jpg video cabinet inverter.jpg (114.8 KB, 150 views)
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Old 07-18-2018, 08:07 PM   #10
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Actually, the recently-reported successes of folks who have been trying out modern high-efficiency 120VAC fridges is the thing that got my attention in this area. I have long assumed that native 12VDC compressors would be vastly more efficient (both in fridges and A/Cs). But, apparently, it ain't necessarily so.

I would still look carefully before deciding, but 120VAC with a well-matched inverter now has my attention.
I think the jury is still out, but I harbor some doubts about this because I think there are some subtle influences that can be difficult to quantify.

Finding a well matched inverter isn't a slam dunk. Capacity is certainly no longer an issue but operating efficiency under load and comparative efficiency in stand-by has to be part of determining whether or not you come out ahead or behind going to 120VAC.

For 120VAC reefer operation to be more efficient than 12VDC operation, it's efficiency would have to be high enough to offset the operating inverter conversion loss. This specification is typically provided for the most efficient operating point of the inverter, but actually, depending on the load on the inverter, it's efficiency may vary from optimum (seems typically around 90%) to something less than that under different inverter load demands.

The variable duty cycle of the reefer makes efficiency even more difficult to quantify with an inverter involved. With a 12V system, when the reefer is off, there is no battery drain. But with an inverter involved, when the reefer shuts off, (assuming no other inverter loads), the inverter goes into standby but still consumes battery power and the manufacturers seem reluctant to publish stand-by drain. The Powerstar units provided by Roadtrek apparently consume 5 amps in stand-by which is similar to the compressor demand when the reefer is operating. The consequence is that while the reefer may only be in a 50% duty cycle, with respect to battery drain, the effective duty cycle is 100%. I notice that the compressor reefers provided by Roadtrek were initially 12V/120V dual voltage units but currently they operate at 12V only.

Perhaps an advantage of 12V native operation is that while on a trip, even if your inverter crashes, you would still have refrigeration.
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