Why can't I find a DC-DC laptop power adapter?

November 5, 2012 10:29 AM

Why can't I find a DC-DC laptop power adapter?

I often use my laptop in the car. My car outputs DC power. My laptop consumes DC power. Why on earth do I need to go Car DC - Power Inverter AC - Laptop DC? Seems like such a waste yet when I search online for DC-DC power adapters I only find one or two, with sketchy reputations or very high prices.

I am no electrical engineer so am I missing something here?

posted by Cosine to Computers & Internet (20 answers total)

My guess would be that the combination of (a) the infrequency with which people need to use laptops in cars and (b) the availability of inexpensive power inverters means the demand simply isn't there for the sort of adapter you're talking about.
posted by alphanerd at 10:34 AM on November 5, 2012

Google "DC-DC converter", there are hundreds... They are usually intended for embedded/industrial applications. Can you specify the voltage and amperage your laptop requires in DC? Scan or type the contents of the label on your laptop's power adapter.
posted by thewalrus at 10:34 AM on November 5, 2012

They are frighteningly common and you can easily find one by Googling "car laptop power adapter." Here is a universal model at Amazon. You can also find them at Best Buy for twice the price.
posted by kindall at 10:34 AM on November 5, 2012

They are frighteningly common and you can easily find one by Googling "car laptop power adapter." Here is a universal model at Amazon. You can also find them at Best Buy for twice the price.

I have 3 ThinkPads, according to comments on that adapter it doesn't play well with Thinkpads.
posted by Cosine at 10:36 AM on November 5, 2012

Google "DC-DC converter", there are hundreds

I have Google'd, lots, I have yet to find anything that:

- Works with ThinkPads
- Isn't shady Chinese off-brand/no-brand
- Doesn't cost $114
- Has decent user reviews.

That is why I posted this here.
posted by Cosine at 10:38 AM on November 5, 2012

The vast majority of Thinkpads require 20V. What's wrong with This?
posted by thewalrus at 10:43 AM on November 5, 2012

Lenovo used to actually make one, but I can't find it in their catalog anymore (and I recall it didn't meet your sub-$114 criterion either). But you may have trouble finding one that's non-Lenovo and still fits your machine. They are amazingly ingenious when it comes to making sure their stuff only works with their stuff.
posted by ubiquity at 10:44 AM on November 5, 2012

Thanks thewalrus, those models don't support the weird pin connector of the T500 series, however I think this:

http://www.bixnet.com/uncardcpoadk.html

Might work, you need to order a $6 adapter to connect to the T510 but at least they say "hey, you need this adapter to use with the T500 series".

Tip

Now, to find such a thing in Canada...
posted by Cosine at 10:52 AM on November 5, 2012

Maybe I'm missing something, but I'm not clear on what exactly using an inverter is a "waste" of.

I have one that's basically a power strip that plugs into the car's lighter. It costs like $30, and I can plug in absolutely anything by just using the regular power adapter the product came with. Seems much less hassle than looking around for weird adapters, but again, maybe I'm missing something?
posted by drjimmy11 at 11:15 AM on November 5, 2012

DC-DC converters are expensive. You should expect to pay between $75 and $175 for a quality one. I have both custom-ordered and hand-built DC-DC converters and the buck/boost modules themselves are not cheap parts.
posted by fake at 11:18 AM on November 5, 2012

fake: You must be right, as evidenced by the lack of popularity and quality of such an item, it still seems odd to me that it's cheaper/easier/simpler to go DC-AC-DC but that's probably why I am not an engineer. (incidentally I found the same issues trying to get DC power supplies for servers in a planned DC data centre that had to be scrapped for similar issues)
posted by Cosine at 11:45 AM on November 5, 2012

(This is not one suitable for a laptop).

Good quality 150W DC-DC converters are not that expensive, such as this one. Where it gets expensive is above 200W or ones with special high voltage input ability such as 72VDC to 144VDC input, 24VDC/48VDC output.
posted by thewalrus at 11:46 AM on November 5, 2012

(incidentally I found the same issues trying to get DC power supplies for servers in a planned DC data centre that had to be scrapped for similar issues)

Sounds like you should have hired a professional. Seriously, you had trouble finding 48VDC power supplies for servers? You were either trying to use the wrong kind of server, or not looking in the correct places, or both. All kinds of 'serious' networking gear runs on 48VDC.
posted by thewalrus at 11:48 AM on November 5, 2012

tw: The issues were more with the co-lo than us. (though HP was having trouble guaranteeing us what we needed at the time DC-wise as well)
posted by Cosine at 12:07 PM on November 5, 2012

I am no electrical engineer so am I missing something here?

Short answer: Because a DC electromagnet doesn't have a magnetic flux that gets flipped fifty or sixty times a second like an AC electromagnet connected to the mains. Its flux just sits there staying the same. Without a wire moving through said flux or the flux changing around it no current can flow through said wire.

So instead of your transformer being $5 worth of copper wire arranged in two coils around an iron flux core you end up with equipment that is far more complicated and expensive.
posted by Talez at 12:24 PM on November 5, 2012

>> I am no electrical engineer so am I missing something here?

> So instead of your transformer being $5 worth of copper wire arranged in two coils around an iron flux core you end up with equipment that is far more complicated and expensive.

Every laptop AC power supply/charger I've seen in the last 5+ years has been a switcher. Getting a replacement/spare one from the manufacturer used to be about $100, so not much less than an airplane or car charger. I do see Sony Vaio AC chargers for under $20 at Amazon, but how much do Sony, Dell, etc. charge for that direct?

Lenovo makes a "90W Ultraslim AC/DC Combo Adapter" for $100 with "A 20V power tip (41R4484) to power your ThinkPad X/T/R/SL/W500 series notebook and a carrying pouch. Optional 16V (41R4343) and 19V (41R4319) power tips are available for older older Thinkpad notebooks and Lenovo, IdeaPad notebooks." and "A wide range of optional Lenovo notebook and peripheral device charging tips are also available at www.lenovopowertips.com"
posted by morganw at 1:17 PM on November 5, 2012

morganw: Wow, thanks so much, that will do it!
posted by Cosine at 2:29 PM on November 5, 2012

Another option for auto adapters is Lind Electronics.

http://www.lindelectronics.com

Not cheap ~$100+ but they work well, are rugged and have models for most laptops.
posted by dknott123 at 3:18 PM on November 5, 2012

"Every laptop AC power supply/charger I've seen in the last 5+ years has been a switcher."

Which, in itself, is basically a DC→AC→DC converter in a single box…

It seems that the real problem is not so much that DC→DC converters for laptop-in-car use aren't available, but that they're not readily available for your particular make/model of laptop.

Which actually surprises me; ThinkPads are - or, at least, were - pretty much the big player (along with Panasonic Toughbooks) in the field tech / mobile worker market.
posted by Pinback at 3:33 PM on November 5, 2012

Which actually surprises me; ThinkPads are - or, at least, were - pretty much the big player (along with Panasonic Toughbooks) in the field tech / mobile worker market.

They are very rugged. I can't count the number of times I've dropped mine, and it still works well.
posted by ubiquity at 12:00 PM on November 6, 2012