Dc powering laptops etc

Options
System
System Posts: 2,511 admin
in Solar Beginners Corner #1
I wish to power my laptop, netbook, ereader via DC and not AC. Anyone have advice on how to do this? I have been told by several eletricians that I will lose power going thru an inverter so they have advised this but do not know exactly how. (some sort of device like those used for cigaratte lighter adapters for cars?) I will be using a 135-watt Kyocera panel, hooking up to 6-volt batteries.
· Share on Twitter

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #2
    Options
    Re: Dc powering laptops etc

    If you have a 12 volt battery bank--most computers and other equipment have 12 volt cigarette lighter plug adapters.

    The major warning is to disconnect/turn off the 12 volts to the 12 volt adapters while equalizing the battery bank. It is not unheard of to have an adapter fail when the battery voltage hits the 14.5 to 15.5 volt range that is used to recharge/equalize deep cycle batteries.

    A couple suggestions. Measure the power used with DC and Inverter supplied power. If you have enough battery/solar panels to make up the extra losses of a small inverter (maybe 6 watts or so)--using 120 AC can be a nice clean solution.

    Personally, I like using efficient/smaller AC inverters to power computers/battery chargers/etc... The inverter is usually designed to operate to at least 15 volts input. And, if you need to send power longer distances from the battery bank--120 VAC is much easier, and sometimes much cheaper (some 12 volt auto adapters are not cheap for laptop computers).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • jagec
    jagec Solar Expert Posts: 157 ✭✭
    #3
    Options
    Re: Dc powering laptops etc

    This guy has converted his Prius to a backup power system. That's interesting, but one of the more interesting facets of the conversion is that he has a special plug that outputs 220 VDC. He claims that most laptop power adapters can take any voltage from 100-240 V, AC OR DC, and will properly rectify and switch in order to arrive at 12 VDC or whatever the laptop needs.

    However, unless you already have a HIGH-voltage power source, the cigarette lighter adapter is a better way to go.

    Or roll your own DC-DC converter from individual components if you're a tinkerer.
    · Share on Twitter
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #4
    Options
    Re: Dc powering laptops etc
    jagec wrote: »
    He claims that most laptop power adapters can take any voltage from 100-240 V, AC OR DC, and will properly rectify and switch in order to arrive at 12 VDC or whatever the laptop needs.
    I am skeptical. DC-DC voltage conversion takes different hardware to implement than AC-DC conversion, and I doubt that the typical laptop power adaptor has it. I don't design them so I don't know for sure, but it would make them more expensive to build and I don't think many folks plug in to 240VDC.

    EDIT: I am looking at my Dell laptop power supply, and the label says:
    INPUT: 100-240V-50-60Hz 1.5A

    Nothing about taking DC as input.
    · Share on Twitter
  • 2manytoyz
    2manytoyz Solar Expert Posts: 373 ✭✭✭
    #5
    Options
    Re: Dc powering laptops etc

    None of the transformers I've seen will work on AC and DC. Mine all use switching power supplies, which requires an AC power source.

    You can buy a DC-DC converter. It will do what you need. Just need to buy one with either an adjustable output (as I have), or get one rated for the voltage of your laptop.

    The issue is DC-DC converters aren't 100% efficient either. So you will have losses whether you're using an inverter, or converter.

    FWIW, I've been using a 400W MSW Vector inverter for this purpose for years. Better than 90% efficient (measured), and only $20-$30.
    · Share on Twitter
  • david3
    david3 Solar Expert Posts: 37 ✭
    #6
    Options
    Re: Dc powering laptops etc

    I've got an HP laptop and an HP Auto/Air adapter that includes a cigarette lighter adapter and works with 12VDC.

    http://www.shopping.hp.com/store/product/product_detail/KS474AA%2523ABA

    Maybe some other laptop manufacturers have something similar, or maybe you can find a generic version that's compatible.

    I've got a pair of golf cart batteries and an automatic charger and a small sine wave inverter that I use as a UPS, and have my laptop run on the golf cart batteries directly with the Auto/Air adapter.

    I don't think it would be a big deal to run the laptop off the inverter, but I had to get a replacement power supply anyway, so it just worked out.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #7
    Options
    Re: Dc powering laptops etc

    The typical switching power supply (as opposed to transformer based wall wart and such) takes the AC input voltage and rectifies it to high voltage DC (typically around 350 VDC or so). It then takes this high voltage DC and switches it down to the needed output voltage(s).

    And Power Factor Corrected switching power supplies can take around 100 VAC to 264 VAC or VDC (and probably higher VDC) and again switch it to a high DC voltage intermediate stage).

    The problem is that most vendors are not going to tell you which supplies are capable of running on high voltage DC and non of the units have been tested/certified to run on high voltage DC (fuses/breakers need to be DC rated--and usually physically larger than the equivalent AC version).

    In the end, yes it could be done, but the safety and identifying/testing required will be your money/time.

    There is an initiative to convert data centers to DC distribution by server companies and data centers (to save money/energy use in data centers and probably to provide battery backup more easily too)--But I foresee there are lots of safety and fault isolation issues with this program and it will be hard pressed to replace the typical AC system in use today.

    Alliance Boosts 380-Volt DC Power Standard

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #8
    Options
    Re: Dc powering laptops etc
    2manytoyz wrote: »
    None of the transformers I've seen will work on AC and DC. Mine all use switching power supplies, which requires an AC power source....

    Most switching power supplies/wall warts, would work with DC just fine. They simply rectify the AC to DC, and run that through a DC-DC converter. I just don't have 100VDC to test one with. Even IOTA chargers have been known to run on DC too.

    The fancy PFC corrected ones may not work on DC though.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

    · Share on Twitter
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #9
    Options
    Re: Dc powering laptops etc
    mike90045 wrote: »
    Most switching power supplies/wall warts, would work with DC just fine. They simply rectify the AC to DC, and run that through a DC-DC converter. I just don't have 100VDC to test one with. Even IOTA chargers have been known to run on DC too.

    The fancy PFC corrected ones may not work on DC though.

    I was under the impression that the first thing in from the input on a wall wart was a transformer. Any DC input would stop there.
    · Share on Twitter
  • drew4justice
    drew4justice Solar Expert Posts: 36 ✭
    #10
    Options
    Re: Dc powering laptops etc

    Maybe it's too simple? Couldn't a simple approriately spec'ed Zener diode clamp the voltage from rising to the equalization voltage at the output?
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #11
    Options
    Re: Dc powering laptops etc

    There can be a transformer on the input that drops the voltage into a set of diodes (bridge rectifier).

    Old fashion and not very efficient... Today, usually used for very small power supplies (less than 10-20 watts or so).

    A switching power supply puts the rectifiers first to get ~350-380 volts DC in a set of high voltage capacitors. Then it uses (typically high frequency of 10's of kHz) and transformers and/or inductors to down convert into low voltage (high frequency allows the use of smaller/more efficient transformers).

    There is active power factor correction that is usually DC compatible... And there are passive forms of PFC which may not be.

    Just looking at the "black box" from the outside--difficult to tell.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #12
    Options
    Re: Dc powering laptops etc
    ggunn wrote: »
    I was under the impression that the first thing in from the input on a wall wart was a transformer. Any DC input would stop there.


    Whoops - two types of wall warts.

    a) heavy with iron transformer

    b) empty feeling, like you got ripped off, Those are the switchers - no large transformer.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

    · Share on Twitter
  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #13
    Options
    Re: Dc powering laptops etc

    These tests are on my to-do list now that I've completed my own Prius-generator conversion. No reason to drag around a big UPS in the trunk if what I want to power will run from a small switching power supply.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
    · Share on Twitter
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #14
    Options
    Re: Dc powering laptops etc
    mike90045 wrote: »
    Whoops - two types of wall warts.

    a) heavy with iron transformer

    b) empty feeling, like you got ripped off, Those are the switchers - no large transformer.

    Ah, yes. I have some of each, now that you mention it.
    · Share on Twitter
  • ArmyVet
    ArmyVet Banned Posts: 20 ✭
    #15
    Options
    Re: Dc powering laptops etc

    I would seriously bring out some sarcasm. But I wont.
    All I can say is Wow. No smarts here at all. <<<<<<watch this as we would like you to keep your comments to subject matters and not of people. had you specified somebody you'd have gotten a temporary ban for it. niel

    Now on to your problem of Laptop conversion.
    DC to DC Conversion is the only efficient way for powering
    them. You can use a Power inverter but the losses are astronomical.
    You lose around 50- 60 % in the conversion itself.

    Now for you laptop. Usually they come with a power pack.
    9 out of 10 laptops have a Dc output on those laptop power packs.
    Most the time its 19 -20 volts.
    There is a device that can do this Conversion for you .
    And the Voltage is adjustable.
    They sale them on Ebay.
    Heres the link to what you need.
    Theres no need for other Feedback because. This is the only thing
    out of 100's I've tested that does work ! With a 90% + efficiency.
    http://www.ebay.com/itm/150W-DC-DC-10-32V-Boost-12-35V-Adjustable-Power-Supply-/270769146593?pt=LH_DefaultDomain_0&hash=item3f0b194ae1

    do note that we frown on ebay links as they disappear soon. i dispute the losses to be as bad as you claim with using an inverter even though i acknowledge them to be at least in the area of 15% to 25%. also note a dc to dc converter is an inverter circuit with a rectified and filtered output. niel
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #16
    Options
    Re: Dc powering laptops etc

    Regarding that DC to DC converter... I would be a bit careful about the specs... If it is a true boost converter (no reason to say it is not), they can only boost voltage, not drop voltage (need a buck or buck/boost converter to drop voltage).

    If it is a boost converter, it cannot usually regulate below the input battery voltage (i.e., you should not be able to get 19 volts out with 24 volts input).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • jagec
    jagec Solar Expert Posts: 157 ✭✭
    #17
    Options
    Re: Dc powering laptops etc
    ArmyVet wrote: »
    I would seriously bring out some sarcasm. But I wont.
    All I can say is Wow. No smarts here at all.

    That's not a very helpful comment. Whose post did you have issues with? What I read was some discussion over whether a standard, designed-for-AC power converter (like the ones which come with laptops) would be compatible with high-voltage DC without modification. The consensus seems to be that if it's not transformer-based, it would work, but may be unsafe depending on fusing, and determining whether a given power supply would work requires an overview of its circuitry.

    Do you disagree with this? Why?
    · Share on Twitter

Categories