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Thread: Charging a laptop from a bike - Inverter or ???

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    Registered User Anyname's Avatar
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    Charging a laptop from a bike - Inverter or ???

    I was thinking of getting a netbook or small laptop for use while traveling. When I looked for DC chargers, most references I found were for using an inverter and the laptop's standard AC charger. I suppose that this would work, but inverters tend to be heavy and are reputed to add substantial electrical load.

    I have seen a couple of direct 12 volt DC chargers (such as the PWR+ sold by Amazon) that are much smaller, lighter and claim to use less power. Any electrical wizards know if these devices are any good?

    I have always heard that DC does not lend itself to readily changing voltage so I am curious what the direct DC chargers are doing to step up or down the voltage.
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    Unfunded content provider tommcgee's Avatar
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    Electronic tech here...

    Be careful using an inverter on your electronic gear, especially a cheap unfiltered one. This is the real-world risk. They output square waves, not sine waves, and not all chargers/computers/phones can deal with that kind of harsh output. THey also do suck up a lot of power just to operate. I popped a Sony laptop about 20 years ago using the inverter method.

    Asus makes a car charger for their netbooks, and other vendors do too. They have appropriate filtering.

    I don't know what you mean by "DC not lending itself to readily changing voltage" because one of the simplest linear voltage regulars is a DC device. Those little lighter-socket with USB charger port devices prolly have nothing more than a 5 volt regulator, a couple of capacitors, and a resistor or two. I haven't opened one, but surely will after I have one fail.

    Google "linear voltage regulator' if you wanna know more. Wikipedia has a good page.
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    Registered User Anyname's Avatar
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    I am currently fond of Apple products and had been looking at a low end Mac Book Air. Unfortunately Apple doesn't make a 12v charger for their laptops.

    It sounds like the cheapo, small DC chargers may actually be more technically sound than an inverter.

    I actually have a Targus inverter which I have previously used on my old IBM laptop. I just dug it out and it's not as heavy as I had remembered, but it's still pretty bulky.
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    Unfunded content provider tommcgee's Avatar
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    Quote Originally Posted by Anyname View Post
    I am currently fond of Apple products and had been looking at a low end Mac Book Air. Unfortunately Apple doesn't make a 12v charger for their laptops.
    The Apple "magsafe" power brick has good filtering. Is that what comes with the Air?
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    Small road corner junkie pffog's Avatar
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    Unless you are going to completely out in the boonies, or plan on using it constantly, you should be able keep it in good shape, by charging it at the motel, or campground every night.

    Most newer laptops will run 4+ hours on a battery charge. For the price of an inverter you could get a spare battery if there will be times away from civilization for a couple of days.

  6. 01-23-2011, 02:24 AM

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    Benchwrenching PGlaves's Avatar
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    Quote Originally Posted by pffog View Post
    Unless you are going to completely out in the boonies, or plan on using it constantly, you should be able keep it in good shape, by charging it at the motel, or campground every night.

    Most newer laptops will run 4+ hours on a battery charge. For the price of an inverter you could get a spare battery if there will be times away from civilization for a couple of days.
    Not where we camp much of the time. No power!

    I have used a small inverter both of the past two summers. My Lenova doesn't seem to mind by the time the power gets through the inverter and then the computer charging cord. Others may pose problems.

    I use a small 80 watt inverter - computer calls for 65 watts.
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    Quote Originally Posted by tommcgee View Post
    Electronic tech here...

    Be careful using an inverter on your electronic gear, especially a cheap unfiltered one.
    So far, I have been lucky using cheap modified sine-wave (really modified square-wave) converters on my laptop computers without any problem. I do such from my RV. But for those who do not want to take any chances, you can safely run ANY notebook computer from a true sinewave converter, but they cost more, of course. An example is here.


    -Don-

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    Quote Originally Posted by Anyname View Post
    I was thinking of getting a netbook or small laptop for use while traveling. When I looked for DC chargers, most references I found were for using an inverter and the laptop's standard AC charger. I suppose that this would work, but inverters tend to be heavy and are reputed to add substantial electrical load.

    I have seen a couple of direct 12 volt DC chargers (such as the PWR+ sold by Amazon) that are much smaller, lighter and claim to use less power. Any electrical wizards know if these devices are any good?

    I have always heard that DC does not lend itself to readily changing voltage so I am curious what the direct DC chargers are doing to step up or down the voltage.
    Look at the DC voltage output of your AC power supply. It might be something like 20 VDC. which means the DC converter will have to have the same output voltage. It might be around 20 VDC or so at 3.5 Amps or whatever. Be sure the 12 Volt converter output matches the output voltage of your stock power supply and the current rating of the new converter should be the same or higher, but never lower, than your stock AC converter. Also, of course, make sure the DC connector and polarity is correct.

    The safest way is to see if you can buy one from the same company that made your computer and claims to be compatible for your model. Check the website for your make of laptop under accessories. It might cost more this way, but at least then you know it will work.

    I have used the small little DC to DC converters on some of my laptops without any problems. Most of these are step up from 12 VDC to 20VDC (or so). They are not as clean as a true sinewave converter, and charging might take a little longer, but they usually work fine. The pure sinewave converter will still require your AC adapter and that gets to be too much stuff for a motorcycle when compared to the small DC to DC converter.

    BTW, many cheap netbook computers run direct from 12 VDC and then a very cheap adapter will work as no conversion is necessary.

    -Don- SSF, CA

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    Unfunded content provider tommcgee's Avatar
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    Quote Originally Posted by DonTom View Post
    Look at the DC voltage output of your AC power supply. It might be something like 20 VDC.
    My white MacBook has a 10.8V battery. My 2010 MacBook Pro has an internal battery, but both machines use the same Apple Magsafe Charger. It's a good bet that the MacBook Air also has a 10.8V battery.

    There's a small switching power supply inside the Apple power brick, and as I say, it prolly deals fine with inverter input. The big problem with the damn thing is the output cord. The strain relief does not do a proper job. YouTube is loaded with videos about how to fix the cable. Most start with a dremel tool. The thing was not designed to be serviced.
    Last edited by tommcgee; 01-23-2011 at 12:11 AM. Reason: voltage adjustments
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    Quote Originally Posted by tommcgee View Post
    My white MacBook has a 10.8V battery. My 2010 MacBook Pro has an internal battery, but both machines use the same Apple Magsafe Charger. It's a good bet that the MacBook Air also has a 10.8V battery.

    There's a small switching power supply inside the Apple power brick, and as I say, it prolly deals fine with inverter input. The big problem with the damn thing is the output cord. The strain relief does not do a proper job. YouTube is loaded with videos about how to fix the cable. Most start with a dremel tool. The thing was not designed to be serviced.
    The voltage required to charge that battery from the DC input on the laptop might be more than twice the battery voltage. Unless you want to remove the battery to charge it, look at the DC OUTPUT of your AC adapter. That will have to match when you charge the laptop.

    Or look to see if the input voltage is mentioned on the laptop itself.

    -Don-

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    Unfunded content provider tommcgee's Avatar
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    Quote Originally Posted by DonTom View Post
    The voltage required to charge that battery from the DC input on the laptop might be more than twice the battery voltage. Unless you want to remove the battery to charge it, look at the DC OUTPUT of your AC adapter. That will have to match when you charge the laptop.

    Or look to see if the input voltage is mentioned on the laptop itself.

    -Don-
    Good point. If we could only get all laptop vendors to mark voltage and current requirements on their products. Chargers usually ARE marked. I don't think I've ever seen a 2X difference in voltage between battery installed in device and charger, 1.5x is more typical. The battery voltage and charger voltage is much closer when charging a standalone battery.

    After you have a charger with the right voltage, and you MUST match charger voltage with device voltage, what's equally important is to match charging current because if the charger can't provide enough of that, the battery will not fully charge.

    My battery comment was about two different Apple products that use the same input connector. I should have been clearer and more specific. Apple does make three versions of its magsafe charger, a 45 watt, a 60 watt, and an 85 watt. The difference is the current capacity -- all three output the same voltage.

    I get bit by this once in awhile because there are at least half a dozen different Apple laptops in the house. They look identical, but if you pick the 45 watt version when you need the 85 watt version, the battery voltage will never make it to 100%.
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    Cam Killer marchyman's Avatar
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    Quote Originally Posted by tommcgee View Post
    My battery comment was about two different Apple products that use the same input connector. I should have been clearer and more specific. Apple does make three versions of its magsafe charger, a 45 watt, a 60 watt, and an 85 watt. The difference is the current capacity -- all three output the same voltage.
    The labeling on the 45 watt charger for my MacBook Air says 14.5 volts at 3.1 amps. If I ever decide I want to charge the laptop on the bike I'll buy an inverter. In the 20 years I've been carrying a laptop I've not yet needed to charge it on the bike. I think that just means I've not done any long, camping only trips.

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    Unfunded content provider tommcgee's Avatar
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    Quote Originally Posted by Anyname View Post
    I was thinking of getting a netbook or small laptop for use while traveling.
    Look at the iPads. They charge from a 5v USB (or lighter to USB adapter) socket and I'm not planning to carry a laptop anymore. Warning: Just don't download Angry Birds or Plants vs. Zombies.
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    +1 on the invertor

    I have been using a small Trip lite for years on a lenovo and now a Dell Mini 9. Absolutely no issues at all. It is run from fused power to my tank bag. In there the inverter will power either the netbook, Zune, phone and whatever else i need.

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