External Battery for Surface Pro?

Discussion in 'Microsoft' started by dgeffs, Feb 12, 2013.

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  1. Steve S

    Steve S Pen Pro - Senior Member Super Moderator

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    Regarding off-nominal voltages, an old reliability study indicated that voltages that were 10% below nominal (in this case 1.2 V below 12 V DC) had no apparent adverse effects on the normal rate of electronic device failures (that is, the failure rate of complex electronic devices was unchanged when operated at 10% below nominal input voltage).

    Conversely, voltages that were 10% above nominal appeared to increase the rate of device failures (I can't remember the specific percentage, but it was significant; 20% or something like that).

    For me, there are two significant take-aways from this study:

    1) 10% is a fairly large margin (1.2 V in this discussion); I wouldn't worry about ~0.1 V (or 0.3 V (no load) for that matter).

    2) If you have to err on one side or the other of a nominal voltage, then lower is better than higher. BUT I'd only start to worry when the voltage starts to get pretty close to +10%...! +1% or +2% isn't anything to be concerned about...
     
    Last edited: Apr 11, 2013
  2. chandlercv

    chandlercv Pen Pal - Newbie

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    Thank you for the re-assurances for regarding the voltage.

    I've been able to eliminate the tip or it's construction as the source of the whining. I found the correct sized jack to add to the 12V supply end of the donor cable. When I use that to reassemble everything, when I plug the Surface Pro into my car, it charges and runs without the whining sound.

    Adding a ferric choke to the end of the cable did not stop the whining when plugged into the xpal. My next step will be to try an LC filter as suggested earlier in the thread. Given that I don't have a scopemeter, are there particularly good values of L and C to start with?

    Thanks again for all the support!
     
  3. bjornb

    bjornb Pen Pal - Newbie

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    You can try something self made like this to start with to see if it has any effect:
    Curing Alternator Whine by KB1MVX
    The capacitor mentioned in the link is 4700uF 35V. It doesnt need to have that high voltage rating since your voltage is about 12V, 25V or 16V rating should be fine. Regarding capacitance value, try something with a few hundred uF or more (maybe you have som old power supplies or other discarded electronic equipment you can pick it from?).

    A different example here:
    Power Supply Filter - AMZ
     
  4. chandlercv

    chandlercv Pen Pal - Newbie

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    Yikes, between the links you just provided and the crash course I've been giving myself in low pass filter design, I'm beginning to think that I won't be arriving at a solution that's as compact as I was hoping. Would just adding a capacitor to ground likely do anything, or should I start looking for a new battery pack?
     
  5. bjornb

    bjornb Pen Pal - Newbie

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    A capacitor alone between positive and ground will also act as a filter. It is worth trying out, try a smaller one to begin with, 100uF or a few hundred uF. (If you use large caps there will be large in-rush currents when you turn on the power, it may damage or reduce the life of the regulator/battery pack circuits).
     
  6. joyce101

    joyce101 Pen Pal - Newbie

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    Can you tell me how you connected this (Energi to go)? I just purchased the Energi-to-go and have my "sacrificed" surface pro connector . I cut the wire and have 4 wires...red, blue, yellow and the remaining silver wires. Do I need to cut the laptop output cable from the energi set? Can I just twist the wires and tape or wire nut together, or do I need to solder them ( sorry to sound dumb...I am a rookie and only have soldered jewlery in the past) or do I need some type of device to connect them? OR is there somewhere I can bring it or send it to do it for me so I know it will work ?
     
  7. chandlercv

    chandlercv Pen Pal - Newbie

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    This information is based on my personal experience working with an xp18000. If you're using a different model, your mileage may vary.

    I already had a "Willy" WI12 step down transformer that I got for an Asus T91. This converts the 19V output down to 12V, which is what the surface eats. The tip on the WI12 seems to match a size N power plug at Radio Shack. I soldered the red to the tip, the black to the ring, and promptly ran into the "whining" problem I've been troubleshooting here ever since.

    I have not tried the 9-12V outlet, which really produces a 10.5 V, 2.0 A output. If you don't already have the Willy adapter, you might want to try that, but I have no idea whether that will work or not. If you do go that route, you'll either need to get an appropriately sized plug, or sacrifice the 9-12V cable that came with the xp18000.

    Solder is required for my approach. I am far from the world's best solderer, and I haven't caught my Surface Pro on fire yet for having done this. There is still that whine going on, though. . .

    I do not know of anybody doing this professionally yet. If you find somebody, please post that here, as until I get rid of that whine, I'm going to be very trepidatious about using my SP with the xpal.
     
  8. joyce101

    joyce101 Pen Pal - Newbie

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    thanks! I am off to Radio Shack to see what pieces and parts I can round up......hopefully I can get this to work!
     
  9. bjornb

    bjornb Pen Pal - Newbie

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    Why not try the 9-12V outlet? Since my Tekkeon MP3750 battery has selectable output I configured it to 10V, seems to work fine too:
    2013-04-12 23.28.23.jpg
    The current while running is a bit higher than 2A though, in standby when charging only it drops to about 2A.
     
    Last edited: Apr 12, 2013
  10. joyce101

    joyce101 Pen Pal - Newbie

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    thanks! I am off to Radio Shack to see what pieces and parts I can round up......hopefully I can get this to work!
     
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