Exelite Portable Battery Jump Pack Today 24 HOURS ONLY $99.00 Save $55.00

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  sonicentropy on 31/01/2014 - 16:11

  +4

  More CAPS please!!

  • 

    Kaboda on 31/01/2014 - 16:31

    LOL

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  alizzan on 31/01/2014 - 16:14

  +4

  Charges electronic devices such as mobile telephones, tablets, cameras, iPods etc in short time

  Excellent. This will save me having to call RACV to jump-start my phone when I leave the screen on and it runs out of battery.

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  mskeggs on 31/01/2014 - 16:14

  I think the capacity on this is too small to be useful.
  If it was a lead acid battery I would neg, but I have never used a lithium battery for this before. Do they offer a higher max discharge rate than SLA?

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  sonicentropy on 31/01/2014 - 16:21

  200A from a package this I am calling BS
  Similar LiPo units on eBay claim the 12V output is 2A enough to charge your battery but not enough to jumpstart

  • 

    Russ on 31/01/2014 - 17:40

    I agree with you thet the 200A claim is BS. This battery might supply that much for a few microseconds if you put a dead short across it, and then hopefully the "overload fuse" would cut off the power before the fire/explosion did. There seems to be an arms race in jump-start cables and car batteries too, quoting ridiculous figures that simply are not needed. Cars typically draw 30-50A when starting, with diesels usually towards the top end of this range.

    However, "jump starting" does not involve the good car's battery supplying all of current/energy to start the dead car's engine. That is a common misconception. All you are doing in jump starting is recharging the dead battery, and then using the previously-dead battery to supply almost all of the current/energy needed to start the car.

    From Wikipedia: "The external supply of current recharges the vehicle's battery and provides some of the current needed to crank the engine." Link: first paragraph, http://en.wikipedia.org/wiki/Jump_start_%28vehicle%29

    • 

      eug on 31/01/2014 - 18:22

      +1

      However, "jump starting" does not involve the good car's battery supplying all of current/energy to start the dead car's engine. That is a common misconception. All you are doing in jump starting is recharging the dead battery, and then using the previously-dead battery to supply almost all of the current/energy needed to start the car.

      That really depends on what state the dead car battery is in.

      If the person left their lights on and the battery is too weak to crank the engine but still has power to attempt to crank, it just needs a boost. You can hook up the donor car and it'll start the other car's engine immediately, without having to wait for any recharging.

      But if the dead battery is run down so low that it can barely crank the starter motor, then it needs to be recharged by running the donor car for a while first.

      • 

        Russ on 31/01/2014 - 19:45

        I think you're agreeing with me, but I'm not sure.

        In the "boost" example you give, assuming the car cranks at 40A for 5 seconds, that's 200 Amp-seconds consumed. Connecting a typical jumper lead, which is usually capable of supplying at least 10A of charging current, that amount of power would be supplied in 20 seconds or less. About the same amount of time it takes to put the clips on, check they're firmly attached, turn around, walk to the driver's side window, and turn the key.

        Admittedly some of that charge current will turn into heat. At a wild guess, I'd say the battery efficiency for power-in to power-out is about 80%. Allowing for this, the charging time only increases from 20 seconds to 25 seconds.

        While it is possible to make jumper leads that will carry the full starting current, the above example shows that 10A-rated cable would be perfectly adequate, and that's what most jumper lead manufacturers depend on. My $9 Supa-Cheap brand jumper leads have thicker copper than 10A mains cable, I estimate they would easily handle 20A in intermittent use.

      • 

        eug on 31/01/2014 - 21:36

        +2

        Connecting a typical jumper lead, which is usually capable of supplying at least 10A of charging current, that amount of power would be supplied in 20 seconds or less. About the same amount of time it takes to put the clips on, check they're firmly attached, turn around, walk to the driver's side window, and turn the key.

        So following your explanation, you are saying you can connect the dead battery to a donor car for 20 seconds, disconnect the jumper leads (to make sure it's not the donor car that's providing the power to crank the engine), and start the dead car right away. Is that right?

      • 

        Russ on 01/02/2014 - 01:53

        +2

        I'll admit I'm only working on theory here, having only ever jumped a car once or twice in my lifetime, and not done voltage or current measurements at those times. I'm now starting to have some doubts about my previous statement, considering that the cranking draws ~40A and the jumper cable can provide up to 20A by my own estimation.

        I like the test you propose, it would definitively prove (one way or the other) whether it is necessary to keep the jumper cables attached.

        I am basing my argument mainly on resistance: the cable from the car battery to the starter motor is about seven times the CSA of the wire in the jumper leads, and the length of the jumper leads is about twice the length of the battery-to-starter leads. Therefore the resistance of the jumper leads alone will be some 14 times higher than the resistance of the battery-to-starter leads, actually a little higher due to the resistance of the jumper leads' clips and their small contact area to the battery terminal. So I expect the majority of the staring current would be preferentially supplied by the flat battery.

        However the flat battery will be at a lower voltage than the donor battery, so substantial current could still be flowing in the jumper leads. Not enough to start the car directly, as demonstrated by your second example above ("so low that it can barely crank the starter motor").

        So now I'm not sure. If the jumper leads were left in place for five minutes, I'd be 99% confident that you could disconnect them and then start the car. If it was one minute, my gut-feel says 80% sure. But I think you're right, I was probably wrong before, 20 seconds is likely not enough to charge the the dead battery enough to start the car.

        Now you've got me curious, and I want to try it out! But my car battery is old and decrepit, nearly four years old, so I dare not try it!

    • 

      outlander on 31/01/2014 - 23:28

      +1

      Read up on A123. They started making Lifepo4 batteries that have anode made from nano particles. The nanosized particles don't improve capacity, but they do increase peak current supply levels. I have a 26650 cell with a peak of 120a for 20s I believe.

      With a few of those, you don't need to jump, it can turn the motor over by itself.

      • 

        Russ on 01/02/2014 - 01:57

        Interesting. The article I read on nano particles (graphene?) said they do increase capacity, so perhaps they are using less volume of the battery for the chemicals (thereby keeping the capacity the same), and using thicker electrodes to increase the current rating.

        I also found an article about model-aircraft enthusiasts using several of their model-aircraft batteries to start a car. Scary.

    • 

      turbodude on 03/02/2014 - 13:49

      I think you are seriously underestimating how much current a starter motor uses when cranking an engine, especially when the engine is cold/unlubricated. I would bet easily 100-200+Amps.
      And if it is using a LiPo battery then 200Amps is quite achievable. The battery for example (which I have) http://hobbyking.com/hobbyking/store/__10308__Turnigy_5000mA… will supply 200AMps and that is at 22+volts rated for 10 seconds (obviously not suitable for a car but you get the idea).

      • 

        Russ on 04/02/2014 - 01:30

        Looks like you're right, I just found a number of graphs of starting current on Google. Initial current shoots up to maybe 500A for less that a tenth of a second, while the motor starts turning, then drops into the 100-200A range once the motor is turning.

        I had been basing my belief on an old Toyota "troop carrier", which has a charge/discharge meter on the dash. It's a center-zero meter, full scale is -50A to +50A. It doesn't hit the maximum when starting, and it appears to be a conventional electric starter. So perhaps the starter current bypasses the meter, which might be showing the solenoid current?

      • 

        Russ on 04/02/2014 - 02:48

        I've just re-done my previous calculations, using the realistic starting current figures. I just had a look at the jumper leads I have, and I estimate them to be about 30 strands of 0.3mm diameter. The wiring chart I have gives roughly 10 milliohms per meter for that wire, and there's a total of four meters of wire in the jumper leads. So the total wiring resistance is 40 milliohms plus whatever the battery clips add.

        At 40 milliohms, the maximum current you can get out of a 13V8 source is 345A - into a short circuit! If I assume the starter needs at least 8V, then the maximum current the leads could supply is (13.8-8)/0.04 = 145A, less than one-third of the initial current. So you must be charging the "dead" battery substantially during a jump start, as it is providing more than two-thirds of the energy for the initial ~500A surge.

        It also appears that in a typical start, the battery voltage after the initial surge is between 10V and 11V. That means the jumper leads could only provide a maximum of 95A during this time, so the "dead" battery must be providing at least one-third of the 150A average current, probably significantly more once the resistance of the (steel) clips on the jumper leads are taken into account.

        So my initial statement, that jump starting is actually just charging the dead battery, and that the dead battery supplies the majority of the power for the start, now looks likely to be correct.

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  seb on 31/01/2014 - 16:36

  +1

  I thought the main problem with LiPo units in this application is the long time sitting in the car boot before it is needed one day - after many many heat-cool cycles and a long time in a "fully charged" state, my understanding is that this battery tech will not perform anywhere near the same as when new and "fresh".

  • 

    Russ on 31/01/2014 - 17:52

    And we all know that LiPo batteries usually only last 3-5 years, with hardly any capacity left after that time. If I take the RRP of this battery pack, and divide it by the number of years I think it will work for, that's a substantial portion of the annual cost of a typical roadside assistance program.

    Still, this would be useful for off-roaders and people living in the countryside. But I'd also consider the non-rechargeable alkaline "jump start" batteries too, probably a better choice for most people.

    For the heat-cool problem, I wonder if you could solve that by storing it under the car - perhaps if you have wind-down-type spare tyre storage, you could find a way to store it inside that wheel, suitably packed?

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  uncyspam on 31/01/2014 - 16:58

  hmm mght be possible http://www.bigsquidrc.com/rc-myths-fact-or-fiction-lipo-car-…

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  [Deactivated] on 31/01/2014 - 23:55

  +4

  I PLUGGED MYSELF INTO IT AND NOW ONLY WRITE CAPS.