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can I add extra lithium batteries to my new merc E300 hybrid?

Discussion in 'Electrics, Vacuum, Ignition and ECU' started by step, Dec 5, 2012.

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  1. step

    step New Member

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    Hi, just ordered car and was wondering if I could pay someone to install say 10 extra batteries in boot and connect them in parallel to existing lithium battery to extend range of electric only driving the 8 miles to work each day.

    In theory I could then install chargers at home and work and not use any diesel during the week :)

    Also I would need to increase current switch diesel engine on speed from current 22mph to say 35mph.

    If I could do this I would also have option of temporarily removing extra batteries if going on long journey.

    Am I too optimistic as to what is possible and would it void warranty?
     
  2. television

    television Always remembered RIP

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    You would have to consider the extra weight to start with. Are these batteries wired in series or parallel, I have never looked at any circuits
     
  3. Still Learning

    Still Learning Senior Member

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    Not impossible, but a big project that would cost many years worth of diesel...

    The additional lithium batteries would need to be wired first in series (to achieve the same voltage as the main battery), then in parallel with it.

    Each bank of the existing series-wired parallel batteries will be connected to a balance circuit. This ensures each set receives an equal charge because as each lithium cell charges, its resistance does not increase linearly like a lead-acid cell.

    If the balance circuit is absent, a reduction in resistance on one bank of cells will cause it to draw more charge current, and may promote a further reduction in resistance. This will result in 'positive thermal runaway' - and WILL be catastrophic (see below about the dangers of lithium-ion cells).

    The additional parallel battery would of course need to be of an equal amp-hour (AH) capacity, have sufficiently heavy duty connectors, and connected to an identical extension of the balancing circuitry. Extensive testing would be required to ensure the resultant expanded bank behaves correctly under all conditions.

    Unless you can source an engineering company (and by that, I mean a company with real engineers, not washing machine fitters), the project has multiple pitfalls which could result in disaster.

    Lithium-ion cells are very dangerous if the correct precautions are not taken, and can catch fire if over charged, over discharged, or over stressed (too much current drawn). Once lithium is on fire, be somewhere else...

    If you aren't put off yet, the 'cross-over' point at which the IC engine contributes to tractive effort is almost certainly hard-coded by Mercedes (see above about over stressing the cells).

    Personally, I'd set the money aside for the diesel! :)
     
  4. Troon

    Troon Active Senior Members

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    Sell it, buy a Leaf for the week and an older E220CDI for long journeys.
     
  5. OP
    step

    step New Member

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    Thanks for your feedback "still learning"

    I was aware that some Prius owners in USA do sometime similar and hoped that it might be practical for my new Merc.

    I guess I will wait until Mercedes themselves release a plug in hybrid or electric car. I am betting on 2015.
     
  6. brandwooddixon

    brandwooddixon Senior Member

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    As well as the substantial cost (not just the purchase and fit of the batteries but also the insurance), could I just point out that such a change would most certainly void any warranty that you'd have on your new car.
     
  7. bigtwin

    bigtwin Banned

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    Decent modern diesel = 50-64 mpg.

    Next.
     
  8. Frontstep

    Frontstep Senior Member

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    As the car will tip toe on a computerised high wire I would imagine trying to attach extra batterys would be tempting an expensive failure.
    Mercedes have not got a good reputation for warranties as it is and altering the battery pack would almost certainly void the warranty.
     
  9. Alex Crow

    Alex Crow Senior Member

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    What is the supposed advantage of running only on battery power, other than the emission benefit?

    Has it been proven to be cheaper per mile than on Diesel?
    I would be interested to know...
     
  10. grober

    grober Senior Member

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    Think part of the "battery argument" comes from energy re-generation where energy that would be lost in braking goes to recharge the battery-- how efficient this is in practice I don't know. Electric motors also develop maximum torque at zero rpm so they have big advantages when starting off------------ all this translates into greater efficiency in stop start city driving------ but would not help much at a steady motorway cruise. My feeling is hybrids come into their own in city driving - where their zero[ minimum ] emissions profile comes into its own. Mercedes and other manufacturers may have developed hybrid technology simply to allow their vehicles to access certain city areas where zero emissions are necessary [due to legislation] more than anything else? ;)
     

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