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Comments 6
  1. Barry    Dec 18, 2006 11:14 AM    #

    When you get a website up and running for the University of EVConvert remember the submit button.
    If you want some inspiration watch “Accepted” http://imdb.com/title/tt0384793/

  2. — Phil Feinstein    Dec 19, 2006 15:47 PM    #

    The Armor Electric contract is supposed to be valued at around $20 Million. I’d feel a lot more confident in what they’re doing if it was a company featuring technologists rather than robber barons. They’re at www.armorelectric.com and they don’t offer anything in the way of what their R&D team is doing or even who they are, but the 3 people on the board have enough red flags in their history to bother me. Their stock is on the OTCBB as “ARME” and it’s trading now for 9 cents a share. I’m very interested in how the deal for NEVs works out.

  3. — Jesse    Dec 21, 2006 12:28 PM    #

    I have been an avid reader of your site but this is my first post. I have re-read your electronics for dogs and battery calculation posts but I can’t quite understand what Ah (amp hours?) has to do with range and performance. Specifically, I see in that battery website you posted: http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=3140
    looks like a good battery in terms of voltage and composition but it seems like it has a low Ah. Most of the cars I read about have comments about the voltage of their packs so it would seem like you could buy three or four of these and be good to go.

  4. — James May    Dec 26, 2006 20:31 PM    #

    Hi Jesse
    The Ah rating (Amp hours) refers to the capacity of the battery. All else being equal, a battery with twice as many Ah will push the same car twice as far.

    Things are not that equal because Ah rating also depends on drain rate and battery internal resistance. This means that if you have a 200 Ah battery and you drain it steadily over 20 hours at a 10 Amp rate it will be empty. (Amps x hours = 200). (20 hours at same current is a common way of measuring Ah)

    If you draw the current faster, more energy is wasted in heating up the battery due to it’s non zero internal resistance and you might get 100 amps for just a little over hour, not two hours like you would expect from a 200Ah battery.

    If you are going to use large currents, you need to choose batteries with a low internal resistance and these will keep more of their capacity at high drain rates. There is a figure sometimes quoted called Peukert’s Exponent which describes how the Ah characteristics change with drain rate. Low Peukert’s (1.0 – 1.25) good, higher Peukert’s (1.25 upwards) not so good.

    You can add lots of batteries together in parallel and add the Ah that way. In general, pairing batteries in parallel can lead to problems and it’s simpler to just buy large Ah batteries.

  5. jerry Halstead    Dec 27, 2006 11:47 AM    #

    (good answer James)

    Hi Jesse,

    There’s also rated Ah and useable Ah. Each battery chemistry type has different abilities in how low it can be repeatedly discharged. A general rule of thumb is not to discharge lead acid based batteries less than 80%. I don’t think lithiums (and NiMH?) have as much of problem with deep discharging, as long as you don’t overheat them. Similarly they can be charged quickly as long as you monitor temperature and don’t exceed voltage/current specs.

    The battery pack in the link is actually composed of ten of these along with an overcharge protection circuit.

    You’ll notice it only has a 40A drain rate. For an EV you’ll need much higher amperage and that means putting a bunch of these in parallel. You also need higher voltage. For the sake even numbers let’s say we need a 148vdc supply capable of 400amps. Ten of these in parallel will provide the 400amps and four of these “packs of 10” will provide 148vdc … for the low, low price of $15,838!

    But, wait, you still need to add a charger and control circuits for managing the batteries: don’t want to burn them up the first time you take the car out for spin or recharge it.

    The ones listed have a simple control circuit to prevent overcharge but that’s not good enough. Better to buy the individual batteries and the protection circuit modules ($1.95 each). Multiply that times the 400 lithium batteries we need and we’re starting to talk real money: $780. Another five hundred to a thousand bucks for a charger and our lithium system is costing us over $17,000.

    And someone needs to wire all of these together…

    Still, the Lithiums have low internal resistance and low weight. 400 of those lithium cells clock in at around 160lbs, which seems pretty fantastic.

    Instead of paralleling lots of batteries for higher current I’d shoot for a higher system voltage, which reduces the amperage requirements. And, if you have $17k for batteries, you might as well get a nice AC Motor/Controller combo with built-in charger. ”:^)

  6. — Jesse    Dec 28, 2006 18:51 PM    #

    That was pretty helpful but I don’t have anywhere near 17k for some batteries. After reading this, I am really starting to understand the battery conundrum. The only problem is I hate waiting and it sounds like nice cheap batteries are a ways off. Have you guys heard anything about those supercapacitors eestore was coming out with ‘soon?’