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Old 04-03-2011, 10:15 PM   #11 (permalink)
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That's if you used starter batteries for the basis of your calculation, which is not quite a valid conversion due to the fact that normally they would not take to deep cycling well. If you used a deep cycle battery with a higher amp-hour rating designed for traction applications such as the electric floor scrubber, high-lo's, electric carts/milk floats you can get closer to 72 watt/kg out of the battery rating and a lower peukert coefficient (k closer to 1.0 is better) but it still would take a lot of batteries especially if you wanted a 600km (375mi) range equivalent to say the standard 16 gallon fuel tank in a 1997 Ford Taurus for an example, if you replaced the engine with an electric machine and installed the required quantity of batteries the weight would be increased by 4559 kg, putting the overall weight at 6079.2 kg vs 1508kg for a standard Taurus

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Old 04-04-2011, 12:44 AM   #12 (permalink)
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Ok golf cart deep cycle battery 220 A/hr X 6 (V) =1320W/hr

1320/67lb= 19.7 W/hr a little better than the average 18 I came up with but clearly in the same ballpark as starting batteries.

And again that is at 20 hour discharge rate! And I imagine peukert bites them the same way as any lead acid but could be wrong.

Imagine if battery technology could match the energy density of gasoline and we
had a 36Kw/hr battery that weighed 7 lb! (or what ever a gallon of gas is)

Then we could say ok I've got 10 of these in my EV that's the same as a 10 gallon gas tank in a ICE vehicle. And the EV would have a 1200 mile range!

Ok I'm just dreaming.
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Old 04-04-2011, 12:17 PM   #13 (permalink)
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Quote:
Originally Posted by 3dplane View Post
Imagine if battery technology could match the energy density of gasoline and we
had a 36Kw/hr battery that weighed 7 lb! (or what ever a gallon of gas is)...
Start with 35 lbs rather than 7 for the gallon of gas, because you have to carry both reactants around with you.

Then tell us exactly why you're doing the comparison against lead-acid batteries. I mean, to begin with, the stuff's about as heavy as, well, lead. If you're doing weight comparisons, it's not really a good idea to start with something that's a metaphor for heaviness, now is it?

Nor is lead particularly energetic, chemically. Look at a lump of lead: what's it do? Just sits there, like thy nuncle, no? (If you remember your Tolkien.) So why not use something that's a) light, and b) energetic, like for instance lithium?
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Old 04-04-2011, 12:41 PM   #14 (permalink)
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I think the two Optima Redtop batteries that are used on Electrathon vehicles weigh about 45 pounds? And I'm fairly sure they provide ~1kWh, so at 33.4kWh / gallon, that results in about 1,500 pounds of batteries to equal 1 gallon of gasoline?

The 60 lead acid batteries used in Dave Cloud's Dolphin weigh 33 pounds each, so the total is 1,980 pounds. He has driven it ~200 miles, and those batteries are used... I think that is about 30kWh, so a little less than 1 gallon equivalent at 1 ton.

The bottom line is I think your initial weight estimate is about 2X too high?

Typical lithium cells would weigh less than half of that per "gallon".
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Old 04-04-2011, 05:17 PM   #15 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
Typical lithium cells would weigh less than half of that per "gallon".
And remember, you only get to use that gallon one time, then it's gone and you have to get another one :-)
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Old 04-04-2011, 05:41 PM   #16 (permalink)
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Quote:
Originally Posted by jamesqf View Post
Start with 35 lbs rather than 7 for the gallon of gas, because you have to carry both reactants around with you.

Then tell us exactly why you're doing the comparison against lead-acid batteries. I mean, to begin with, the stuff's about as heavy as, well, lead. If you're doing weight comparisons, it's not really a good idea to start with something that's a metaphor for heaviness, now is it?

Nor is lead particularly energetic, chemically. Look at a lump of lead: what's it do? Just sits there, like thy nuncle, no? (If you remember your Tolkien.) So why not use something that's a) light, and b) energetic, like for instance lithium?
I'm talking about driving down here on earth where we don't have to carry our own oxygen.

I'm doing the comparison with the metaphor for heaviness because....that's what my batteries are made out of.

Lithium looks about 4-5 times better than lead but other than a few RC lipo packs,I don't have any significant amount of them.

I'm not bashing lead acid nor the efficiency of ICE powertrain.
I'm simply trying to come up with an answer to what is a fair/realistic way to relate to the amount of battery pack power available in an EV to certain amount of gallon used in an ICE powered car for the same distance driven under similar driving conditions,similar car etc.

Let me put it this way. There is an employee at my work who comes up to me once in a while and asks me when are they coming out with the electric car? (he does that about once a month)

I reply it's already out. He would then ask how far does it go?
I reply 200 miles. Then he asks why only 200 and not 400 miles?
This is where I wish I had a simple answer for a simple man and say: Because it would require X amount of lead acid or X amount of NiMh or Lithium to match the energy contained in the amount of gas the ICE used up to drive 400 miles!

I clearly understand that due to the efficiency of the EV, to drive X miles we do not need the crazy amount of batteries that my stupid energy comparison shows but that's besides my point.

Or this question. If my electric golfcart is powered by a 72 volt 100 Ah pack...( all used/murdered mismatched auto batteries 2p 6s) What size is my "gas tank"? (400+ pounds of lead)

I can drive it for 10 miles before the weakest battery will go below 12 volts (and stay there with no load) while the rest of them are around 12.2V (no load)

So I got a 7.2 Kw/hr pack. Can I say that I have a .2 gallon "gas tank"?
(7.2/36.6=0.19)

Sorry for the long babble.
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Old 04-04-2011, 05:51 PM   #17 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post

The 60 lead acid batteries used in Dave Cloud's Dolphin weigh 33 pounds each, so the total is 1,980 pounds. He has driven it ~200 miles, and those batteries are used... I think that is about 30kWh, so a little less than 1 gallon equivalent at 1 ton.

The bottom line is I think your initial weight estimate is about 2X too high?
I think you are right it's probably fair to use the 2000lb number. I was compensating for peukert by going 2x the weight.
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Old 04-04-2011, 06:22 PM   #18 (permalink)
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The 36.6kWh / gallon is a little higher than the numbers I have heard; which are 33.4kWh and 33.7kWh / gallon (X-Prize and EPA respectively).
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Old 04-05-2011, 10:23 PM   #19 (permalink)
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Electricity doesn't weigh anything at all!


It's the container for it that's kinda heavy...


I've calculated my car as roughly 130MPGe.... but my "gas tank" is about a cup!

Gasoline has a CRAZY amount of energy in it. THAT'S WHY WE LOVE IT! It really is hard to get away from gasoline when it is SOOO CHEAP and SOOO POWERFUL.

Great, now I am jones'n for a big gulp of gasoline. May as well get the gas bong out right now! Woot!



yeah, you're right. That's crazy. We're just shooting ourselves in the head with this stuff.

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Old 04-05-2011, 10:33 PM   #20 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
The 36.6kWh / gallon is a little higher than the numbers I have heard; which are 33.4kWh and 33.7kWh / gallon (X-Prize and EPA respectively).
I think the 36.6kWh/gallon figure is for straight gasoline and the other figures are for the energy content of gasoline after all the additives are factored in.

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