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Old 05-18-2011, 12:25 PM   #4751 (permalink)
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Some thoughts on mileage

A quick aside/question about fuel economy. I want to calculate mpge but I want to be as fair as I can. I have been averaging about 340 wh/m out of the wall including everything (230 wh/m measuring the dc actually being put into the batteries. This is a mixture of city and highway (70mph) not trying particularly hard to get good economy but driving like a gasoline car (I've seen 180 wh/m into traction pack under optimal conditions).

Anyways using 340 wh/m I calculate 108 mpge but I'm wondering if this number is misleading. The same car got about 25mpg under similar driving conditions when gas powered. Over a 400% increase! But.....

Looking at the big picture in my area we are very roughly 75% coal, 15% natural gas, 5% nuclear, less than 5% renewable. So for a conservative estimate I'm going to assume we are mostly fossil fuel powered with approximately 40% conversion efficiency and 10% transmission loss. So now I calculate my electric car to get:
.4*.9*108 = 39 mpge for my electric car.

I've heard that in the refining/transportation of gasoline you lose about 20%, so really my gasoline version was getting 25*.8 = 20 mpg.

So my electric car is about twice as efficient well-wheel as the gasoline version when using fossil fuels. How you charge obviously has a huge impact on efficiency...my uncle charges his car right next to the hydro dam at lake wenatchee so he's looking much better than me since he's 100% renewable.

Anyways, I just feel like us electric people can be quick to throw out huge mpg numbers that make some of the other hyper-milers look bad. Am I missing something?

On the flip side, the plants that make my electricity are probably on the order of 10 times cleaner in terms of emissions per watt than my gas engine was, and I'm probably emitting slightly less carbon than I used to (since coal emits about twice the carbon as gasoline for equivalent energy...natural gas is much better), but hey, we could use some global warming here in Michigan anyways . So for me its more about cleaner energy, less $ to big oil companies, and better efficiency than huge mpg #s. Plus if I throw up a big wind turbine in my backyard I'll be way ahead!

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Old 05-18-2011, 12:50 PM   #4752 (permalink)
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My thoughts on MPG Equivalent -

Don't bother calculating in efficiency of a coal plant OR how much energy it takes to find and dig oil wells.

If you really want to do a true "wells-to-wheels", it gets VERY complicated (and political) very fast.

Measure power from the wall and gas from the pump. It's the only fair way to do it.

An electric car being about 4 times as efficient? That sounds about right.

And remember, with an electric car, you can get your electricity from solar panels, wind power, nuclear plants, coal plants, hydro, etc., etc. - it's your choice - you get to choose where your power comes from.

You can't do THAT with gasoline.
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Old 05-18-2011, 02:26 PM   #4753 (permalink)
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Agreed Ben

I get most of mine from solar and wind!
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Old 05-18-2011, 03:33 PM   #4754 (permalink)
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Good point, it makes sense to compare apples to apples, and that's the efficiency of the vehicle itself. That's awesome that you're able to generate your power with solar and wind dave. I wish I had that capability. I'm not trying to discredit the awesomeness of electric vehicles (seeing as how I drive one), I just want to be fair in how I represent mine, because I am still using fossil fuels, and I'm willing to bet that the majority of plugins are as well. But you make a good point Ben about the well-to-wheel efficiency being a very complicated issue and it seems mpge is the most cut and dry method of comparing two vehicles.
Still, just because a vehicle CAN operate on renewables doesn't mean it does. Crap, you can run most newer gas engines on straight alcohol or a number of different mixtures of renewable substances if you want to, you still get to choose where your power comes from, but most people choose not to .
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Old 05-18-2011, 05:54 PM   #4755 (permalink)
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My car doesn't have a neutral, its direct drive with no clutch or gearbox! Better not have a controller failure. However, I use a precharge resistor of 500 ohms and the main contactor won't close until the voltage comes up to about 80%. I hope that a controller fault that meant applying full voltage to the motor would prevent that.

There is a guy here with a Toyota Celica who claims 10t w-hrs per km - about 170 w-hrs per mile - which is about as efficient as I have seen.
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Old 05-18-2011, 07:18 PM   #4756 (permalink)
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Quote:
Originally Posted by MPaulHolmes View Post
Luke's controller blew up! Fortunately he is OK. It sounded like Ben's and Joe's situation. At least one mosfet was failed shorted, and when the contactor closed, the car tires spun out and lurched forward.
Sorry to hear about the failure. So far mine is working fine after a week and 400 miles. For precharging I have mounted a 240v 50w light bulb (I am running a 48 cell Lifepo4 pack) under the dash. I can see the glow while precharging, if it doesn't go out then I have an indication of a problem and hopefully remember not to close the controller contactor. Easy and cheap way to precharge.

A couple of questions, I set pc-time to 70 but the wire from the controller to close the contactor doesn't seem to energize when I checked it using a 12 volt test light. How is this supposed to work? The config command shows it being set and the controller won't work until after 7 seconds. I seem to recall there being an issue with precharge circuit on the early controllers, I built mine from Paul's kit in Jan 2010.

Another thing I noticed is the controller gets warm. up to 60-70 Celcius. I just have the supplied steel base plate and was hoping I could get away with that in Scotland. But ebay to the rescue and have just got a nice aluminium heatsink the right size to replace it, so I will do the spacer mods on the bolts at the same time so I don't have the same problem that Ben and Joe had.

I will get some pictures and videos up soon of the car, but got to have a ride in a Tesla today around Arthur's Seat in Edinburgh. Man that thing is quick! In return I have promised him a ride in mine. Seems like a fair trade.

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Old 05-18-2011, 09:03 PM   #4757 (permalink)
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What's supposed to happen is, the middle wire of J3 should go from around 0v up to 12v after 7 seconds. Hmm... I can't remember what stage the code was at in December 2009/January 2010. Hey, what version does it say when you just hit <enter>?

I can't wait to hear how it does with a heatsink! You could mount the baseplate to the heatsink (there's an extra 4 holes in the baseplate just for that reason), but it's probably not as good as having the heatsink bolted directly to the aluminum heat spreader.

With those lithium batteries, 3.3-3.4v is nominal, right? 158-163v sounds a tiny bit scary, but if it's working then I say go right ahead! hehe.

The guy that ran his controller at 192v nominal blew it up just after a charge. He was driving it pretty aggressively when the pack voltage was probably around 205 or 210v.
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Old 05-18-2011, 09:30 PM   #4758 (permalink)
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Is this the 500A controller you are discussing?
Mine has been working fine with a charging voltage of 162V and I also modified the software somewhat to increase the current to a bit over 600A by scaling the sensor o/p. It handles those numbers without any problems. The serial data still thinks its 512A max though, so you have to do a bit of mental arithmetic if you want the real current from RTD.
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Old 05-19-2011, 05:05 AM   #4759 (permalink)
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Mine's the 2c with version 11b of the software. So the contactor control wire should be working with this version? I will have to investigate when I open the controller to fit the heatsink and new bolt insulators, might be down to me.

Originally I was going to have a 45 cell pack, when ordering the cells I said I wanted a 45 cell, 144 volt pack. A price was agreed from the Chinese suppliers and when I received them some months later and opened the crate, I had 48 cells. Well I wasn't going to leave 3 cells out, so in they all went. Actually I should clarify, it really is 144 cells, 40 ah, connected 3P48S. These are in 4 boxes, spare wheel well, under rear seats, along central tunnel and in the front. Result is the interior still has all the seats and the car looks mostly normal.

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Old 05-19-2011, 07:55 AM   #4760 (permalink)
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Wow Greg, sounds like you have a SAWEET setup! You've probably got a sweet range. 48 cells would be what...178 volts fresh off the charger? Probably very little sag too with that many ahs. I feel a little more comfortable with my 168 volts fully charge now . I've been using the light bulb method too, coupled with a voltmeter just to be sure, but mines a 25w 110 bulb, probably similar resistance, I can't believe it hasn't burned up yet.
Also, I'm using two computer heatsinks from a G5 mac (they're huge because apple doesn't like their fans to run). I think you'll be pleasantly surprised at the difference the sinks will make.

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