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Need some advice, especially if in person in the Sacramento area!

2197 Views 7 Replies 3 Participants Last post by  kaliforniakarl
So I am wanting to convert a 1978 Fiat Spyder convertible to electric. I bought it for the purpose and it has broken down twice since, so I will take that as a sign :) I originally wanted the super 1 million+ mph 0-60 in a nanosecond type car, but am now willing to settle on something more "reasonable." This is my first project, so any advice would be useful.

Please let me know what kind of information you need about the car if you're not familiar with the type of car. It is small (Li-Fe-Phosphate!) and looks like this :

http://ettenw.org/cars/My-Cars/MyCars/1973Fiat124.jpg

1. I want to be able to drive on the freeway, at least 75 mph (so I can safely pass other cars if necessary). What kind of motor and how many volt's battery pack do I need? I was thinking 144 V is the minimum?

2. I want a 40 mile range. Will settle for less, but it would be great to get to Davis and charge with their electric car charging stations in their parking lots there. How many Amp-Hrs do the batteries need? 100?

3. What about those wheel-mounted motors I've been hearing about? Does anybody know if they are commercially available, how big they are, and how much they cost?

4. The car does not have A/C, but it would be great to have. How difficult/space consuming is it to install a compressor and other necessary components?

Thanks!
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Hi Karl,

I'm not in sacremento, but willing to give your questions a shot. :)

1) 144v would be the absolute minimum to attempt that sort of speed. 192v would be more likely to get you there. The higher the voltage, the faster the motor can turn, the faster the motor can turn under load, the more efficient it is.

2) 40 miles is an obtainable goal in that car, but I would venture a guess that you won't hit 40 miles at a 75 mph speed, but perhaps at 40 mph. 100Ah isn't going to have enough capacity to haul you at your "at least 75 mph" speed for 40 miles.

3) Hub motors are an interesting concept, but like any direct-drive setup, they will require big amps to get you moving. There are easily obtainable hub motors, but they are not sized adequately for your application. Furthermore, the ones that are available that would work well in an EV that will weigh as much as yours when complete may weigh too much for your suspension, adding significant unsprung weight, which translates into poor ride and handling. It is more effective for most folks (unless they're on an unlimited budget) to utilize an existing gearbox to perform gear reduction to make the job easier on a larger sized motor.

4) If the vehicle was offered with AC to begin with, you may be able to find the parts required to add it to your conversion. Otherwise, an aftermarket unit may be required, which typically is a box with a blower, evaporator, and a few vents which is designed to mount under the dash (typically in a pickup truck or other "large under-dash space" vehicle like a large american classic car). Not saying it's impossible if your car didn't have the option of an AC when it was new, but will certainly take some clever fabrication. There are many ways to handle the compressor, check the wiki for some ideas on that subject.

I don't want to rain on your parade, but I think you may need to refine your speed and/or range goals, given the limited payload capacity of your vehicle, unless you can afford tens of thousands expense in LiFePo4 batteries and associated items like BMS and charger.

Good luck, and hope to see your project progress. :)
 

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Discussion Starter · #3 ·
Thanks for the post! Yeah, LiFePO4 is a must, I agree. It will also be expensive. Understood. I am trying to figure out how expensive. Your post was a bit discouraging, but great to know.

So I went through some of the Wiki, and did the following calculations. They said cars require 200-400 Wh/mile, and this is a tiny little convertible (not sure about the aerodynamics), so I assume 200 Wh/mile.

40 miles X .2 kWh/mile = 8 kWh
8,000 Wh/192 V = 41.67 Ah
to ensure 20% charge, 41.67(1.25) = 52.08333
because of fast discharge, (52.08333)(1.05) = 54.6875001 Ah

i found this 50 Ah 3.2 V LiFePO4 batt online: (which brings us to the next question: where is a good place to buy such batteries?)

http://www.beepscom.com/product_p/ba-lb-50-3.2.htm

192/3.2 = 60 units.
at $130/unit, that is $7,800. which is 3 expensive beers/night for a year. so i'll figure out some way.
they didn't have dimensions, but at 4 lbs/unit, the pack will weigh 240 lbs. I'm guessing the current ICE weighs more than that.

In previous calculations, I assumed 144 V and saw I required 75 Ah. Using 100 Ah 3.2V, (45 of them), the cost would be $11,250, 348.75 lb total weight, and since each weighs 2"X6.3"X11.1", would be 103 liters total volume. A bit big for my car, especially with ventilation, but with a little bit of work I might make that work.

Am I being overly rosy in my calculations?

Appreciate any comments whatsoever!
 

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I think you're barking up the right tree... for sure.

If you're using NiMh or LiFePO, draining down to 20% should be OK. If you end up using PbA, I'd say not.

I am building my truck around the notion that I don't want to drain past 50% to get about 40 miles, and then doubling the result of the equation. More or less. I can't really say equation, because I'm SWAGing the whole thing. :)

I doubt my truck will get 200 Wh/mile, probably closer to 500, so I'm padding the numbers across the board and hoping for the best. I want 144v with about 200 Ah.

We'll see how that turns out soon enough. If I can get as much as 60 miles I will be stoked.

If you can justify the extra cost, then certainly go that route- it will end up being better for you in a small car like that, but also- know that there is far more to contend with than just the batteries in a system like that. You also need a charger that can be programmed to the correct charging profile for the batteries, and a BMS that can help keep everything in jive. You also need to be sure the batteries you're looking at are even capable of discharging at the rates necessary for the current draw you're going to put on them.

I don't know a whole lot about the more advanced chemistries, but there's a lot of info here on the forums, in the wiki and in the EVDL archives about those types of batteries. :)
 

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I doubt any vehicle will run as cheap as 200 Watts/mile if you're going that fast. Most of those power numbers are measured at much lower speeds and considering that the drag increases more or less exponential with speed, I'd say there's no way in the hotter regions you can get speed AND range with that pack. It's gonna cost much more than that, I'm afraid.

HOW much I can't say, really. Do you have a MPG for the car in that speed? That'd make it easier to guess...
 

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Discussion Starter · #6 ·
I think it gets around 30 mpg on average, but that is with an old engine from 1978. The car is really low to the ground, and though I'm not sure about the aerodynamic characteristics and weight, I would guess it weighs around 1400 pounds with the engine in it.
 

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I think it gets around 30 mpg on average, but that is with an old engine from 1978. The car is really low to the ground, and though I'm not sure about the aerodynamic characteristics and weight, I would guess it weighs around 1400 pounds with the engine in it.
See http://ev.kfib.org/DonorCar.shtml for a formula to convert MPG to EV-range. Note, this formula is just a rough estimation and also disputed! Use at your own risk. :D
 

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Discussion Starter · #8 ·
From wikipedia, the energy density of "lead acid battery" is .09-0.11 MJ/kg, and the energy density of a "lithium ion battery" is .54-.72. So let's say we conservatively multiply my pack (192 V, 50 Ah) weight (240 lb) by five and apply the formula:

5X240 = 1,200 lbs
30X1200/420 = 85.7 miles. did i do something wrong?
 
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