Talk me through an EV! I'm tempted to build, but no real knowledge!
 

Right,

I have a hairbrained idea that building an EV version of a car could be a fun way to get a cheap commuter- that and a decent way to use some of the scrap and guff over at my unit.

I currently have a 64 mile commute each day- taking upto 1.5hrs each way, with no option to charge at work (although I could ask nicely!)

Charging would likely be at home overnight off my domestic supply


As I understand it, I need the following

1. Vehicle to be converted (likely RWD for ease of connecting to gearbox/bigger motor/skidz!)

2. Electric Motor

3. Potentiometer

4. Batteries

5. Controller

6. Charging system

7. Regen braking setup


So I need you folks to advise me on the following points

Electric Motor

What size do I need? 70 mile range at 50+mph

I understand that its amps drawn that's the key to matching output/heat/range?

Batteries

What type?

How many Volts?

How to connect and balance?

Read the sticky above: Electric Vehicle Information - Start Here

Looks like a good place to Start...... :thumbup:

I've already read about the Forkenswift and Ben's car, and had a read through the direct drive EV that NachtRitter posted.

The reason I'm asking re motors and batteries is that none of the above projects have the range that I'd require, so I was looking for some pointers on what sort of spec would be needed-and whether it'd be viable (say, against building an IC car that was hyper efficient)

thanks

First off, to go 130 miles per day, you are going to need a huge battery pack, say 300 amp hours at 144v if you can keep your electrical draw down to 300 watt hours per mile and my figure there gives you a small buffer so you don't over discharge your pack and destroy it right away.
Anyway, you'll need to go with lithium batteries and just the battery pack is going to cost you at least $15,000 and weigh 1,000 pounds, if you want a "cheap" battery pack that will give you that range, you'll have a lead acid pack that weighs no less then 4,600 pounds, at that point you'll for sure need a truck frame, trucks out there tend to get 500-600 watt hours per mile... so double the size of the pack and suddenly your truck isn't big enough.

You have three options that I see, take out a loan to build your EV, move closer to your job, convince your workplace to let you charge at work or find a car that burns fuel that gets good mileage.

Hi, thanks for the response!

My commute is only 64 miles total, so I'd only need 70 miles range. Hopefully that'd make the battery pack smaller and more affordable?

Nissan Leaf 4DR HB SV | eBay

so you can get a production ev for like $17k, but even then 70 miles is iffy.

I have looked at them over here- the prices are not too bad- but most have battery hire deals tied in etc that munch away at savings

Oh yah, forgot about that leaf battery rental fiasco. "lets hide the costs so it looks better!" I don't even spend $100/month on gas, can't imagine spending it on battery rental for so few miles.

Yes, that will make the pack size you need about half, I would still go with lithium because needing over one ton of lead acid batteries is just insane! and lead acid batteries are not even half the cost of lithium batteries any more, so after 3-5 years when you have to replace your lead pack with another lead pack you will have spend more money on lead acid batteries, plus you'll have a poor performing EV because you were hauling around an extra ton of weight!

Sure, used lead acid batteries are an option... if you are going short distances, but if you go with used batteries figure you'll need twice as many for the same range... again that really adds up!

You asked about rear wheel drive and motor sizing, transmissions are nice because they give you a range of gear ratios to use, most people use 2nd gear only around town and 4th gear once they are up to highway speed, front wheel drive cars work great and they tend to be lighter weight cars then rear wheel drive.

As for selecting a motor, NetGain and some other motor companies tell you what size vehicle their different motors are ideal for, then compare the physical size of a motor you found used to see what it is close to and if it will work for you, I would look at motors that are 9" around or larger, 9" will be about as small as you'd want to go, using it for a long commute you are going to want to make sure you have a blower on it to keep it cool.

This is basically what you want:

http://ecomodder.com/forum/showthrea...nge-22955.html

He still spent $11k on batteries.

70 miles at 50 mph is no big deal. Get a big motor (11") and have external cooling so it will stay within temperature limits. More mass absorbs more heat. Use as high voltage as you can. Your contoller selection will likely limit voltage. If I'd go DC motor route I'd get something from Soliton series and use 250-300V pack. Those controller can limit motor voltage. You can use thinner cables as pack currents should stay low. Or then you could get suitable AC setup with controller from HPEVS for example. Voltage will be limited to 144V or something like that but then you can use batteries with bigger Ah rating. This will solve regen braking issue at the same time (can't do it using DC easily).

Oh, cost. Assuming your vehicle consumes 0.3kWh per mile (300Wh / mile) as mentioned before. 70 miles * 0.3 kWh/mile = 21 kWh. CALB batteries (LFP chemistry) cost about 440$ / kWh, so your pack alone will cost 9240$. You don't want to run the pack empty every time you run the car so let's leave some margin. 80 pieces of 100Ah cells make a good pack (25.6kWh). Price bumped to ~11k$. This pack will allow you to do ~70 miles in one go and still have 20% left. Your cells should last well over 100 000 miles this way. Even double that is within reality, though no-one using these cells hasn't driven that much yet. No real life evidence on that yet. But looking good so far.

This is not to shoot your idea down. Just to give some thoughts about it. Sometimes driving and owning an EV is not about money saving or being green. Heheh.

I've driven my EV for about 3 years. I calculated it takes less than 25 000 miles for me to "break even". About three years of driving. Almost there, heheh. Battery cost vs. gasoline cost I mean. But here gas goes for over 8$ per gallon.

I agree with going with as high of voltage as you can, at some point speed controllers start costing more for higher voltage, but 144 to 300v is becoming more and more common, but up to 144v can be bought or made cheaper.

It's important to remember when building your car that you want it to last 100,000 miles, that is, if it's worth building for a 65 mile per day range.

Even if you have a 65 mile range, it's worth asking your work place about being allowed to plug in, if you can offer to take the least appealing parking space, 40 seconds of extra walking per day is good for you and it could save you a ton of money or at the very least give you a full charge on your way home.

EEEk!
That’s a lot of pennies!

These figures seem to suggest that there may be an argument for a diesel car in the interim, until battery tech and cost becomes better

I hear you re work charging- means I could build for a 40 mile range instead

I'm a fellow noob, but I've been researching lots. If your one way commute is 32 mi. and it takes 1.5 hours you must have a lot of stop and go or traffic jams to contend with as well, do you? are you planning on converting one of your existing cars? You didn't tell us what your budget was.
If your budget can take it, I think you should go AC. You get the regen you want and less maintenance. Price for a HPEV AC50 is not that much more than a new DC setup and I don't think you would want to go the cheap forklift motor route with as much driving as you plan on doing. A forklift motor may be fine, I plan on using one eventually, but they will be a little less efficient and maybe a little less reliable long term. Plan to go Lithium for sure, it will be cheaper in the long run. The gray CALB cells are getting good reviews and have a higher discharge rate. Don't know who has them in the U.K. If you are using large cells for range, though, it may not matter as much and you may be able to get away with cheaper ones. This might be a source. Sinopoly Cells $1.10/AH - All Sizes, Worldwide Delivery - DIY Electric Car Forums
There seems to be a lot of debate on balancing cells so you will have to make your decision on top or bottom balancing and if you want a BMS or not. Personally, the bottom balance camp seems to make a lot of sense to me and saves the expense of a BMS system.