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1 Posts
Discussion Starter · #1 ·
Im a 20 year old college student,
recently got inspired to build an EV.
I did a lot of research in the past several weeks,
however some things i still dont understand.

Here are the suggested questions that i need to answer for recommendations from other users:

Your skill level with auto mechanics and fabrication: Never done any major engine work
The range you are hoping to get (how many miles/charge): >50mile
What level of performance you are hoping to get: performance doesent matter i want to maximize the range
How much money you are willing to put into your project: not including the vehicle itself 1000-2000$ maybe a little bit more...not by much.
What parts you've already considered, if any. - non specific.

To begin, i still dont know what donor car to choose,
but i am considering a VW Beetle at this point.

Next up, i want to note that i actually want to build a hybrid-type car,
essentially i want to have an electric motor run of off several batteries (like 4), and then have something like a lawnmower engine power a DC generator that would feed the electric engine.
I cant decide what engine to purchase however, im not looking for 0-60 in 5 seconds, but i do want the car to be Highway speed capable aka 65-70 mph.
However 60% of my driving is in city limits with speed limit of 45-50 mph.

Next, the motor controller, there are so many of them, i dont even know what the difference is between them?
An average controller that i found is like 1000$?
i dont see why they are so expensive it seems like they do a very basic function? Again, not trying to drive a sportscar...

Next, the charger, also found them to be quite expencive, but i may not be looking for the right thing? ive seen portable car battery chargers for low prices not (in the 1000's), but i may be missing out on some of the details?

Potentiometer (throttle control) is pretty understandable, nothing new here.
What else am i missing? Ignition Parts?

Am i taking on too big of a project for me to handle?
How hard is it to integrate the motor into an existing transmission?
plates & adapters and such?
Suggestions about a good donor car? (like i said so far thinking about the VW beetle)

Thank you,
your input will be much appreciated.

· Registered
4,005 Posts
65-70 mph.
Performance (yes, speed is performance), range, budget, pick two.

The range and speed you want require lithium, which requires adding a 0 to your budget.

You could do the first two with forklift or other used/homebrew components and lead acid batteries, if you keep it to 30mph or so.

· Registered
139 Posts
Next up, i want to note that i actually want to build a hybrid-type car,
essentially i want to have an electric motor run of off several batteries (like 4), and then have something like a lawnmower engine power a DC generator that would feed the electric engine.
I cant decide what engine to purchase
If you are looking for an engine to drive your generator, I would pick a Kohler engine. Kohler engines can be converted to run on LPG which is a very handy option and it helps reduce your fuel costs. Kohler engines are reliable and start easily and adhere to CARB emission standards.

Kind Regards

· Registered
42 Posts
I'm assuming that your priorities are price, range, and speed in that order.

Motor - Look at the thread post on choosing a forklift motor. Call ahead to wrecking yards and ask if they have old forklifts. It will be the least expensive option, but do your research before you buy a motor.

Batteries - Lead has the smallest upfront cost, but lithium will cost you less over the longer run. Lead will last 3 years, and you'll need to limit your discharge to 50% of it's usable capacity, and the Peukert effect will limit how fast you will want to accelerate. They also have trouble with cold weather. Lithium will last maybe 8 - 10 years, you can use 80% of their capacity, and have a much smaller Peukert constant (1.08 vs 1.2), so driving them harder won't be such an issue. One last thing, the capacity of lead batteries are rated for a 20 hour discharge, while lithium are rated for a 1 hour discharge. Basically, you get less capacity than what you pay for in a lead acid battery in this application.

However, given your budget, lead will get you on the road. See if you can negotiate battery prices through your college. For an off-grid solar electric system I was able to get a 25% discount through a university account at Batteries Plus. Maybe you can arrange a deal with a college employee.

Controller - If you can follow an electrical schematic, you may want to look at building yourself an Open Revolt controller. Otherwise, you need to wait to buy a controller that will match or exceed the power of your motor.

Hybrid - Everything I've read here says "don't do it". There are no motor controllers on the market that will handle the gasoline side of the house. Basically, you'll need a 10kW+ generator if you only drive at city speeds. It will be heavy, loud, and inefficient. Invest the money in a larger battery pack if you have "range anxiety". Or a charger.

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42 Posts
Let's consider the 1998+ Volkswagen Beetle.

Curb Weight: 2800 lbs
Drag Coefficient: 0.38
Frontal Area: 22.7 Sq FT
CdA: 8.63
Rolling Resistance: 0.015

Assuming an average speed of 35 MPH, and assuming you keep the weight neutral by removing as much weight as you add... That would be:

6.86 kW to maintain speed
196 Wh/Mile

OK, so let's compare battery packs based on a 50 mile desired range:

Lithium pack
(90Ah Thundersky 1-hour rating):
45 cells * 3.2 V * 90 Ah = 144 V nominal, 12.96 kWh
Peukert's Constant = 1.08
DoD = 80%
Range = 52 Miles
Pack Weight = 317 lbs (6.1 pounds per mile)
Pack Volume = 7.75 cubic feet (6.7 miles per cubic foot)
Pack cost = $4,250 (slow boat from China, $81.75 / mile)
Lifespan = 4000 cycles (200,000+ miles), 10 years

Lead pack (160Ah Mastervolt AGM 20-hour rating):
12 cells * 12.8 V * 160 Ah = 153.6 V nominal, 24.58 kWh
Peukert's Constant = 1.20
DoD = 60%
Range = 43.9 Miles
Pack Weight = 1,150 lbs (26.2 pounds per mile)
Pack Volume = 8.53 cubic feet (5.1 miles per cubic foot)
Pack cost = $4,851 (with 25% discount from West Marine, $110.50 / mile)
Lifespan = 1000 cycles (45,000 miles), 3 years

As you can see, because lead packs aren't meant to be discharged so fast, and because you must do a shallower depth-of-discharge on them to maintain their cycle life, the economic scales tip heavily in favor of lithium. 3 times the lifespan, 1/4rd the weight, 3/4 the volume, and 3/4 the price for the usable range.

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42 Posts
By the way, the Volkswagen Beetle may be cheap, but is is one of the most un-aerodynamic cars available. Take a look at this infographic I put together that compares vehicles at 35MPH. The Volkswagen Beetle is near the bottom of the list. Choose one higher up and you won't need as much battery to go the same distance. The Geo Metro or Honda CRX will both be inexpensive cars and will give you >25% more range for free.

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