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We regularly get email questions about making or driving an EV. I try to respond to all of them (yeah, even the free energy guys!) as best that I can. Rather than just leave these nuggets sitting in the sent box of my email client I realized they should be shared with everyone. Better yet, you folks can correct or expand upon my answers by sending comments via email and I'll revise the list.

  1. I need more conversion info!
  2. Terminal Types
  3. Using pack battery for 12v accessories
  4. How to determine DOD of batteries
  5. Making a Fast/Fun EV
  6. Range and charge time
  7. What HP do I need?
  8. How about Solar power?
  9. New battery technology
  10. Can I use an automatic transmission?
  11. Gas powered electric cars
  12. Who can I get to convert my car?
  13. Can my car become an EV?

I am trying to figure out where to get started on finding information about converting my own vehicle to electric. I am thinking about getting a small car and converting it. I have been looking for books and information. Can you tell me what is the best book for information and places to order parts if needed etc. I am looking for the best prices etc..

First off it’s great that you are considering a conversion. Learning from others is probably one of the first things I’d suggest. Check out all of the EVs at the EVAlbum. My first conversion diary is at Jerry’s EV, which may help. Eve, our current conversion, has run into a few delays but there’s still quite a bit of information in the progress to-date. We also get to share pics and progress reports from a handful of other EV conversion project owners, so check the homepage regularly.

Bob Brant’s book is pretty good for an in-depth, technical look at EVs, especially if you like to have a physical book to reference. A lot of the pictures and info is dated, but all in all it is still applicable and the formulas and electronics haven’t changed. That and other ev related books along with EV suppliers are on the EV Resources page.

Of course once you get started be sure to drop us an email with pictures, specs, and status reports!


What type of terminal did you use on your lead acid batteries?  (Universal terminal, threaded stud etc.) My local Trojan Dealer is recommending a threaded post type terminal with a 5/16 stud.  I would have to buy 2/0 lugs with a 5/16” hole.

I used the threaded stud for the first EV and it worked well.  The guys on the EVList swear by the “normal” terminal (like a car’s regular battery) but those always seem iffy to me.  Some have complained that newer batteries (Trojan?) with the stud couldn’t take the recommended 75lbs tightening torque.  I never measured the torque on mine, just firmly tightened it, then drove a bit and checked each to be sure none are warm, then after driving it for a few days in a row re-check/tighten.  Never had one break and the connectors (look at my first EV weblog for pics) were very solid after using a heavy duty crimper.


The question I have has to do with supplying 12 volts to the existing car’s circuitry. Why can one not use voltage drop across the first battery in the battery pack to get the required 12 volts?

If the high voltage ground is kept isolated from the rest of the circuits, then we should have no problem using the voltage drop across the first battery OR any one battery for that matter in the battery pack?

This isn’t normally suggested, for a couple of good reasons:

1. it disproportionally drains one battery more than the others in the pack, leading to a mis-balanced pack. Depending on your car’s 12v load you could end up with one battery in the overall pack getting vastly out of sync with the others.

2. safety: typically the high voltage pack isn’t tied to ANY of the car’s electrical (not even ground) so as to keep it isolated. Let’s say you tap off the first battery in a 144vdc system. Now your car’s “ground” is part of the pack, so if you (or a wrench or a frayed wire) touched ground and somewhere along the pack you’ll be exposed to up to 122vdc and all of the current the pack can provide: quite a bit!

A DC-DC converter isn’t all that expensive and it will turn the high voltage into an isolated 12vdc which can feed the rest of the car’s electrical system and charge a small accessory battery. Other than the DC-DC hookup you’ll want to keep the two power systems completely separate and this includes NOT hooking the battery pack’s ground to the chassis of the car.

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Something that still has me baffled is how do you know the DOD of the battery?. For example I am running a 120V system down the road, how do I know when its 50% DOD, 80% DOD etc..

Mostly it’s a matter of statistics and wild estimates!

I think the way most DOD (depth of discharge) meters work is that they monitor the charging of the battery and when it gets over a certain “full” voltage for a period of time the meter resets itself to flag the batteries as “full.” Then, when current is drawn, the meter keeps track of the amp hours used and compares that to what the user programmed in as the pack capacity. Some other formulas, like peukarts, can help improve upon this estimate based on the rate the power is being drawn. But it’s still hard to take into account every factor, like the age of the batteries and things like really cold weather.

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I’m very interested in making a FUN car, something to be taken to drag race, track events, perhaps drift events (can you tell im a 22 year old?) I think with the torque possibilities of the electric motor it would be quite fun to race a little 80’s bmw or even a Z3.

For drag racing you’ll definitely want to head over to NEDRA if you haven’t already. Also, if you are looking for a role model, John Wayland has been racing his little electric Datsuns for years.


How long does it take to fully charge an electric car and what is the average range of one per charge?

That’s sort of like asking how long it takes to fill a gas tank and how far can I go on that gas. It depends! Is it a hummer or a honda insight? 10 gallon or 30 tank? How fast does fuel come out of the hose?

Same with an EV. You build the EV to fit your needs. If you need fast charging then you spend extra money and buy a 240vac charger. If you need lots of range you get a streamlined car with appropriately sized and/or technology batteries.

My first EV was used to commute to work and back, around 12-15 miles. I used a slow charger that probably took 3 or 4 hours to charge the batts back up. But, since I plugged it in when I got home at night, it charged while I did other things and didn’t worry about it. On the other hand I never had to make extra time to swing by the gas station on the way to work.


I have heard that an electric motor is 8-10 times the actual hp rating. So therefore if I am replacing a 180 hp combustion engine I then look for a 22.5-18 hp motor?

Those are the same numbers I’ve heard. The size of the motor needed depends a lot on the size of the vehicle you are going to convert (i.e. weight & aerodynamics/efficiency) and what kind of performance you need out of it. A combustion engine rated at 180hp is probably what it was able to do only when mounted on dynamo without any other loads (ac, steering pump, etc..). Your day to day hp needs are significantly less

Plug the car into the EV calculator and see what kind of results you get for HP at the various speeds and gears.

The motor I use is an ADC FB-4001A, which has an average rating of 28 hp.

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Is it practical to think you can charge a car like this totally off-grid? How long does it take to charge the car on solar and does it take a huge solar panel to charge it?

There are folks who do this, although much depends on how much power (i.e. range) you need in a given day and what your alternative power options are capable of producing.

A fellow up our way who was a professor at Dartmouth and commuted each day with an EV put a huge array of solar panels on his barn roof. Rather than feed the EV, he sold the power to the power company to “offset” what the EV needed each night. In this way he didn’t have to store it in yet another set of batteries to feed the EV each night.

We’ve had a couple articles featuring Peter’s Solar Electric Van (and Part II). Peter has done some fantastic work and documented it quite well on his website.

There’s quite a bit of money and custom electronics in his setup and yet it isn’t able to rely solely on wind or solar for power.

My suggestion is to take the “home” approach where you mount the solar and/or wind panels in a fixed location optimized for harvesting sun and wind all day. Sell the energy back to the electric company to offset what you’ll need to charge the EV. Don’t add the additional weight, cost, and complexity to your EV in an attempt to snag a few watts with solar.

If you are looking for a Solar Car Charger, stop by Café Electric to see Otmar’s modified pocket inverter.

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Lead acid batteries are such old technology! Why don’t you use {some amazing new storage technology announced yesterday}?!

Yes, lead acid has been around forever. In fact back before gas powered cars really took off people were tooling around in lead-acid powered 1912 Baker Electrics. There’s been a number of alternatives over the years, but nothing that has had quite the power to cost ratio of lead acid. To their defense lead acid batteries are well documented and understood, are highly recyclable, and do the job.

Which brings us to your question: every week it seems there’s a new battery technology announced, yet trying to find them for sale is often impossible as their first markets are often military or space agencies. Those you can buy are typically very pricey. As of 2007 it will still cost over $10,000 to buy enough lithium batteries to power a moderate sized EV, and that’s not including the specialized battery chargers you’ll need.

Super-caps, flywheels, and fuel cells have been just around the corner for decades; a new-breakthrough finally bringing them to the masses comes and goes every year.


My wife doesn’t drive a stick, why don’t any of the EVs have an automatic transmission? Do I have to use an AC motor in order to keep the automatic transmission?

You can make an automatic EV with DC just as easily as you can AC. The trick with an automatic is you need to have the motor slowly spinning ALL of the time to keep the hydraulics pumped up. Maybe you could find an old donor car that uses a CVT transmission, I don’t think they need the hydraulic pressure and they are automatic.

There are some AC motor setups that have been designed to replace the transmission as well, which might be what you are referencing. No reason you couldn’t run a DC motor with the same gear box, that is if someone will sell it to you and you can adapt it to the spline.

Depending on your driving you don’t necessarily have to shift that much, if at all. I only did city driving on my EV (under 40mph) and pretty much left it in 2nd gear all of the time.

Lee Hart posted the following on the EVList a while back:

If it’s a budget conversion, I’d say keep the automatic. Let the electric motor idle, just as it would with the ICE. Use a motor with a rear shaft, so you can put a pulley on it and drive the old alternator and other accessories (air conditioner, etc.).

Idling wastes a little power; it will generally draw 1-2 amps from the propulsion pack when stopped. This is low enough that you could leave it idling for a day or two before it discharged the pack.

Automatics that don’t have a locking torque converter are a little less efficient, so they will cost you 10% or so in range.

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I have always seen battery technology as the weak link in EVs.

I thought I might shed some pounds from the vehicle if I were to replace the battery bank with a Kohler or Onan marine generator – I have one of each and they both run about four hours on a gallon of gas. [@ 50mph = 200+mpg !]

The problem is that these generator engines are not very efficient and are certainly not very clean. In the end you may end up doing a whole bunch of work to make your own “hybrid” and end up with something that pollutes more than the original engine AND gets worse gas mileage.

Also, unfortunately, you can’t always do math like: 4hours * 50mph = 200mpg. Why not drive 100mph and get 400mpg?! But seriously, 4 hours supplying how many watts? At what voltage? My first EV sucked down 75amps at 120 volts while driving on flat terrain at 35mph. That’s around 9,000 watts. Generators usually put out AC, which will need to be converted to DC (you lose power at each conversion step).

I did a quick search and found a 10kw generator for around $2,200. It weighs 300lbs which is more weight that needs to be hauled around, more weight, lower car efficiency (even with a gas auto). Also, I suspect if you ran a typical generator set at full load it would suck gas like there were no tomorrow and die an early death. You can get heavier duty gensets, but they will cost more, weigh more and still not be as efficient as a purpose made setup like a Toyota Prius.

The bottom line is that trying to simply turn gas into electricity to power an electric motor will typically use MORE gas than just keeping your existing gas engine. The reason hybrid vehicles do a good job is that they are precisely engineered to use electric power (via batteries or generator) to power the vehicle at take off, slow speeds and during heavy loads. This way the gas engine can run at its most efficient, with the electric filling in the rest of the time. They can then use a smaller and more finely optimized gas engine that way and, thereby, get better gas mileage. More info here

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I’m a klutz/too busy/not mechanically inclined: are there companies that can convert my car to an EV?

There are a few companies that spring up from time to time to do conversions. I suspect it’s not a very high profit industry and insurance might be tricky, which is why they don’t last very long. Check out the resources page for links. Also, some of the EV Parts dealers might have a better ideas who is available in your area.

Some that I’ve heard of recently:EVAmerica has started adding car conversion shops, Left Coast Electric, and Canandian EV has done some.

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I want to know if my car [insert any ol’ car here] is a good candidate for conversion to electric power.

Much of it depends on what you want out of the vehicle (performance, range, seating, coolness factor) and how much money you want to invest. Check out this article for some ideas and guidelines: Choosing a Vehicle.

Remember, putting an electric motor and batteries into your car doesn’t necessarily make it a better or more efficient vehicle. If you convert a heavy, gas guzzling car to electric it will most likely be a heavy, electricity guzzling EV.

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