Converting my BMW Z3 into electric

Hi there,

My colleague and I are very eager to convert my BMW Z3 into an electric car. We are planning to use Altairnano batteries and were curious how to start with the conversion… i.e. what motor to get to allow at least a travel distance of 150 miles and acceleration around 5 or more m/s. Anyone eager to help us with some good advice through this project… our budget is around US$ 25000. Any help is appreciated, since both of us have only limited mechanical understanding,


Yamaha yz450f

Love Z3s particularly the coups.

m/s is a speed. Usually people quote a zero to sixty time or a quarter mile time.

Are you including the car in the $25,000 budget?

I have not seen a price for the batteries or anybody that is actually selling them.

One of your first decisions will be to go for AC or DC motor. Ac is generally more efficient but DC is much cheaper.

Warp9 DC motor $1,700.
zilla 1000/2000 amp controller $2000-3000/$3000-5000 depending on voltage (6month lead time).
Dc/Dc converter (to run radio etc) $250
Charger will depend on what the batteries require, guess $2000.
Figure another $5000 in stuff.
If it were regular batteries figure another $1,500.+. I would guess a 35kw altair pack would be $10,000+.

I agree with you, the z3 is a great car… and we think that due to its weight and dimensions its perfectly suited for a conversion. No, the car is already bought, so 25.000$ is just for the conversion. The engine will definitely be AC, but the question remains… how would I calculate what engine I would need to get the car to accelerate from 0-60 in about 5-6 secs. And secondly, given that engine what stack of batteries would I need in order to keep the car going for at least 150 miles? Any easy way to calculate it?

Thanks for your response!

Percodan rehab forums

There are a few of these out on the net:

Here is a good AC ev conversion:

Good Luck

My guess is, if you can get the Altair Nano batteries at all now, they will meet or exceed your $25,000 budget.

I’d advise you to enjoy the Z3 as it is for 2-3 years and wait for these li-ion batteries to become a mass production item before doing your conversion. In 2-3 years you’ll also be able to get PML Flightlink’s wheelmotors at a reasonable price. Save your money for a couple more years and you will be able to build an EV you will be truly satisfied with.

Well put Jack.

In the mean time you can do research and learn to do the calculations yourself for peace of mind and as a check so you make sure that recommendations on sites like this and those of vendors jive with your requirements.
I recommend picking up a copy of Bob Brant’s “Build Your Own Electric Vehicle”. It’ll give you a good understanding of EV propulsion system design theory. The information in the book allow you to approximate the numbers you need so that when you contact a vendor you will be more knowledgable. They always will talk longer and more in depth with someone that understands what they are saying.


Thanks for the replies guys,

But since we consider this as a business project, it is important to us to start with this project ASAP. The budgeted amount can be expanded if necessary, we simply aim for this target range to start off.

We did read Bobs book on how to build your own EV. Its a good one and gives some great insight into the matter. Nevertheless the data from the book seemed a little outdated and therefore we would like to ask around for your peoples suggestions on what suppliers to use for AC motors, controllers and other parts. One thing that we were somewhat confused about (and possibly its our calculation mistake) was the formula on calculating values. Accoding to this formula… if you do not change the acceleration figure and increase the required travel distance, you would need a higher HP rating of your engine… and that didn`t sound correct to us, so probably we made a mistake. Again, what horse power rating would you suggest for a car with a weight of approximately 1200kg to have it accelerate from 0-60 in something around 5-6 seconds?

Thanks for your input guys!

Recall depakote

Curb weight of a 97 Z3 is 1500kg. Without knowing battery specs, one is left with following the norm. Normally ev conversions are much heavier than the ice was. How are you getting your weight numbers?

It is critical that you get your battery specs before you do much else. Have you found the specs and prices for these batteries? If so please post a link. Until you know how much the batteries actually weigh there is no way to calculate the HP needed.

BMWs are nice but they are heavy. A 97 Z3 had 190 hp (142kw) engine and 0-60 in 6+ seconds. It would appear that the proposed vehicle will have to be heavier and you want to be quicker. You do have the advantage that electric has max torque at 0 rpm. As a guess I would say 150+kw. Other questions will also effect things. Will you use a transmission or direct drive?

Apologies, Lazlow… its not the curb weight I wrote about, but assumed stripped down weight and as you said battery weight will add to it. Again, thanks for your replies, as it really puts us on track.

We are still trying to negotiate a good rate for the batteries with Altairnano… I will let you know, once we finished the process… as you might have guessed, they are eager to make a buck and we want to save us some cash :slight_smile:

I guess you are right, probably we should try to stay with 6+ second range for acceleration values, since the engine we have been looking at that would be in the 150KW range would use a 100KW on continous, or in other words, consume too much energy to get us on a 20, 30 or 70 KW battery pack (these are the ones we are negotiating for) very far. Other engine options are a 100KW with a 55 KW continous (550 N x m (406 lbf x ft))
, 75KW with a 30KW continous (240 N x m (177 lbf x ft)) or a 35 KW with a 23.5 KW continous (380 N x m (280 lbf x ft)).

Can you suggest some options, if the battery pack of our max. 70 KW will be around 17.5 kg?


I still do not have any actual specs on the battery packs(Volts, amps, weight of entire pack not just 1 unit, dimensions, etc). Just knowing that they are 70kw is really not enough. How big of an amp load can you put on the battery in any one instant before it blows. Will you have to run a capacitor pack to balance the draw if your motor draws more instantaneous amps than the pack can supply? If so, how big? If you run without a capacitor pack how much will the high current draw reduce your range as compared to the same battery packs with a capacitor pack? Will you be running direct drive or through a transmission?


Did you get the torque ratings switched on the 75kw and 35kw motors? There is something funny about that.

I’m amazed Altair Nano is selling to individuals at all.

If you’re doing this with the idea of starting a conversion business, maybe you should hire an expert to design your drivetrain rather than try to hack it out on an underpopulated EV forum. Have you thought of travelling to an EV meet to talk with people/vendors who have done conversions.

Here’s another idea if you are a business - why not hook up with Wayland, the guy who built the White Zombie drag car (3 sec 0-60)?

Lazlow, again, thanks for your reply… actually, the data I gave in regards to the engines were not mixed up, but copied from the company`s datasheet. I will write more about the battery specs, once we got the details from Altair nano.

Jack the R - thanks for your post too. Both my colleague and I are from service type industries, but both of us are very tech-curious. Of course we will hire someone professional to do the conversion, it will be worth the additional investment, but for us it is important to get some basic understanding of what people offer to us, what is required for the conversion etc. As pointed out before… if you have a decent understanding of what components you need, suppliers are actually more willing to work with you and to offer you better prices & services.

The idea to contact Wayland is a good one and I will see what we can do about that. Keep up with the posting… your advice and feedback is very welcome.



Here’s an article on the Hymotion plug-in conversion for the Prius:


They say the Prius conversion can do nearly 40 miles electric on a $10,000, 160 lb battery pack. Very impressive. Hymotion is being finicky about who they sell packs too, but if you’re a business you can likely get a better deal from Altair Nano anyway. This gives you a ballpark figure on price at least.