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Im embarking on a electric conversion of my BMW e39 528i for various reasons. Im decided to approach this logically using my knowledge as a automation and robotics machine designer, and my experience as a race car fabricator. I decided not to research the ins and outs of previous builders so that I can approach this open minded without being shadowed by others ideas or shortcomings. But, being open minded, I would welcome any input on what I am proposing.

First, I plan on using a water cooled DC motor running on LiPo batteries for the simplicity of electronic motor control and directional changes. Im familiar with the torque curves of such motors and will choose my transaxle gearing accordingly without the use of a transmission. The drive motor will be mounted in the stock trans. location and coupled directly using a modified factory driveshaft. I will use the other end of my motor shaft to drive the std 12v alternator for running and charging the 12v auxillary system.

The 12v auxillary system will consist of two 12v deep cycle marine batteries. This system will power all accessories, and also to drive a small auxillary motor coupling a pwr steering pump, water pump, a/c compress, and a small vaccum pump for the braking system. The water pump will be used for cooling of the primary drive motor and to provide heat in the winter. I will also be using the stock radiator. Since all accessories (climate control, etc) are electrically operated, there is no need for a vaccum pump other than for the abs system. And since the 12v system is continually running, everything will operate normally while at a stand still, or when moving.

On to the computer....we decided to leave all the engine sensors plugged into the main harness for testing. Our thought is that everything on the car works while in the "run" position without starting the engine. So, we should be able to test in this mode, albeit the dash will be lit up like a christmas tree. Even the speedometer will work since it's wheel sensor driven. We will determine which sensors aren't needed and what sensors will simulate a running engine for the sake of the ecm.

Well, thats it for now. But Im sure more ideas will come along. Any feedback on what Ive proposed so far would be greatly appreciated.
 

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Water cooled DC motor ????????? - like hen's teeth
Water cooled motors are usually AC
DC commutators and water?

Why use an alternator? - much much lower efficiency than a DC-DC

Why use deep cycle batteries they are more expensive and much heavier? - if your alternator or DC - DC is the right size you will never actually discharge your battery
 

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I suggest that you look at several other successful conversions and then make a decision which components you will use.This approach is not good.
If you have enough money and time to experiment with the wrong components, then ok..
 

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For vehicle applications, used vehicle batteries are now the optimal solution from a price per unit range perspective. Batteries from crashed Volts or Leafs are available in the US from wreckers for reasonable prices, and will likely be cheaper than your LiPos.

There is no need to water cool the motor. Air cooling is more than adequate if you're going to go with the conventional series wound DC motor.

Using an alternator is a lossy approach, and of course will only generate anything when the motor is spinning. A DC/DC converter will be more efficient and easier to install, as well as being more reliable once installed.

Suggest that a bit of reading here will point you in new directions worth considering. It's of course your project and you will do it the way you see as best for your situation, but as a wise man once said, only an idiot learns solely from his own mistakes- wise people learn from the mistakes of others...

Eliminating the transmission is possible with a big DC motor if you can afford to give up on either top speed or off the line acceleration- and assuming you have a controller and batteries capable of a large current draw. Keeping the transmission gives you options- it allows you to make better use of a limited speed motor. Yes, by eliminating the transmission you're saving a little space, a little weight and reducing losses a little bit, but you're giving up a lot of functionality by going with a fixed gear ratio. Not a good idea in my opinion, and it gets to be even less of a good idea the heavier your car is. The clutch is optional- many conversions have adequate shifting ease and speed without a clutch.

Best of luck, and happy reading.
 
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