# Reusing ABS(Anti Braking System) and AC air compressor



## Matthew Yee (Oct 30, 2014)

My EV conversion project has come with an ABS and AC compressor system that is integrated with the BMW engines and will be reuse after EV conversion. So far researching into it i can't find a good source that clearly shows how to salvage these systems. 

My first idea that i jotted down for salvaging AC compressor System is to recreate that same belt system the BMW engine has only with an electric motor. Seeing as how an engine and electric motor behaves differently this may not be a good idea. 

My second idea for the AC compressor would be to installed a High compression sensor and have a micro controller handle it. 

As for ABS I have no clue I know it is electronically controlled by the BMW ECU and I might consider replacing the ECU with the EV controller, still I am not sure how to salvage the ABS (I could be wrong to replace the ECU) 

How do you convert a car with these systems and salvage it ?


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## twright (Aug 20, 2013)

I don't know about your specific car, but most BMW's have a separate ECU that controls the brakes. That means that you just have to keep that system powered with 12 volts to maintain your ABS. The engine computer has nothing to do with the antilock brakes.


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## gunnarhs (Apr 24, 2012)

Matthew Yee said:


> My EV conversion project has come with an ABS and AC compressor system that is integrated with the BMW engines and will be reuse after EV conversion. So far researching into it i can't find a good source that clearly shows how to salvage these systems.
> 
> My first idea that i jotted down for salvaging AC compressor System is to recreate that same belt system the BMW engine has only with an electric motor. Seeing as how an engine and electric motor behaves differently this may not be a good idea.
> 
> ...


It depends on the situation there is no one solution that.
But there are two options when converting
1) Keeping as much as possible of the original car 
or
2) Designing a new electric drivetrain with the original chassis (new motor, new gearbox/transmission/differential or a reinforced adaption of the old, vacuum-pump for brakes and/or power-steering, new cooling system.

But now to the specific problem regarding AC-unit (I am not only looking at the compressor here).

1) Keeping the original setup needs finding a motor and a pully which fits so you can mount a belt from the motor to the AC-system. Usually you need a motor with "two axis ends" Assuming you find this you need some further adaption and your controller must allow your motor to idle at least 600 RPM ( I do not recommend keeping the belts for start/stop application)

The main problem here is obviously finding an adequate electric motor/controller which fits into this application.

The advantage can be:
1) You have an existing alternator and you can save the DC-DC-converter which gives you also the advantage of a completely isolated 12V system (as long the controller does not fuck this up)
2) You can keep the old cooling - and climate-unit of the car if existent
3) In some cases it keeps also the Power-steering as is.

To the specific problem regarding breaks (I am not only looking at the ABS here).
The ABS has to main functionalities, controlled braking by not locking the wheels and in more advanced systems providing traction control
1) The first problem is as you have removed the original engine you need an external vacuum pump to apply pressure to the brake(-fluid).
2) As the ABS (at least the one I know) does control the pressure either through an external valve / CU or through the existing ECU depending on car you would have to adapt the existing ABS to your new Vacuum pump control. So by removing the engine you have already in most cases messed with the existing ABS.
3) If the electric motor is AC and has regen enabled this adds further problems, in some situations motor and brakes will be fighting (the brakes win usually against ice at lower speed, sometimes not against the high torque-ing e-motor)
4) Sensors. The original ABS-sensors and system do often not work well with e-motor due to different reaction time and Electromagnetic interference
5) ESP (when using 4 sensors) will not get into that here.

So my advice if possible skip the original ABS with e-motor for elder vehicle at least.
If you must have it redesign it according to the requirements of your vehicle.

PS: To clarify 
You can keep the existing ABS unit to prevent the warning lamp coming up, but to make it work like it did with original motor you need (at least in my opinion) an adaption.
Just remember when using (strong) regen, regen wins for good or bad


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## mizlplix (May 1, 2011)

If the car has ABS as well as traction control then the ECU and ABS controllers both may be necessary to function. 

Miz


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