Hybrid PWM/Contactor controller turbo-boost

[bennelson]

Reading through one of the threads on here got me to thinking about an idea that was kicking around a while back.

A Hybrid PWM/Contactor EV controller.

The basic idea is that contactors are stupid, but work well and with variable voltages.

PWM controllers are great and smooth, but expensive.

Why not combine the both to get the control of the PWM with the speed and power of the contactor connection.

My basic idea would be to have a 72V max PWM controller hooked up to the motor and 6 (12V) batteries. One or two more batteries would also be in the car.

With some sort of a basic switch control, contactors would disconnect the controller from the circuit, and connect the spare battery or two into the circuit.

This would raise the system voltage by 12 or 24 volts and max out the available amperage - Turbo Mode!

I would think that a reversing contactor would work best for this. A reversing contactor is an A/B switch, instead of an On/OFF switch. By default, it completes one set of connections. When power is applied to its field coils, it disconnects the primary set of connections, and engages the secondary set of connections. This is a "break before make" kind of a switch.

The contactor could be engaged by either a big red button on the dashboard marked "TURBO". (Or maybe a button on the stick shift?)

Otherwise, it could be a microswitch attached to the potentiometer that engages when the pot maxes out. Press the pedal to the metal and the contactor kicks into overdrive.

What's the minimum number of contactors needed to create this configuration, make everything work right, and NOT fry my controller?

I'm not sure if I would need two contactors, or if I could get away with one reversing contactor.

Here is the motor, batteries, and controller as they are wired right now.


Here is how they would be wired in the higher voltage by-pass mode:


I would imagine having the reversing contactor located physically close to the PWM controller.

There are two cables going to the controller - one from the battery, and one from the motor. Would I need to break both cables?
For example, is there any reason why I couldn't leave a cable permanently connected between one end of the extra battery and the cable going to the motor? Without the other post of the battery connected at the same to anything, it's not sending any voltage to the battery or motor. (Imagine the little red line is a switch that can swing back and forth to connect the main battery pack string to either the spare battery or the PWM controller, but not both at the same time.)




Your thoughts on this?

It also just struck me that the bypass could also be used as a "limp-mode" to move the car in emergency if something happened to the PWM controller.

PS: Yes, you would have to make sure all the contactors are rated for high amperage....

[MetroMPG]

The EVDL guys have chewed over this before, and the biggest obstacle is that when you go back into PWM mode from Contactor/Turbo mode, you can fry the controller.

There will be back EMF (... if I'm not mistaken ...) in the motor for a short while which will feed back to the controller at a level higher than its rated to handle.

[MetroMPG]

I still like the idea though. And (memory kicking in) I think you can get around the controller exploding problem by simply not reconnecting the circuit right away following a turbo boost.

You would have to do something like:

PWM la la la
TURBO CIRCUIT!
FULL POWAH!
RELEASE POWAH WHEN DONE RACING TESLA
COUNT: ONE MISSISSIPPI
RECONNECT PWM

I could live with that. However someone not trained on how to use the car could get into trouble. You'd need a "valet" mode if anyone else was ever going to use the car.

[bennelson]

Electro-Metro vs Tesla!

[Clev]

Originally Posted by MetroMPG

The EVDL guys have chewed over this before, and the biggest obstacle is that when you go back into PWM mode from Contactor/Turbo mode, you can fry the controller.

There will be back EMF (... if I'm not mistaken ...) in the motor for a short while which will feed back to the controller at a level higher than its rated to handle.

Not only that, your "turbo" batteries will cycle at a different rate than the rest of the pack, resulting in different charge and discharge characteristics, and eventually, earlier or later replacement than the rest of the pack.

Plus, you're better off just going higher voltage to begin with. Put those batteries in the circuit always, and all of the batteries will last longer, because you'll need fewer amps for the same power output, and you'll have longer range, so less depth of discharge in normal driving.

[bennelson]

Yep, yep, yep.

I agree with all that.

My concept here is assuming that you DONT have/ CANT Afford a higher voltage controller.

Having different cycling characteristics to the "spare" battery isn't an issue. That would just be charged up off a separate 12V charger.

I am also imagining a circumstance where a low-budget EV might need to travel a short section of higher speed road. Near me, it's all 25 mph roads except right outside my house, where it's 45, and it's a 55 mph zone just on the other side of the hill. A 48 volt controller, with a bypass to 60 or 72v would work great in that instance.

[Clev]

Originally Posted by bennelson

I am also imagining a circumstance where a low-budget EV might need to travel a short section of higher speed road. Near me, it's all 25 mph roads except right outside my house, where it's 45, and it's a 55 mph zone just on the other side of the hill. A 48 volt controller, with a bypass to 60 or 72v would work great in that instance.

Ooh, maybe 96V worth of batteries? Run them in parallel strings at 48V with the controller, with a bypass contactor that series-connects them at 96V? That way, your batteries always still get discharged at the same rate. Just make sure that you're below the top speed of the 48V controller before cutting the controller back in.

[bennelson]

I started playing with this.

Because the controller actually has 4 power cables running to it, not 2, disconnecting the controller gets a little complicated a little fast.

I disconnected the A2 cable. After looking at the difference between 3 and 4 connection controllers, it looks like the A2 connection is only used for plug braking, so I disconnected that.

I left the battery+ cable to the controller connected, because that one is hardwired straight to both the batteries AND the motor.

I setup 2 reversing contactors - one each disconnects the power to the BATT- and MOTOR- connections to the controller. With the contactor coils powered up (24V coils) they snap into the second position and connect the six main batteries to two additional batteries, directly to the motor.

I already tested the reversing contactors, with power NOT connected to the additional 2 batteries. Under load (driving), hitting the "TURBO" button interrupts power to the controller. Sure enough - it instantly kills the car.

I am planning on testing this with power to the extra batteries, then kill it with the main contactor, wait a sec or two, and then kick back to PWM control.

I think this will work.

If no body hears from me in a few hours, please contact my next of kin.

[MetroMPG]

Agreed Clev: a series/parallel setup would be best. Plus you could keep using your 48v charger.

Another consideration, Ben: precharging the controller. Depending on how long you're in turbo mode, the caps will drain down, then you need to precharge them before going to your full connection (if you want the caps to live out their full, normal lifespans).

[Daox]

What about using a large cap to keep them powered up?