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bennelson 02-08-2009 08:52 PM

Hybrid PWM/Contactor controller turbo-boost
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 02-08-2009 09:27 PM

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 02-08-2009 09:33 PM

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

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 02-08-2009 09:54 PM

Electro-Metro vs Tesla!

Clev 02-08-2009 11:10 PM


Originally Posted by MetroMPG (Post 86944)
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 02-08-2009 11:25 PM

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 02-08-2009 11:29 PM


Originally Posted by bennelson (Post 86962)

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 02-09-2009 03:08 PM

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 02-09-2009 03:21 PM

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 02-09-2009 03:26 PM

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

bennelson 02-09-2009 03:55 PM

Holy K-Rap!

I just broke 60 MPH in a home-built cheap-o electric car!!!!

The batteries are urgently recovering on the charger.....

This thing is fast.

Put the car in 4th - get up to 45 - let off the gas pedal and kick in the turbo - it will push you into your seat (just a little, but it does!) and then take it up to 55. I made it to just a hair past 60 mph.

Wait a minute, that was in a 55 zone. There's that speeding thing again. I still got passed by by an F-350...

Why should I need to precharge my controller caps? They can't hold a charge for a minute or two?

I do need some sort of amperage limiter. My ammeter went straight to the top of the scale and stayed there! It just sucks as many amps as the batteries can give.

I pulled over and felt all the cables, the batteries, motor, and contactors.

The motor, contactors, and most cables were dead cold. The cable between the most positive battery and main contactor was warm. I think that's an issue because that's where the fuse, and a couple other small power connections are. I think I need to clean it up and put a better terminal on there.

I also felt all the batteries. One of the middle ones in the back was warm. That's one that I know always has lower voltage than the rest.

The Turbo seems to work pretty good.

I am not planning on engaging the turbo again without a few minor changes, but man does it work!!!

MetroMPG 02-09-2009 04:13 PM


I hear it's warm (relatively speaking) in Wisconsin today. Evidently you've got tinkerer's spring fever.

MetroMPG 02-09-2009 04:15 PM

PS - your amp limiter when doing a direct battery-motor connection is your gearbox. Downshift a gear next time you do it and you won't peg the ammeter (ensuring you know what speed is your max safe motor RPM for that gear beforehand - don't want you grenading your motor!).

rmay635703 02-09-2009 06:34 PM

I was always under the impression you could leave your controller in place but use a contactor to put a battery in series between the motor and the controller giving higher CONTROLLED speed. Basically that battery would always be pushing through the motor & flyback diode so you would need to have sufficient speed so you don't push too many amps. Also note that the battery on the flyback side would always be pushing current even if you try to let off the gas (which is a bad idea in this configuration).

Issue is you can also fry your controller if you let off the gas without a contactor to shut off the pedal to the motor and you can also fry the controller if it can't handle the increased amp level.

I was positive that a battery on the "other side" of the controller didn't push the volts too high because it was apart of the motor side flyback circuitry, maybe someone else here has done more experiments than I with this alternative method.

bennelson 02-09-2009 06:53 PM

I'm not sure about adding a battery to the string AFTER the controller.

Sounds like trouble. Also, since there are at least three cables connecting the batteries, motor, and controller, I am not quite sure where you would actually want to add that battery in.

I wanted to take my controller totally OUT of the equation, so that I DONT fry the controller.

I will have to do some testing on limiting amps, because my batteries are NOT happy pulling that many through - can you say Puekert Effect?

No, really, can you? I have no idea how you pronounce it. Lets just say that when you pull amps fast, your batteries run out even faster.

I actually pulled over on the way back just to rest the batteries for a bit.

I e-mailed a couple guys saying what I did, and one response was good enough that I need to repost it here.

Be carefull sounds like another ticket. You speed deamons could make us ev'rs look dangerous like those bikers! OOPS you are a biker also. HA HA.

bennelson 02-09-2009 07:28 PM

OK, here's some actual details on what I did.

I started by digging up two reversing contactors out of my box of parts I have stripped off forklifts. Forklift parts are great because they are BEEFY! (and cheap)

I cleaned up the contactors a bit, including bending back one bent terminal. They are almost pure copper, so they are very soft. You have to be careful wrenching them down.

I cut a scrap of plywood to fit under the hood and over the motor. Both contactors got screwed down to it.

Then I disconnected the M- and B- connections from the controller, and ran them to the contactors instead. That means that I had to dig through my pile of forklift parts again to get more cables to make all the connections.

The extra cables were all connected so that the contactors went to the connections on the controller, batteries, and the motor.

The two middle connections on the contactors go to that yellow Anderson connector (disconnect) which is run to inside the car, where the cables connect to two additional batteries.

That's right, I am out of space and now resorting to just placing the batteries on the floor. No passengers allowed in experimental flights anyways!

I ran a pair of control wires from the front to the batteries on the floor here. Those connect 24v of power to the contactor coils to engage "Turbo Mode"

I ran that power through a momentary-on three way switch pulled, again from my forklift parts pile. The switch is rated for up to 200 volts.

With the drive wheels jacked off the ground, I drove the wheels with the PWM controller and then flipped on Turbo Mode. The car instantly dies, because I have the Anderson connector to the extra two batteries disconnected.

Phase 1 testing looks good.

I then (with the car still jacked up) get the wheels up to speed with the PWM controller, let off the go pedal, and hit the Turbo. Instantly, the wheels get another burst of speed. I turn off the main contactor, and disengage the turbo.

Phase 2 testing passes well. No smoke from the magic box!

I then took the car out on the road, got up to speed, let off the gas, and hit the turbo. It's like it has a whole 'nuther gear - more powerful, like a low gear, yet faster like a high gear! How is this possible? Only through the magic of high-voltage!!! :thumbup:

As I rocket down the road, the issue of suspension and steering suddenly come to mind. Even though the car is two batteries heavier (about 150 lbs more) the suspension doesn't seem bad. I think part of that is that higher-speed roads are usually a bit better designed for smoothness.

Steering wasn't a problem either. It drove like a real car!

I have heard lots of hints on web forums about people theorizing about how to design all sorts of different types of controllers.

Well, I can tell you, it's a whole lot more fun to ACTUALLY DO IT than just talk about it.

If I end up frying my controller, I will dissect the whole thing and figure out what went wrong, and tell you all about it!

xtian999 04-20-2009 09:24 PM

turbo mode
So, instead of tossing the old contactors on my Citi, I can re use them for a turbo circuit? cool!
and since the turbo batteries are not charged or run with the others, they can be different? (older,smaller,cheaper)
and the main controller can be smaller, cheaper?
And the dash gets a shiny, candy-like button?
The best!

bennelson 04-20-2009 10:34 PM

Yep, you pretty much summed it up.

ev59rag 05-25-2009 02:13 PM

any news or progress? did you finalized your setup? using it regularly? any issues? did you change anything since your last post?


bennelson 05-25-2009 08:32 PM

More than anything, it was just a fun experiment.

I would much rather just go to a higher voltage controller than anything else.

Voltswagon 05-10-2011 12:47 AM

Did you ever run the turbo again? I have a 120V vw bug and was considering doing something similar to kick it up to 144v.

bennelson 05-10-2011 06:54 PM

I only ever really made a couple of runs with the "Turbo" button.

I was talking to somebody the other day, and it came up in the conversation.

The big issue is that you have NO SPEED CONTROL WHAT-SO-EVER when you directly connect a motor to a bunch of batteries.

It's just a matter of what speed you are doing and which gear you are in while you hit the turbo. I was working on a single long, straight stretch of road with a higher speed limit than the 72V Metro could do.

You are FAR better off with just a higher voltage PWM DC motor controller.
I didn't have one of those, and am just a little crazy, and had the parts to make the turbo-by-pass, so what the heck! :thumbup:

It was fun, but never was built into any sort of final design.

bennelson 05-10-2011 06:55 PM

Also, you need to charge the additional batteries separately, because they will get used a different amount from the rest.

Voltswagon 05-11-2011 04:01 PM

Spark of death?
How did your system function on disconnect? How many amps would you be pulling after reaching top speed and how much arcing occured on disconnect? Were any plasma monsters sighted?

I would plan to use mine when in the front of the traffic pack, so clear road ahead, running up to 35 mph or so in 2nd at 120V (I top out at 45 in 2nd) then throwing in some turbo power to get up to around 55.

I also envision this as a possible chance to use a mad scientist switch for something awesome.

bennelson 05-12-2011 10:26 AM

My system worked fine after disconnecting.

As for arcing when disconnecting - I'm not sure about that. The reversing contactor was up under the hood where I couldn't see it.

Rigging up a light and under-hood video camera would be able to tell the answer to that one.

I'm also not sure exactly what happens, due to magnetism, when you break that large current with that contactor. Is there back emf or high voltage that really needs to be looked at? I'm not sure. I just took a basic electronics class and now know just enough to at least know what to think about.

Again, with any contactor system, you do need to make sure that the contactor is rated for the type of current you are dealing with, and that you have redundant systems to be able to shut down the vehicle in an emergency situation.

You might also need to figure something out so that the capacitors in the PWM controller stay charged while in "Tubo-Mode" so that there isn't a sudden in-rush of current to them when you switch back to the controller.

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