Paul & Sabrina's cheap 144v motor controller

[MPaulHolmes]

There are 3 basic parts to an electric car:

Motor Controller
Batteries
Motor

Freeway capable EVs are more expensive than slow EVs because you need more batteries (sometimes: could use buddy pairs at lower voltage) and a high voltage controller. The same motor can often still be used, just by advancing the brushes, and maybe adding a blower to keep it cool.

So, it seems to me that the best place to focus efforts to making freeway capable EVs more affordable (under $1500?), is to focus on the controller. About $1200 or so can be shaved off the cost of a new controller.

So, here's my plan:
First, I'll make a smaller controller. I plan on it being 72v 40amp. Then, I'll try to scale it up. I'll test the smaller controller on my ebike, which has a brushed dc motor.


Today, I ordered most of the components and tools needed to make the bike controller. As they come, I'll take pictures of the things and the process. I'll try to get the bike controller done before school starts in January.

Some of the more important parts I ordered include:

50 MHz two channel oscilloscope
Ten IRFB4110 mosfets
IXDD414PI mosfet gate driver
Five STTH6002CW freewheel diodes
Atmel STK500
ATMega8 microcontroller
7.5 to 76V in, 5V out DC-DC
7.5 to 76v in, 12v out DC-DC
Twelve TS-ED 200v 470uF Panasonic Capacitors

[MPaulHolmes]

So, how do you make a controller?

The microcontroller (ATMega8 in my case) can generate pulse width modulation (PWM) signals. So, it listens to the throttle, and then sends a PWM signal to the mosfets' gate driver. The gate driver amplifies it a bit. The gate driver's job is to turn the mosfets on and off according to the PWM signal. Then, the mosfets massively amplify the PWM signal. That signal is sent to the motor, and you drive down the road. That's it!

The microcontroller can also monitor things like battery pack voltage, temperature, or whatever you want!

[Daox]

Very interesting! I'm all ears on this one.

[MPaulHolmes]

I think for the car's version, the controller will be powered by the auxiliary 12v battery, or by some other 12v source, rather than by the full pack voltage. However, the pack voltage ground will still not share a ground with the 12v battery, unlike in Kelly Controllers (aahh!).

The cost of components is about the same, but there are several advantages:

First, have you noticed that controllers say things like 48v-72v, 84v-120v, etc... That's because inside the controller is a DC-DC converter to step down the voltage, and it has a limited input range. So instead, my controller will have an available pack voltage input of 12v to 156v or something like that. As long as it stays clear of 200v, it will be fine, since I'll be using 200v mosfets.

Second, you can have the controller take care of pre-charging it's own resistors, rather than having that be something external.

Third, the high voltage input dc-dc converter has quite a few extra external components needed to make sure it will function properly. The 12v-12v option doesn't have any, so it's much simpler.

This represents 6 hours of Saturday research. My eyes hurt. good bye!

[captainslug]

Originally Posted by MPaulHolmes

Third, the high voltage input dc-dc converter has quite a few extra external components needed to make sure it will function properly. The 12v-12v option doesn't have any, so it's much simpler.

Also very true. High voltage input DC-DC converters can be as abhorrently expensive. Especially when compared to the cost of simply adding a 12V battery (of appropriate AH rating) and simple 12V charger.

[Intrigued]

Wow. You're really gonna make this happen, aren't you?!?!

Some thoughts on all this:

1) Can you say "Patent"? You should learn to, if you can't... This sounds a whole lot more interesting that trying to explain "2x=6" to a bunch of smart-mouths who don't care!
2) I'm more than all ears on this one. I'll be all eyes on the emails for replies to this thread, too.
3) This looks to end up being a controller and pack voltage indicator in one. Way Cool!
4) Will you be selling your version 1.0 controllers cheap when you get to 2.0???

[MPaulHolmes]

Hey, Intrigued, if only teachers could whoop students as if they were a red-headed step child, I would teach for free. If you are going to be excited about each post, I'll have to really make sure I actually have something interesting to report!

This is a modified version of Ian's "speedy" controller. His was for a 24v trolley. This version is 72v, and powers the mosfets and the micro-controller with the 12v auxiliary battery (that powers the lights and blinkers and other stuff). It doesn't share a common ground with the battery pack.

Notice that the PWM output from the ATMega8 is the PWM input into the gate driver. The driver amplifies the PWM signal, and then opens the floodgates of all the mosfets at the same time!

By the way, if you have ever wondered why a pre-charge resistor is important, it's because there are TONS of huge capacitors inside the controller! They don't like to be short circuited! OOH, so we need just a little more stuff inside that schematic to have it pre-charge when the 12v battery power is applied.

[Intrigued]

Originally Posted by MPaulHolmes

Hey, Intrigued, if only teachers could whoop students as if they were a red-headed step child, I would teach for free.

Huh. If they pay there like they do in Missouri, you're pretty close to that pay level already! My mother is a retired Special Education teacher. She says the worst part is that the kids KNOW that you can't touch them.

Originally Posted by MPaulHolmes

By the way, if you have ever wondered why a pre-charge resistor is important, it's because there are TONS of huge capacitors inside the controller! They don't like to be short circuited!

FINALLY!!! All I needed was for it to be put in words I understand!!! YESYESYES!!! I remember enough from my learnin' during my "first college-hood" days back in the 70s to finally understand what's going on. You dump enough electrons into a circuit that is wanting to soak them up, and something's gonna give...

Whew! <wipes forehead...> I finally got a decent handle on EV range vs. battery technology, and now I understand "flux capacitors"!!! (That's from somewhere in Darin's thread, I think...) Now it's on to the rest of the pieces parts. Maybe in 20 years or so I'll have everything figured out in my "gotta-understand-it-thoroughly-or-too-chicken-to-try" brain, and I can do it all by my lonesome!!! (Thanks, MPaul!)

[MPaulHolmes]

So far, the big capacitors, mosfet drivers, little itty bitty MLCC (multi-layer ceramic chip) capacitors, and the awesome mosfets came today. The oscilloscope is in the mail. I also got some sheet metal and wrist strap to make a static free workbench in the garage. Great news! I get to solder those MLCC's!!!! What the heck?

[TheSGC]

What are you using for current limiting? I too am working on a controller but won't get to it until classes are over. I am using a PIC controller, hall effect current sensor and 100 volt MOSFETs for my prototypes. I am working on a modular controller that will be limited to 60 AMPs, but be able to connected in parallel for more juice.