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Inexpensive ASIC DC Series controller, no uC, DSP or programming

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Inexpensive DC Series and ACIM ASIC controllers, no uC, DSP or programming

Hi everyone. I have noticed a trend towards the use of DC series traction motors in DIY EV projects.

In this thread I am going to design an inexpensive, very basic, easy to build
but also efficient DC series motor controller with modern ASICs,
based on PWM control of the applied DC voltage and hysteretic control of the maximum motor current.

Why? I'm going to buy an EV for daily use, building one is mainly for the fun of it.
I don't have a lot of spare time or money to spend on it, so a DC traction conversion is the best option for the next couple of years.
A drivetrain based on a DC series motor is by far the easiest and least expensive way to get traction (high start-up torque) from a DC power source.
As demonstrated in a recent video of a €1000 build and in every ICE car with a DC series starter motor.

DC series motors have been used for propulsion for ages and back in the pre-IGBT era,
torque and speed of DC series motors were controlled by shifting a tap on a huge, high power series resistor bank.
Very inefficient of course, but that is the way it was done when I was EE student in my first year.
At the core, the driver of the vehicle is the most important part of the control mechanism,
being both the feedback path and the input. A very elegant control solution because of its simplicity.

In the design in this thread the resistor bank will be replaced with modern silicon in ASICs.
Yes, application specific integrated circuits, so there's no time consuming complexity from microntrollers,
digital signal processors, unnecessary and potentially unstable controllers (PID) in software and the biggest issue: bugs and programming errors.
The electronics only kick in automatically when the response of the driver is too slow for the protection of the power electronics and the motor: overcurrent protection.
That is what "very basic" means, but it takes very little effort to dress up the controller with whatever (automated) (protection) feature is wanted.
Examples: cruise control, monitoring (warning lights, gauges), reduction of the maximum motor current when there's not enough air flow across the cooler.

The schematic shows the heart of the controller: only three SOT-23 devices, the lvc4066 and the lvc14 can be replaced with a single lvc3157 SPDT device.
Current sensing for overcurrent protection is done with a low cost LEM sensor.
Hysteretic control is implemented with a low cost comparator (MCP6561) and a LTC6992 has a suitable frequency response for the conversion of the throttle input into a PWM signal for the power stage.

EDIT: The all hardware ACIM controller is introduced later on. Thanks again, Damien!





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That is very, very interesting. I am (was) planning to use Paul Holmes old 500A controller logic board as the basis for controller build. I love the simplicity of this however. I might add an overcurrent shutdown option. LM393 should do the job. Thanks Tony :)

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1,953 Posts
i've used a similar circuit for current monitoring but added a low-value capacitor in parallel to R1.

This adds filtering against noise (PWM) and can be tuned to soften the hysteresis transistion (change slope and round over the edges).

i think you are using R2 and R3 to set the threshold voltage. If so then R3 should be tied directly to ground and the C3 cap should be on the node between R2 and R3.

One other consideration might be a light pull-up resistor to 5V on the output of the comparator.

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121 Posts
Nice work.

Damien could you please upload "your brain" to github I would love to be able to do what you can.

I know what +ve and -ve is i could do with your knowledge to fill in the rest to be a EE :p

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746 Posts
Discussion Starter · #12 ·
You've beaten me to it once again, Jack. Man, you're fast.

I think I'm going to steal your PCB design for the test runs.

But I see you haven't put in a car yet.

Well, I've got a similar piece of ICE sh*t you've bought for your €1000 build.

Nah, I think it's actually a bit better. No smell.

Battery pack is on its way.

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746 Posts
Discussion Starter · #15 · (Edited)
A car with this controller isn't going anywhere without a power stage.

I'm not a big fan of a lot of mosfets in parallel, so I've picked the IXYS IXTN550N055: 550A, 55V, Tjmax 175C, max dutycycle @48V,400A : 50% (200A terminal amp limit).

Repetitive avalanch current 200A

Gate resistor turn-off starting point: 5R. Turn-on: 1R
Driver: the usual IXDN609

Freewheel schottky DSS2x160-01A

Effectively 8kW+ per power stage isn't bad at all. Lots of torque at low RPM.

@Damien: brake input is a very good addition, but please drive slowly in the vicinity of petting zoos. ;)

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746 Posts
Discussion Starter · #16 ·
The design for the idle control is done.

Now the nexr circuit: The "HOLD" circuit for the the battery fault input from the BMS.

It holds (captures) a fault from the battery that indicates a too large static (internal voltage) or dynamic (impedance) difference between sections of the battery pack.
It is part of the controller because this fault condition has to lower the output amps to the motor and the wiring to the hysteretic controller has to be as short as possible.

A total shutdown is unwanted. A sort of "limp home" is better.

i'm going to use a thyristor. Similar to commutating thyristors in early 3phase motor inverters, the "hold" status can be reset by bypassing the current through the thyristor.
No flipflops needed for this. Very simple circuit. Design is ready.

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746 Posts
Discussion Starter · #18 · (Edited)
@ jackbauer: Definitely. Can't do without precharge. Seen anything you like?

Next: the very simple gate driver for the 55V,550A (1375A peak) IXYS mosfet.
It is very clear that desat has no benefits in this low voltage, single mosfet design.
The TRACO 12 to 15V isolated power supply does not need a high dV/dt rating, since the source of the mosfet is at ground level.
But a step-up of the 12V is needed, because the UVLO of the optocoupler has a 13.5 V upper threshold.

With the insulated mosfet at ground level, the cathode of the freewheel diode and its cooler are at battery+ voltage.
This way the coolers cannot act as high power antennas.

The turn-off gate resistor has a high value (10 Ohm).
For a major part the stored energy in the parasitic inductances has to be dissipated in the mosfet
during turn-off to prevent a very high Vds voltage spike and an avalanch current that is above the spec limit of 200A.

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746 Posts
Discussion Starter · #19 ·

I've entered a PTC in series with a 11W (and 5x overload spec for 5 seconds) wire wound resistor in the schematics for precharge.

Only used when the power stage is connected to the baterry pack via a fuse: it's a low voltage system, no need for additional safety devices or relays.

And: I'm maintaining the AT, so it's impossible to start the controller in a drive position.

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Discussion Starter · #20 ·

With a big wink, this fan controller complies with all applicable key words of the thread name except ASIC ;).

I'm going to use an automotive tangential fan to produce linear flow along the fins of the coolers.

In series I'll connect a NTC thermistor, mounted on the cooler of the mosfet: inexpensive fan control.:D

Really works well. Applied it to a number of low cost designs.
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