Paul & Sabrina's cheap DIY 144v motor controller

[MPaulHolmes]

final launch of space shuttle discovery in 1 MINUTE!!!!!

[MPaulHolmes]

I finished a rough draft of the next version of the code, for the 1000amp controller. Now it closes a precharge relay. Then after verifying that the caps have precharged, it closes the main contactor. Since the current into a capacitor is i = C*dv/dt, and C is about 0.026 F worst case (20% more than 0.022 F), just check the voltage at fixed intervals, and when the change in voltage is sufficiently small, that means the current flowing in is sufficiently slow, so it's safe to close the contactor. It also will check that the voltage is sufficiently large, so that it isn't a short circuit situation.

Also, there's a programmable max voltage. It is self protecting, so that if you are driving it really hard at a very high voltage, and a voltage spike exceeds the max voltage, the max motor amps is scaled back for a certain amount of time (maybe a couple minutes. I'm not sure yet). That will get the spikes under control because the spikes are proportional to the motor amps. It will re-enable the max motor amps after a little while, in case the voltage was high because of a high intial surface charge, which is common with lead acid.

Um... Also, I'm adding a "if pwm duty is sufficiently large (or is increasing, I don't know yet) and current is zero, then fault".

[flores]

Question about the 'old' controller:

How bad would it be to use just steel bolts to bolt down the busbars instead of brass ones? Those brass ones are hard to find.

[MPaulHolmes]

I think Adam tried that. It seemed like they got hot and there were some discolorations or something. I forgot. Yo, Adam! What happened, you steel using rebel...

[DawidvC]

Steel has a higher electrical resistance than brass. This means you will have to go with bigger bolts than what you would use with brass bolts. Remember that the washers used will also have an influence on the effectiveness of the connection. Industrial equipment that uses steel bolts uses a special washer that bites into the conductor material.

I hope that helps.
Dawid

[DJBecker]

Originally Posted by DawidvC

Steel has a higher electrical resistance than brass. This means you will have to go with bigger bolts than what you would use with brass bolts.

Steel has a much higher resistance than copper. Some alloys are only 3% as conductive. There is no way to make up that conductivity difference, no matter how large the hardware.

Brass is %25-%30 as conductive as copper, which makes it at least workable. (The low thermal and electrical conductivity is a surprise to many, since most brass is 50-90% copper.) If you don't need corrosion resistance, you get far better performance by using pure copper and relying on other materials for strength.

Remember that you can't just increase the cross section to keep the same conductivity. It's a 3D flow problem. If the conductivity is too low, there just isn't enough contact patch area available to make up for it.

[adamj12b]

The bolts I was using were just some I had around.

They were 5/16-18 steel bolts. The held the copper cable end right against the bus bar.

I cannot remember if they got warm or not. I will check in the spring when I can get the golf cart out of the garage.

-Adam

[DJBecker]

Originally Posted by adamj12b

The bolts I was using were just some I had around.

They were 5/16-18 steel bolts. The held the copper cable end right against the bus bar.

That's a different situation: the bolts are just providing the compression, rather than providing a conduction path.

I read the question as asking about the connection from the bus bar to the circuit board. The brass bolts are part of the conduction path.

[flores]

Originally Posted by DJBecker

I read the question as asking about the connection from the bus bar to the circuit board. The brass bolts are part of the conduction path.

That was the question indeed..

[vwdevotee]

Hi, so I'm actually on page 75 of 112 now and had a couple of questions. Please forgive me if they've been answered, I'm still cruising and will reach them eventually. Anyway, I was just wondering if it would be possible to build a low profile version of the Cougar? I've got a purdy old amplifier that I was thinking of stealing the extruded aluminum case from. The whole unit could only be about 2 inches tall though to fit inside. My other questions are less aesthetically driven. Are there enough open I/O ports on the MCU to provide gauge feedback? Could a pulse signal be generated to mimic the tachometer pulse feed? What about controller temp sensor being used to drive the engine temp gauge in an instrument cluster? And the pack voltage to drive the fuel gauge in the cluster? Thanks in advance for all your input!