Paul & Sabrina's cheap DIY 144v motor controller

[adamj12b]

Originally Posted by MPaulHolmes

Hey, I soldered my first surface mount components (in my whole life! for the bms):
This is a 1.25v reference (+/- 0.2%). It costs like $2.80 just for that microscopic little sucker! I thought it was a piece of dirt when it was on my desk.

Looks like a SOT-23-3....Am I right?? Dont you like how those little parts stick to the iron more then the board your soldering them to??

Its not too bad once you get the hang of it!!

-Adam

[hybriddriveguy]

Has anyone looked at MiniBMS?

It has some decent functions and more reasonable than a lot I have looked at. It would be great to get something we could customize for any Lithium battery pack at a resonable cost.
Thanks Paul

[jackbauer]

Just a quick question. How does the contactor connect to the drive circuit on the main pcb? Is it open collector or grounded?

Yesterday we took the bmw out for a short drive. Managed to pump 250 battery amps through the controller during acceleration. Heatsink never went above 30 degrees C. thats with an additional diode and gate resistor on the igbt for faster turn off.

[MPaulHolmes]

Hi Jack, do you mean the contactor for the controller? or the bms above? For the controller, the contactor is disabled while pin 13 is high. If the software sets it low, then that turns on the LED in U9, which causes the gate of Q1, (which is normally pulled high to battery 12v), to suddenly be shorted to about 0.3v, which turns on the p channel fet (Q1), which connects 12v to the coil.

I haven't heard much about the mini-bms. A couple concerns I have is that it continuously draws "less than" 10mA, which could mean 9mA. hehe. people that leave their car parked for too long or sent in for repair could destroy their batteries. It would take a pretty long time though. It also can only shunt 0.75amp for a little while, rather than continuously. I think it shuts off the charger if one of the shunts gets too hot, so the rest of the cells may not have a chance to balance. I'm also not sure how it will work in a noisy environment. Some people have had problems with this sort of thing under heavy acceleration I think.

Mine (from Fran's ideas haha) will use like 1uA (1 millionth of an Amp) when not in use, shunt any amount of current you want (continuous) from 0amp up to 2 amps away from each cell for as long as you want, causing anywhere from 2amp down to 0amp go through the battery until the rest are completely balanced (the programmer can have that 2 to 0amp be whatever he wants based on the "topping off" profile). This shortens the time necessary during the balancing phase. Each 25w power resistor is off board, on aluminum. Also, the charger and controller will know the exact voltage of every single cell, so you can output it to a laptop or something and watch the state of each and every battery while charging or discharging. Also, because CANbus is used, the communication will be very noise tolerant. ya!

[jackbauer]

so .........the output on the control board goes to +12v at the end of precharge? So i'd just connect the contactor positive to the control board o/p and the ground to 0v? Sorry for the silly questions.

[MPaulHolmes]

Ya! Exactly. That's not a silly question. Connect ground of the contactor coil to the 12v battery negative, and the Positive end of the contactor coil to the Contactor Pin on the control board (middle pin of J1).

[etlaare]

And another relay parallel with he contactor with the resistor to charge the caps directly from 12V initiated by the normal contact key switch.

* digs his memory on how to calculate the charging time again in an RC-circuit to set the proper rc-time value with the rtd-explorer *

[regmeister]

Hi Paul,

How's your SR design coming along? I'm interested mostly in the power stage. Have you cnc'd any boards yet?

I figure it will be awhile before the surface mount control boards are all the rage, so I figure I can patiently wait for all that goodness.

Cheers, Richard

[MPaulHolmes]

RC time constant:

You need about 5 RC time constants for the capacitors to be 0.99 full. Well, to be (1 - exp(-5)) full.. hehe.

So, capacitance*Resistance is 1 time constant. The capacitance is around 820uF each:

5*820uF*16*ResistorSize = time in seconds.

////////////////////////////////////////////////////////////////////////////

I designed the power pcb section for the SR controller, and did most of it in GCode, but there's a tiny bit left. I'm going to redo the control board for SR to use 2 drivers for mosfets, and 2 for freewheel mosfets. There's not much to add. I'm waiting on my tax returns to get the pcb done.

It's also going to have CAN, and interface with the bms if there is a bms to interface with.

[dave koller]

Good to see lots of EVer's from DIY in here

Jack, adamj12b, etc.......:

This might be good for me as I am a ROBOT builder, a lurker of this site, an EV builder and a hardware software old guy... Like the controller and that is that

Dave