Paul & Sabrina's cheap DIY 144v motor controller

[mcudogs]

D8 when forward biassed has a maximum voltage drop of 0.875 volts @3A. Therefore you could get an input voltage of 5.875 volts on the A to D input pin. The absolute maximum voltage for any input pin is 5.5VDC.

When you are dealing with high frequency induced spikes you really have to be carefull with A to D inputs. Another option is to use a ferrite on the cable to help attenuate any spikes.

The probable reason that the LEM300 is causing it more than the LEM 500 is that at high currents the output of the LEM300 is pretty close to the 5 volt point so any induced spike more easily pushes it over the max voltage.

[roverT]

Originally Posted by MPaulHolmes

Digi-Key - MM74HC00N-ND (Fairchild Semiconductor - MM74HC00N)

I think anything in the family 74HC00 14 pin quad NAND gates would work. Fran suggested to me NOT to use LS or HTC, but I don't know what that means.

Here's the LEM 500:
Digi-Key - 398-1067-ND (LEM USA Inc - HASS 500-S)

I believe the HC family has faster rise and fall times, better suited for higher speed applicatons than the LS or HTC series.

[blowncurtice]

Calling Squigles and all other Australian participants. We are trying to see how many are interested in a bulk buy for Australia, I am told that Mouser and maybe Digi-Key offer free freight as well as their quantity discounts on orders over $200.
Anyone interested please go to
www.aeva.asn.au/forums/forum_topics.asp?TID=1160
which is AEVA Forums / Technical Discusion / Electric Motors and Controllers / Open source DC controller.

[sawickm]

"So, I believe we should change from a LEM 300 to a LEM 500 or 600. Sorry Joe! I mailed yours a couple days ago. It sounds like you will do some hard driving, so we probably need to get you a LEM 500 or 600. It's easy to unbolt the LEM and stick in a new one. You will have to reprogram the microcontroller with the new LEM in mind. I'll make the necessary changes and I can email you the program if you want. Those dang things are like $27! Makes me mad! I'm glad we haven't done a large group order yet! That would suck. I think I have enough from donations to order a LEM 500 for you, Joe. Adrian is sort of far away. Hmm... I'm not sure what to do about that."

Hi Paul,

I read about this Current Sensor IC (Sentron CSA-1V) in another forum that is designing an AC motor controller. Check out there datasheet and application info (see link below). The sensor is rated up to 1000 Amps. A pcb would have to be made with with a connector and some descrete parts. That would needed to be mounted directly to the buss bar with nylon screws. The good news is the low cost of this sensor around $2.00, plus the cost of the PCB and descrete parts.

Search

[jyanof]

doh!

no worries about the current sensor though. Paul shipped the controller and it's supposedly arriving today, but I'll probably have to do a bunch of work to get it installed anyway - remount the controller, make some bus bars, tin some things, redo the wiring...

maybe if I order it today, it'll be here early next week!

how'd the testing go?

[MPaulHolmes]

testing currently underway. Don't order LEM 500 yet (or LEM 600 might be better?). Here's the plan:

Try to get latch up of LEM 500. If I can't, remove R6 (temporarily) and try to get latch up with LEM 300, just so we know with certainty that the output of the lem (through noise pickup or whatever) is causing latchup.

Back to testing! Son will wake soon. don't have much time! haha!

EDIT: It may be better to have D8 and D9 on other side of R6 if things continue to be a problem with latchup. We'll change it if we have to! ya!

[MPaulHolmes]

I tried it with the LEM 500, and I couldn't get it to latch up in 1st gear. I would come to a stop, floor it (really really really fun, by the way. Very good acceleration. I think better than my gas car), get to like 20 mph, stop, repeat.

Then I put it in 2nd gear. come to stop. Floor it. It latched up again! I still haven't been able to get the hardware overcurrent to come on yet. It's just not using enough amps. It COULD be the result of noise getting onto the throttle. Right now, if I make a single read that shows the throttle is outside a particular range, I have the car lock up. That could be what I'm interpreting as the microcontroller latching. I'm going to find out. If it's not the throttle, next I will remove R6, and repeat the experiment of putting it in 2nd gear, come to stop, and floor it. That will guarantee that the problem is a voltage spike getting into the current A/D input. Then we can go from there.

One fix is to put D8 and D9 on the other side of R6 (as suggested by my patron saint engineer, who periodically checks up on my progress here. hehe)

EDIT: It's NOT the throttle! I forgot that I commented out that part already. haha! So, I feel very confident it's the current input to the A/D. So, I guess remove R6. Sigh! Well, I should quit wasting time and get busy!

[jyanof]

Originally Posted by mcudogs

Paul, the LEM300 output is from an op amp that is fed from the +5vdc supply on the control board.

The schematic confused me for a while too until I looked up the part number - the triangle-looking U8 is a comparator, not an opamp. I think that this comparator triggers the hardware overcurrent when the LEM output rises above a specified voltage.

Paul, another thing to consider - i noticed there isn't an output vs input graph on the LEM datasheet. when i looked at the Tamura brand, they have a graph that shows this and the output is only linear in the rated range (like, 600A for a 600A sensor). After that, the slope decreases - thus, if you're assuming a linear relationship, it'll take more amps than you predict to get to the sensor output voltage required to trigger the overcurrent protection.

However, I don't know if this is also true for the LEM sensors...

here's a link to the tamura datasheet
http://www.mouser.com/catalog/specsheets/L03SXXXD15.pdf

I also notice they're $10 cheaper and the same size - any reason for going with the LEM vs the Tamura? (of course, my tamura also needed +5V and -5V to work, so it'd require more parts).

[chapper]

jyanof
The Tamura data sheet you referenced states the supply voltage is to be +/-15 volts, not +/-5v. That would seem to require a serious re-design.
John

[jyanof]

Originally Posted by chapper

jyanof
The Tamura data sheet you referenced states the supply voltage is to be +/-15 volts, not +/-5v. That would seem to require a serious re-design.
John

oh hm, interesting - i had interpreted that as max supply voltage, and the 50A component i'm using seems to work with +-5V... but it does look like they specify +-15V.

Nevertheless, I agree that supply voltage redesign might be undesirable, especially if the cost savings are negligible.