| Hmm. That's strange. |
by Longfist |
2014-12-31 07:35:09 |
LongFist is teaching Electronic Engineering at the High School level. No, not what he expected either. But the situation has gotten a little... ...weird.
The local (to somebody else) High School has an AVT (Advanced Vehicle Team) competing in the Shell Eco-Marathon in Detroit this year. Somehow (there's a story in there, for sure) LongFist was selected to teach two teens how to build an EV DC three-phase brushless motor controller with an Arduino Uno. The building blocks are all present, as is the previous (undocumented, misunderstood) controller. Sounds like it should be pretty simple, shouldn't it?
Well, it's not. Not by a longshot. We have a 36V battery that powers everything, and a million rules to follow, but the most interesting part is that somehow the previous controller managed to get 45+ V to the motor, making it run extremely inefficiently and red-hot! The motor coils all test out okay, but in the interests of "doing it right" LongFist *needs* to impart some voltage controls pronto.
In a perfect world, I'd set up a voltage divider to "chop out" 9VDC with which to feed the Arduino Uno (allows the Arduino to provide 5V logic signals without endangering the onboard voltage regulator like 12VDC can) and the rest (up to 36V, nothing more) to the driver/output stage of the controller - made up of 6 MOSFETs triggered by the Arduino PWM pins.
But LongFist is hung up: the battery voltage will most assuredly "drop off" during the 6-mile journey that this car will have to make. A simple resistor-network voltage divider looked to be perfect, except that output voltages *also* drop as the input (source) voltage drops as well. It's a ratio, not absolute. Considered a 7809 voltage regulator for the Arduino, but will have to make some further voltage drop upstream or the 36-50VDC (sometimes they overcharge the battery pack) will roast it easy-over: not good. Zener diodes (reverse-bias as voltage regulator) may be the ticket, but calculating the inline resistance (to prevent short circuiting) has been a bear, especially since the motor doesn't present a steady-state resistance. And as more options make themselves known, the whirlwind continues...
...never should have gotten involved in all this digital stuff! Now I find my analog design capacities have deteriorated incredibly! And technology has come up with some really amazing stuff - I must admit that I haven't kept up with it all!
Anybody out there got any hints as to how I might attack this directly? We have a long way to go and a short time to get there... |
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[ Reply ] |
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Load regulation circuitry is available. | by wwill | 2014-12-31 15:06:37 |
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Off-The-Shelf DC-DC Converter. Maybe quite small. | by pbarnrob | 2014-12-31 15:19:40 |
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For the Arduino supply, I'd use a DC/DC converter | by ttlogic | 2015-01-01 07:35:47 |
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Agreed on the DC/DC. | by OddParity | 2015-01-01 11:13:46 |
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Is 1 A enough? Recom model R-78C9.0-1.0 | by OddParity | 2015-01-01 15:22:46 |
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The Arduino Uno likes 7-12V @ 1A | by Longfist | 2015-01-01 22:27:23 |
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s/LM7757/LM5575/ | by OddParity | 2015-01-01 11:16:40 |
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D'oh! Thanks for correcting. (n/t) | by ttlogic | 2015-01-01 13:10:10 |
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Let me share this with you: | by Longfist | 2015-01-01 22:36:53 |
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Proportional, AND Regenerative, braking might | by pbarnrob | 2015-01-02 01:08:24 |
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For now, regenerative braking is out. | by Longfist | 2015-01-02 18:01:14 |
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Okay, we're in CRUNCH TIME now! | by Longfist | 2015-01-08 19:48:48 |
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I just dove the web for things that do almost what | by wwill | 2015-01-08 20:45:09 |
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If it weren't for lack of a hole in the middle, | by LongFist | 2015-01-09 04:59:35 |
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2N3055s are 15A power transistors. What if we | by LongFist | 2015-01-09 06:56:23 |
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You WANT the parallel! | by ideur | 2015-01-10 10:12:37 |
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A hint: | by ideur | 2015-01-11 02:49:40 |
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Buck converter will do, switching regulator at | by wwill | 2015-01-11 10:46:56 |
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Battery overcharge isn't so much a problem. | by LongFist | 2015-01-12 13:11:51 |
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The VR chip or Zener holds the voltage and causes | by wwill | 2015-01-13 09:18:11 |
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In re the three links. Number one looks good, | by wwill | 2015-01-13 09:26:51 |
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Working on it. | by LongFist | 2015-01-14 13:08:08 |
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Did you measure the battery under load? | by ideur | 2015-01-11 03:06:49 |
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For what? Not sure where you're going, here... | by LongFist | 2015-01-12 13:23:09 |
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Just wondering why a 36V battery should have 48V | by ideur | 2015-01-12 20:44:25 |
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Aaaaand *NOW* you see what's so special | by Longfist | 2015-01-13 04:02:37 |
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Crowbar Circuit. Haven't seen that in ages! And | by Longfist | 2015-01-13 04:13:52 |
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Hmm ... Let me see .... | by ideur | 2015-01-16 06:09:38 |
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Looks like I'll end up paralleling a *BUNCH* of | by LongFist | 2015-02-02 07:57:30 |
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Discussion Forward -> In Board Discussion | by LongFist | 2015-02-03 06:42:45 |
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I wonder what happens when a power supply rated | by Longfist | 2015-02-08 17:45:48 |
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UPDATE - NEW PART FROM MAXIM | by wwill | 2015-02-15 08:42:02 |
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THAT'S IT! THAT'S WHAT I NEEDED!!! | by Longfist | 2015-02-15 16:38:17 |
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PROJECT STATUS UPDATE! (Final for 2015) | by LongFist | 2015-04-06 14:06:48 |
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Your diode solution, simple yet brilliant. | by wwill | 2015-04-07 11:23:09 |
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Groovy! I can't thank you enough! Gonna' try to | by LongFist | 2015-04-08 11:37:53 |
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PROJECT STATUS RESULTS (2015) | by LongFist | 2015-04-16 11:09:39 |
