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Old 02-28-2009, 10:09 AM   #471 (permalink)
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For current sensing, how about just tap some points and calculate the current from the voltage drop?

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Old 02-28-2009, 10:11 AM   #472 (permalink)
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Did you ever hear how the american astronauts couldn't get a pen to work in space,
i know it.
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Old 02-28-2009, 10:13 AM   #473 (permalink)
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Quote:
Originally Posted by NiHaoMike View Post
For current sensing, how about just tap some points and calculate the current from the voltage drop?
If points on copper bar - than copper has high resistance deviation by temp.

If for MOSFET voltage drop ... Rdson is rising with temp and this aproach we've discused some pages ago for over current protecrion, but not for current mesurement.

page 17:
http://ecomodder.com/forum/showthrea...r-6404-17.html

See datasheet IR2127 irf.com desaturation protection.

Last edited by motor_control; 02-28-2009 at 10:44 AM..
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Old 02-28-2009, 10:51 AM   #474 (permalink)
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If it's using the copper as the shunt, and finding the voltage drop from that, it would work (it's what I use in my EV! It works great!), but you would have to know the copper's temperature. Copper's resistance increases about 0.4% per degree celcius above 20degC. I guess it would work really well to just compute the voltage drop from the copper shunt, monitor the temperature of the copper with a nice thermistor, and compute the current with the micro-controller, but my hardware overcurrent shutdown would not work then. Any ideas?
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Old 02-28-2009, 11:58 AM   #475 (permalink)
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You need good OpAmp like OPA335 - Texas Instruments - and some circuit for transfer current mesure signal from floting shunt to near ground ADC input. May be like that is in INA198. Fnd some cir. for powering floting OPA335.

In circuit floating with shunt we can use optocoupler 4n35 (or faster one - 6n136) for overcurent signal transmition to turnoff MOSFET driver.

Last edited by motor_control; 02-28-2009 at 12:05 PM..
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Old 02-28-2009, 12:03 PM   #476 (permalink)
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ADuM5400 Analog Devices, Inc.
is multychanel two-way isolator with biltin isolated DC-DC power source. Very FAST !

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But ! LEM - is professional style. In any power invertors LEM modules are used - it's right way IMHO.

Last edited by motor_control; 02-28-2009 at 12:08 PM..
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Old 02-28-2009, 12:13 PM   #477 (permalink)
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Thanks, motor_control! You are awesome!
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Old 02-28-2009, 03:45 PM   #478 (permalink)
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I have the new 2 wire throttle with all the noise immunity stuff working now. I only tested the output of the PWM. Next I need to test the hardware current shutdown.

It was super annoying! The AVR Studio people need to change something that is super-de-duper annoying about their program! When you go to program the micro-controller, it doesn't automatically put your project onto the chip, but puts the last project that was programmed onto it! And you can't see what that project is unless you click on a certain stupid box. I kept thinking there were bugs, but I kept uploading an old program from a previous project onto the chip! I even wrecked a dang ATMega8 by plugging it in backwards while trying to figure out why nothing was working! makes me mad! Just have the stupid programmer program the chip with whatever project is currently open! Idiots!

Flaming anger!

-Paul
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Old 02-28-2009, 05:43 PM   #479 (permalink)
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free VMLAB simulator is awesome ! and only 4 mb. Realy cool tool for AVR in ASM and C.

amctools.com

Visual Micro Lab :: AVR Freaks

See example project with sinewave, pot, opamp and ather stuff



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Old 03-01-2009, 03:17 AM   #480 (permalink)
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2/3rds of the way done soldering mosfets. The copper pad for the gate on the PCB comes off when soldering (glue melts) things to it. Fortunately, the gate is a very low power part of the mosfet. 2 resistors also need to be soldered to the gate, so since I can't really effectively use the copper, I'll use the resistor legs for that purpose. I'll also use a lower wattage soldering iron for the gate.

As I go along, I'm finding that there are several processes that can really be improved. The next controller will be much easier to assemble and a little better too.

I have the comparator portion of the control circuit done. Now I need to add the flipflop. I did a bunch with the software too, so that all the new numbers for the new components are taken into account, like current limiting and thermistor values. We also bought some plexiglass stuff from home depot and some aluminum angle iron (hehe iron). Maybe I shoudl just glue the plexiglass to the angle iron. I also bought some bolts for it, but I don't know.

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