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Author Topic: Need help about high voltage measurement.  (Read 1197 times)
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jirawatk
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« on: November 13, 2008, 10:06:33 10:06 »

Hi all, I need some help or some suggestion about high voltage measurement.
My circuit look like below.

  _____ to diff amp +
 |
---
 -        last battery, I'd like measure this one
---
 -
 |_____ to diff amp -
 |
---
 -        12x19 = 228V
---
 -
 |_____ to GND

My old method is using differential amplifier and microcontroller to measure each battery voltage (20 batteries is series), but not working because voltage at pin +,- of op-amp is higher than Vcc.

Any idea about high voltage measurement using microcontroller?

Thank you.
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zzilot
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« Reply #1 on: November 13, 2008, 11:06:19 11:06 »

I remember that I had the same problem when needed to measure current (expressed in voltage) in some power electronics circuit. I used 1 OP amplifier with several resistors that had to be trimmed very well to reject common voltage (in your case it is Vcom=228V). There is component with that capabilites (with trimmed resistors), I cant remember designator it was long ago. At least you can use optocoupler if your measured value is not with high dynamic.



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beque
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« Reply #2 on: November 13, 2008, 01:48:11 13:48 »

This application in attachment is that you need...
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Wizpic
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« Reply #3 on: November 14, 2008, 07:40:11 19:40 »

jirawatk what is your ip locator all about ?

I hope you are not able to store data REMOVE it all you will be muted
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charnyutk
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« Reply #4 on: November 21, 2008, 10:15:08 10:15 »

Hi, Jirawatk
All of above was right" In addition, if you don't memtion about addition isolated power supply. may be you can try to use a "LM231 - Precision Voltage-to-Frequency Converter". This IC is a national semiconductor IC.After build the protype, you can connected with opto-coupler to send frequency data to another IC such as microcontroller. If you want an analog output, you can use a "LM2917 - Frequency to Voltage Converter" to convert your frequency data.

Thankyou and good luck.
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strabush
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« Reply #5 on: December 27, 2008, 10:24:44 10:24 »

You can use a high vce breakdown PNP transistor at the output of the measuring OpAmp. connect the transistor as a current source and its collector sourcing the current to a small resistor which its other side is connected to ground. The voltage on the resistor then is the measurement output and it is refered to ground.
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TomJackson69
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« Reply #6 on: December 28, 2008, 12:45:22 00:45 »

jirawatk ,

I think you can use voltage divider to get your measure voltage down to <5.0 Volts; than the PIC can measure it with A/D converter. Since your total voltage is 228 Volts, if you divide by ten than the measur voltage is 2.28 Volts.
Use .1% or .5% or 1% tolerance resistor for voltage divider. Select the wattage as need by the resistance of R2 and R1. Some PIC offer 16 channels of A/D converter; if you vant to monitor all 16 batterries. The top battery reference to GND would be 2.28 Volts (after use voltage divider) and the last one would be  .12 Volts. With 10 bits A/D you can measure the voltage quit good.

If you only need to measure one voltage, than you can use one A/D pin. For more presision measurement, go with a 12 bits or 16 bits A/D from MAXXIM and connect the output (serial or parallel depend) to the PIC for reading the voltage. A LCD display and a couple of buttons to control the PIC.

Your application need to measure the last battery, than, use only TWO A/D pins to measure, one at the Neg and one at the Pos of the last battery. In PIC program subtract the Pos-reading to the Neg-Reading.

Hope that help,

Tom
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