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Author Topic: help need for developing UPS  (Read 2548 times)
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prawin
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« on: March 23, 2009, 08:28:17 08:28 »

Hi friends i m praveen working on micro controller based line interactive UPS with PUSH PULL INVERTER.Can anyone help me how to detect mains failed. In my circuit i am having 3 inputs for MAINS.

First one is to Analog channel-0 RA0 of PIC micro controller 16F72.
Second one is zero crossing input given to external interrupt pin RB0.
Finally third is output feed back given to Analog channel-2 RA2.

Help me thank you


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looser
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« Reply #1 on: March 23, 2009, 09:55:18 09:55 »

Pravin
how fast you need to get the mains failed info.

A slow one something like a relay fed from mains and drops his contacts to provide the kick to your pic or
A rezistor divider to mains for powering an optocoupler continuously and  check the power existancy at each half cyle  passing a few miliseconds after zero cross.

regards
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prawin
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« Reply #2 on: March 23, 2009, 11:07:41 11:07 »

THank you sir for reply,I will be thank full to you sir if i can solve this problem in my project....

i need to detect mains failed in less than 10 milli second using relay change over.That is this relay i have to activate it in less

than 10 milli second.
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looser
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« Reply #3 on: March 23, 2009, 12:51:31 12:51 »

Dear prawin

I guess we are missing some points.

Detecting the failure of mains is something and action after detection is some other thing.
A fast acting relay on the average can swing the contact states in about 40mS. Activate a mechanical relay less than
10mS is very hard to achieve. You should think of solid state relays. ( Opto coupler and triac combined packages)

regards.
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prawin
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« Reply #4 on: March 24, 2009, 06:49:56 06:49 »

Is it but the already developed UPS is having relay of 24V DC transfering it in 6-7 milli second.they are activiting with micro controller.
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looser
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« Reply #5 on: March 24, 2009, 12:03:48 12:03 »

Ok if you can find such one go ahead. but I suggest obtain that relay first for your projects.
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prawin
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« Reply #6 on: March 25, 2009, 12:10:35 12:10 »

I want the logic to activate the relay using micro controller. That is when mains failed it has to switch to inverter mode in less than 10 ms...
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ALLPIC
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« Reply #7 on: March 25, 2009, 12:18:00 12:18 »

Microcontroller can activate a relay in microsec but you have to calculate a delay because of relay magnetism.. one way arround that I am useing is I kept relay voltage on higher side that means if relay is of 24v then I will apply a voltage of 30v by putting current limiting resistance you can protect a coil. This will increase a response time. Keep in mind that To make relay on is always faster than to making it off...

Hope this will help you. If you can put your schamatics and code then I can help you more preciously

regards
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emotion2000
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« Reply #8 on: March 25, 2009, 12:54:32 12:54 »

maybe this helps

http://www.vsholding.com/datasheets/7105_D5G500A20.pdf
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Walkura
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« Reply #9 on: March 25, 2009, 04:01:41 16:01 »

Microchip has a datasheet about a UPS .
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en010947
But to detect mains voltage i would either measure linevoltage or detect zerocrossings (or combine those 2 data)
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sohel
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« Reply #10 on: March 27, 2009, 08:03:19 08:03 »

hmm

crystal value ?

topology (modifide or sine)?

10ms = whats the value for instruction ( i think there huge time to make sure with 4 mhz)


first u may use normal relay for chenge line to ups .

why u want to use zero crossing ?

you must to see when drop line voltage (low cut , high cut)
use only one adc for detect line volt ( if line_volt < 1** volt ac. or line_volt > 240v ac then go to ups mode)

« Last Edit: March 27, 2009, 08:10:57 08:10 by sohel » Logged

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prawin
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« Reply #11 on: March 28, 2009, 01:19:12 13:19 »

hello sohle sir after reading the adc pin for mains failed my problem has'nt solved it is taking 150ms time to switch over to inverter.My design is line interactive 600 VA using PIC controller and i am working on 20 MHZ frequency.I am having three inputs for MAINS:-ADC input,zero crossing and feed back input.

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« Reply #12 on: March 29, 2009, 09:40:54 09:40 »

Which PIC are U useing. I am useing PIC16f72 for my one of design similar to you and I connected zero cross of mains to interrupt and all relay operation I am doing in Interrupt vector. because of this I am gatting 6ms.
At crystal frequency of 4mhz and 6ms is changeover time that means this is relay turn on time...

If you can please share your schamatics and source then there will be easier to give you right soulation.

I done this design for some of customer and that is NDA so I can't share my design, but I know this can be achived my putting every thing on interrupt



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sohel
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« Reply #13 on: March 29, 2009, 10:22:33 10:22 »

ok, have u any hardware design? it will clear all things. my all product are ups mode .
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« Reply #14 on: April 05, 2009, 02:03:50 14:03 »

you may use timer0 for the pwm and scr firing both  a frame of 200us will do every thing for you. 
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« Reply #15 on: April 06, 2009, 05:45:12 17:45 »

Hi prawin,

You can use this circuit : 

The circuit senses mains failure using opto TLP620. It has dual LED input which means that while mains is present, during both phases the input LED will be ON and the output transistor will be ON, thus 0v at the output. But when mains failure occurs, the input LED will be OFF and the output transistor will be OFF, thus 5v at output. This means, when mains is present there will be 0v at the output but 5v at the output when mains fails. Using this and connecting the output to your uC and writing code in that way, you can sense mains failure in less than 1ms.
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« Reply #16 on: April 17, 2009, 10:03:11 10:03 »

I seem to remember in the dim and distant past a circuit for a 'Missing-Pulse' detector using a standard logic IC.
The mains was stepped down to logic level volts, and full-wave rectified (no capacitor filtering), the resulting waveform fed into the IC (can't remember which.. re-triggerable flip-flop maybe?)
Capacitor timing was applied for the frequency period (100Hz) if one pulse was missing, this action produced a logic 1 at the output.
I'll see if I can find this circuit, among the tons of data I have here ;-)  The one thing I remembered.. it was fast.
And yes, I have an 'Offline' 1250VA UPS here under my workbench, this changes very fast..using a relay on a mains brown-out or failure.

Steve
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« Reply #17 on: April 23, 2009, 01:17:03 13:17 »

 i tried the 4n35 and moc3020 opto couplers with respect to tahm1d circuits and it worked well.
the switching time was very fast and it is easily adaptible to uc.
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