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measuring 1000 volts, using AVR ?

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faraday

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Hi guys,
how can I measure 1000 volts with ADC? I know just up to 5V is allowed for AVR pins, but I heard it has an interesting way to do it
(Apologize for probable grammar mistakes :p )
 
If your question is no more complicated than stated, and paying a lot of attention to electrical safety, a simple resistive voltage divider will work nicely. Accuracy will require appropriate resistor selection.
 
I'm guessing this is 1000 VAC right? You may be able to use a transformer, I have seen a case where a 480 VAC line was connected to a transformer to take it to 5 VDC to measure on a micro controller, the voltage output varies almost linearly with the input. I don't know if you can get a 1000 VAC to 5 VDC, you may be able to use some combination of a divider and a transformer. And again, be sure to be careful, there is a danger of a fire, explosion or electrocution.
 
We don't know if he wants to measure AC or DC.
We don't know if the 1000 volts needs to be isolated.
 
That's true, I came back to change this but as it's already got a response I'll leave it alone. Anyway, not knowing is why I left it non-specific.

If you use a voltage divider make sure you use high enough resistance to keep the power below the resistor's rating, I can explain further if needed. Also, this may be obvious, but in case it isn't, be sure the system is fully powered down before you work on it, how to be sure of this depends on the system.
 
You want a 'christmas tree', a load of resistors in series so that the volatge rating of each isnt exceeded, I've seen such ideas on industrial equipment.
 
thanks all for answering.
input voltage is DC and I wanna use voltage divider, and I noticed voltage ratings of the resistors :)
this is my design, is it correct ?? ( for more security, Calculations were based on 1500 volts)
**broken link removed**
and finally how can I isolate DC voltage?
 
You need to reload the attachment: it's "invalid".

and finally how can I isolate DC voltage?

Once you've got the proportional voltage from the divider, you could run the signal through an OpAmp unity follower circuit to isolate it from the ADC. It'll take, however, some precision components to achieve a high level of accuracy.
 
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I've made an analog 1KV interface to arduino before. I used a HCPL 4731 ultra low current optocoupler with a current limiting 20MΩ resistor. It cannot measure analog voltage well because the output of the opto is nonlinear, but in the range of current permissable by the 20MΩ resistor, it put the output in the "butter zone" of the curve where the output is almost linear. It was just for a "tripwire" (EX. below 800V, output fault) and not for an actual accurate measurement so it worked out fine.
 
thanks all for answering.
input voltage is DC and I wanna use voltage divider, and I noticed voltage ratings of the resistors :)
this is my design, is it correct ?? ( for more security, Calculations were based on 1500 volts)
**broken link removed**
and finally how can I isolate DC voltage?

How much resolution and accuracy do you need for the measurement?

How many volts of isolation do you need?

What is the minimum update rate?
 
How much resolution and accuracy do you need for the measurement?

How many volts of isolation do you need?

What is the minimum update rate?

(sorry for answering late)

-because of using avr, the resolution is 10 bits.

-I want to isolate a 1000volts DC power supply.

-I wanna show the results on 7 segment and update rate isn't so important to me, just 10-50HZ is enough.
 
I think we need to clarify what the term 'isolation' means to each of us.

I was asking if you need galvanic isolation. This means that there is no continuity between any part of your 1000 volt power supply circuit, and the microcontroller circuit. AC line power supplies have anywhere from 2500 to 4000 volts of isolation, even though the highest voltage you have on either side is usually less than 400 Volts.

If the zero volt common point of each circuit can be tied together, then you do not need galvanic isolation. All you need is a simple voltage divider that puts 5V (or whatever your A2D max is) at the measuement pin when you have 1000 volts (plus a little headroom) at the top of the divider. You do need to observe the max voltage rating of the resistors in the upper part of the divider. But that just means to divide the total upper resistance among a few resistors in series.

If you do need galvanic isolation, that is more complex. But we'll deal with that only if necessary.
 
thanks for your good descriptions Mr hrisP58.
I think galvanic isolation isn't necessary for this project, but I'm interested in to know how I can do it and what is it's circuit.
(I know about series resistors, thanks for warning)
 
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