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Converting AC to Dc and tracking parameters

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Wond3rboy

Member
Hi i want to convert 220Vac in to ttl levels or a small DC voltage(<10v) but want to keep track of the parameters(particularly current).I know that a transformer will vary both so can i still map them or not?Any other ideas.


Thanks.
 

dknguyen

Well-Known Member
Most Helpful Member
Generally, if you're lucky enough to have AC to start with, you want to step it down as much as possible while it is AC before converting it to DC. THis is because it is much easier to efficiently step down AC than DC (you just use a transformer, while to do the same thing you have to use switching converters which basically turn DC back into AC to be stepped down and then converted back into DC again).

You can just stick a current sensor to measure the DC...there isn't any real point to measure the AC and it's also more difficult. YOu can always work backwards with some math and find out approximately how much AC current you are drawing from your DC measurements.
 
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Wond3rboy

Member
I do intend to use a transformer but i want to know wil i be able to track the variation in current and to successfuly map them for a digital input(microcontroller). I want to check for a lamps short circuit current and normal operation current.
 

Thunderchild

New Member
put a very low resistor on the output and check the voltage drop accross it, use ohms law to work out the current, resistor value depends on the amount of current your talking about
 

Wond3rboy

Member
I already worked out the DC part used a pullup and a pulldown resistor combo to detect open and short ciruit.I acheived detecting a short or open ckt of an led but i want to map AC in to DC so it can be applicable.Thinking about measuring the current consumption of the lamp and then doing the math to calculate it at the output of the transformer.Thanks for your reply.
 

Thunderchild

New Member
if you want to measure AC amps in do the same with a resistor but retify it before applying it to a pic, i beleive an opamp circuit can provide voltage dropless rectification. I have to say your requests are not entirely clear
 

crutschow

Well-Known Member
Most Helpful Member
If you want to safely measure the current and voltage in the 220VAC circuit then you will need two transformers, a voltage transformer across the line and a current transformer in series with the load. The outputs of these can be rectified to give a DC representation of both.
 

Wond3rboy

Member
if you want to measure AC amps in do the same with a resistor but retify it before applying it to a pic, i beleive an opamp circuit can provide voltage dropless rectification. I have to say your requests are not entirely clear
I want to keep the 'integrity' of the parameters(current to be exact) intact when i change the coltage from AC to DC.
If you want to safely measure the current and voltage in the 220VAC circuit then you will need two transformers, a voltage transformer across the line and a current transformer in series with the load. The outputs of these can be rectified to give a DC representation of both.
I will look in to this.



Thanks for your replies.
 
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