Hello,
i have a transformer rated 230/12-0-12, 500mA. What is this 500mA?
Is it for the LV or HV?
i have a transformer rated 230/12-0-12, 500mA. What is this 500mA?
Is it for the LV or HV?
The current rating is for the Low voltage side.
Bertus
You appear to be using a mains to low -voltage transformer "backwards" as a current sensing transformer. If that is what you are doing, I suspect that you may be infringing some safety regulations, but that aspect I will leave to others better qualified to comment.then check the attachment.
Am i went wrong???
Can i use the arrangement for current measurement?
I have posted a similar thread earlier.... but my doubt was not cleared..
Check the attachments in detail..
ExactlyYou appear to be using a mains to low -voltage transformer "backwards" as a current sensing transformer.
no problemthis will not give the desired result.
i need some voltage from the transformer which i can use it safely. I can calibrate it to work with a comparator(LM324) using a preset. see the attachment.[/QUOTE]Magnetizing current errors would reduce these values
purchasing a small CT is not a big thing for me. Is it impossible to design with my plan. if not, what are the corrections i have to take.Bottom line: get a proper current transformer and you can hope for safe and predictable results
yes of-course, i know the inductance comes into picture. What ever, is it not possible to get at least a safe 5v DC.???You appear to have used the low voltage winding resistance to predict the transformer output
I think your basic idea will work, but I think the voltage you'll be getting will be too high for your comparator. I think both voltages (the measurement and the reference) need to be within certain limits, and those limits are related to the power supply for the comparator. I don't think they can be both purely floating, as you've drawn. You've shown a ground symbol, but it's not clear what that means. You'll need to work out how ground loops are dealt with.i need some voltage from the transformer which i can use it safely. I can calibrate it to work with a comparator(LM324) using a preset. see the attachment.
A shunt resistor across the input would certainly reduce the risk, but it would need to be very substantial to avoid going open in the event of a fault, with potentially disastrous effects for the connected equipment. A purpose-made shunt resistor would be preferable. The value of the shunt should be as low as possible, but the output voltage would be rather small.You could shunt the primary of the "CT" with lets say 0.1 ohm resistor, which should leave you with a voltage transformer sensing the current, with some amplification (or attenuation if you use it the other way around). The resistor will dissipate 10W at 10A, so this should be pretty safe and predictable, definitely more than using the transformer as a real CT.
Also you will need some low-pass filter after the diode so that you measure average current and not instanteneous.
okbut I think the voltage you'll be getting will be too high for your comparator.
I can use a pot(voltage divider) to get in safe limits.I think both voltages (the measurement and the reference) need to be within certain limits, and those limits are related to the power supply for the comparator.
see the attachment[/QUOTE]You've shown a ground symbol, but it's not clear what that means. You'll need to work out how ground loops are dealt with.
of-course NOT. But, i wan2 try with this type....but is it worth all the effort compared to using something designed for the job?
what do u meant by "if something went wrong" ?What would be the legal position if something went wrong with such a lash-up?
Definitely a bad idea. You really don´t want to get the mains voltage anywhere near the low voltage circuit. For example if the resistor for some reason goes open, you will have 230V right in the circuit burning everything in its way. And killing you aswell if you accidentaly touch anything.One more thing, instead of that transformer, if i use 0.1Ω, 1/4W resistor, can i directly connect it to the comparator....(see the attachment)
Ok.....then .... any suggestions about my transformer idea????Definitely a bad idea.
Real CTs are specified by their current ratio and a burden value. For example you have a CT with 5:1 ratio, max current 5A, burden <1ohm. That means if you have 5A through the primary, you will have 1A through the secondary which has to be burnt in a resistor of 1ohm or less so that the core doesn´t saturate. You then measure the voltage on the resistor (or current through that resistor if that suits you more, which is here not the case). The burden resistor has to be allways connected to the transformer or it will create very high voltage on the secondary as it is trying to force the secondary current through it.Ok.....then .... any suggestions about my transformer idea????
and, suggest me CT. Im first time using the CT. I dont know how they specified..
This is making more sense now. I think you'll want to divide down the signal to the comparator, to avoid an overvoltage at its input.ok see the attachment