I want to Interface a 300A/5A CT with Arduino to measure the current of Industrial Generators upto 100 kVa (Single & Three Phase) for a project, the problem is 5A current on Secondary coil.
want to know the calculations done for it.
Thank You in Advance.
Regards Obad Zafar
I take it you are using the emonTx Shield? And your Arduino has an analogue input range of 0 - 5 V?
There are two possible approaches:
You need a burden resistor that will give you approx 1.6 V rms at the maximum current that you want to measure. Presumably that will be 300 A. Therefore, the value of that resistance will be 0.32 Ω. The power rating will be 8 W. You will almost certainly need to approach a manufacturer of industrial instruments to have a meter shunt made to that specification. You can leave the existing burden resistor on the Shield p.c.b, it won’t materially affect the calibration (it’s 33 Ω in parallel with 0.32 Ω) but if you wish, you can adjust the value of your external burden to 0.323 Ω to suit. My concern here is the VA rating of your 300 : 5 c.t. You must check that - it needs to be at least 8 VA.
A much better solution would be to add an interposing current transformer. For that, you need a 5 A : 50 mA c.t. You use the 5 A secondary winding of your 300 : 5 c.t. as the primary winding of the interposing c.t, and you connect the secondary winding of the interposing c.t. to your Shield exactly as you would connect the standard YHDC 100 A : 50 mA c.t. If you cannot find a 5 A : 50 mA c.t, then you can use (say) a 20 A : 50 mA one with a 4-turn primary winding.
A suitable one that comes to mind is the Watcore WC1-025-MA100. That’s 25 A : 100 mA,
so if you use a 5-turns primary winding for that, and install a second 33 Ω burden resistor in parallel with the existing surface-mount burden on your Shield, that should give you what you want.
Thank you Robert for your Reply.
Your both solutions are good but in my case it is not optimal as i’m using it Industrial Generators.
In my research i also find a solution which will be perfect for me as it will convert 5A to 4-20mA loop output using operational amp but i want to make my own circuit. Like this one.
I hope you can help me again.