Hi,
Could anyone suggest a 230V current transformer which measures up to 100A AC, with a 5V DC output voltage? Does this exist? I can find 50A here.
(Split Core Current Transformer with 0-5V DC output - Denkovi A E LTD)
Thanks
Did you ask your search engine befor posting?
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Current transformers do NOT produce a voltage output, they produce an AC current output. The one you linked to has some extra components built in (as shown in the schematic on that page), giving it a voltage output. Those components are selected based on the desired current range.
Instead get a plain current transformer, so you can add the components you need. You have to rectify the AC output (a simple bridge rectifier is fine - the diode drop doesn't matter as it's a current source), and then add a sense resistor. Add a capacitor to smooth the ripple. A zener (max 5V) is a good idea to help protect your input pin in case there's a current surge.
Sense resistor value depends on the current transformer's turn ratio, the maximum current you want to measure, and the desired output voltage range (if measuring with an Arduino that'd be 0-1.1V - use the internal ADC reference or you'll never get stable results).
PS current transformers should cost a few USD at most. The price that site lists is crazy high.
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have a look at SCT013 current clamp - it is none-invasive being clamped around one of the target supply leads
I have used three 100amp versions to measure house house load over time, e.g.
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How will you measure the CT output?
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you can build your own circuit to offset the AC for input to a microcontroller ADC
I now use a ESP32-4-Channel-Mains-Current-Sensor
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Thank you for the detailed answer, I have been looking at doing with a plain CT and some additional components but wanted to see if there was a simple all in one option before starting down this route
@arbarr1
I have also looked and have not seen a 100A model with a DC output
So my plan was to use the analog input of the Arduino or maybe a digital pin with the DC voltage.
Assuming that Imax = 5Vdc and Imin = 0Vdc
For context for my application I want to use the incoming current as a switching input for load shedding.
For 100A supply, if incoming current>50A switch. It doesn't need to be particularly accurate, if it switches at 55A-70A it wouldn't make a huge difference.
the SCT-013 current clamp gives an AC output say -1.5 to +1.5 volts
unless you have a bipolar ADC you need to offset this to give a signal 0 to +3V
you can build a circuit - see electricity-monitoring-with-arduino or buy a module, e.g. the 4 channel sensor I references in post 6 or a ESP8266 single channel Mains Current Sensor
the ADC gives a voltage proportional to the AC current at that instant
you have to sample over several cycles to get the RMS current
it is worth getting a current clamp meter to check your calculations
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Thank you for the detailed information you've given over your last couple of posts. I will have a read through the posts you have suggested.
Well first you need a 100A CT.
Does it need to be the open type (clamp) or will a closed type be OK?
If you tell me which I'll provide you with details on how to connect to an Arduino
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The open type would be preferred as it doesn't require removing meter tails. Thanks
Look for one with a high secondary turn count, a 1:5000 model will do great. Then 100A in the primary (the single wire that goes through the clamp) gives you 20 mA RMS in the secondary.
R1 is the sense resistor, it gives a 0-1V peak signal. This circuit requires you to sample the ADC for at least 10 ms and get the highest value (the peak value of the wave), to get the actual value. R3 is just to protect the pin in case of current spikes, thus voltage spikes in the detector.
If you don't care too much about the actual value, it's quite easy to add a basic peak detector to it, and make the sampling a little easier.
With peak detection. Value of R1 amended to give a bit higher output voltage, compensating the voltage drop of about 0.5V across D1. C1 and R2 are a peak detector and smoothing circuit. Higher values for both C1 and R2 are fine, up to about 10µ and 100k.
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