emonTx4 and Clip-on CT both on AC and DC side

Hardware emonTx
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1

Hi,

is there a way to have some CT sensor on AC side and some other in DC side?

Thanks

2

No. A transformer - any transformer - relies on a changing magnetic flux created by an alternating current in one winding to generate a current or a voltage in the second winding. If the magnetic flux is constant, which it will be for a direct current, then no voltage or current can possibly be generated in the second winding.

You can use a Hall effect device on direct current, but one of those is not a transformer. The emonTx V4 was not designed to work with a Hall effect device, though with some development work, you might be able to use one.

4

Thanks Robert for the clear answer.

Yes, I would like to try to develop it. I’ve found some DC current sensor Hall effect based that I can use.

I should

Is it right?

Thanks

5

That is the path I would take.

You must of course fully understand the input voltage range that the analogue input accepts (0 - 1.024 V) and ensure that the output from your sensor conforms to this.

I have not looked at Github - I am too busy working on the next version! I believe the library you refer to is based on the old emonLibCM, so yes, it should be a good starting point. However, you must make certain that you add the minimum processing load. Trystan has already had to slow the rate at which the ADC is read, because there was not enough time to process the results, read the temperatures and count the pulses.

6

However, you must make certain that you add the minimum processing load. Trystan has already had to slow the rate at which the ADC is read, because there was not enough time to process the results, read the temperatures and count the pulses.

Ok, thank you.

I have found a DC Hall sensor like HSTS016L (datasheet attached) that could be fine.

Following emontx4/docs/other_sensors.md at main · openenergymonitor/emontx4 · GitHub, I can connect the sensor to a CT channel that I am not using and then make some little changes to the emonTx4 firmware in order to see the ADC value in the output.

But I have a question: I have a emonTx4 and emonBase powered with a emonVs-PSU; Can I use the emonVs to power also the HSTS016L sensor without any issue?

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Thanks

7

I think this might be possible, but @TrystanLea will need to confirm this. I don’t have the power calculations at present.

You will also need to attenuate and possibly ‘level-shift’ the Hall effect sensor output so that it is always constrained within the range 0 – 1.024 V.

8

You will also need to attenuate and possibly ‘level-shift’ the Hall effect sensor output so that it is always constrained within the range 0 – 1.024 V.

Can I use a simply voltage divider?

# Vin => from the hall sensor output
# Vout => to the emonTx4 CT input channel
R1 = 22kΩ
R2 = 4.7kΩ

# When the measured current is null
Vin = 2.5V
Vout = 0.44V

# When the measured current is the maximum forward current
Vin = 3.125V
Vout = 0.55V

# When the measured current is the maximum reverse current
Vin = 1.875V
Vout = 0.33V

@TrystanLea can you confirm it?

Thanks so much.

9

If the output range you get from this will give you adequate resolution (± 440 counts approximately), then it is the simplest solution.