I am using a 100A SCT-013-000 CT sensor to monitor my Thermia heat pump. I noticed that the heat pump monitoring bundle ships with a 50A and 20A CT sensosr.
Checking the datasheet of my heatpump is rated for a max power of 3.6 KW and 25 A current. Does using the 100A CT clip mean measuring will be inaccurate versus using the 50A clip?
Thanks,
Ray K
Partly, but you ABSOLUTELY MUST supply and use a burden for your SCT-013-000 to convert the 50 mA output at 100 A to a 0.333 V output at whatever maximum current you wish. If you connect without, you risk damaging the input of heatpump monitor.
I advise using the recommended 0.333 V output c.t’s that the inputs of the heatpump monitor are designed for.
Sorry for not being clear here. My heat pump is being monitored by the spare EmonPi1, that I bought a few years back.
I was referring to the heat pump bundle as reference only. Asking, should I be using a 50A CT clip because that is what is appropriate for heat pumps?
I’m sorry I answered what appeared to be the question you were asking - is the SCT-013-000 compatible with the Heatpump Monitor. Remember, all we know of your plans or installation is what you write here. There was no mention your emonPi.
As has been written on this forum very many times, you should use a c.t. appropriate to the current you are intending to measure, meaning its rating should be higher than but as close as possible to the maximum current demanded by the circuit. You need to find what that is from the manufacturer’s data. However, the range of lower rated c.t’s with 50 mA outputs suitable for use with the emonPi1 is limited (again, mentioned many times here, e.g. Voltage CTs on emonpi1/emontx3 - #5 by Robert.Wall) so you might find the probable improvement in accuracy does not justify the trouble and expense. The way I’d look at it is, it’s likely that the lowest current drawn by the heat pump is below the listed minimum for the 100 A c.t. (linearity is not specified below 10 % of the rated current, i.e. 10 A), and then you probably should use a lower rated c.t.
Thanks Robert.
Something definitely appears to be off. The EmonPI never records a power usage above 100-120 watts for the heat pump. I tried swapping the CT cable and updating the firmware, and does not appear to make a difference. This is way (way) off, so I am guessing this is not accuracy issues
I am clamping on the Live Wire of the Heat Pumps Isolation Switch.
Is this the emonPi you can’t get working?
Explain. The cable is permanently attached to the SCT-013-000, so you can’t have swapped this part. Is there something else?
Have you carefully inspected your c.t? Is it damaged? Are the two cores intact and not cracked? And the cable - does this show any signs of damage? If you’ve got a multimeter, measure between tip and sleeve of the plug. You should see about 110 Ω.
Are you sure? Have you got anything else you can test the c.t. on, like an electric kettle?
Do both inputs of the emonPi give the same (within a percent or two) reading? Remember to do a controlled power-down and power-up with the c.t. connected when swapping the inputs. Rebooting the Pi does not reset the ‘emon’ front end.
A 240 Ω resistor in series with the a.c. adapter will give you a little less than 50 mA, that is, plugged in to the c.t. input, the emonPi should report 100 A (24 kW) or thereabouts. A higher value resistor will read less, of course.
I have a multi-meter and I will measure.
I tried two completely new YHDC SCT-013-000 CT, pre-made with a 3.5mm jack on them, both straight out of the box.
Yeah, I had that thought also - I will give that a try.
Yes, I have swapped between inputs 1 and 2 several times.
Both inputs read ~45 watts when the pump is idle, and similar max out at 130watts.
I will try swapping them around again.
When you say a.c. adapter, you mean this right?
That would require me wiring a female barrel connector to a 240 ohm resistor, to a 3.5mm jack. Should the resistor be on the live or neutral cable. Forgive questions I am not an EE.
Yes indeed. I assume you have the a.c. adapter - when it’s not connected to the emonPi’s voltage input, the software will assume 230 V (or maybe 240 V) so you don’t need a second one just for this test. It doesn’t matter which side the resistor is, it’s all low voltage anyway. The power dissipated in the resistor will be 0.3 W, so a normal 0.3 W or higher resistor will suffice, as it will only be in use for a few minutes while you check the reading. But it will get quite warm. A 470 Ω resistor will read about 50 A (12 kW or so), and so on.
A further thought before you go out and buy components: have you specifically updated the emonPi’s firmware? Can you use the Serial Config tool in emonCMS to reset the ‘emon’ part to the default values? You could get ‘silly’ output if the input calibration, either voltage or current or both, had been set to the wrong values; and if those had been saved into EEPROM, I suspect they would survive a complete new copy of emonCMS on a new SD card. The defaults in the sketch should be close to the correct values.
So the version of the ATMega firmware appears to be out of sync with the version of EmonSD.
This causes the serial config tool to wait indefinitely for ‘waiting for configuration from device’.
The firmware doesn’t appear to understand the ‘l’ command. If I just use the firmware automatically downloaded by the update tool 20-04-23, it updates to the latest firmware which doesn’t work, even after I fix the serial speeds in emonhub.
Instead, I tried to align the dates of the emonSD release emonSD-17Oct19, with the firmware release V2.9.2 | Firmware (17Nov19), but that has led me to the incompatibility issue above.
Any advice? Shouldn’t emonSD release just indicate which fw versions are compatible as part of their release notes?
I haven’t had a hand in the emonPi software - apart from writing emonLibDB, since my work to get the ‘CM’ version of the emonPi with the associated library for the RFM69CW was rejected and the powers that be decided to use LPL instead. And without a spare SD card larger than 8 GB or the time and inclination to shrink the download to fit, I can’t actually run the Feb 24 version.
But you’re right, you should be able to write whatever you downloaded to the SD card and put it into your emonPi, update the front end with whatever is on the SD card, and it should work - as Brian wrote. And it’s that belief which made me write last time:
because I don’t know whether the front end gets updated automatically. It used to - but the inference now on the Admin page of my version as you do the update is it doesn’t:
