I’ve done a quick search and didn’t find an exact answer in a form I understood so I was hoping someone could enlighten me on a few details.
I have a emonTx 3.4 with 3 SCT013 connected to CT1, CT2 and CT3 with default 22Ω burden resistors. CT2 and CT3 are never going to see above 3KW and much more likely to be in the 0-2.2KW range.
What I’d like to change:
CT2 and CT3 will almost always be in the bottom 10% of the SCT013 range, from what I understand, this isn’t ideal as it’s less accurate.
- Ignore the inaccuracy and leave things alone
- Use SCT013 on high sensitivity inputs
- Use SCT006 with 22Ω burdens
- Use the existing SCT013 but loop the wires
I’ve had a quick look through the reports by @Robert.Wall, unless I’m misunderstanding, the SCT013 looks pretty good down to 0.5A. Should I even be trying to improve things?
If the SCT013 is used on a high sensitivity input it has a 18.8A/4.5KW max which fits well with my scenario. How does this effect the accuracy at the lower end of the SCT013 range? Is it improved when compared to a normal input or is it inherent due to the CT? Converting CT3 looks easy enough.
The SCT006 should be perfect for the range I need and again, Robert’s report seems to suggest it should work well with a 22Ω burden. I assume the sketch would need updating to account for the alternative CT, are there any suggested settings?
The last option is probably the easiest, I would need to extend two wires to give enough slack to loop through. I’d need to check how much the cable will be de-rated giving it’s effectively a bundle. Assuming the max current would be 13A, a single 2.5mm² can probably be looped 4/5 times and still be fine. The CT may act as a heatsink given it’s a hunk of metal and the cables will be touching it?
As always, any thoughts even if it’s just to correct me are much appreciated.