Using Byram BL3-200-RV001 CTs

I have a standard US 220 power setup and the CTs that came with the emonpi will not fit the cables. I purchased the Byram BL3-200-RV001 CT and have installed them. I have not removed the burden resistors because I am confused as to whether I should be removing them or replacing them. Can someone please help with with this?

The information on my emonpi website shows the BL3-200 returning 1-3W, but if I used the CT that came with the kit (too small to use longterm), I get a 65-70W reading.

See Learn | OpenEnergyMonitor

Your c.t. already has an inbuilt burden, so you don’t need two. You need to remove the ones on the Pi’s p.c.b.

I’m assuming they are the resistors at R17 and R28? Do I need to close that circuit after removing them or do I simple remove them from the board?

Hi Bob,

I’m in the US too. You should have a 240 Volt system, as that’s the standard in the US.

Definitely not.


Yes, you are correct. I fat fingered the 220… it is 240. Thanks for getting back to me so quickly.

Actually it was Robert Wall that answered your earlier post.
I noticed that it had been some time since he posted, so I
thought I’d jump in and help.

Have a good1!

I removed the resistors off of both the CT connectors. I have only one of the new CT’s connected and it’s reading 3424. The CT connector that doesn’t have anything connected to it is reading around 4300. The VRMS is reading 106.7. Can you makes sense of this for me?

Sorry - I was only cooking my dinner and eating it. I have to have a bit of time off sometimes - sleeping and eating are a bit important to me. :innocent:

Is 3.424 kW reasonable? It sounds as if it might be.

That is quite independent of the c.t. inputs. You can calibrate it by changing the appropriate value in the line “scales = …” for node 5 in emonhub.conf. It’s the “0.01” and needs to be about 0.0112 if you have a solid 120 V. Tweak it to get the actual measured voltage correct.

But the powers are dependent on the voltage, so you really ought to calibrate those as well.

It’s anybody’s guess what that will read with nothing - but absolutely nothing - biasing the input to the proper place. That input is picking up anything floating about in the air. If you want it to read a good zero, plug in a 3.5 mm jack with tip and sleeve shorted together.

Yeah, Non Maskable Interrupts are a bummer somtimes, eh? :grinning:

No, maskable interrupts are a life-saver. :smile_cat:

Is it normal to see erratic movements in the output? Power1 will display 208 then jump to 655 in a few seconds then maybe back down to 198. Similar behavior is found in the Power2 input also. During that time it seems nothing should be changing in the power consumption of the home. I also can see solid evidence that the consumption goes up or down based on turning on and off an appliance.

I have never checked the Pi for noise performance, but 200 W on a scale of 24 kW (120 V, 200 A full scale?) is scraping the barrel. Your current, when it gets to the ADC, is only about 3 counts rms.

So yes, we do expect to see some variation at any current, but it’s more noticeable at low or no current, from noise and quantization effects.