CT from Digikey

I purchased an Iotawatt before Xmas, and it should be here soon (shipping to the GWN is slow…)

Anyways I am looking at Digikey CT the AZ-0500 from Talema https://www.digikey.ca/en/products/detail/talema-group-llc/AZ-0500/4172201

Will this work for Iotawatt? Any recommendations for a TVS diode?


Answers are in this thread.

Yeah I saw that thread. Pretty complicated stuff - no clear answer if I can use the AZ-0500 or not. No clear info on what TVS diode to use.

You certainly can, I think the main question is it worth the effort. I got the TVS diodes overeasy recommended and used mini plugs with screw terminals to attach the wire and TVS. The provided leads are pretty short (less than a foot) so you may need to extend them.

I connect a 50 Amp clamp on and the AZ-0500 on the same circuit and your can see a difference at very low currents. I still need to send the samples to overeasy for his testing.

IotaWatt works with a lot of different CTs. Different CTs will have different accuracy, repeatability, linearity, etc. Some of the lower quality ones probably aren’t worth buying, but it depends on accuracy requirements and desires. People often say they want the most accuracy possible, but they aren’t willing to “pay” for it. I still have a strip of power measuring ICs for a project I was going to start more than a decade ago (because I wanted more channels and more accuracy than the solution I had at the time, it didn’t work with my generator at all).

I am using the CTs that I bought with a prior system. I “calibrated” them by comparing them to the known ones that I got with the IotaWatt. I was able to get them to generally agree to about a 1% or so.

As far as TVS diodes go, just about any would work. Bob put a link to one that looks fine and easy to use. I have some zener diodes that I wire back to back to do the same thing.

But, why not just use the 50A ones that Bob sells? I have several of them. They are bigger than the really small ones I have, but smaller than most of the ones that I have seen. I was going to replace all of my small ones, but they are working well enough that it is not a priority for me.

Let me explain.

I am in Canada. The shipping from the US is either “cheap” and very slow, or expensive and slow or stupidly expensive and fast. Also the conversion rate makes what seems to be an inexpensive item start to get beyond my budget. As an example, the Iotawatt I ordered is taking a minimum of 5 weeks to get here and has cost me at least $231CAD (I will still have to pay brokerage fees when it arrives). I buy 10 $15USD CTs and they would end up costing me $300CAD by the time I am done, and wait 5 weeks. That makes this little hobby project way to expensive.

Digikey and Mouser have arrangements with shipping companies to keep costs way down, eliminate brokerage fees and are 2 day delivery. So, unless I am really forced to go somewhere else, I prefer these suppliers. eBay and US boutique suppliers are just too expensive/slow.

To keep costs down, I am happy to attached my own cables and diodes.

I also have a very cramped panel. I doubt I could fit 10-14 split cores. Small solid core CTs would work much better.

So rather than have you guys sift through digikey and mouser for me, I thought I would suggest one an see if anyone has tried them.

Other manufacturers of economy CTs from digikey/mouser would be: vacuumschmelze, Pulse, Talema, Kemet, CR Magnetics. Has anyone tried the economy version of these with any reasonable success?

I looked at your order. It has indeed been 5 weeks. It’s a unique situation. It was ordered on Dec 12th - a Saturday - so shipped on Monday the 14th. The northeast USA, where I am, got 2-3 feet of snow that week along with a huge influx of Christmas packages mailed. It was a disaster and so your package didn’t get to Canada until Jan 7th. You are in western Canada. It is taking Canada Post a long time to get it to you.

I don’t want to get into a long grievance discussion concerning the various postal services. On balance, they work extremely well and are economical. This is an exceptional circumstance, and has been characteristic of problems caused worldwide as a result of complications of Covid.

The vendors that you talk about are mega suppliers. They have the volume to get better rates and exceptional service. Those are not available to me. I tried shipping UPS to Canada. They gave me a pretty good rate and then turned it around and charged the customers $50 “processing fees”.

I don’t want to leave Canadians with the impression that your 5 week ordeal is typical. Postal service to Eastern Canada has been restored to a reasonable 2 week average.

I have no issue with folks using other CTs. In fact, the ability to support any number of third party CTs and VTs was a primary design criteria. I have built test equipment to calibrate the CT parameters including phase-shift and am committed to adding any CTs that folks supply me samples of.

I was afraid I would get this response. I dont want to get into USPS shipping times/costs to Canada. I live here and have extensively used USPS for shipping for years. I know how long it takes for USPS to deliver - especially during covid. This is not about you or your service.

This is about me simply wanting to get some inexpensive CT I can get from Digikey or Mouser.

If you dont know of any - that is fine - hopefully someone else will chime in.

Since you are in The Great White North ( my mom was born there), you might try these:
Donut CTs - Brultech Research Inc.

I use the Micro 40 ones. I have a couple of the Micro 80s, but they are not in use right now. These CTs have 2m length cables of very thin gauge wire (which is great for fitting many in a single conduit). They do NOT have TVS diodes, so should never be unplugged while the circuit is energized.

The accuracy rating is not as high as the ones in the IotaWatt store, but I find they work fine. It did take a little effort to figure out a reasonable value for the calibration.

I used the ECM-1240 for years before the IotaWatt was a gleam in Bob’s eye. It was great in its day, but the IotaWatt is much better in every way. I thought about the GEM, but I was not sure about the accuracy (since I had mixed results with the ECM-1240). But, the CTs are decent and more than good enough to see small changes in load. I am not looking for revenue grade accuracy (I would like it, but not really willing to pay what it would cost, and don’t really NEED it).

Since they are in Canada too, shipping should be reasonable.

As far as shipping goes, I ordered a part from eBay at the beginning of the month. The seller shipped it right away, but it got stuck in Iowa for 2 or 3 weeks. I wondered if I was ever going to get it, but it eventually showed up. Meanwhile, I ordered something from Digi-Key and it showed up a few days later. But, it didn’t have to go through Iowa.

Great - thanks frogmore - I will investigate.