AC current measurement with simple passive circuit, how? - Page 1
Forum section: electronics / projects

author: Finderbinder
author_rank: Regular Contributor
timestamp: March 31, 2023, 07:06:27 pm
content: The goal is simple - measure 50Hz AC current (max: 20A, min: few mA) by probing VAC or better VDC (if it is possible with passive circuit).A current transformer is the way to go, I thinkBut I'm not sure about accuracy/linearity in such a wide range with current transformer aloneOtherwise a circuit should be as simple as possible, with minimum components; at least not requiring active supply to power circuit.I know I may find a detailed study works with many formulas and circuit variations but... I just need to measure, not to invent a clamp meterAnyone knows a suitable circuit with known component values?

author: jonpaul
author_rank: Super Contributor
timestamp: March 31, 2023, 07:11:29 pm
content: LEM ( Switzerland) current Sensorsj

author: Finderbinder
author_rank: Regular Contributor
timestamp: March 31, 2023, 07:51:52 pm
content: AT 20 B and AK 50 C10Not cheapAnd a bit bulky, because few nominal values share the same body.Interesting what is inside them

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 31, 2023, 08:12:33 pm
content: What kinds of voltages are we talking here? Do you just want a simple analog readout or are you going to process this info somehow?Quote0-20A can be pretty simple if it's not true RMS... But if you also want to be able to distinguish between 100mA and 200mA, then you're going to need some sort of range switching as well.

author: Benta
author_rank: Super Contributor
timestamp: March 31, 2023, 08:25:39 pm
content: Is this a one-off or for production?

author: Finderbinder
author_rank: Regular Contributor
timestamp: March 31, 2023, 08:33:26 pm
content: Quote from: Kim Christensen on March 31, 2023, 08:12:33 pm230VAC. Only analog readout is enough, dedicated logging device processes this info further.Automatic range switching (in this analog part) is not desired because of simplicity/passivity. Manual range switching would not be possible in every situation, because values may vary over logging time.True RMS is not necessary but desired.

author: Finderbinder
author_rank: Regular Contributor
timestamp: March 31, 2023, 08:36:06 pm
content: Quote from: Benta on March 31, 2023, 08:25:39 pmOne single device. For my own use.

author: Benta
author_rank: Super Contributor
timestamp: March 31, 2023, 08:54:18 pm
content: Well, suitable current transformers can be bought for ~5 Euro.I'd go for a >50 A type to stay away from saturation effects such as crest factor issues.A 100:1 type would probably fit, that'd give 200 mA a 20 A AC current.

author: Shay
author_rank: Regular Contributor
timestamp: March 31, 2023, 09:11:26 pm
content: I've used those:https://a.aliexpress.com/_EIq8dZzInside you have a burden resistor which you can replace to change the output voltage.

author: Finderbinder
author_rank: Regular Contributor
timestamp: April 01, 2023, 06:27:22 pm
content: Problem solved by using this:https://wiki.volkszaehler.org/hardware/channels/meters/power/emt7110Enclosure exactly as was desired, analog part ready for use 1 AAC = 1 VAC, only few wires needed to come out from an enclosure (or better socket)

author: Alti
author_rank: Frequent Contributor
timestamp: April 01, 2023, 08:39:10 pm
content: Quote from: Finderbinder on April 01, 2023, 06:27:22 pmWe have 1 April, not Halloween. The circuit is not isolated, it is a shunt with opamp that amplifies the voltage. All at mains potential, including few wires that come out from enclosure.