where is this board power supply? - Page 1
Forum section: electronics / projects

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: April 23, 2018, 10:36:42 am
content: Hi,I have teardowned one of the schneider Flair22D Fault passage indicators to see what's inside, they are self powered along a lithium-ion battery, but I wonder how do they get their power from the external CT's and do not ruin the measurements data? also there is VPIS-VO input that can be used for power of the system, I have asked the technician in the field and they said their VPIS-VO voltage is nominally in the range of 100-250V AC and when there is no indicating system installed the voltage could go as high as 1Kv, because it's a scaled version of the main grid with cap's which is about 20Kv, So do you have any idea how this thing would get its power? I do not see any high voltage parts on this board,so far these are the identified partsMCU PIC18F46K20Op-amps MCP6044Input protection diodes are marked with 24 only and I think maybe they are 1.5SMC24AT or maybe they are RR264M-400, there is a 5pin sot23-5 part near the battery with the RUMRDG marking, maybe this is a battery charger, and 3 maybe TVs parts near the VPIS-VO connector with the KV42A markings, any Ideas are welcomed

author: Rerouter
author_rank: Super Contributor
timestamp: April 23, 2018, 10:43:46 am
content: This is all my guess, based on how I would do it, seeing as there is both Bulk storage capacitance (likely for the relay) a supercapacitor (likely for a few days runtime with the battery unplugged) would be to switch off the charging circuit, take your measurement, then turn it back on, always having a parrellel load for the current transformer, because when your not measuring, you dont care, and even if your measuring once a second, you likely only take a few ms to measure.

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: April 23, 2018, 11:01:46 am
content: Thanks for the update, But these are generally fast and they are used for short indication, here is the other parts, the lamp which is a simple two diodes with 18CA on first line and GP605 on the second line, the PCB marking is DZ1 and DZ2, do you know their part number? a 270 ohm and a 3 ohm resistor , and two LEDs! and the CT's are made of IRON core which can be forced to open in one side and let the main wire pass trough, there is a huge gap between the center and the CT in the order of 10cm, and there is wire around the core, how can I measure the CT parameters, like number of turns? I think they have made the core with some Iron that is somewhat like a spring!!! it's very simple and In the specs it said it can get it's power for more than 2A current in the main wire! how this can be done when the space between the center cable and the core is more than 5cm!

author: Rerouter
author_rank: Super Contributor
timestamp: April 23, 2018, 11:10:01 am
content: ... Its a low power device until a short occurs, likely between 10s to 100s of uA, so even with low coupling its likely enough to power it, and again, even checked every second there is still plenty of time to charge,The ampacity of a connection tends to align fairly well with its thermal mass, you throw a crowbar across a server rooms busbars, you have multiple seconds before things get hot enough to do series damage, you short 1mm light wire, it takes several seconds to start melting the insulation, Because of this, I genuinely doubt its response is "Instant" in all cases,

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: April 23, 2018, 11:18:36 am
content: ThanksOk, suppose it take less than 1ma, how does it convert 100v-250v AC nominal or in open conditions of 1Kv to say 5v, 1ma?

author: Rerouter
author_rank: Super Contributor
timestamp: April 23, 2018, 11:24:28 am
content: The line voltage is not the concern, its the coupled current out of the current transformer, the gap in the transformer hints at the fact they want the coupling to be really low.The current passing through the measured conductor induces a current in the output of the current transformer, the board would likely have this fed into some shunt regulator, shunting the measured current so the voltage to the device is mostly constant when not measuring,

author: westfw
author_rank: Super Contributor
timestamp: April 24, 2018, 02:51:18 am
content: QuoteThat's NOT an LiION battery, but a "primary" Lithium Cell.

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: April 24, 2018, 12:22:17 pm
content: Thanks,QuoteSo what does that tells us?

author: Gribo
author_rank: Frequent Contributor
timestamp: April 24, 2018, 12:54:13 pm
content: It is not rechargeable. Most likely, it is used for keeping the MCU alive.

author: westfw
author_rank: Super Contributor
timestamp: April 24, 2018, 06:36:15 pm
content: Well, I was going to suggest that since the thing is LCD-based, it might in fact NOT be powered except for the battery (and still have an acceptable product lifetime.) But then I read the web page where they specifically say that it's "input powered" and that the battery is a "backup"...

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: April 25, 2018, 06:17:27 am
content: I have done some measurements on the CT, I could pass a precision 1A till 20A pass trough the center of it, with a short Meter at the outside,First of all the inductance of the CT is about 4H, and there is a bobbin only in a small part of it.With 2A primary, I got only 800uA secondarywith 10A primary, I got 4.21ma secondarywith 20A primary, I got 8.5ma secondaryThe outer diameter is 120mm, it's made of 14 layers of Iron core, each should have a size of 0.35mm, the core al value is 5200nH/turn and to my calculations it should have a 2500 turns of 0.25mm wire!In the catalog it said it can work with 3A in the middle, the termination resistors are only 6.8 ohm, and the CT's would generate about 1.2ma @ 3A primary, So how the device would be powered? and could measure correctly the Current?These devices are present on the board and I know that they must consume more than 1mA, 3 MCP6044 op-amp's , one PIC18F46K20, one icl7660 device, the LCD, and some sot23-5 pin parts that I could not find any info on them