Electronics > Projects, Designs, and Technical Stuff

3 phase 4 wire(480V) AC to 12VDC (100mA) power supply for energy metering applic

<< < (5/5)

ogden:
Those chips are for current shunt sensors. You are welcome to show meter reference design where voltage channel is isolated. Perhaps I missed it

Sent from my F5321 using Tapatalk

coppice:

--- Quote from: ogden on September 09, 2019, 01:18:09 pm ---Those chips are for current shunt sensors. You are welcome to show meter reference design where voltage channel is isolated. Perhaps I missed it

Sent from my F5321 using Tapatalk

--- End quote ---
The ADI chips provide two isolated sigma delta modulator channels. One for a voltage divider sensor, and a high gain one for a current shunt.

The relevant device numbers are ADE7978, ADE7933 and  ADE7932.

ogden:
Yes you are right. ADE79xx are nice isolation ADC's. Thank you.

Sent from my F5321 using Tapatalk

Sultanpepper123:

--- Quote from: Sultanpepper123 on September 09, 2019, 07:45:43 am ---
--- Quote from: capt bullshot on September 09, 2019, 05:49:49 am ---Quite a time ago, I've seen a circuit like this in a three-phase meter (L1,L2,L3,N connected).
It uses a simple SMPS to step down and isolate the 12V suppy from an intermediate (ballpark 150V) DC voltate, derived from the line voltages by capacitive droppers having rather high series resistors. For the rather low power requirement that you have, this should also work.

Stress voltage across the diodes is reduced to said intermediate voltage, higher frequency components are dealt by the rather high impedance resistors in series with the capacitors. I don't remember the actual component values. Capacitors have to be rated for the line voltage, resistors are requires to be robust  (pulse load, max. voltage rating) and silent failing to open circuit. No fuses required, the resistors are expected to cost way less than appropriate fuses.


--- End quote ---

Just a followup for people who may end up in my situation, i've read and quite alot of implementations using this circuit. I'd like to point out that maybe the diode between line and neutral are reversed maybe ? .

Regards


Reference : http://www.ti.com/lit/df/tidr430/tidr430.pdf
My apologies to you sir for not making the post clear enough , but i've just updated the picture as it is just a block diagram of the module ( it's internal components ) . Can your suggested circuit work with the inputs ?


--- Quote from: NiHaoMike on September 09, 2019, 02:57:58 am ---Use 3 half wave rectifiers, each must be individually fused with proper HRC fuses, but it's OK to put the EMI filtering and inrush protection after the rectifiers. You can consider using microwave oven diodes for the rectifiers, since they're fairly cheap but quite robust.

--- End quote ---
My apologies to you sir for not making the post clear enough , but i've just updated the picture as it is just a block diagram of the module ( it's internal components ) . Being bridge rectifiers, will it work with the inputs (L and N ) ?

--- End quote ---

splin:
An important aspect that you haven't stated is where this meter is to be installed as it very significantly affects the surge/transient voltage ratings the PSU has to withstand. https://www.tequipment.net/cat-ratings-explained/] [url]https://www.tequipment.net/cat-ratings-explained/[/URL] is a good guide.

Being three phase 480V it is likely to be cat II, cat III or cat IV 300V, as defined in IEC 61010-1. Cat II means it has to withstand 2.5kV impulses from a 12 ohm source. Cat III and IV withstand voltages are 4 or 6kV impulses from a 2 ohm source respectively which significantly limits the choice of off the shelf PSUs and they will be rather more costly than the common CAT II models. This assumes you need to be compliant with 61010-1 or equivalent of course but it would be risky, legally and ethically, to ignore the standard.

If you don’t need an isolated supply things are easier; ie. if your meter does not have any accessible ports including USB, serial or parallel I/O etc. Either way it still has to be safe when subject to the test voltages without catching fire or resulting in an uncontained explosion of one or more components – there is a lot of energy available from a 6kV 2ohm source.

You could use a lower category PSU and add additional protection components (the IRM-20-12 is spec’d as 3kV AC isolation). It would be interesting to know how cheaply a CAT III and IV 300V low power supply can be implemented but I have to agree that avoiding the need for HRC fuses (very expensive) has to be a good starting point, but 6kV+ capacitors and diodes aren’t cheap either. Diodes have a tendency to fail short circuit which won’t help in creating a low cost, safe design. I’m no expert here so hopefully someone experienced in the field will help out – preferably without the patronising ‘leave it to the professionals’ type responses beloved of some sparkies/gas engineers.

Note that those test voltages apply where the insulation is defined as 'BASIC INSULATION and SUPPLEMENTARY INSULATION' (ie. double insulation). If it is 'REINFORCED INSULATION' (eg. a multimeter test lead), those test voltages increase to 6.4kV and 9.6kV and creepage and clearance spacings double. I doubt that this will be an issue as I assume most equipment uses double insulation.

Navigation

[0] Message Index

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod