Help from EE's on Power Meter (AN220)

[SteveB]

I ran across Microchip’s application note AN220 Watt-Hour Meter (which uses the Cirrus Logic CS5460A Power/Enegry IC) and am interested in using this design for a project. As I am not an EE, I would like to have some advice from those of you who are.

1) As has been pointed out in another thread, Microchip engineers are human and can make mistakes, and on occasion their AN’s can have errors which could be a safety concern. Anyone see any problem’s with this design?

2) My application is a bit different. I am planning on using this design for a 240V (Single-phase – No Neutral Available), 30A application.

a. Based on this, I am most concerned about the current sense transformer T1 being adequate for the application (and what would be a good replacement if necessary, maybe this?).
b. I shouldn’t have any trouble working out the resistor values that need changing. But again, some of you can do this stuff in you sleep, and any help/tips/advice would be welcome.

3) The PIC/Display/Interface part of the circuit where I plan the major changes. Mostly using an 18F series PIC, a 16X2 LCD, serial comm. with PC and/or data-logging on flash/EEPROM. There shouldn’t be any problems with this end. Where I would like the help is on the power supply circuit.

a. I should be able to use the rectified “Vin” (prior to Volt Reg) to power the LCD backlight with appropriate current limiting resistor. Based on a voltage and typical LCD backlight specs, probably a 510ohm/1W resistor should be adequate (possibly 620). Anything wrong with this idea, or a better solution to power the backlight? (I got the idea from reading one of Melanie’s posts a while back, but can’t find it anymore)
b. I’ve seen similar power supply circuits with a diode across the Volt Reg for reverse current protection. Good idea or not needed?

Well, that’s enough to get started. Thanks to anyone that is willing to help.

Steve

[mister_e]

The current transformer is not a problem. From one model/brand to another you may need to change the Burden resistor (here R21) and do some calibration. No real problem.

Thew whole design, in general, seems nice. There enough insultaion to be safe. The harder part will be the software.. as always

I can't confirm the CS5460 performance as i never used it before. But it seems nice.

There's no problem to use the unregulated power supply for you LCD backlight. I do it often here too. an extra 7805 (or else) regulator could also be use instead of a resistor... it's up to you. HPWM control is also another idea.

Usually the diode across a voltage regulator is needed IF the external world COULD be disconnected from the PSU... e.g. bench PSU... It's a good idea but not a must in most case.

[SteveB]

The whole design, in general, seems nice. There enough insultaion to be safe. The harder part will be the software.. as always

Au contraire!

It depends on how you define "easy". The software bit is the FUN part , and it's a lot "easier" to do what you really enjoy vs something that is not so fun. For me, all the bits of metal, plastic, and such are just the means to an end, a necessay evil, a hinderence which slows one's progress toward the final result. Especially when dealing with fine pitch SMDs , which has made me a little concerned about tackling this project. Even with good eyes, SSOP parts a pretty small, to say nothing of trying to do a homebrew pcb for this baby. I much prefer twiddling with bits and bytes than Solder and Wire.

Thanks for the words Steve,
Steve B

[mister_e]

hehe, i agree. SMD, fine pitch are nice when you don't solder them yourself

But with some experiment.. it comes 'easy' even at home

http://www.infidigm.net/articles/solder/

Au contraire!