Tweet a watt power meter display incorrect reading

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charlie110
 
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Joined: Tue Dec 03, 2013 12:00 pm

Tweet a watt power meter display incorrect reading

Post by charlie110 »

My tweet a watt power meter is displaying .95A current intermittently with nothing plugged in(figure 1 and figure 2). When It's plugged in with a lcd monitor, The .96A also shows up periodically. Any ideas why? Please help.
Attachments
FIGURE 1, 0.95A with nothing plugged in
FIGURE 1, 0.95A with nothing plugged in
IMG_0373-comm1.jpg (63.1 KiB) Viewed 1166 times
FIGURE 2, 0A with nothing plugged in
FIGURE 2, 0A with nothing plugged in
IMG_0372-comm1.jpg (61.21 KiB) Viewed 1166 times

adafruit
 
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Re: Tweet a watt power meter display incorrect reading

Post by adafruit »

No idea, could be wiring, the kill-a-watt is damaged, or the kill-a-watt doesn't like modification. you could try another one

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greyf350
 
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Re: Tweet a watt power meter display incorrect reading

Post by greyf350 »

Not sure if this applies in your case, but...

If you have a recent KAW like mine, there's not enough juice to run the XBee. The issue with hooking the XBee on the 6V opamp line is it's used as a reference voltage. The 6V is then passed through a 5V regulator used by the MCU and is also used as a reference voltage. Dips on 6V mess up the opamp levels and they show up on the 5V reference as well.

Easiest fix for me was change the 0.47uF cap on the AC board to a 1uF. Make sure it's an X1 or X2 rated capacitor; I got mine from an old switching power supply. That will double the amount of current it can supply.

Instead of hanging off the opamp rail,I'm running my XBee directly off the 15V output from the AC board using a standard 1117 3.3V regulator that's rated accordingly so I don't jolt the 6V reference voltage creating measurement errors. I also use 2pcs of 2200uF 25V caps on the 15V supply instead of the 10KuF 6.3V on the opamp supply to give me about the same amount of 'dying gasp'. 6-8V dips on the 15V don't show up downstream. One thing to note is the 1117 draws a couple more mA of quiescent current than the one that comes on the adapter (and the pinout is different)...not a problem with the bigger cap.

I'd be interested to compare notes with you when you get the rest of your stuff working.... I've gotten mine to track within 2% of the KAW reading while running a <80% PF load... So far so good...it's been running outside in the freezing weather behind some solar panels of mine for 2wks now and I can monitor with my phone via web from inside my house :-)

charlie110
 
Posts: 3
Joined: Tue Dec 03, 2013 12:00 pm

Re: Tweet a watt power meter display incorrect reading

Post by charlie110 »

adafruit wrote:No idea, could be wiring, the kill-a-watt is damaged, or the kill-a-watt doesn't like modification. you could try another one
It turned out my kill-a-watt was damaged. The second one doesn't have this problem. However the value shown on the receiver vary from what is shown on the transmitter. I've built two transmitters and them both have the same issue. The offset could be as high as 35% off. Do you know what could be the problem?
Attachments
with high constant load
with high constant load
with high constant load.JPG (120.88 KiB) Viewed 1084 times
with light constant load
with light constant load
with light constant load.JPG (119.64 KiB) Viewed 1084 times
nothing plugged
nothing plugged
nothing plugged in.JPG (108.6 KiB) Viewed 1084 times

charlie110
 
Posts: 3
Joined: Tue Dec 03, 2013 12:00 pm

Re: Tweet a watt power meter display incorrect reading

Post by charlie110 »

greyf350 wrote:Not sure if this applies in your case, but...

If you have a recent KAW like mine, there's not enough juice to run the XBee. The issue with hooking the XBee on the 6V opamp line is it's used as a reference voltage. The 6V is then passed through a 5V regulator used by the MCU and is also used as a reference voltage. Dips on 6V mess up the opamp levels and they show up on the 5V reference as well.

Easiest fix for me was change the 0.47uF cap on the AC board to a 1uF. Make sure it's an X1 or X2 rated capacitor; I got mine from an old switching power supply. That will double the amount of current it can supply.

Instead of hanging off the opamp rail,I'm running my XBee directly off the 15V output from the AC board using a standard 1117 3.3V regulator that's rated accordingly so I don't jolt the 6V reference voltage creating measurement errors. I also use 2pcs of 2200uF 25V caps on the 15V supply instead of the 10KuF 6.3V on the opamp supply to give me about the same amount of 'dying gasp'. 6-8V dips on the 15V don't show up downstream. One thing to note is the 1117 draws a couple more mA of quiescent current than the one that comes on the adapter (and the pinout is different)...not a problem with the bigger cap.

I'd be interested to compare notes with you when you get the rest of your stuff working.... I've gotten mine to track within 2% of the KAW reading while running a <80% PF load... So far so good...it's been running outside in the freezing weather behind some solar panels of mine for 2wks now and I can monitor with my phone via web from inside my house :-)
Hi I don't see the .47uf Cap on my transmitter circuit board. Do you mean 47uF/4V capacitor C2?

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greyf350
 
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Re: Tweet a watt power meter display incorrect reading

Post by greyf350 »

Sorry...havent logged in for a while

The .47uf cap I'm refering to is the big block on the AC plug board

I also discovered thw XBee sample rate is closer to 1.2-1.3uS, not 1.0uS

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