EEVblog #880 - Mailbag

[sean0118]

Let's do the math then: At 3A the voltage drop across them is 0.36V. 0.36V at 3A is a bit more than 1W of power dissipation.

In a h-bridge only half of the mosfets are active at the same time, so the avarage power power dissipation is 0.5W per mosfet. That's ok without a heatsink.

That's true and I did not think of that! ...But they wouldn't last at 6A. 

[jitter]

When I saw the PE-747R I thought that it looked familiar.

Under the Dynatek brand I have a 9020a that I bought in 1997. Though not yet CAT-rated, and lacking the input protection we would take for granted nowadays (it does have HRC fuses), I think it's a pretty good meter (despite the presence of a transistor tester ). Tear down here.

[NVX]

The IC with the number rubbed off on the plug in power meter is a Cirrus Logic CS5460A https://www.cirrus.com/en/pubs/proDatasheet/CS5460A_F5.pdf - note this is not the slightly fancier pin-compatible replacements for this part CS5461A or CS5463, the latter of which has in-built line frequency measuring on the IC although showing the mains frequency is a feature of the power meter so the mains frequency detecting so this must be done on the chip on board blob.

At least this is the case for the unit I have and reverse engineered (I searched by package for power metering ICs and compared pinouts, then got talking to it via its SPI interface.

~Tiernan (But not the one in the video!)

[SA007]

The chip with the rubber-off numbers int he plug power meter is probably a clone of the Analog Devices ADE7755.

Used extensively in basic, only kW/kWh meters, and therefore there are a few copies of it floating around.
The original is quite a nice chip, i have tested devices with a known clone in it and they performed roughly identical.
So it is probably a easy chip to clone.

I am missing calibration options/pads, this is usually done by solder pads to bridge a couple of resitors in path of the voltage measurement.
It could be in high-resolution mode and calibrated in the software in the blob next to the lcd, but i doubt that.

As for the capacitive dropper, that is the default design used in electricity meters, nothing new there.
Regulations state that they must be double insulated, and to measure the shunt (which is in line with the phase) needs to be to the ground of the measurement chip.
So your electronics can't be isolated, the device must be, so why add a isolated power supply, it is just more expensive.

[photon]

What's wrong with this picture?

I am an amateur collector of old technical books and Dave's mailbag pointed out this treatise not in my collection. Thanks Dave.

Though I do buy the old books, I am highly allergic to them. So I always look for a PDF. Surprisingly, I found the complete collection of these volumes in free downloadable PDF's. Go here https://archive.org and search for "cyclopedia of applied electricity".

[rsjsouza]

why does Dave regard the transistor testers so poorly?

a) They're useless

I don't disagree... The DMMs usually measure the transistor's h_FE (DC current gain), which greatly varies with the applied bias on its terminals and the internal transistor construction (power, general purpose, RF, switching, etc.). If you know the tester's limitations, it becomes clear they are somewhat useful for a quick good/no-good check, though.

b) They're a sure sign of a crap multimeter. When you see a transistor tester you know you're in for a laugh if you open up the meter and look inside.

Not quite. I have two Radioshack meters (2200087 and 2200039) where the h_FE test outlet is enclosed behind a plastic shield. The construction is reasonably solid.

[rrinker]

 Interesting, I wonder who the OEM is for that Rat Shack meter. Also had to LOL at the box label - "if you have a question about the features of this meter, just as a Radio Shack sales associate" The last person working for Radio Shack that could answer technical questions on multimeters (at least in the US) quit working there around 1986 (not so coincidently when I quit working there  )

[djacobow]

Regarding that PE-747R meter, I have a CIE-branded meter (8007) that is 100% identical. I bought it new in 1992 or so and it has worked well and is still in spec today. Because I have Fluke and other better meters now, I gave it to my little boy to play with, but I still often grab this one because the "toy" is in the house rather than the workshop. It works fine.

[Neilm]

why does Dave regard the transistor testers so poorly?

a) They're useless

They were usually found on cheap meters that didn't meet IEC61010. The reason being that meters that DID meet it, realised that  transistor testers are connected to the 0V of the meter, which is also connected to the negative terminal. So if someone left a lead in it connected to the mains and touches the transistor will result in a shock. The latest version of 61010 specifically addresses this possibility. The earlier version simply hinted at it.

[Hsimah]

Hi!

Where is the tear down of the E-Toll Tag?

I am unable to locate it on the EEVblog2

Thanks 

[michelinux]

Ritocco: Italian language

It means: "touch up", "retouch".

http://it.bab.la/dizionario/italiano-inglese/ritocco

[nerone]

Hi,

Sorry for replying on a very old post, but I would really like to see how the e-tag teardown we have exactly the same model in Sweden and always thought it was some sort of RFID. Anybody know what happened to that video on eevblog2? Can't find it

https://youtu.be/5bWEiyx6Bns?t=515

Kind regards