Wood's smart strip failure - power strip

[kleung]

So...

This is my second wood's power strip / smartstrip that has failed

I believe it is made by CCI and I see that the new ones are a different color (I don't actually know if it's the same model/ design).

They last between 2-5 years and in this case, the controlled outlets would no longer turn on.

I thought it was a bad cap but upon disassembly, I see it is a burnt out / cracked resister (at least on this one).

I have appended pictures but will not attempt a repair as 1) power strips scare me...I've done computer power supplies but there, they are surrounded by a metal to contain the heat hopefully.

Anyways, in case someone has the same power strips and find that they are failing, this might give you an idea of where to look.

[stj]

Re: Wood's smart strip failure - power strip

check the thermal fuse against the mov's
if it's dead then the mov's have failed.

[eccerr0r]

Re: Wood's smart strip failure - power strip

Hmm..interesting. Wish I had one to take a look at.

I'm not sure about the thermal fuses-MOVs, though those are typical failures, I don't believe the 'smartstrip' feature depend on those (though I could be wrong). The overheated resistors are possible however as they may be sense resistors. I'm not exactly sure how the SCR fits in, usually used for latching but you want the strip to turn off... A detailed picture of the back side of the board would be interesting. And I wonder what that PT-77341 is...just a coil?

[R_J]

Re: Wood's smart strip failure - power strip

That pt-77341 looks like a current transformer (sensor) It detects current from the load device then switches on the remaining outlets. The burnt resistor may be for the dc supply for the circuit, as it has current flowing through it all the time it might have just opened up.

[budm]

Re: Wood's smart strip failure - power strip

The 48VDC relay coil and the circuit that drives it probably uses the capacitive coupling power supply, we need GOOD CLEAR straight shot pictures of the whole bottom side of the board to trace out the circuit.

[redwire]

Re: Wood's smart strip failure - power strip

The trouble is finding out the cooked resistor's original value. The resistor should not heat up unless the relay coil is on?

It's a basic circuit, the CT turns on the SCR, which rectifies mains and is filtered to DC by tiny C3, which drives the relay coil.

The Song Chuan 801H 48VDC relay needs only 7.5mA

There must be 25 patents on Smart Strips, but I could not see which (SCR) one Woods is using.

[momaka]

Re: Wood's smart strip failure - power strip

The 48VDC relay coil and the circuit that drives it probably uses the capacitive coupling power supply

I second this - probably a failed capacitor-coupled power supply that's burned that resistor and making the strip not function.

I have appended pictures but will not attempt a repair as 1) power strips scare me...I've done computer power supplies but there, they are surrounded by a metal to contain the heat hopefully.

Well, this power strip appears to have a thermal fuse. So if something goes wrong, it should cut power off.

On that note, almost every power strip with MOVs and no fuse could be potentially unsafe (i.e. catch fire). Spark gaps are safer, but more expensive I think.

[stj]

Re: Wood's smart strip failure - power strip

not so sure, once a spark gap arc's it can sustain the arc in the plasma field at much lower voltages.