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Is that a capacitor?

Rumpltzer

Rumpltzer

Diamond Member
Drunk driver took out a power pole in my neighborhood and we all lost stuff. I lost most of the surge protectors in the house, the FiOS box, my coffee maker, and my expensive Japanese toaster oven (the latter three weren't on surge protectors).

I ripped open most of the surge protectors and the toaster oven to see what had blown, and in most cases it looks something like there are two capacitors in parallel (one bigger and one smaller), and the smaller one is usually exploded.

I threw away the dead surge protectors, but I'm trying to save the toaster oven. Here's the damage inside:

I'm calling 1, 2, and 3 the smaller cap, larger cap, and a resistor. They're in parallel with one another (looking at traces on the PCB).

TO1.jpg


I de-soldered the parts to test the resistor (measures ~2.6Mohm) and larger cap (DC open). What's bothering me is that the thing I'm calling the smaller capacitor is marked with that symbol -N- (VD101). I've Googled around, and I can't figure out what that symbol represents.

TO2.jpg


This is a picture of the smaller capacitor. The side with the device label is gone.

TO3.jpg



So, anyone out there have any ideas? My intention is to replace the smaller capacitor and bring my toaster oven back to life, but I don't know what value to install. It looks like a cap to me, but the symbolage is bothering me... that, and I have no clue about what value to install.

The larger cap is labeled 100nk125 which I take as 100nF and 125V (although I find only 100V, 250V, 400V, 600V and not 125V).

Hints?
 
C1 said:
- "VD" is in all likelihood a varactor (ie, voltage-controlled capacitor or varicap; symbol is a diode with a capacitor by-passing it). The "N" could simply be a reference to "non-polarized" or simply the symbology used by the manufacturer for that type of component.
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I'm not a sparky, but couldn't the symbol be a variable capacitor symbol (capacitor with a slash through it, like a variable resistor symbol has a slash through it)? That would fit in with it being a voltage-controlled capacitor.

Edit: I think you're exactly right - I found this diagram with an N-like symbol showing capacitance as a function of voltage:
AR_4071_L_F5.jpg
 
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I would third that. Often there is a fuse or sacrificial resistor in the area also that will likely need replacing when the VD blew.
 
PottedMeat said:
should be a Metal Oxide Varistor commonly found on surge protectors and it looks like it did its job.
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So this would have an adjustment screw(on one side) wouldn't it? A variable seems to suggest an adjustment.....I'm no techy just asking. Or does it mean it can change depending on the NEED at hand?
 
No, the name comes from the fact that the ohm rating varies based on voltage. IE it might have 10mohm at 170volts but may drop to 50 ohms at 250volts etc. The idea that a spike over 170 volts gets directed in to something else like a resistor to dissipate the surge as heat or to neutral etc.
 
imagoon said:
No, the name comes from the fact that the ohm rating varies based on voltage. IE it might have 10mohm at 170volts but may drop to 50 ohms at 250volts etc. The idea that a spike over 170 volts gets directed in to something else like a resistor to dissipate the surge as heat or to neutral etc.
Click to expand...


Gotcha,
Just trying to learn but its a huge curve 🙄
 
Agree that IS a Metal Oxide Varistor (MOV). That symbol you see on the board - looks like a capital "N" with lines to each side - may be more recognized if you turn it 90 degrees so it looks line a Z with leads up and down. That is one of the common symbols for this device. I think that comes from the observation that it behaves a little like two Zener Diodes connected in parallel but opposite directions. At lower voltages its resistance is high, but once a threshold voltage is exceeded it conducts very well, dissipating the overvoltage by allowing substantial current flow through itself. It is the "sacrificial component" in a voltage limiting circuit. Once it has done its job (limiting a voltage surge), the circuit is non-functional until that component is replaced.

Your problem, OP, is that there are no visible markings on the destroyed unit, so identifying a replacement is an issue.
 
All right, metal oxide varistor! Like a dual-polarity Zener. You guys are awesome.

This also makes sense; I found similar setups (with exploded varistors) in all of the surge protectors that got taken out.

So, the problem is that I need to figure out the replacement value without device markings. The device value seems to be very physical; depends a lot on volume, area, and thickness. Maybe I head over to Fry's to see what the 130V parts look like.

What have I got to lose, right?
 
You will likely need more than 130v if that is in the AC circuit. 120V is nominal peak voltage is around 170V. If it is in the DC path then use the rated voltage.

250v seems common for 120vac while 500v for 240vac / multi-region supplies.
 
If they are listed and rated for RMS then you are good to go. Worst case it explodes when you plug it in right? Just wear safety glasses.
 
Bah! It's the Highly Technical forum... is reading the thread really necessary? 😀


So, update: Bought the metal oxide varistor from Fry's for less than $2, and soldered that into the board. Nothing. No life at all. 🙁

Kept poking and probing at it, and found a couple of 47uH inductors that were blown. You can see both of them in the pics from the OP; they look like mint green resistors. Expect them to be dc short, and find them to be dc open. On closer inspection, I see that they're either popped or cracked but the damage is facing the PCB so I didn't previously notice.

Couldn't find the exact replacement in my local shops, and I didn't know if I should go up to 100uH or down to 10uH, so I ordered ten of them from a Bay Area shop off eBay ($3 shipped). Soldered those in today, and the toaster oven is alive!


Total of $5 in parts. Learned some stuff. Amused myself. Toaster oven is alive again.

Thanks for the help!

TO4.jpg


TO5.jpg
 
Rumpltzer said:
Kept poking and probing at it, and found a couple of 47uH inductors that were blown. You can see both of them in the pics from the OP; they look like mint green resistors. Expect them to be dc short, and find them to be dc open. On closer inspection, I see that they're either popped or cracked but the damage is facing the PCB so I didn't previously notice.
Click to expand...

nice.

they were probably just low power filtering inductors, you probably could have just shorted them and it would work acceptably.
 
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