Water heater rated 110v plugged on 220v

[Benji]

I have a Panasonic NC-EH22P thermo pot rated 110v and it got plugged somehow to a 220v outlet. 

The power supply board looks like it has a fuse blown and another mystery component:


That's a close-up of the component and the symbol looks like a Z and the label is ZNR. To be noted that it is connected in parallel to the big cap behind it rated 275v.


This is the remains of the component:


And finally this is an image of the board taken from the internet to see how it should look like pre-blowup:


So my question is what is the mystery component?

I don't have high hopes but I figured I might as well try even if it is just for the sake of curiosity. 
Thanks for reading!

[tanveerriaz]

"ZNR" stands for Zinc-Oxide Non-liner Resistor, the product name of a voltage-dependent resistor
use as Transient/Surge Absorber.

[Ian.M]

Probably a metal oxide varistor for transient overvoltage protection or to 'mop up' transients from the relay contacts opening.  It will probably run without it after the board has been thoroughly scrubbed to remove the conductive residue it left, and the fuse replaced, but it *SHOULD* be replaced if you care about its future lifespan.

[Miyuki]

It did what it should do
It might be fine with the new MOV and Fuse

[SeanB]

Fuse is a solder in fuse, and the other device was a 205V metal oxide varistor, which did it's job and clamped the massive transient to a level that blew the fuse.

https://www.digikey.com/products/en?keywords=V130LA10CP&v=18

fuse is just a regular solder in 3.15A fuse,

https://www.digikey.com/en/products/detail/bel-fuse-inc/RSTA-3-15-AMMO/4968186

Just the first ones that looked like they will fit there, but there are other manufacturers of these 2 parts. Water heater should work afterwards, as they likely saved the rest of the components from damage.

[IanB]

That was a good choice by the designers, to crowbar the fuse and prevent the whole circuit board from blowing up.

[Benji]

Thank you all for your answers, most informative to me !

So here is what I have done :
- Cleaned the board
- Soldered a temporary fuse (just to test)
- Scavenged an MOV from a power supply in my graveyard and soldered it on the board

and here is what happened 

https://youtube.com/shorts/5iArVpoYgoU
(I guessed I goofed with the link but it should become available on YouTube when processed)

Only the MOV blew up so I figured and I'd give it a second try since Ian mentioned that the appliance could probably work without it. The appliance turns on and flashes two leds 4 times which indicates to me that the microcontroller is alive but that a fault is detected. I could not find that fault code even in the service manual and that's where I am at.

[Stray Electron]

  I'm curious about where you are and what kid of local AC system they have in your area and how you managed to plug a 110VAC device into a 220 AC outlet. That's pretty well impossible in any place that I have seen.

[Benji]

I am relocated a lot for work. I have appliances from the US but I live in Egypt. In order to use those appliances, I have a big step-down converter which should handle 2500W.

But, because the converter has also a step-up mode, its front panel has two 110v outlets and one for 220v.

Since we have only two outlets and three appliances around the converter, my maid thought "hey, why don't I plug the water heater in the third outlet instead of playing musical plug?" and boom.

To be honest, it's my fault, I left this thing there knowing that one day someone will make a mistake and even if it took two years to happen, it did. I should just have made it impossible to make the mistake one way or another. Live and learn…

[themadhippy]

That's pretty well impossible in any place that I have seen.

piece of p155
1)remove the plug that dont fit your sockets
2 replace with plug that does or just jam the bare wires in
3)act surprised when things go bang and blame the manufacturers

joking aside think it was telemecanique who had an industrial 3 phase lighting track,were it was possible to put the plug in across 2 phases instead of phase and neutral

[IanB]

But, because the converter has also a step-up mode, its front panel has two 110v outlets and one for 220v.

It's really annoying that these step up/step down transformers tend to put 240 V on NEMA 5-15 (120 V) sockets, rather than using NEMA 6-15 (240 V) sockets for the incompatible voltage. These two socket types are deliberately designed so you cannot put a plug in an incompatible socket.

[fzabkar]

Can you attach the service manual or provide a URL for it?

I was wondering if it ever occurred to any manufacturer to design a heating element in two sections so that they could be wired in series for 220V, and in parallel for 110V?

[tooki]

That's probably what dual-voltage travel hair dryers do.

[TheBay]

Check the SCR isn't faulty.

[Benji]

It's really annoying that these step up/step down transformers tend to put 240 V on NEMA 5-15 (120 V) sockets, rather than using NEMA 6-15 (240 V) sockets for the incompatible voltage. These two socket types are deliberately designed so you cannot put a plug in an incompatible socket.

Even worse than that, the 220v socket is a universal one and the two 110v are NEMA 5-15. This makes sure you can insert anything and connect it to 220v.

Can you attach the service manual or provide a URL for it?

Here is the link : Service manual. Unfortunately, it's one of those website where you can look at the manual online but not download it.

Check the SCR isn't faulty.

Good thinking, I just checked it and the multimeter shows 10M\$\Omega\$ between anode and cathode even when I connect the anode and gate. But when I apply 6v (because it is the value specified in the datasheet) on them it flows up to the current limit of 100mA without connecting the gate. I guess the multimeter applied tension is not high enough and the power supply test means it fried and failed open?

[Benji]

Sooo...

I found a copper trace that looked a bit swollen. It's right under the MOV explosion site. I tested for continuity between what the two pins that were supposed to be connected and it was open. I scraped it and made a good old fashion bridge with a wire and a blob of solder. And... Bingo it works.

I left the SCR as-is and didn't populate the MOV (yet). I don't understand what was wrong with my tests of the SCR. Maybe because I did it in-circuit? Not sure...

[IanB]

That sounds good. For the MOV you will want to look for one that passes negligible current at 120 V but passes a large current at 240 V.

Bear in mind that if you don't replace it and a similar accident happens again there could be a lot more smoke and damage, even a possible risk of fire.

[Benji]

I'll keep that in mind, thanks!