Burnt electrical “item” in power board – need help knowing what is it called

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#1 21669821 18 Sep 2013 07:54

Ahmed Ramahi Ahmed Ramahi

Anonymous

Post #1
21669821 18 Sep 2013 07:54

I got a 120v coffee maker back with me from US to where I currently live where they use 220v.
I got with me a 1600w step-down transformer from Radio Shack (the machine is 900w) but it seems that it was faulty because when connected to power, the coffee maker "popped" and smelled like burning plastic.

I decided to give it a shot and see if i can fix it. I reached to the point of locating the problem which is a burnt blue rounded electronic item (sorry I'm a Network Engineer not electrical, so i know only what capacitors, diodes & resistors are lol).

Anyway can you have a look at it and tell me what is its name so i check in the market and replace it if it is replaceable. What's your advise?
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#2 21669822 18 Sep 2013 08:33

DAVID CUTHBERT DAVID CUTHBERT

Anonymous

Post #2
21669822 18 Sep 2013 08:33

If I'm not mistaken the device you have is not a Transformer, it is Voltage Converter. It is designed for use with resistive heating elements only and can damage devices having electronics, such as your coffee maker.

The visibly damaged device appears to be an MOV (Metal Oxide Varistor) used to clamp voltage spikes. The Voltage Converter probably applied voltage high enough for the MOV to conduct and it burned up.

If you have access to 120 VAC you can remove the MOV and check to see if the circuit works correctly. If it does work correctly the MOV can be replaced with one rated for 120 VAC or it can be left out of the circuit at the risk of the circuit being damaged by a voltage transient.
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#3 21669823 18 Sep 2013 09:05

Ahmed Ramahi Ahmed Ramahi

Anonymous

Post #3
21669823 18 Sep 2013 09:05

So you are basically saying i need to test the circuit first with 120VAC to see if it wasn't damaged?

The label writing on the MOV is gone as you can see, so if i want to replace it, do MOVs come in specific shape/color/size for each model? Because I want to buy it online (I couldn't find a decent electrical shop in here), but i'm looking around the net and I noticed that they are different in shape, size and color, similar to the fuses used in car fuse box. I need an expert's advice before purchasing anything that is useless for me.

And you're right, it is a voltage converter
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#4 21669824 18 Sep 2013 10:59

DAVID CUTHBERT DAVID CUTHBERT

Anonymous

Post #4
21669824 18 Sep 2013 10:59

Well, you will need a source of 120 VAC not only to test the coffee maker but to run it everyday.

To find a suitable MOV find one that is has a rating of 130 VAC and is about the same physical size.

The MOV was in the circuit to enable it to pass the UL line-to-neutral transient test. This test is an RC network that discharges 0.3 uF charged to 800 volts.
#5 21669825 19 Sep 2013 06:05

DAVID CUTHBERT DAVID CUTHBERT

Anonymous

Post #5
21669825 19 Sep 2013 06:05

This link to Digikey is for a suitable MOV.

http://www.digikey.com/product-detail/en/MOV-10D201KTR/MOV-10D201KTRCT-ND/2408231

Here is the datasheet.

http://www.bourns.com/data/global/pdfs/MOV10D.pdf

120 VAC is needed to operate your coffee maker and a transformer is the device to use. The travel converter, I believe, chops the 240 VAC waveform so the RMS voltage is 120 VAC yet the peak voltage is still the peak of 240 VAC (340V peak). This works for resistive heating elements such as the heater in your coffee maker but does not provide the electronic control board with the 120 VAC (170 V peak) it needs.
#6 21669826 19 Sep 2013 09:02

Ahmed Ramahi Ahmed Ramahi

Anonymous

Post #6
21669826 19 Sep 2013 09:02

I don't know how to thank you enough for the information and the time you took to explain what's going on. Really thanks a million.

I have purchased 5 MOVs (keep 4 for spare lol) and i will go back to use the huge box transformer I bought from ACE Hardware when we first got the coffee maker. Thinking that Radio Shack voltage converter would save me space on my kitchen top instead of the transformer box proved to be a wrong idea! But the most important thing is now I know why; thanks to you! Will let you know how things go once i receive the parts, that's the least i owe you.

It's true when they say: If it ain't broken, leave it alone!
#7 21669827 06 Oct 2013 01:45

Ahmed Ramahi Ahmed Ramahi

Anonymous

Post #7
21669827 06 Oct 2013 01:45

Hello David,

Just want to tell you that the coffee maker is kicking alive again! Thanks a lot for all the help I really appreciate it.
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#8 21669828 06 Oct 2013 08:07

DAVID CUTHBERT DAVID CUTHBERT

Anonymous

Post #8
21669828 06 Oct 2013 08:07

Ahmed, that's great that you can drink coffee again! I'm having a cup right now.
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Topic summary

A 120V coffee maker rated at 900W was used with a 1600W step-down voltage converter from Radio Shack in a 220V region, resulting in a burnt blue rounded component inside the converter. The damaged component was identified as an MOV (Metal Oxide Varistor), which protects against voltage spikes but failed due to the converter's waveform characteristics. The voltage converter is suitable only for resistive heating elements and not for electronic devices like the coffee maker, which requires a true transformer providing a stable 120VAC supply. The MOV can be replaced with one rated for approximately 130VAC and similar physical size to restore transient voltage protection. Testing and operation require a proper 120VAC source. A recommended replacement MOV model is the MOV-10D201KTR, available from Digikey, with datasheet specifications provided by Bourns. The original voltage converter likely produced a chopped waveform with a peak voltage of 340V, unsuitable for the coffee maker's electronic control board. The user successfully replaced the MOV and reverted to a large transformer from ACE Hardware, restoring the coffee maker's functionality.
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Burnt electrical “item” in power board – need help knowing what is it called

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Topic summary