Wrong supply source ! - Page 1
Forum section: electronics / beginners

author: Amtotuna
author_rank: Newbie
timestamp: July 28, 2025, 05:26:48 pm
content: Hello,I've used a wrong voltage on an electrical appliance (220 V instead of 120 V). Result ? A blown componentI don't have the faintest idea about this component, marked ZNR1 on the PCB. It looks like a capacitor, not at all a Zener diode, as the name suggests. Any idea about its value, if capacitor ?I hope only this is damaged, not other components. It seems this capacitor (!) protected the fuseThanks for helping !

author: themadhippy
author_rank: Super Contributor
timestamp: July 28, 2025, 05:29:54 pm
content: Zinc-oxide non liner resistor to give it its sunday name,or mov for us commoners

author: BennoG
author_rank: Frequent Contributor
timestamp: July 28, 2025, 05:43:14 pm
content: the MOV has probably done its work and blown the 15A fuse next to it.The brown squared part is a 15A 250V fuse that should be blown open.Benno

author: mtwieg
author_rank: Frequent Contributor
timestamp: July 28, 2025, 05:44:50 pm
content: It could be a MOV, but from the photos it look like it's in series with the fuse, in which case it is probably an ICL (an NTC thermistor).

author: Amtotuna
author_rank: Newbie
timestamp: July 28, 2025, 05:46:31 pm
content: Thanks for the fast answer ! I don't have the electrical diagram, unfortunately ... I can't find any cross reference to this component. Any help would be greatly appreciated. What should I buy ? It seems the fuse is unaffected, in my opinion.

author: Gyro
author_rank: Super Contributor
timestamp: July 28, 2025, 06:24:32 pm
content: Quote from: mtwieg on July 28, 2025, 05:44:50 pmIt looks the me as if the mains is applied between the tag in the corner and the tag marked ACL (AC line?) before passing through the fuse to the MOV in parallel with the input of the mains filter (the yellow caps and common mode choke and other downstream components. This needs to be confirmed - an underside PCB photo would help.Strange that the fuse should be 15A. I don't know what the appliance is, but that's a lot of current. The one piece of information you do still have is the diameter of the MOV, which will give some idea of the energy rating but not voltage. For a nominal 120V supply rating, I would expect this to be somewhere in excess of 150V.The worry is that, with the MOV blown apart and fuse still intact, other downstream circuitry will have been exposed to full 220V mains voltage (the MOV is designed to absorb mains spikes rather than constant overvoltage).

author: Amtotuna
author_rank: Newbie
timestamp: July 28, 2025, 06:52:46 pm
content: Hi Chris, thanks for the documented answer.I'll buy a varistor for 120 V, no matters which oneThis unit is a part of a coffee roaster 1500 W, had to buy a step-down transformer in the meantime; I'll replace the varistor, with the hope no other downstream components are affected (the yellow one, by ex. - at least for this I know clearly what to buy).I've attached other pictures, scraps included; yes, the power is connected to the 2 aluminum lamellas.Best regards,MariusP.S.: Diameter 14 mm.

author: kloetpatra
author_rank: Regular Contributor
timestamp: July 28, 2025, 07:08:13 pm
content: If only the MOV is broken, the power supply would still work.

author: Amtotuna
author_rank: Newbie
timestamp: July 28, 2025, 07:13:26 pm
content: Thanks, this is my mainly hope

author: kloetpatra
author_rank: Regular Contributor
timestamp: July 28, 2025, 07:18:16 pm
content: I guess you didn't understand correctly. Obviously more components must be broken. The supply would work even without the MOV.You made 5 pictures. And still there is not one picture where we can see all components.

author: Gyro
author_rank: Super Contributor
timestamp: July 28, 2025, 08:12:49 pm
content: The top side of the PCB is badly charred in the area, I think the MOV burned for a while. You will need to scrape it back with a blade or rotary tool until you get down to clean glass fiber (hopefully before you get through the full thickness of the board! At least the tracks are ok). The charring is conductive and poses a fire risk at mains voltage. More work I'm afraid, but it needs doing for safety. The yellow capacitor looks ok though.Regarding the MOV rating, the closest match I can see with decent clamping capability is something like the Bournes GMOV-14D151K, 150V RMS, 420V clamping @ 6kA, 84 Joule, which is 16.5mm diameter. It is probably rated for significantly higher clamping energy than the original. Maybe even enough to blow the fuse but no guarantee. They are very cheap so there is really no reason to go for a lower energy part.P.S. It's difficult to judge how much electronics there is in a coffee roaster these days, maybe fairly rugged power control, but I suspect there is a microcontroller in there somewhere. You might want to cost a European spec coffee roaster against the price of a suitably rugged step down transformer too. It might make better coffee!

author: Amtotuna
author_rank: Newbie
timestamp: July 28, 2025, 08:34:08 pm
content: Thanks, I'll clean it !I have already an European coffee roaster, but a basic one.This is more sophisticated, coming only from USA. I neglected to study the box, it was clearly indicated: 120 V, 60 Hz. At least the frequency is a match)))