I found some varistors at the best electronic component store in the area. They had a wide variety of voltages. One was 120v (part number CNR-07D121K). We have 110v AC (measured) here. On the outside of the plastic bag with five parts was a store printed label that included "120v1ma +- 10%". If that 10% applies to the max voltage, then that may explain the failure of my varistor. 120v * .9 = 108v. Perhaps it was working just fine, but it was at the low end of the tolerance range. The next voltage up on the supplier's shelf was 150v. The more I learn about these things, the less I think I know. A datasheet I found was 24 pages long!

Replacing them with better parts is definitely a good idea. Unfortunately, I'm limited in what I can buy locally. I have to order them from another continent if my local electronics store doesn't have them. I may just cut them off the PCB and replace them at a future date.

Has anyone else seen a varistor/MOV failure in a power supply?

I recently had a 120v varistor fail on a HLK-PM01 breakout board (thanks @sundberg84 !). The varistor now shows a resistance of 262 ohms. The low resistance took out the 200ma AC input fuse (as expected).

The odd thing is I have six nodes powered by HLK-PM01 breakout boards and each board has exactly the same varistor. Only one has failed, so I doubt if it was an AC power problem. We haven't had any lightning strikes and the APC power supply on my PC didn't record any power problems. All of these nodes have run for several months without problems.

Has anyone else had a varistor fail like this?

I'm really nervous about this because in one month I'm going to be away from the location where these nodes are installed for about six months. The nodes control heat pump systems which will control the humidity while I'm away and the home is closed up. I'm considering just removing the varistors rather than risk a bad varistor taking a node off line.

These are the varistors that I bought on Aliexpress: https://goo.gl/2qhnaR

Below are photos showing the varistor and its markings.

This looks like a great PCB and I'm interested in ordering a few from DirtyPCBs, however OpenHardware.io shows this project as "Work in Progress". Are there any plans to do additional updates to this PCB?

Is it reasonable to hand solder the SMD components on a board like this?

@nca78 said in Combining orders at OpenHardware.io?:

Just make a paypal donation of the PCB price difference to MySensors for that. Maker of PCB will lose their share but it's pretty small and it ends up given as donation to MySensors most of the time.

Excellent idea!

@hek,

Thanks for the info, that is what I suspected. It occurred to me that I could download the files for each PCB that I want to order, then upload the files to the PCB manufacturer and skip ordering from OpenHardware.io. However, I've never ordered PCBs by uploading files, so I'm concerned that I might make a mistake and end up with a bunch of unusable boards. Also, I have no desire to cut the owner of OpenHardware.io out of any well deserved revenue from that website.

Is there some way to combine multiple orders from the same PCB vendor at OpenHardware.io to save on shipping costs?

(Background)
I recently ordered two different PCBs (10 each) from PCBWay (the cheapest vendor including shipping) at OpenHardware.io. The shipping for each set of boards was $11 USD to my location. I was surprised to have both orders arrive in the same box. It seems to me that one of the shipping fees wasn't necessary but it was impossible to avoid since each set of boards had to be processed as a separate order. If the shipping was just a few dollars this wouldn't be a big deal, but paying $22 to ship $30 of PCBs feels a little excessive when it should have really been $11. Perhaps I just missing something.

By the way, I'm very happy with the two PCBs that I ordered. They even included an extra board (11 total) for each of the PCBs. PCBWay did a nice job of packing the boards for shipment.

I just have a general question about ordering PCBs on OpenHardware.io. Where should I ask my question?

I don't see a "New Topic" button at the top of the OpenHardware.io discussion. How do I post to this discussion?