Introduction: Household Surge Protection
The photo shows a lowly metal oxide varistor, or MOV. These cost less than a dollar and are the main component of a surge protector. They are effective, even though a high quality surge protector also includes other things, like coils of wire known as inductances or chokes. Back about 30 years our church lost some telephone equipment due to surges from nearby lightning strikes. I added an MOV between the green telephone wire and ground, and another between the red telephone wire and ground. We had more lightning strikes in the area, but never lost telephone equipment after I installed the MOVs.
An MOV normally does not conduct (presents an open circuit). In the presence of a voltage spike that could damage electronics, it suddenly conducts and shunts the spike safely to ground. An MOV does not last forever, but can become spent, like a match that has been struck, after a really heavy spike. If you know you had a strong lightning strike and neighbors lost electronic equipment, it might be good to replace MOVs you are using for surge protection.
Once MOVs were available in stores like Radio Shack. I bought this one on-line from an electronics parts supplier.
Step 1: What Do You Want to Protect?
The photo shows the MIG welder I won in a metalworking contest at Instructables four years ago. It has an electronic circuit board inside it, like many other modern devices do. Its warranty began the day the welder was made, even though it sat in a warehouse for a number of months before I came to have it. Now that it is out of warranty, I want to install surge protection. I could add the surge protection to the electrical wiring in my workshop, I want to add it to the welder in case I take the welder to a job site away from my workshop.
Step 2: A Suitable Location
I want to install my MOV as near the entrance of the power cable into the machine as possible. The blue connector in my hand is from the power cable and connects to a circuit breaker that protects the welder from current overloads. The white wire carries power to the electronic circuit board. I am mounting one wire from an MOV as close to the body of the circuit breaker as possible so the blue connector attaches as securely as if the MOV were not there. I soldered the lead from the MOV to the metal spade, but avoided using excess solder.
Step 3: A Connection to Ground
The ground connection for the green wire in the welder power cable bolts to the metal frame of the welder. That is a good place for me to attach the other leg of the MOV. I am using a large closed crimp connector on some monster speaker cable.
The white wire from a 120 volt power cable and the green ground wire connect to the same strip in the circuit breaker panel and both are grounded. If your power cable does not have a third green wire, use a connection to the white wire to ground the MOV. I did that once with a Sangean solid state shortwave radio.
The grounding bolt is common 1/4 inch x 20 thread. I added a nut to secure the connection. I decided not to disturb the factory connection by using its nut.
The second photo shows the lead from the MOV wrapped around the end of the monster cable and ready to solder.
The third photo shows the finished solder connections. The spade connector from the power cord fits nicely where it belongs, even though it shares the connection with an MOV.
The MOV and the wire to the grounding connection are neatly out of the way. Nothing is in danger of shorting to anything. It is time to put the welder case back together.
You may not need to protect the circuit board in a MIG welder, but your stove or refrigerator or washing machine or microwave oven likely has an electronic circuit board vulnerable if lightning comes near. Those circuit boards can be expensive to replace, and as time passes they are sometimes difficult to find. What I did by adding an MOV to a welder is a sort of paradigm for what is possible for unrelated equipment you have. The more MOVs as surge protectors on your system, the better your whole house is protected. MOVs act together like a team. See the fourth photo. When it is not feasible to open a device and install an MOV inside it an MOV can be mounted in a male wall plug. The plug can be located in an unused outlet very near the device to be protected. This is an inexpensive male plug. I used a burr bit on a Dremel tool to make a slot that fits the MOV.
Step 4: Flat Screen TVs
Our 12-year old granddaughter is doing her schooling on-line from our house this year. I showed her an electronics experimenter‘s kit and she got excited about a couple of projects. A few days later she had managed to drag home someone’s 70 inch LED TV that went completely dead after a nearby lightning strike. (It is not the one in the photo.)
See the second photo. This is the power board from that defunct 70 inch TV. The green disc is marked on the circuit board as a resistor. Next to the green disc to the right is a honey colored MOV. Next to it on the right is a fuse. It is good to know this brand (VIZIO with parts made by Sharp) includes not only a fuse, but also an MOV for surge protection. An Ohmmeter should show no circuit through the MOV, but a circuit pathway through the fuse. But, lightning strikes do not always enter a TV through the power board. In the end, it appears the lightning strike near this TV sent a surge in through auxiliary components, like a DVR or an HDMI connection, Things connected to a TV also need surge protection.
Step 5: Undoing the Damage
There are numerous videos on the Internet for troubleshooting and restoring a flat screen TV. If you watch one such video you think it will be easy. Watch a few more videos and you begin to realize it could be more complex than you expected. The testing procedure is mostly a matter of checking for correct output voltages at various pins. There is supposed to be a table of voltages expected at particular pins imprinted on the power board. This VIZIO TV did not have that table. In the end, I strongly suspected the main board was faulty, not the power board and not the T-conn board. Auxiliary equipment connects to the main board. If a surge from lightning entered through an HDMI cable, and the main board likely failed, the MOV and the fuse on the power board would still be good. I found a set of the three primary boards for $112 US (delivered) at ShopJimmy (dot) com. (I have no connection to them other than satisfied customer.) After installing the three primary boards, the TV worked like new. I had my granddaughter do the work to give her a sense of fulfillment and confidence. All we needed to do was mount boards with screws and connect ribbon connectors. ShopJimmy will answer your questions and help you get your TV working again.
Step 6: Surge Protection for Auxiliary Components
These two photos show the main board (front and back sides) from the TV my granddaughter brought home. A surge that gets into an auxiliary component can enter an otherwise protected TV through the signal inputs to the TV’s main board. You might be able to attach MOVs to solder points on the backside of the main board, but space is very limited and it could be very tricky to do. If you want to add surge protection to a coaxial cable, it might be easier to buy a surge protection power strip with coaxial connectors attached. Those are widely available. Do add surge protection to auxiliary devices like VCRs and DVRs or DVD players.
Surges are not all caused by lightning. A few years ago I lost the keyboard on my PC when someone hit a power pole in a traffic accident and it caused a surge.
MOVs are not perfect surge protectors, but are a big help in limiting damage to your devices from surges, whether caused by lightning or some other cause. They are inexpensive and not difficult to add to your system. Just be careful not to cause any shock hazards.
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