The NTM Tech Center continues to improve the PV solar electric equipment we supply to missionaries around the world. Part of this improvement includes incorporating new technology into existing products.
Metal-oxide varistors (MOVs) have long been the mainstay of lightning protection. MOV’s act like very fast acting switches. When the voltage across them exceeds their voltage rating they create a short circuit and reduce/divert the voltage surge away from your equipment. Power surges cause cumulative damage to MOVs. In high lighting areas or where the town power has lots of voltage surges, MOVs should be replaced every 4 years. For a number of years we have wanted to make it easier for missionaries to replace MOVs. Currently the MOVs have to be cut out and new MOVs soldered in their place. This can be a difficult and time consuming process, and many missionaries never replace the MOVs.
When a normal MOV wears out or experiences a power surge it cannot handle, it often fails catastrophically, exploding into bits of molten metal. This can be dangerous if the MOV is placed over a dry grass roof. It is also very difficult to determine if an MOV is still operational.
One MOV manufacture, Littelfuse, has developed an MOV with a built in Thermal Fuse. A thermal fuse blows due to excess temperature, not excess current. This prevents the MOV from exploding. In addition, the MOV has a third lead which allows monitoring circuitry to indicate if the MOV is still functioning. An LED is lit when the MOV is functional and does not light when the MOV needs replacement.
Because of these advantages the NTM Tech Center has begun incorporating these MOV’s in many of our surge suppression products. Many of the new surge suppression products we manufacture will also include an Easy Change terminal block to quickly and easily allow the replacement of MOVs. Since these three legged MOVs are polarity sensitive, one side of them has been painted to match a painted mark on the MOV terminal block. The color of the paint is also an indication of the voltage rating of the MOV.
Due to the expense and installation difficulty, we are not recommending that missionaries retrofit older equipment with the newer three legged MOVs at this time. However many of the products that the NTM Tech Center produces will include this new three leaded MOV with LED indication and Easy Change terminals.
The NTM Tech Center has had questions from missionaries regarding MidNight Solar’s “Midnite Surge Protector”. This is a good single stage surge suppressor design incorporating large MOV’s. It also includes LED indicators. It is far superior to many other older surge suppressors that are nothing more than wires spaced in epoxy. However, our surge suppressors include two or three additional stages of surge suppression namely: EMI filter, Second layer of MOVs and Gas Discharge Tube. These additional layers of surge suppression help to reduce the voltage surge your solar equipment experiences.
These limitations and the higher cost of the “Midnite Surge Protector” is why we don’t use it in the products manufactured by the NTM Tech Center. If you are retrofitting an existing solar electric system that does not have sufficient surge suppression you should definitely consider adding surge suppression. It is wise to have surge protection for your expensive equipment, especially if you are serving on a remote mission field.
One missionary who did not install surge suppression lost several thousand dollars worth of equipment after only four days of use due to inadequate surge protection. He had to wait months for replacement parts to arrive.
Recently in Mexico, a missionary did install three stage surge suppression. When lightning struck a power pole, a large power surge was absorbed by the MOV’s. His inverter and charge controller continued to operate without damage.