If you have ever tried to measure the winding resistance of a transformer or a motor by using a micro-ohmmter, then you are probably aware that it won't work. You have to have a special ohmmeter call a winding resistance meter. (Some old folks might call it a bridge because of the salt bridges once used to make winding resistance measurements). Good news! Sonel makes the only micro-ohmmter / winding resistnace meter combo! and its priced less than most micro-ohmmters! Check out the MMR650.
Measuring resistance of a breaker contact is as simple as passing a known current through the breaker and measuring the voltage drop. Any micro-ohmmeter can do this whether its 10A, 100A or 200A output. However, even the best micro-ohmmeters are useless when measuring transformer and motor winding resistance. This is because inductive objects make it difficult to get stable test current through the winding. For the measurement to stabilize, the core of the inductor must magnetize completely before the test current stabilizes and the measurement can be made accurately. For this reason, winding resistance test sets are equipped with more powerful outputs compared to a micro-ohmmeter. For example, a ductor (micro-ohmmeter) may have an output up 200A , 6V (1200W max) whereas a winding resistance meter may have an output of 60A, 60V (3600W max) so it can provide enough power to charge the core of the transformer. If you are in the market for a 200A micro-ohmmeter, you can expect to spend $5K-7K. Then for a winding resistance meter you're looking at $15-20K for a good one with a DEMAG function. Or for a three-phase winding resistance tester its about $25K. Its all very expensive. But it doesn't have to be. Some gurus have finally figured out how to combine the micro-ohmmeter and the winding resistance meter into one test set for under $7K. It even has the Auto DEMAG built in. Its made by Sonel and distributed through Nemec Industries. Please contact Louis Nemec to set up your free demo of this versatile ohmmer. You can test breakers, bolted connections, transformers, and motors with Sonel MMR650.
Louis Nemec (770) 331-1393 Louis@nemecindustries.com