What is the easiest way to test a resolver?

[fastfixer]

Folks,
What is the easiest way to test a resolver? I'm looking for a simple test that can be performed to determine if a resolver is bad without getting overly technical. Any help would be appreciated. thanks!

[Cheller]

So if you're looking for the easiest way to test a resolver, I have some relatively simple suggestions, however no one line answer to the question.

First of all, the basic definition of resolver: It is an analog electrical device that is coupled to a motor. It can be physically connected externally or internally depending on the motor design. From an electrical standpoint, it is a type of rotary transformer used for measuring degrees of rotation on the motor to which it is coupled.  The most common type of resolver in industry today is the brush-less resolver.

In any event, there is actually an industry standard for the color of resolver wiring. Many, if not most manufacturers follow this standard. There are three coils in a resolver for a total of 6 wires. An excitation coil, a sine coil and a cosine coil.

Typically, red/white(+) and black/white(-) are the excitation coil. Yellow(+) and blue(-) are the sine coil, and red(+) and black(-) are the cosine coil. There are manufacturers that will use yellow/white instead of the black/white of the excitation coil. If you encounter an alternate color scheme, you may have to use an ohmmeter to determine the three coils to be sure.

As for the internal wiring of a motor resolver, it contains three individual coils. The easiest way to test a resolver is using an ohmmeter to check these coils for resistance. These can be tested with either an analog ohmmeter or a digital VOM. You should see identical resistance on the sine and cosine coils, and the excitation coil will be different.

Here is an easy test using a multimeter. Configure your meter to measure ohms for this test. This is a static test performed with the power off, of course. Check the coils individually for ohms. If any of these three coils show infinity on your ohmmeter, your resolver will need replacement. If all three coils show different resistance readings, then your resolver probably has a damaged winding and will need to be replaced or rebuilt.

In some cases, broken wiring on the connector or internal circuit board could be you only problem. A visual inspection is the key here. Get out your magnifying glass if necessary.

There are instances where external motor resolvers can also be interchanged with known working parts as a process of elimination test. Swapping identical resolvers can help identify a resolver as a failed component. It's important to remember that some resolvers may need to be zeroed, or indexed, according to the motor manufacturer's recommendations. This is accomplished using procedures an/or software provided by the manufacturer. This will depend on the application.

If you have an obsolete resolver and you're convinced you need a replacement, Check eBay for availability.

If anyone can add to these suggestions, or if you have some other resolver testing methods, that would be great...

[benklassne]

Nice job with the resolver testing. These are black boxes to a lot of people who just swap parts.