Chuck Yung
EASA Technical Support Specialist
One of the more common sources of exasperation for a winder is rewinding a motor that has odd turns. How would you like to find a better way to deal with odd turns? Here are some tips to make life easier for the winder:
Odd turn coils are not a problem when the span is even (1-14 or 1-12), because each slot contains the same total number of turns:
When the motor has an odd span (like 1-15) even the best winder can get frustrated. Every other slot is tight, increasing coil insertion time:
Some winders are even tempted to reduce the total circular mils in order to make it easier to insert the coils. This increases the winding temperature, and may reduce insulation life. It can also reduce motor efficiency.
Make Life Easier!
There are a couple of simple ways around this, without resorting to a redesign which might change the motor’s characteristics. Let’s use the above 1-15 span, with 6 groups of 8, and odd turns of 3 and 4 as an example. If the number of coils per group are even, it is easiest to loop the coils 3-3-4-4-3-3-4-4. Each slot now contains the same number of total turns. No more cursing every other slot:
Still another trick is to make the cross-over on the opposite end from the leads. This way, every coil really does have 3.5 turns. This method is easier when a motor has odd grouping, but keeping the cross-overs straight can be awkward.
Taking Data
The time to identify odd-turn motors is when taking data. Rewinding a motor with the wrong turn count leads to poor motor performance and premature failure. It is especially important to count turns/coil for a full group. Some windings have odd turns such as 6-5-5-5-6. By counting only 2 adjacent coils, as is customary in many shops, it is easy to miss this arrangement.
Don’t overlook the fact that parallel circuits must each contain the same number of turns.
Try one of the above methods the next time you have a motor with odd turns and an odd coil span. Your winders will thank you, and time values will improve.
ANSI/EASA AR100
More information on this topic can be found in ANSI/EASA AR100
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