Ans. One made of some non-magnetic material such as copper, brass, or zinc.

If iron cans be used, they are liable to be attracted by the field magnets, and thus possibly catch in the armature.

Ques. What is the indication of insufficient lubrication?

Ans. The bearings become unduly heated.

Ques. What precaution should be taken with new dynamos?

Ans. They are liable to heat abnormally and for the first few days they should be carefully watched and liberally supplied with oil.

After a dynamo has been running for a short time under full load, its armature imparts a certain amount of heat to the bearings, a little more also to the bearing on the commutator end of shaft; beyond this there is no excuse for excessive heating. The latter may result from various causes, some of which are given with their remedies, as follows:

  1. A poor quality of oil, dirty or gritty matter in the oil;
  2. Journal boxes too tight;
  3. Rough journals, badly scraped boxes;
  4. Belt too tight;
  5. Bearings out of line;
  6. Overloaded dynamo;
  7. Bent armature shaft.

  1. A poor quality of oil, dirty or gritty matter in the oil;
  2. Journal boxes too tight;
  3. Rough journals, badly scraped boxes;
  4. Belt too tight;
  5. Bearings out of line;
  6. Overloaded dynamo;
  7. Bent armature shaft.

Ques. What is the allowable degree of heating?

Ans. It may be taken as a safe rule that no part of a working dynamo should have a temperature of more than 80° Fahr. above that of the surrounding air.