626
��Popular Science ^Monthly
���ductor for the magnetic lines of force, the air-gap can be very short, thus el^ect- ing a large saving in the magnetizing current. At the same time, unipolar dynamos can be very much overloaded without danger of burning the insula- tion, as the magnetizing coil, the only piece that need be insulated, can be wound with asbestos-covered wire. Con- sequently, the temperature can rise as high as necessary to carry a big over- load for a long time, this overload being limited only by the capacity o f the prime-mover, in the case of a shunt-wound gen- erator. This is a great advantage over multipolar d y n a m o s, as in these, cotton-and- shellac insulation is so profusely used, that a com- paratively slight overheating i s sure to injure the windings.
The table on page 625 furnishes some idea of the relations of size, voltage and output of the most efficient types of uni- polar dynamos.
The only serious drawback of the uni- polar dynamo is the low voltage that it supplies, but on account of the simplicity of the c o n- struction, sev- eral machines c a n be con- nected in se- ries, or a ma- chine with several disks can be used, and then the voltage deliv- ered is large. The uni-
��Fig. 4. Unipolar dynamo with two disks revolved in op- posite directions
���Fig. 5. Unipolar dynamo
with two disks revolving
in the same direction in
opposite magnetic fields
��polar turbo-generator presents, as a whole, the most compact and efficient equipment known. The turbine is econ- omical, and the unipolar requires no gears to be coupled to the turbine, and so receives the whole turbine power.
��An. Electric Soldering Iron
AN electric flatiron may be used in making an electric soldering copper by removing the coil and fit- ting over it a piece of brass tubing, 1" by 5. Cut a slot in one end to receive the plug contacts, and into the same end fit a handle in a bushing; into the other end fit a bushing holding a copper point. The plug from the flatiron may also be used, and can be quickly separated from the soldering tool — S. Bernstein.
���A COPPER POIMT i'oiA E BPASS BUSH.U'DIA fiTHICK
B BRASS BUSH ^'DiA 3ZTHICK r IRON HOD i'DIA
C CO/L FROM OLD FLAT IRON G HANDLE
D A' BRASS TUBING I VIA
\ The coil from an old electric flatiron is used in making the heating element of this elec- tric soldering iron
Storage Battery Hints
SINCE the introduction of the electric starting and lighting for automo- biles, hundreds of thousands of people have becomiC acquainted with storage batteries, while the expansion of the field of electric passenger automobiles and trucks has brought thousands of storage batteries to garages for charging and overhauling. Charging a storage battery is not the simple thing it may seem, and much damage is done to batteries by careless handling. A few simple instru- ments, designed to remove all guesswork from charging, have just been brought out by a Philadelphia concern. They are as follows:
A rubber bulb-syringe for filling and equalizing the acid in the batteries.
A pocket thermometer, graduated from 20 to 220 degrees Fahr., especially de- signed for use in batteries while charg- ing. The temperature of a storage bat- tery should never be permitted to rise too high.
A hydrometer syringe, containing a hydrometer graduated especially for such work. The sharp point of the syringe is inserted in the storage cell opening, and the central portion of the syringe filled with the liquid. The hydrometer inside the glass cylinder will indicate the state of the battery: 1300 stands for fullv charged; 1275 for 75%; 1250 for 50%: 1225 for 25% and 1200 for exhausted.
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