THE ALUMINUM ELECTROLYTIC CONDENSER 49 



These determinations were made with a voltmeter, ammeter and 

 wattmeter at 60 cycles, and were in conformity with measurements 

 over a range of frequencies made on an impedance bridge. In the 

 cases of measurements made with unidirectional potential applied, 

 suitable bias was provided by superimposing the alternating current 

 by means of a transformer in a battery circuit, the d.c. potential of 

 which could be varied by changing the number of cells in series. 



The apparatus for these measurements is shown in Fig. 5. It 

 will be noted that a high-capacity blocking condenser is required 

 in the a.c. voltmeter circuit, but is omitted from the potential circuit 

 of the wattmeter. This condenser is inserted to block the unidirec- 

 tional potential, which otherwise would be read by the voltmeter, 

 but the power that the wattmeter indicates due to this potential is 

 of no importance, and except for direct-current leakage would actually 

 be zero. 



Losses in Aluminum Cells and their Effect on 

 Electrical Impedance 



In the matter of electrical impedance characteristics, the electrolytic 

 condenser does not approach a perfect capacitance as nearly as the 

 more familiar forms of static condensers. Three sources of energy 

 loss in the electrolytic condenser impart to it an equivalent series 

 resistance, as a result of which the condenser current leads the im- 

 pressed voltage by a phase angle somewhat less than 90°. 



The first of these losses is the dielectric hysteresis loss, which, 

 as in the case of the paper condenser, is approximately proportional 

 to the frequency. The second loss is due to the resistance of the 

 electrolyte and, in the case of aluminum condensers, may be of 

 appreciable magnitude because of the low electrical conductivity of 

 suitable electrolytes. This electrolyte resistance remains practically 

 constant over a wide range of frequencies. 



The third possible loss is due to the leakage-resistance of the film, 

 which in its effect is similar to a high resistance in parallel with the 

 condenser. Ordinarily this loss is negligible because the leakage 

 current is less than a microampere per sq. cm. of film surface. 



Conditions Affecting the Life of Condensers 



To be successful from a commercial point of view an electrolytic 

 condenser must have long life and must not require frequent attention. 

 Otherwise the advantage in the matter of mounting space and the 

 cost per unit capacity is ofTset by the depreciation and maintenance 

 costs involved. There are two common conditions affecting the life 

 4 



