IT'S ALL ON THE AIR

NZ Truth, Issue 1126, 30 June 1927, Page 2

IT'S ALL ON THE AIR

"B " BATTERY CHARGERS

Testing and Working The Rectifier

For Results

(By "Crystal.")

We described m these colums last week an electrolytic rectifier for charging "B" batteries at home.

BE3FORE ti-yin_r out' the rectifier on the battery.it should be tested m a suitable manner .to ensure that it is functioning correctly.Assuming that the instrument •as described last week has been made up. correctly, '; all that remains to be done is to -wire up to the house mains. .When the instrument is first put into action a 60 watt lamp or a : smaller one should be placed m the . lamp socket, the wires for the rectifier current should be left unconnected. ''■'.'■:.. ■"'.:■ The 230 V A.C. current should then be turned on, the 60 watt lamp will at llrst probably glow; with its usual full brightness, ! but ' should then, slowly go dimmer until it is oniy just glowing; this may take; spnie minutes. The aluminium : rods will then be noticed to "present a beautiful appearance when; they are ifnmersed m the phosphate solutiphi" as they scintillate with '.'".' innumerable , tiny,^,, twinkling sparks. '.. ' • '-.-.. Should this effect ; not be obtained When first .starting up, try temporarily raising the' aluminium rods until they j_re only, just immersed m the phosphate'solution;' This will; start it off and the rods may then be slowly lowered ..-into their original and proper positions. They are . no\yA "conditioned" and ready for use.' : ; To charge 'the accumulator, connect the wire from the two lead plates of the rectifier which 'tire'- joined .together, to ; tiie negative terriiinal of the battery, and the wire from the joined alUniiniiim rods to the positive terminal; '.'■",:.' Thelamp m the rectifier will now light; up again, arid the scintillations.- on tho aluminium rods will -'-ceasei A'".A' '-•:•■";' ■ This is correct and^ as! it 'should oe; it. is desirable, and is recommended to

include an ammeter or milliam meter m the rectifier circuit. The size of the lamp controls the current produced. .-, By constructing a smoothing unit consisting of .two iron core chokes having an inductance of approximately 8 hendies ' (two small ignition ctfils .wil} serve the purpose), and a four microfarad condenser .the following arrangement may ,be used which dispenses with the ''.—" .', -battery altogether. ■.-, It is only suitable where critical adjustment of the'"B" voltage is not required. '' A The "choke" coils should be inserted m series -vyith the positive and negative leads from the output, of the. rectifier 'and', the "B" terminals of-, the receiver, the four microfarad condenser being shunted across the two leads immediately after the chokes. 'This arrangement is' hot really suitable for everj'day use.' , , A more useful arrangement for average reception, work «an be done with the A.C. switched on and the battery floating. This should be done by connecting the positive- terminal of the rectifier to the positive of the "B" battery and then the. lead extended to the correct terminals on the receiver, the negative lead being connected m a similar manner to its correct .'terminals. ■.■■'.-'' The deteptoi" can be tapped as usual from the battery. "With this arrangement a slight A.C. ■hum. is" ■noticeable, but it is not sufficient to interfere with any but -very weak signals. '■"*■'..- ' ■ '■ A In any case it is far better toAiave this than to have to hold up reception While the battery is being- charged. • ' ■ In the case of the rectifier described, ,the running costs are very low. .The current passed by a 60 watt lamp (230 V 50-cycle A;c.) rectifier and V"B" battery when charging, is: one; unit m 27 hours. At 6d. per unit this ;is 4% hours for a penny.- •:;,;:■ . The above rate of charging gives about .07 ampere through the .battery.'.; -':.' v A -A" Too much care cannot be- taken to ensure that the surface of the aluminium, is absolutely . , clean before' placing it m the. cell. A "