IS MY “E” BATTERY DONE?

Manawatu Times, Volume XLIX, Issue 3479, 15 October 1926, Page 9

IS MY “E” BATTERY DONE?

The broadcast listener often' asks the above question. How often has a now battery been purchased, only to find that it was not really necessary? Probably the fault lay elsewhere? However, by following the remarks herewith, you should in the future be able to assist yourself in this matter. In the first place, a small pocket typo vol-meter reading from zero to 50 volts, is now easily .procurable from any radio dealer at a reasonable price, and is worth the investment.

The usual mistake made in testing "B” batteries, and often "A” batteries, is to take the voltage test when the set is not operating, perhaps even after the batteries have been lying idle for several hours. This is useless as due to the recuperative powers of the chemical ingredients of the battery colls, the voltage has- “picked up,” unless, of course, they have been in use so long that the powers of recuperation have become weak. To secure the most satisfactory test, tho set should bo allowed to remain in operation for fully half-an-hour,. and then the readings taken by means of tho voltmeter. By doing this tho recuperative powers have been allowed for and the test will bo an “operating” one. Under such circumstances new batteries are recommended when the readings arc as under: — 225 volts read 18 volts or less. 45 volts read 38 volts or less. 90 volts read 78 volts or less. Many may bo surprised at the rapidity with which a comparative-, ly new battery, say, of 45 volts, will drop to 40 volts under the above test. However, such is quite a common occurrence. It, may do so even in (he first week or fortnight, but after that it is again surprising the length of time which will elapse, unless the battery is faulty, before it drops to tho critical 38 volts. No very definite idea can bo given as to what the life of a “B” battery should bn with a given set. Much will, of course, depend on the battery itself, but usually tho prime factors arc;—• (a) Number and type of valves. (b) Average nightly operation. (c) Grid-biasing used. (d) Efficiency of operator.

To enable the enthusiast to work out this little problem himself, the rough data herewith may bo useful. Milllampcres Per Valve. No With Grid-bias. Grid-bias. Type. -06 JAmp .06 JAmp Detector .. .2 .3 Amplifier 45v 1. 1. -4 Amplifier 90v 3.6 3.75 1.17 1.6 Tho approximate life of the usual size "B” batteries is roughly:— Hours. Current consumption 2 milllamperes 1800 •Current consumption 5 milliamperes 1000 Current consumption 8 milliamperes 500 Working on these rough tables an average 5-valve set say. using Jamp type of valve, would be: 2 R.F. valves taking 7.5 1 Detector v. taking .3 2 Audio valves taking 3.2 with bias Total H.O m.a. Thus, the usual 45-volt. “B” batteries would have an approximate life of 400 hours, or, at tour hours per night, 100 days, equivalent to ! about throe months. Due to tho | fact that this is a fairly high estii mate, and also allowing for the recuperative power of tho cell ingredients, tho life will bo in actual practice nearer five to six months. For other sets, the listener can quite easily work out the problem according to the number and type of valves used.