LEAD ACID BAT­TERY EV­ERY­THING YOU NEED TO KNOW

You’d soon get cranky with­out one, says Fuzz

Classic Car Weekly (UK) - - Living with Classics - FUZZ TOWN­SHEND CCW’S MASTER ME­CHANIC

The hum­ble car bat­tery is of­ten over­looked and reg­u­larly ne­glected, un­til it’s too late. Only then are its virtues ap­pre­ci­ated. In the ear­lier days of the mo­tor car, the bat­tery’s du­ties were rel­a­tively hum­ble, pro­vid­ing a reser­voir of elec­tri­cal power for ba­sic light­ing equip­ment and the ig­ni­tion cir­cuit al­though, in the lat­ter case, the mag­neto pro­vided self-con­tained spark gen­er­a­tion. Start­ing power was down to the deft swing of a crank­ing han­dle, so the bat­tery had a rel­a­tively easy life.

How­ever, the mo­tor in­dus­try quickly be­gan to add such trin­kets as elec­tric start fa­cil­i­ties, more pow­er­ful light­ing and heaters with elec­tri­cally pow­ered fan mo­tors. All of these re­quired some form of sta­ble elec­tri­cal sup­ply and so the bat­tery be­came in­creas­ingly im­por­tant.

Lead-acid bat­ter­ies had been in ex­is­tence for quite some time, with rea­son­able speed of charge­abil­ity, rel­a­tively long life and sta­bil­ity chief among their ad­van­tages. The dy­namo was tasked with the job of keep­ing the bat­tery charged, so as long as the car was bowl­ing along at a de­cent lick with­out too many of the elec­tri­cal trin­kets be­ing em­ployed at the same time, bat­tery charge could be main­tained at a sat­is­fac­tory level.

How­ever, as driver ex­pec­ta­tions be­gan to grow, more and more pres­sure was in­flicted upon cars’ bat­ter­ies and charg­ing sys­tems. Higher com­pres­sion en­gines re­quired ever greater crank­ing power and so bat­tery tech­nol­ogy had to de­velop in tan­dem, as did that of the charg­ing sys­tem, with the al­ter­na­tor soon be­com­ing the gen­er­a­tion method of choice, thanks to its abil­ity to charge at low en­gine revs.

In-car en­ter­tain­ment pro­vided a fur­ther drain on bat­tery power, as did com­puter-con­trolled and elec­tri­cally-op­er­ated ev­ery­thing, and still the hum­ble bat­tery re­mained – and still re­mains – as the sta­ble reser­voir of power, all be it with up­dated ma­te­ri­als and con­struc­tion.

The ba­sic prin­ci­ple of the bat­tery re­mains the same as ever. Lead acid bat­ter­ies do not gen­er­ate their own power – they are a stor­age fa­cil­ity for gen­er­ated elec­tric­ity and so need to be charged in or­der for them to work, hence the ini­tial charg­ing of a bat­tery and its con­tin­u­ous ‘top­ping up’ by a dy­namo or al­ter­na­tor.

A 12-volt car bat­tery typ­i­cally con­sists of six cells, each with a charged ca­pac­ity of 2.1 volts, giv­ing an over­all out­put volt­age of 12.6 volts. Each cell con­sists of a pos­i­tive and neg­a­tive plate, in grid form, each of which is made from a lead al­loy. The neg­a­tive plate is coated with ‘sponge lead’ – com­pressed, finely di­vided lead. The pos­i­tive plate is coated in lead ox­ide and be­tween them is a layer of in­su­lat­ing ma­te­rial, with the whole sub­merged in an elec­trolyte so­lu­tion of deionised wa­ter and sul­phuric acid.

‘As ex­pec­ta­tions be­gan to grow, more and more pres­sure was in­flicted upon cars’ bat­ter­ies and charg­ing sys­tems’

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