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Your tough­est mo­tor­ing queries an­swered by our tech­ni­cal edi­tor, Steve Roth­well.

Car Mechanics (UK) - - Contents -

In the March 2018 is­sue of CM, the fea­ture on the 2010 Ford Fo­cus 1.8 petrol warns read­ers never to jump-start a car fit­ted with a smart charge sys­tem. Am I cor­rect in think­ing that smart charge has be­come the norm for most cars made since 2010?

One of my daugh­ters has a 2011 Fi­esta 1.25 Zetec petrol with en­gine num­ber BD78430 and what ap­pears to be a smart charge al­ter­na­tor. Both the Ford User Hand­book and the Haynes man­ual make no men­tion of it hav­ing smart charge and both books have de­tailed in­struc­tions for boost start­ing. My other daugh­ter has a 2012 Vaux­hall Corsa 1.2 petrol Ex­cite AC with en­gine num­ber 19YR8754 and the orig­i­nal battery. Does this car have smart charge? Is it safe to jump-start ei­ther of these ve­hi­cles?

The Fi­esta has its orig­i­nal Ford sil­ver­cal­cium battery in use with no prob­lems so far. I be­lieve that the sil­ver-cal­cium de­scrip­tion re­fers to al­loy con­stituents of the lead acid battery re­plac­ing an­ti­mony, which gives dif­fer­ent char­ac­ter­is­tics and re­quires that re­place­ments be of the same type. Are these widely avail­able and what is the cost com­par­i­son? Are there any elec­tronic parts con­cealed within the moulded case re­quir­ing the re­place­ment to be coded to the ve­hi­cle or are they a straight swap?

Fi­nally, I have read on­line that dis­con­nect­ing the three-pin con­nec­tor from the side of a smart al­ter­na­tor re­verts it to a ‘dumb’ al­ter­na­tor. Is this the case and, if so, does it make it safe to jump-start a car which would oth­er­wise be un­safe? Can the car be run like this long-term or should I re­con­nect the multi-pin lead once the battery has had time to recharge or else get an ECU soft­ware remap to con­tinue ‘dumb’ charg­ing? Martin Keat­ing

Jump-start­ing any mod­ern ve­hi­cle re­quires cau­tion as elec­tronic com­po­nents and con­trol units are sen­si­tive to cur­rent spikes. For this rea­son, us­ing a booster pack is a far safer op­tion.

Jump-leads can be used on both your daugh­ters' ve­hi­cles so long as you ad­here to this pro­ce­dure: first, make sure all ac­ces­sories, lights, etc, are turned off. With the donor ve­hi­cle switched off, con­nect the pos­i­tive lead (red +) on the donor battery to the ve­hi­cle to be started. Next, con­nect the neg­a­tive lead (black -) to the donor battery and then to a suit­able earth on the body of the ve­hi­cle to be started (this can go di­rect to an earth on the en­gine). Start up the donor ve­hi­cle and al­low it to idle for a short time, so the volt­age sta­bilises be­tween the two ve­hi­cle bat­ter­ies. Now start up the ve­hi­cle with the flat battery and al­low it to idle for a few min­utes, then run the en­gine for a fur­ther few min­utes at a fast idle. You should turn off both en­gines be­fore dis­con­nect­ing the jumpleads in the re­verse or­der. The dan­ger with smart charge sys­tems is that if you re­move the jump-leads be­fore the flat battery has suf­fi­cient charge, the smart charge sys­tem will boost the cur­rent in an at­tempt to bring the battery up to volt­age, caus­ing an ex­ces­sive volt­age spike.

Your daugh­ter’s Ford Fi­esta does have a smart charg­ing sys­tem, but I would not rec­om­mend dis­con­nect­ing the con­trol plug as this will pre­vent the sys­tem from charg­ing above 13.8 volts. An ECU soft­ware change would not be pos­si­ble as the smart charge con­trol unit can­not be remapped. The con­trol plug con­tains three wires: the al­ter­na­tor feed­back, the al­ter­na­tor re­quest and the ref­er­ence volt­age. The al­ter­na­tor will not charge on crank­ing. From the data I have, your other daugh­ter’s Corsa does not have a smart charge sys­tem, which can be con­firmed by check­ing the feed wires. There should be only two wires: the large battery feed and the small con­trol wire.

The sil­ver-cal­cium battery is ba­si­cally a stan­dard lead acid battery, but with the an­ti­mony on the neg­a­tive and pos­i­tive plates re­placed with cal­cium. This re­sults in low wa­ter loss and re­duced gassing, as well as re­duc­ing self-dis­charge, which means the battery has a far longer shelf life. It does not have any clever in­ter­nal elec­tron­ics and does not need cod­ing to the ve­hi­cle. Note that sil­ver-cal­cium bat­ter­ies are more de­mand­ing when they need charg­ing, which is one of the rea­sons a smart charge sys­tem is fit­ted.

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