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