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Posted: Thu Jan 17, 2013 6:49pm

Post Subject: Double charging?

I recently accidently ran my engine for a short period whilst connected to the shoreline and thus charging my battereies through the charger which was also switched on at the time. As the alternator and charger were both attempting to charge the batteries at the same time, is this likely to have caused any issues.

Tony-B
Tony-B

Posted: Thu Jan 17, 2013 7:19pm

Post Subject: Double charging?

It is the batteries that control how much currant can flow into themselves. If they are well discharged they would happily accept more current than the alternator and/or charger can supply. Both protect themselves form being overloaded by reducing the charging voltage so it can only push their designed maximum current into the batteries. AS the batteries charge they accept less and less current until the charging device(s) are running at their maximum output. While this is happening the charging voltage automatically gradually rises. Unless steps are taken as the batteries charge up the charging volatge would go on rising and eventually would be at a level that destroyed the batteries. To prevent this at a certain level of charging voltage the alternator or charger starts to regulate the output volatge to a safe level, Typically 14.2 to 14.4 volts+ on modern alternators. In your case there are two possibilities. If it was early in charging well discharged batteries then the voltage would be low enough so the alternator and charger were both charging at their maximum output. This is perfectly safe because if it was not the batteries would have refused to accept such a charge. If it happened later in the sequence the most likley outcome would be for whichever charge source had its voltage set to a lower value to simply assume the batteries were fully charged and shut down. It is unlikely that both devices would have absolutely identical voltage regulation settings but even if they did the batteries would simply refuse to accept any more charge than they wanted. All is fine. Tony Brooks

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Posted: Fri Jan 18, 2013 12:43pm

Post Subject: Double charging?

Tony, Thanks for the reassurance and detailed explanation. Duncan

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