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As I understand it, an MPPT algorithm adjusts the charging voltage until it finds the point where maximum power is delivered into the battery. If a 12V lead-acid battery is used, is there an upper limit for the applied charging voltage? If for instance, the MPP is at 18V, is it ok to apply 18V to a 12V battery? Is this something the battery data sheet would mention or is there a rule of thumb for this?

Thanks!

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    \$\begingroup\$ This should be in the batteries data sheet, but yes 18 V is too high for a 12 V lead acid battery. \$\endgroup\$ – Colin May 2 at 10:37
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    \$\begingroup\$ Your MPPT should be smart enough to realise that it cannot charge a 12V battery at 18V. Can you set an upper limit of the charge voltage? \$\endgroup\$ – Steve G May 2 at 11:27
  • \$\begingroup\$ @SteveG I'm looking to make my own, that's why I want to know about upper limit because I will have to program it myself. \$\endgroup\$ – BdT141 May 2 at 11:49
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    \$\begingroup\$ Look at batteryuniversity.com - they have a large amount of information about lead acid charging. You definitely MUST set an upper voltage limit. Ideally you want a CC charge mode, a CV boost mode whose duration varies based on certain parameters and then a CV float mode. \$\endgroup\$ – Russell McMahon May 2 at 13:47
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    \$\begingroup\$ BU lead acid - batteryuniversity.com/search/search&keywords=lead+acid and lead acid charging - batteryuniversity.com/search/… \$\endgroup\$ – Russell McMahon May 2 at 13:48
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An MPPT controller only works at the Maximum Power Point drawing Maximum Power, if it can dump whatever power it draws into whatever is downstream. If that's a battery, and it's fully charged, then the MPPT has to be told to stop being an MPPT, otherwise it will damage the battery.

As long as it is of limited duration, 15v is OK on a lead acid battery, in fact it helps prevent sulphation. However for indefinite application, 13.8v is the maximum you should use.

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Your Question: " If a 12V lead-acid battery is used, is there an upper limit for the applied charging voltage?" Answer: If ANY battery is used there must be a limit for the applied charging voltage. Charger is forced to drop from MPPT mode for that, beacouse battery can't consume enough power.

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