Re: Marine Batteries?


From: Dan Tayloe-P26412 (
Date: Tue May 20 1997 - 16:52:00 EDT

     From: "Bob Edwards, W4ED" <>
     Organization: SmS
     X-Mailer: Mozilla 3.0Gold (Win95; U)
>> The easiest homebrew thing to do is to build a regulated supply for
>> 13.8v. This is the nominal "float" charging voltage for such a
>> battery.
>Caution, with this common 13.8 volt value. Check the
>owners manual for your battery.
>My deep cycle marine battery (DC27-850) manual has the
>following table:
>State of
>Charge Voltage
>------ ------
>100 % 12.7 V
> 75 % 12.4 V
> 50 % 12.2 V
> 25 % 12.1 V
>Based on this table, I use a heavy duty power diode
>in series with the 13.8 V DC power supply.
     This table as stated is absolutely true. You can determine the charge
     state of the battery by its terminal voltage as this table states.
     However, it does not tell the full story.
     The open circuit voltage *delivered from* a fully charged 12v lead
     acid battery is not the same as the proper *charging* voltage for that
     battery. 13.6 to 13.8 is the correct *charging* voltage for float
     charging a 12v gel cell/lead-acid type battery. This is just an
     inherent part of the lead-acid battery chemistry.
     This does not mean that you cannot charge the battery with a lower
     voltage. You clearly can. It is just that it will take *much* longer
     to charge it to full charge using only 12.7v as compared to the
     "float" voltage of 13.8v.
     - Dan Tayloe, N7VE, Phoenix, Az, QRPL # 696, Az ScQRPions

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