# [EVDL] Will float voltage ever fully charge a battery?



## EVDL List (Jul 27, 2007)

A float voltage is use to maintain the battery at 100 percent State of 
Charge. A 6 volt battery is consider to be 100% SOC at 6.37v or 12 volt at 
12.74v. A battery may be self discharging with no load, or in case of a 12 
volt accessory battery that has a small continuous load, like a E-meter and 
motor controller, the battery charger will supplied the current while 
keeping the battery at 100% SOC.

You can charge a battery that is below 100% SOC voltage at 13.5 volts which 
is over 13.5-12.74 = 0.76 volts. Now lets say the battery needs only 0.1 
more ampere hour to get to 100% SOC and the battery charger float charge is 
0.1 amp, then it will take about 0.1/0.1 = 1 hour to charge the battery to 
100% SOC.

I am using a on board Schumacher 12 volt smart charger which may charge the 
12 volt accessory battery which only takes less than one minute and than it 
will go to a float charge at a voltage between 13.3 to 13.5 volts.

I do not like to use the IOTA DC-DC converter for this application, because 
I would have to change the voltage from 14.5 to 13.5 volts every time I park 
the EV.

This on board 12 volt charger now has been maintaining my accessory Trojan 
deep cycle battery since 2002 at 20 to 22 hours a day at a voltage of 13.3 
to 13.4 volts with no problems.

Roland


----- Original Message ----- 
From: "David Delman" <[email protected]>
To: <[email protected]>
Sent: Thursday, May 05, 2011 6:56 AM
Subject: [EVDL] Will float voltage ever fully charge a battery?


> I have 13 Sears PM1, 12v 100 ah AGM batteries in series.
>
> Sometimes one or two of my individual modular chargers flake out and shut 
> off. Typically when I restart a charger that has shut down it will then 
> say that the battery is fully charged and thus it enters its 13.5 volt 
> float mode.
>
> Will applying the 13.5 Volts for long enough time, fully charge the 
> battery? If so how long is "long enough"?
> Thank you,
> David Delman
> via Thunderbolt
>
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