Author Topic: Battery Charging Question  (Read 1309 times)

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edy252

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Battery Charging Question
« on: July 02, 2004, 02:27:17 PM »
hi all...


as we know, a battery would bring a dc voltage to 12 volts until it is full....


my question is: can i know that the battery is full just by using a voltmeter and see if the voltage rises above 13 v (for example)???


thx in advance

« Last Edit: July 02, 2004, 02:27:17 PM by (unknown) »

Ungrounded Lightning Rod

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Re: Battery Charging Question
« Reply #1 on: July 02, 2004, 04:54:12 PM »
Yes.


There are tables available for lead-acid battery voltage versus state-of-charge.  They're pretty accurate if you use them correctly, but several things can foul them up.


 - The main one is for use when the battery is unloaded or lightly loaded (and has had at least a few minutes of light load after the last charging to remove "surface charge").


 - A second one is available for use during moderate charging.


Expanded scale voltmeters are available for hanging across a floating wet lead-acid battery bank either continuously or with a pushbutton.  They have one section showing approximate state of charge when the battery is discharging, one when it's charging.  Available at boating and trailer supply stores.


Tables and expanded-scale voltmeters will give inaccurate readings if:

 - The battery temperature is significantly above or below room temperature (correction factors are available).

 - The battery is charging and sulfated.

 - The battery has BEEN charging but isn't charging now - it will have a "surface charge" until it has been moderately loaded for a few minutes.

 - The battery is under significant load.

 - The battery has within the last few minutes been under extreme load (i.e. cranking) and is now under even minor load (it will be "polarized" - have a layer of depleted material near the plate, and this makes even minor loads make it read low).


Hydrometers are always right, but a pain.  An expanded scale voltmeter (and a table or state-of-charge markings) is a good device for a quick check.

« Last Edit: July 02, 2004, 04:54:12 PM by (unknown) »

Ungrounded Lightning Rod

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Re: Battery Charging Question
« Reply #2 on: July 02, 2004, 04:56:09 PM »
Oops:  Jell and flooded lead-acids have different voltage vs state of charge curves, so use the right tables or meters.  (If it doesn't say, it's for flooded.)
« Last Edit: July 02, 2004, 04:56:09 PM by (unknown) »

Tom in NH

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Re: Battery Charging Question
« Reply #3 on: July 02, 2004, 05:38:45 PM »
In my situation I am charging Nicd batts, not lead-acid, using solar panels. I was trying to design a controller that would read the voltage of the battery and shut off the current when the voltage got to a certain point. What I discovered was that the battery voltage floats up and down depending on the load and the voltage coming from the solar panels. The problem was that in bright sun the voltage would be high enough to make the controller think the battery was charged, but then at night or when a cloud passed over, the voltage would drop indicating an incomplete charge.


The battery voltage changes so much as to make it impossible for me to use voltage to detect the charge state of the battery. Maybe with a constant supply voltage it would be a reliable measure, but if you have a varying charge voltage, I'd urge you to be wary of your readings.


Tom

« Last Edit: July 02, 2004, 05:38:45 PM by (unknown) »

Nando

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Re: Battery Charging Question
« Reply #4 on: July 02, 2004, 07:42:18 PM »
Lead Acid Batteries :

Lead Acid Battery has a NOMINAL 2 volts per Cell when the charge is around 80-90 %.


To charge a Lead Acid Battery there is the need to have a power source that can supply 2.37 Volts per cell -- so for a 12 volts Battery ( 6 Cells ) the charger must be capable of supplying 6 * 2.37 volts = 14.22 Volts -- this equalizes all the cells when fully charged.

For Float charge the voltage is maintained at around 13.8 volts


For Nicads the Nominal voltage is 1.2 Volts and the full charge voltage is 1.37 volts.


For Ferro Nickel ( Iron Nickel ) the voltages are 1.2 and 1.57 volts per cell respectively.


Regards


Nando

« Last Edit: July 02, 2004, 07:42:18 PM by (unknown) »

wpowokal

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Re: Battery Charging Question
« Reply #5 on: July 03, 2004, 02:25:09 AM »
Home Power artical on battery volt V state of charge etc


http://www.homepower.com/files/battvoltandsoc.pdf

« Last Edit: July 03, 2004, 02:25:09 AM by (unknown) »
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