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Computer-controlled battery charging

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J_Nichols

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Just I'm building a battery charging controlled by Pc software.
The basic thing that the software does is to read the battery % charge and switch on or off a circuit that connects to a power source (around 14 VDC, 1000 mAH).

How I know when the battery is charged? Because the computer needs to know it to disconnect the charger from the battery.
I have also tried to charge the battery from the energy coming from the collapsing magnetic field of an electromagnet and it has given me good results too.
 
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How I know when the battery is charged?
That depends on the battery chemistry. I suggest you read up about battery types and how to charge them SAFELY.
 
That depends on the battery chemistry. I suggest you read up about battery types and how to charge them SAFELY.

Is a Lead-Acid Battery. I'm checking for info in the internet, but information is welcome.
I know there must be a way because the mobile, or any other kind of charger switches off when they detect that the battery is 100% charged.
 
It is common with lead-acid battery charging to use a constant-voltage source and series resistor for current limiting. As the battery voltage rises to its fully-charged value so the current reduces to a trickle. The battery voltage measured at its terminals depends on the current, because of the finite internal resistance of the battery. A '12V' car battery is typically regarded as fully charged when its terminal voltage reaches 13.8V off-charge, but it's on-charge voltage may be 14V or more. An on-charge voltage above 14.3V is excessive/dangerous and likely to damage the battery.
 
It is common with lead-acid battery charging to use a constant-voltage source and series resistor for current limiting. As the battery voltage rises to its fully-charged value so the current reduces to a trickle. The battery voltage measured at its terminals depends on the current, because of the finite internal resistance of the battery. A '12V' car battery is typically regarded as fully charged when its terminal voltage reaches 13.8V off-charge, but it's on-charge voltage may be 14V or more. An on-charge voltage above 14.3V is excessive/dangerous and likely to damage the battery.

So, an option would be reading the battery voltage, and, if this voltage is higher than 13.8 it means that the battery % charge is 100%?
I'm also interested in this because I want to put in the computer program the % of the charge of the battery, to help the user to know the battery's state of charge.

I've charged it with an electromagnet collapsing magnetic field (the energy that the electromagnet puts on the circuit in the instant you disconnect the magnet from the power source), and it has worked very well. The strange thing is that first I read 12.9 Volts after charging it about 3 hours. The battery is 12 VDC 7 AH. Now, after connecting it for a minute to the inverter I read 18.4 Volts in the battery?
 
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if this voltage is higher than 13.8 it means that the battery % charge is 100%?
As I said, that's what is generally regarded as fully charged, for a typical car battery, but only when the battery is off-charge. Not all lead acid batteries are equal; so there will be variations between different brands and constructions.

I want to put in the computer program the % of the charge of the battery, to help the user to know the battery's state of charge.
That's not so easy. The battery voltage does not vary linearly with charge state.
You would have to know the capacity/charge/voltage characteristics for your particular battery.
 
That's not so easy. The battery voltage does not vary linearly with charge state.
You would have to know the capacity/charge/voltage characteristics for your particular battery.

so, if I know the capacity/charge/voltage characteristics of my battery I could know the charge % right?
the next question is how I can know that.
 
A reputable manufacturer of the battery would make that info available, probably as a downloadable datasheet/specification. Check any labels/numbers on your battery and search online for the info.
 
Ok. The following comments are based on my understanding of the pdf (I don't speak Spanish, so I could be mistaken).

Page 1:
The battery capacity (CA?) varies with the discharge rate from 7Ah down to 4.56Ah. Let's assume an 'average' of 6Ah. In the discharged state the battery voltage will be 10.5V.
A constant-voltage charge at 14.5V to 14.9V and a maximum of 2.8A is specified for cyclic use of the battery.
A trickle charge at a constant 13.6V to 13.8V is also possible for standby use.
The charging voltages may need to be adjusted according to ambient temperature.

Page 2:
At top right, the charge profile is for a '0.25CA' charge. I take that to mean a current starting at 0.25 * 6 = 1.5A. The curve shows the charge volume reaches 100% at about 18hrs, by which time the voltage has plateaued at about 13.8V and the current has dropped to about 0.02CA, i.e. about 0.02*6 = 120mA.

If you monitor the charging current with the PC that should give you a fair indication of the charging progress.
 
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