Lead Acid Battery-LtSpice Model

[Arshad Ali]

Hi Guys,
I'm looking for an LtSpice model for 12V, 200AH lead acid battery. Help me find one...Please.

[jeduffy]

What part of the performance of a lead-acid battery do you need (what are you simulating)?  Not all batteries are created equal, and most spice components are idealized anyway, it's unlikely you'll find exactly the battery you're looking for.
If you're just doing transient (couple of seconds) analysis, a source with a series resistance will probably do just fine, if you're trying to model discharge that will be more difficult.

[Arshad Ali]

I am designing a three stage battery charger
1-Constant Current (fast) charging
2-Constant Current (Slow) charging
3-Constant voltage charging
and to achieve this purpose i want to simulate the charging and discharging characteristics of the battery.

[Kalvin]

For a quick and crude simulation model you could use a DC voltage source in series with a huge capacitor and a small resistor. The DC voltage source will provide the "empty" battery voltage and the capacitor will model the charging and discharging state of the battery. The series resistor will model the internal battery resistance (typically few milliohms or so). The model is not accurate but it should be a usable starting point so that you can get started with the simulation until you find a better model.

For a nominal 12V and 200A car battery the model could be something like this:

- Capacity 200Ah
- Minimum battery voltage 11V (fully discharged)
- Maximum battery voltage 13.5V (fully charged)

Thus, the model can be constructed as follows:

- DC voltage: 11V.
- Capacitance: 288000F.
- Resistance: 5 milliohms.

The capacitance value can be calculated as follows: C = Ah * 3600 / V, in which the V is voltage difference between the maximum and the minimum battery voltages. For example in 200Ah battery case the capacitor C can be calculated like this: C = 200 Ah * 3600s / 2.5V = 288000 F. (Yes, it is a huge capacitance value)

You may find the following article useful:
http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

[Zero999]

For a quick and crude simulation model you could use a DC voltage source in series with a huge capacitor and a small resistor. The DC voltage source will provide the "empty" battery voltage and the capacitor will model the charging and discharging state of the battery. The series resistor will model the internal battery resistance (typically few milliohms or so). The model is not accurate but it should be a usable starting point so that you can get started with the simulation until you find a better model.

For a nominal 12V and 200A car battery the model could be something like this:

- Capacity 200Ah
- Minimum battery voltage 11V (fully discharged)
- Maximum battery voltage 13.5V (fully charged)

Thus, the model can be constructed as follows:

- DC voltage: 11V.
- Capacitance: 288000F.
- Resistance: 5 milliohms.

The capacitance value can be calculated as follows: C = Ah * 3600 / V, in which the V is voltage difference between the maximum and the minimum battery voltages. For example in 200Ah battery case the capacitor C can be calculated like this: C = 200 Ah * 3600s / 2.5V = 288000 F. (Yes, it is a huge capacitance value)

You may find the following article useful:
http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

I don't see how that would work. When it discharges past its empty voltage, the capacitor will just charge up in reverse. This is even worse if SPICE is set to calculate the initial conditions, then the voltage source, between the capacitor and 0V, won't even make any difference to the circuit operation.

This could be fixed by connecting a diode would need to be connected in parallel with the capacitor, but the voltage drop would need to be accounted for, when determining the empty voltage source's value.

[Kalvin]

For a quick and crude simulation model you could use a DC voltage source in series with a huge capacitor and a small resistor. The DC voltage source will provide the "empty" battery voltage and the capacitor will model the charging and discharging state of the battery. The series resistor will model the internal battery resistance (typically few milliohms or so). The model is not accurate but it should be a usable starting point so that you can get started with the simulation until you find a better model.
<snip>

I don't see how that would work. When it discharges past its empty voltage, the capacitor will just charge up in reverse. This is even worse if SPICE is set to calculate the initial conditions, then the voltage source, between the capacitor and 0V, won't even make any difference to the circuit operation.

This could be fixed by connecting a diode would need to be connected in parallel with the capacitor, but the voltage drop would need to be accounted for, when determining the empty voltage source's value.

Here is my quick simulation test with a charging current of 200A for one hour and a discharging current of 200A for another hour. It works as intended when you skip the initial operation point solution. Probably one needs to tweak the simulation model a bit if the initial conditions are problematic.

[Kalvin]

Here is another model using a behavioral voltage source, and it doesn't have problems with the initial solution.