Battery simulation

[tshegod]

I have to simulate a battery by designing a customized simulator using a digipot as the internal resistance of the battery, which is the best digipot to use for this purpose and is this the best idea or is there a better way to simulate a battery. This simulated battery will be used to test a battery charging circuit.

 

[ericgibbs]

I have to simulate a battery by designing a customized simulator using a digipot as the internal resistance of the battery, which is the best digipot to use for this purpose and is this the best idea or is there a better way to simulate a battery. This simulated battery will be used to test a battery charging circuit.

hi,
LTSpice can used to simulate a 'battery', you have not said which type of battery you are considering.

The Yahoo LTSpice user group has examples of battery models.

 

[tshegod]

I am simulating a lithium ion battery. i am designing and building a charging circuit test jig to test the charging circuit on a vehicle tracking unit.

 

[ericgibbs]

I am simulating a lithium ion battery. i am designing and building a charging circuit test jig to test the charging circuit on a vehicle tracking unit.

OK, I would recommend that you join the free LTSpice user group,, **broken link removed**

Look thru the Files/Lib section for battery models, if the one you need is not shown, you can build your own battery model.

 

[crutschow]

The simplest battery simulation is an ideal battery in series with a resistor. More elaborate battery models would have a resistance varying with the state of apparent charge of the battery as you suggested doing with a digipot (in the simulation).

But you said you are building a circuit test jig to test the charging circuit. Are you trying to simulate a battery to test the actual circuit?

 

[ronsimpson]

I see you are building real hardware not simulating.

What voltage, what AH, what charge rate, what part number of battery..........?


None of the digipots will handle the charge current.

A battery is something like a zener with some resistance. I can show you how to make a power zener with a power transistor + parts. A 50 watt 12 volt zener built with 1 ohm internal resistance will take no current below 12V. It will take 1A to get to 13 volts and 2A to get to 14 volts. That is something like a battery. You could make the power zener programmable so it can be changed to 13 volts after 10 seconds and 13.5 in another 10 seconds. This way you can see how much current your charger will output into 12 volts and then check to see if it tops out at 14 volts and then goes into stand by mode.

 

[Sceadwian]

Simulating a battery accurately is not an easy task, a digital pot is really not particularly useful.

The only way in my mind I can see to do it would be to use a single power Mosfet an ADC DAC and a sense resistor. The mosfet would act as the variable resistance, the ADC would be fed from the sense resistor so how much current and it's direction could be measured and the DAC would be to control the gate of the Mosfet. You could probably do it all in analog circuitry for a specific battery type but using a micro controller would allow you to program the 'simulator' to any battery type, any capacity and even simulate fault conditions.

If you could flesh out the details of exactly what you're trying to do we could better suggest how to go about it.

 

[nsaspook]

Simulating a battery accurately is not an easy task, a digital pot is really not particularly useful.

Completely agree. To mathematically simulate a batteries response to varying loads and charging rates requires more than a simple I/R circuit. The quick way without a complex model or circuit is to generate a table of charge internal resistance profiles from a real battery at the rates you want to simulate then use that data to drive an electronic load.

An example of Battery-Modeled Load.
**broken link removed**

 

[ronsimpson]

An example of Battery-Modeled Load.
**broken link removed**

I was looking at the VI graphs in the maxim data. On a first order this circuit is close to the graphs.

 

[nsaspook]

I was looking at the VI graphs in the maxim data. On a first order this circuit is close to the graphs.

What missing is the current integrator that changes the decay slope with varying charging current.

Figure 3 shows the typical V-I waveforms obtained while simulating the charging of a Li+ battery up to 4.2V. Two test runs are shown: one with an initial fast-charge current of 1A (traces B and D), and one with a fast-charge current of 2A (traces A and C). In both cases, the CC phase continues until the termination voltage reaches 4.2V. After that point, current decays exponentially while the simulated battery voltage remains constant. The shorter time to termination for the 2A run is just what you would expect after doubling the charging current for a real battery. Notice, however, that doubling the current does not halve the total charge time; it only halves the time required to reach CV mode, as is the case with a real battery.