Core Technology of Battery Internal Ohmic Measurment | (Download PDF)

Recommended technology of battery aging status measurement by IEEE 1188-1996

1. By applying a AC current to battery, and measuring resultant AC voltage drop. Compute the resultant “impedance” using“Ohm’s law”→ Not calculate cosθ

2. By applying a AC voltage to battery, and observing the AC current values. Compute the resultant “Conductance(S)” by “Ohm’s law”→ calculate cosθ 3.

3 By applying a load across the cell/unit and measuring the step change in voltage and current(Vdt/Tdt), calculate “Resistance”. Remarks; Difference between method 1 and 2 is that whether they are;y considered with cosθ of AC current in-phase, or not .

Remarks; Difference between method 1 and 2 is that whether they are;y considered with cosθ of AC current in-phase, or not.

Battery Internal Equivalent Circuit

By Utilizing AC Testing Techniques, the impedance (or conductance ) of the battery can be determined with no resulting discharge of the battery and little if any interruption in the service it provides. The impedance is actually the resistance of the cell to the flow of AC current as presented vy the resistance (R) and inductive and capacitive reactance (XL and Xc respectively) of the internal components. The impedance of the cell is freqency dependant, utilized. However the impedance can generally be expressed as:

If lower testing frequency, measurement accuracy can be higher.

THe cell’s electrical makeup also includes a huge capacitor, which is shown in the simplified electrical model in Figure 2. The typical value of the capacitor is 1.5 farads per 100 ampere-hour of cell capacity. Various authors and electrochemists have discussed different cell models showing the placement of the capacitor, but there doesn’t seem to be agreement on any one model presented.

Figure 2, which is generally accepted model, has grouped the various internal resistors into two general resistors labaled R1 and R2 and is shows the internal capacitor in parellel with R2. An application note about impedance and conductance testing written by Johnson Controls a few years ago assigns 40% of the total cell resistance to R2. The author will use a value of 45% since this is more consisten with results calculated from field testing.

DC measurement method by Step Current duration

When a cell is placed under load for a short duration, its terminal voltage will depress while the load is on and then recover after the load is removed. Figure 3 shows the voltage of a cell initially floating and then subjected to a three second load of approximately 72 amps.

Comparison of between internal impedance versus internal ohmic value (R1+R2) as Battery Status of Health

Battery aging status measurement method by manufacturers

Ripple influence by charging ripple current

The large amount of ripple current present will interfere with AC test measurments and it is not uncommon to see 25 amp rms ripple current flowing through a 300 KVA rated UPS battery. The amount of ripple current present depends on how much load is applied to the UPS. An AC test device will typically show different readings for the same model battery when the readings from two differently loaded UPS systems are compared.

1. In case of UPS 300Kva, ripple voltage present on + – battery terminal is higher than measuring impedance signals, so measuring reproduction is affected by ripple voltage.

2. In case of high ripple current over 0.02C, a lot of problems of measurement discrimination will be arise.

3. As a result, whether it has a ripple-removing algorithm (as Powertron s) or not, is coreripple removingPowertron’s) technology in AC measurement method.

Limitation of test current (commented by ALBER)

Another very important factor is the amplitude of the test current used. In the noisy environments in which ohmic measurments have to be performed, it is imperative that a high test current be used. This is true for both AC and DC test measurments. It is important to have as high a signal to noise ratio as possible. A lot of the test devices being used today use a test current as low as on amp.

CONCLUSION; ripple-removing algorithm

1. High testing current will affect Battery health, therefore Latest developed measurement algorithm uses under 1A current

2. 200μΩ: 25% change is 50μΩ, therefore Impedance voltage by 1A current is a very minute value, 0.05mV level,value 0 05mV level than ripple voltage.

3. That is why Powertron’s ripple-removing algorithm will be latest technology to design the circuits because it have higher accuracy under the noise environment.

Comparison of Eagle Eye Power Solutions vs B company On-Line Model

Relation between internal ohmic measurements and measuring current

Below graph is shown that the result of internal ohmic measurements by changing measurement frequency about brand-new and ended life battery.

IBEX has high discrimination compared with H company’s.

Stability and Convenience of maintenance after installation

Powertron’s connection point is a quarter of other’s so, its maintenance is much easier. As a result, misconnection troubles can be minimized and easy to replace battery. BDS/pro is special designed as 24 cell unit for telecommunication.telecommunication Each BDS/pro(20 sets connection is possible) connected by RS485 communication.

Operation Reliability by increasing battery strings