## 5 Experimental Results  
In this section, the functionality of the above design was tested and conclusions concerning the results are made. In all of the following tests, capacitors were connected in parallel to each HVED cell to simulate the series impedance of a battery cell. Since one of the design goals is to obtain a voltage reference that distinguishes itself compared to other voltage references in its quiescent behavior, the HVED was first tested at sub-threshold voltages. A 1 M\(\Omega\) resistor in series with a 56 k\(\Omega\) resistor was used in parallel with the 20 M\(\Omega\) internal resistance of the voltmeter to obtain a 1.003 M\(\Omega\) current measuring resistance. The cell voltage was measured on the PCB. The following result of a single HVED cell was obtained. From Figure 6, it is clear that the quiescent current at the nominal voltage is below 10 \(\upmu\)A (9.87 \(\upmu\)A to be precise). On a yearly basis, this means a capacity decrease of 0.3%, which is considered to be an outstanding result. From there on out the knee starts to form with a 41 \(\upmu\)A current at 3.65 V, sufficiently small enough to assume a sharp knee. To observe this characteristic at higher currents, initially, a single HVED cell was tested to above 400 mA. A large number of data points were selected over a 10 min measurement to indicate the temperature influence on the HVED cell voltage. In Figure 7 the result is shown. The cold threshold voltage amounts to 3.86 V, which is a fraction higher than the 3.85 V that was estimated in the previous section. Due to the temperature coefficient of the LED and BE-junction of the BJT, the HVED cell voltage at 390 mA is reduced to 3.81 V. This results in a 10 \({}^{\circ}\)C temperature increase. Above 380 mA, the voltage rises again as is foreseen due to the presence of the 10 \(\Omega\) dissipation resistor. A 10 \({}^{\circ}\)C temperature increase is something very common in any vehicle if parked in the sun, for example. Temperature differences of up to 30 \({}^{\circ}\)C are likely. Figure 6: Cell voltage vs. balancing current (non-equalizing). This would lead to a 0.15 V reduction in the threshold voltage. For a design with a 3.65 V threshold, the warm threshold would thus be 3.5 V, which is still well above the nominal voltage. Depending on the influence the overcharge has on the batteries, this method can still be opted to decrease the threshold voltage. This influence is to be evaluated in a later phase. In order to draw a conclusion regarding an entire pack of HVED cells, all eight cells were tested simultaneously to observe if the threshold voltage and I-V characteristics show mutual differences. If there is a faulty cell between the normal cells, it will be detected by the LED at the end of the circuit for each cell shown in Figure 2, as well as the voltage-sensing circuit as shown in Figure 3. A large voltage range is represented in order to examine possible differences between cells in quiescent and equalizing mode. The obtained result is represented in Figure 8.  
In this case, the lowest HVED cell voltage at a supply current of 294 mA is 3.65 V in cell 4 (C4), with the highest being 3.72 V in cell 8 (C8). There is a noticeable increase in mutual differences between cells at higher currents. When assessing the differences, it is clear that cells located in the middle of the PCB are affected by the heat production of the surrounding cells and show a larger temperature effect than the border cells. One would expect that the voltage of cell number 8 and cell number 1 show little difference, which does not correspond to the measurement. This is due to the testing setup. The resistor used to obtain the supply current also generates heat with increasing current. In the test, this resistor was located nearest to cell 1, thereby explaining its increased voltage drop. In Figure 9 the I-V characteristics of one cell is presented.