Proper wiring and probing/contacting are critical to making successful measurements. When testing cells or batteries, using good engineering practices is important to avoid noise pickup, signal degradation, and unwanted voltage drops through wiring and contact resistances.
If you’re testing cells or batteries at high currents, resistance will be a critical consideration. As test currents rise, the resistance in the wires and in the contacts will cause significant voltage drops.
Wire-Path Resistance Voltage Drops are Problematic During Battery Discharge
这se voltage drops can cause problems during the discharge of a battery into an electronic load, as electronic loads have a minimum operating voltage. Note when I say electronic load, this could be a benchtop electronic load or the discharge circuits in a battery tester (sometimes called a battery cycler). As the battery voltage drops during discharge, the battery voltage may approach the minimum operating voltage of the electronic load.
If large voltage drops occur in the wiring, then the voltage at the input to the electronic load may drop below its rated minimum operating voltage. When the electronic load is operated below its minimum operating voltage, the available current will be derated and you may not be able to draw the required current out of the battery.
比较两个放电案例
让我们看一下两种排放高容量锂离子电池的电线和接触电阻的影响（请参阅表）. Thefigureshows a schematic diagram of the discharge setup.
这figureshows a schematic diagram of the discharge setup.
电线和电压在输入处的电阻（a）对电子负载或电池排放器（b）的影响。
所以,成功的放电开放的关键ration are:
- Use the shortest wire possible.
- 使用厚的电线将电线中的电压降至最低。
- Use good quality probes to minimize contact resistance.
这些对于保持总电阻较低是必不可少的，因此在放电期间，在高电流下的电压下降最小。
其他考虑因素
电缆是构造良好还是弯曲电缆会改变电阻？从通道到通道的电线电阻不一致可以使某些通道正常工作，因为它们符合电线电阻标准，以在绘制高电流时将电压保持在电子负载最小输入电压上方。同时，其他频道具有太多的阻力，因此无法正常工作，从而导致通道到通道行为的变化。
接触电阻会随着时间而变化吗？触点可能会磨损，针型探针可能会脱离对齐，从而导致压力不一致和电阻不一致。灰尘和化学物质也可能会变得肮脏。监视使用和执行预防性维护（清洁，对齐和替换）的周期数量可以减少这些影响。
此外，由于电池接触可能被氧化，电池本身可能是不一致的接触电阻的原因。触点通常是由材料制成的，这些材料随着时间的推移很容易建立氧化物涂层。
接触电阻对电压测量的影响
Now let’s look at a measurement of voltage. Is contact resistance important there? Can measurements of cell voltage be distorted or impacted by contact resistance?
简短的答案是否 - 接触电阻不会影响电压的测量。电压测量是用配置高阻抗输入的DMM进行的。对于典型的DMM测量电压，输入阻抗是数百个Megohms甚至GigaOhms。因为输入阻抗是如此之高，所以几乎没有电流流入DMM测量端子。如果没有电流流动，则路径中的电阻对测量没有影响。
但是电池测试仪呢？电池测试仪上的输入阻抗是否像DMM上的电池测试仪一样高？
Achieving very high input impedance on a measurement instrument is challenging. Most battery testers measure voltage in the same manner as a DMM, although the input impedance is not usually gigaohms because battery testers aren’t trying to measure the wide range of devices that a standard DMM is expected to measure.
例如，KeysightBT2152A是一种电池测试仪器，专注于测量锂离子可充电细胞的自我放电。（有关测量锂离子细胞自分泌物的更多信息，请单击here）。当用BT2152A测量细胞电压时，输入阻抗为10MΩ。在4.2 V（典型）和10MΩ的最大电池电压下，进入BT2152A输入的电流流量为420 Na。This value is found using Ohm’s law of V = I*R or I = V/R, so for a 4.2-V cell connected to a measurement system with 10-MΩ input impedance, current is calculated as 4.2 V/10 MΩ, or 420 nA.
由于输入阻抗为10MΩ，因此只有420 Na的电流将流动。远低于1Ω的总线路径电阻（请参阅表），跨导线的电压下降低于420 NV。Even if wire and contact resistances were to become thousands of times bigger than what’s shown in the table and climb to 10 Ω, the voltage drop in the wire resistance would jump to 4.2 µV, which is insignificant measurement error compared to the 4.2 V being measured on the cell. As you can see, thanks to the high impedance input, the resistance of the wires and contacts don’t impact the voltage measurement.
However, whenever you’re making voltage measurements, noise pickup needs to be minimized by proper grounding and shielding, but that’s the subject for another article.
