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Current-carrying clip
Resistance was also measured for this "poor" connection. The measured resistance was 3.4 mΩ, more than 3
mΩ higher than the better connection.
Kelvin (4-terminal) Clips
Commercial Kelvin clips that resemble an alligator clip with two isolated jaws are available. One example is the
Mueller Model BU-75k. Unfortunately, it is limited to currents of 10 A and below.
A higher current alternative is the Mueller Model BU-102BK which is a large 400 A Kelvin clip. You must do
some modification to the clip to get convenient access to the sense side of the clips.
General Suggestions for High-current Connections
Even with 4-terminal connections, you should not ignore the quality of the current-carrying connections.
High-current connections to commercial batteries and supercapacitors are generally made using large-diameter
bolts, like those found on the Reference 30k front panel. This can lead to very-low-resistance contacts.
Remember that copper is an excellent conductor, so copper washers, bolts, and nuts are preferred. Steel's bulk
resistivity is more than six times higher than that of copper.
Contact area is also important. Flat surfaces make better contact than uneven surfaces. Copper has a second
advantage over steel in this regard: copper is softer than steel so it can deform to contact a larger surface area.
Caution:
can lead to cell damage and hazardous conditions. Cell manufacturers specify maximum allowed torque
allowed on the terminal bolts.
Small alligator clips are a poor choice for high-current contacts. Standard alligator clips are typically rated for a
maximum current of 5 A. The surface area of the contact between the alligator teeth and the cell terminal is
generally very small.
Suggestions for Cell Connection – Kelvin (4-terminal) Clips
Bad 4-Terminal Clip Placement on a Battery Terminal
Sense clip
Do not over-tighten the terminal bolts on commercial batteries. Over-tightening
Figure 5-2
Battery
41
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