from chemistry to pack
For many applications contactor mass doesn’t matter, but for aviation every gram counts and hence we wanted to look for a trend. Contactor mass plotted versus continuous current rating. Not very much data with just 23 parts, but it appears that we are seeing distinct masses based on frame size. Hence a relationship to continuous … Read more
Contactors are the only moving part in a battery pack and although simple there are a number of contactor faults that will stop the operation of the battery pack. Introduction to Contactors There are two main types of contactors: Normally Open (NO) and Normally Closed (NC). A NO contactor does not allow current to flow … Read more
As a vehicle level systems engineer who spent many years working with an HV battery team, I naturally have some thoughts about opening and closing contactors. Here is my starter for 10 on the topic of ‘Control contactors’ 😇 Contactor Control is another one of those areas where responsibility is divided between a vehicle’s system … Read more
for Cell Contacting Systems and Busbars Aluminium busbar products are used in manifold applications in batteries and battery systems due to their favourable structural, physical, and chemical properties. When it comes to cell contacting systems and busbars, electrical (and thermal) conductivity are decisive for balancing component resistance and cross-section to meet the designed space. However, … Read more
What is the optimal busbar joint overlap? It should be noted that the experimentally derived optimum is for plain busbars and does not include a hole for the fixture. Braunovic [3] shows the impact on resistance of the joint overlap. The resistance ratio is the ratio of the resistance measured across the joint divided by … Read more
The Electrical Contact Resistance at a metal to metal contact is primarily governed by: The surface structure can be further described by the surface flatness, surface oxidation and water adsorption. These joints in a battery pack will either be welded or bolted. Initially the easiest to think about is the bolted busbar joint. The bolt … Read more
When the battery pack contactors are closed onto a motor and inverter there will be an inrush of current into the inverter capacitor. This very high current is at a minimum likely to age the contactors, it could permanently damage the contactors. Therefore, when we closed the contactors on the battery pack we do this … Read more
Let’s take a tiny step and understand how IR is measured in the first place. How are resistances measured? A small current is injected into the component and voltage is measured across it and then resistance is calculated by R=V/I; yes! This is how a multimeter does its’ job; it’s not rocket science. There are … Read more
When we connect cells in parallel to increase the capacity we might also want cell level fusing. This fusing being by definition designed to disconnect a cell that for some reason is sinking or delivering high currents. The fusing can be inside the cell and sealed or external to the cell, sometimes both internal and … Read more
The isolation resistance of the complete HV system to ground with the contactors closed should be >500Ω/V and hence for a battery pack its resistance target must be specified by the HV System designer, typically >1,500kΩ. The NHTSA list values for a Tesla in their Tech Note [4] : It is important that a battery … Read more