Category: Electrical

If you have been around electronics, or industrial equipment, you have probably seen an “Anderson” connector. You may have not known it by that name, or even any name at all. They are somewhat ubiquitous and are used in applications from kids’ electric scooters all the way up to massive RV’s and industrial machines.

Having more than likely worked in or near a factory at some point, you have probably seen it on an electric forklift, which seems to be its primary market.

These connectors are great for a quick disconnect of a DC load. With an asexual (genderless) design, you don’t have to stock but two part numbers (the housing and two pins) in production or maintenance of these. Standard crimp tools can be used for smaller versions of this connector, and an impact-type crimper (the same as what is used on automotive and other large power terminals) can be used to crimp the larger terminals. They are available to handle currents up to 450 amps. Make/break force is low and special configurations, such as single and stackable poles, and make-before-break staggered pins are available. This style of connector is available from a variety of manufacturers. If you’re like me, you’ve seen this connector style for many years, and I was curious as to where it came from.

The “Anderson” connector gets its name from its manufacturer, Anderson Power Products. The proper name for their connector is the “Storage Battery Connector”  and it was first introduced in 1953 to be used in, you guessed it, the forklift industry. Manufacturers had been looking for a better way to connect their forklift batteries, and this connector was definitely it. The design has remained largely unchanged since that first design although many varieties and iterations have followed. It has also been replicated as I mentioned by many other manufacturers. TE Connectivity offers an impressive and diverse offering of these connectors in it’s Power Series of connectors (https://www.te.com/catalog/bin/TE.Connect?C=16714&M=FEAT&P=186051&U=&BML=10576,16973&LG=1).

Figure 3: TE Connectivity Amp Power Series

As the demand for higher and higher currents in Hybrids, EVs, electric motorcycles, and other medium to large systems increases, this “historical” product continues to evolve and increase in market size. Aside from being used in these areas, they also are widely used by hobbyists and shadetree mechanics for battery disconnects, trailer wiring, and various other home projects that require large-current DC connectors.

Have you ever used one of these connectors, or (potentially) have an interesting use for one today?

You may have seen my recent blogs on Lithium batteries. When it comes to Lithium batteries, the most important design aspect (and also the most frequently overlooked) is battery management. Lithiums, like other rechargeable chemistries, require some intelligence while charging. Unlike other chemistries, they are much less forgiving to improper charging (risk of internal damage or leakage). Maintaining proper cell voltage, temperature, and charging current is critical to insure that the health of the cell is maintained.

It is imperative that Lithium batteries be maintained within their specified voltage range. Lithium Iron Phosphate (LiFePO₄) chemistries typically want to be operated between 2.0 and 4.0 volts. If the cell is allowed to run down below this voltage, or charged above this voltage, cell damage may occur. This could come, at the minimum, in the form of diminished capacity, or, at the maximum, in a thermal event that could result in venting, physical damage, or collateral damage to surrounding items. Every chemistry is different and some of the more volatile chemistries can produce a much larger thermal event similar to what Boeing and others have faced. Typically, an under-voltage event will not cause anything other than a loss of capacity, but over-voltage usually results in over-temperature (if not otherwise controlled) which can result in thermal runaway and physical damage.

Temperature monitoring is crucial. This is the only real physical characteristic that something is going wrong with the cell. The following chart, taken from Electropedia (https://www.mpoweruk.com/lithium_failures.htm) provides a great overview of what can happen when operating at unsafe temperatures:

Some applications may require active cooling (common now in the EV market). Use at higher currents creates heat, in what might already be a warm environment. Regardless of whether there is cooling, monitoring is an absolute must, coupled with controls to be able to disable use or charging when cells begin to reach an unsafe temperature. This is not just to avoid damage to a cell, but to maintain the safety of the system.

As you may suspect, charging current needs to be monitored (and managed) as well. Charge requirements vary by chemistry and manufacturer, but generally Lithium cells are charged initially at a constant current, then as the target “charged” voltage is reached, charge current is dropped. Most Lithium cells can handle ½ C (or more). C refers to the capacity of the cell in Amp-hours (Ah). A 2 Ah cell then could be charged initially at a rate of 1A, then fall back to a rate of about 0.2A as the target voltage is reached. Max charge currents vary quite a bit, but exceeding the max recommended or operating at the high side of the recommended charge current generally results in excess heat.

Charge controller ICs (for one or a few cells) or full-blown battery management systems or BMSs (for larger arrays) have been employed to manage charging, voltage and temperature monitoring, and charge status. In some cases these incorporate shunts to allow an array of cells in series to shunt charge current around them once they are full (to better balance the pack). As you may know, in a series array of cells your total charge capacity (in Ah) is only as great as the weakest cell. If you continue to draw current or run a series array past what the lowest common denominator can deliver, you may damage that cell.

Before developing (or choosing) a battery management scheme, check to see what is available and what is typically used for your technology or your application. Also, as with any technology, consult your supplier or manufacturer for the proper technical specifications and min/max operating parameters. Your particular component or application may have different requirements or special caveats.

You may have seen my recent blog on Connecting EV Batteries. This generated a lot of interest, particularly in what was not covered- what about connecting smaller Lithium batteries?

In the EV world, Lithium batteries (specifically, individual cells) are rather large, hulking items that require large connectors both for mechanical security as well as the high current demand. Bolted joints are frequently used in conjunction with large bus bars. Other cable connectors are similarly large to deal with the high currents and keep voltage drop and power losses low.

But that’s for EVs and very large batteries. What about smaller (much smaller) ones? There are several alternatives that are readily available, all with their own advantages. All of these options originated well before Lithium cells, coming primarily from earlier rechargeable technologies such as NiCd (Nickel Cadmium) and are found available for most battery chemistries.

Solder Tabs

Perhaps the most common method of connecting Lithiums is using solder tabs. Solder tabs are very versatile; you can

connect the solder tabs together to form a pack of multiple cells, you can solder them directly to the board, you can solder on wires and use a connector to attach to a PC board or cable assembly. Their versatility drives popularity, especially with Lithiums in applications that do not need much in the way of serviceability. That is the chief downside- soldering these tabs to other tabs, PC boards, or wiring typically is a manual process due to the very high heat requirement (batteries are great heat sinks). In high volumes this process can be automated, but will require a specialized process to do so (excepting some smaller coin or watch cell holders).  Also, the battery or cell you may be looking for may not come with solder tabs on them, and attaching them to a battery requires spot welding. Once you have this process, though, tabs can be spot welded to each other, making assembly of a pack much more reliable and much faster.

 

Battery Holder

Yes, that’s right, a good old-fashioned battery holder. This is by far the easiest option for field replacement. It’s also a handy solution if board space is at a premium (but overall enclosure space is not). It’s also a pretty mindless solution

that doesn’t require a lot of planning. It’s great for quick and dirty projects. Batteries are plentiful in these sizes, assuming that you stay with relatively common sizes (typically cylindrical, such as the familiar AA, AAA, C, D, or various coin/watch flat cells) or slightly less common (such as less familiar A, N, sub-C, etc.). The downside to this connectorization is, of course, cost. While not expensive in an absolute sense, in consumer electronics or other low-margin, cost-sensitive products, pennies count. Reliability also is only as good as the unit itself, and how it is mounted. This can be spotty in lower-cost units that can be flexible or have poorly plated contacts. Once batteries are in a holder, though, connecting them to a PCB or a harness is a simple task of managing the cabling with a good wire-to-wire or wire-to-board connector.

 

Other Methods

While these two are the chief methods of connecting smaller lithium batteries, there are several others and variants on this. Watches are a great example. Typically they will rely on pressure or friction to hold the cell in place, much like a

traditional battery holder. Consider this a custom holder, built into the final device packaging. There are also adapters of all sorts and sizes to adapt various cells to fit in various other cell holders. While this may not be cost effective in production, it shows that with a little ingenuity and packaging effort, you can adapt a wide variety of cells to different applications.

 

Other Concerns

Keep in mind when designing a battery pack or connecting your battery, that the size of tabs, straps, cables, and connectors need to be rated for the fuse that you end up using on-board. This is critical with batteries as they are usually MUCH more capable of driving into a short circuit than you would think. Also, remember that when using Lithiums proper battery management to control charge and discharge current, temperature, and over/under voltage conditions is critical to ensure the safety and reliability of the cell.

A few months ago, one of my daughters broke her arm (badly) when she fell off of a neighbor’s playset. As you may guess, my wife and I spent a fair amount of time in and out of the hospital, waiting for various reasons (x-ray, doctors, surgery, etc.). My daughter is fine- her arm is now stronger than ever, thanks to some great doctors and a little titanium. She had to get used to, though, using just her right arm (thankfully she is right-handed). It made me think, though, about how important an arm is, allowing our hands to do everything that we need them for in the course of a day. This got me thinking about connectors, and how useful connectors can be in attaching things.

Board-to-board connectors

We’ve all used these. Whether you need more real estate for components on a board, or you have to overcome mechanical packaging issues, you build a daughterboard or secondary board to stack onto your primary board. How do you connect it? Board to board connectors. These come in all shapes and sizes, and with all manner of electrical capabilities (good old fashioned 0.100” headers, shielded, high speed, power distribution, etc.).

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[/span4]Figure 2: Various TE Connectivity Board to Board Connectors

Typically other hardware will be used, but these types of connectors are usually critical in locating a secondary or daughter printed circuit board. In many cases these might be very stressed, and in some cases, the ONLY mechanical link to the second board. That is rare but nonetheless, the mechanical function of this connector is as important or more important than the electrical one.

Bulkhead connectors

Many bulkhead connectors are just as mechanical as electrical. A good example of this is the J1772 charge connector for EVs. It serves as a physical holder/hanger for the heavy cables, and incorporates an easy-to-insert (and remove) pistol grip and button for release.

This bulkhead connector is typically mounted to the body of the vehicle, or in a recessed “cup” behind what looks like a fuel filler door. It is rigidly mounted to accept the abuse of being cycled up to several times daily. These cords are heavy, containing conductors that are 12, 10, or even larger gauge. These cables also tend to be trip hazards and get tugged on frequently. The jack and connector both have to handle an extreme amount of physical abuse. The electrical connection itself is not trivial, but its physical application is much, much more stringent than the electrical one.

Think of any RF test equipment you have used in the past. Whether it be long cables, heavy cables, or hanging various accessories from the bulkhead connector, they have to tolerate a lot. Various BNC, F, or N connectors take lots of abuse- whether it is frequent use, heavy cables, harsh environment… these bulkhead connectors are subject to quite a bit of mechanical torture but still remain in service and in spec for many, many years. Again, the electrical piece of this can’t be underestimated, but often takes a back seat to the physical component.

Board-to-wire connectors

In many applications, board-to-wire connectors have to be very mechanically sound. Similar to bulkhead connectors, many applications are subject to harsh mechanical loads that require a robust physical connection. Take for example appliance and consumer electronic wiring:

A lot of appliance and consumer electronics manufacturers use the TE Mate-N-Lok connectors. Various manufacturers sell similar connector series. These are used in everything from washing machines to home PCs. While the primary function is not mechanical, they are subject to a lot of abuse. Vibration from small appliance motors, harsh environments, frequent maintenance activities (hard drive power connectors!) … there is quite a bit of mechanical stress applied to these connectors daily.

As electrical designers, it is easy to overlook sometimes the mechanical nature or requirements of a lot of what we design. What other connectors or items do you think we take for granted “mechanically?” Please share.