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HomeElectronicsBattery contacts: An underappreciated problem

Battery contacts: An underappreciated problem

Batteries are getting lots of consideration and R&D effort lately, for a lot of causes I don’t want to elucidate to this viewers. The main focus is on each major (non-rechargeable) or secondary (rechargeable), with chemistries starting from the venerable and nonetheless essential lead-acid sort to more-exotic lithium mixes, and in measurement from tiny button cells to a lot bigger packs utilized in EVs and grid-scale storage.

However there’s a side of batteries which doesn’t have the glamour that these electrochemical energy-storage models have: their bodily contacts and connectors. Whether or not it’s microamps and milliamps from a tiny cell to a whole lot of amps from an EV  large-scale backup system, the way you join the batteries to the circuit the battery is crucial.

In some circumstances, it’s a matter making a tiny-scale mechanical match; in others, it’s an apparent mechanical connection that should reliably and persistently carry a whole lot of amps with low resistance in difficult circumstances of vibration, excessive temperatures, and extra. Ohm’s Legislation says all of it: when you’ve gotten just a few hundred amps going by way of just a few  milliohms contact resistance, you’ve simply wasted a non-trivial fraction of voltage and energy from a battery that could be delivering a comparatively modest nominal voltage, and you’ve got additionally dissipated tens of watts or extra as warmth.

Some battery connectors seem like pretty easy equivalent to those historically used on 12-V lead-acid car-battery posts, whether or not single cable or multi-cable, Determine 1.

Determine 1 The fundamental 12-V automobile battery clamp on connector is crucial in passing a whole lot of amps to the automobile’s electrical subsystem, and with low contact resistance, for a few years regardless of a harsh working setting, whether or not it’s a fundamental single-cable model (prime) or a multi-cable variation (backside). (Picture sources: Nationwide Automotive Elements Affiliation/NAPA; Nationwide Luna/South Africa)

(Be aware that I stated “easy” and didn’t say “trivial,” as one of many many issues I’ve realized over time is that there is no such thing as a part which is trivial. No matter how easy that part could also be in its look or perform, there’s lots of expertise, supplies science, design subtleties, and manufacturing know-how wanted to make it work reliably at an affordable price.)

It’s not simply “heavy obligation” connectors which have challenges, and the battery-connection points are compounded when that you must join a number of batteries in sequence or parallel, even a really low voltage or present ranges. For instance, I not too long ago opened an inexpensive, 20+ 12 months outdated “give-away” scientific calculator that was nonetheless working with its authentic batteries; admittedly, the show was dimming, however I used to be nonetheless impressed that it labored in any respect.  (Why did I do that? Simply the same old engineering curiosity, coupled with the always-welcome alternative to take one thing aside which doesn’t essentially want be reassembled into working unit.)

Inside I discovered two button cells (AG12, equal to 386 measurement) in sequence which have been barely corroded however nonetheless in a position to present sufficient energy for the calculator. What I discovered most fascinating  was how the 2 cells have been electrically linked. If I had been doing the design, I most likely would have taken two customary button cell holders and wired then in sequence through a discrete wire, or with a PC board observe if I used  surface-mount cell holders.

As an alternative, this calculator ha a button-battery holder in contrast to any I had seen beforehand, and I’ve “dissected” many button- and coin-powered units. The holder was designed to not solely maintain the batteries but additionally present the wanted sequence connection, Determine 2. To do that, there was one small steel strip (punched, I presume) doing a number of obligation of connecting the rim (+ terminal) of the battery on the left facet to the underside (- terminal) of the one on proper facet with out want for interconnecting wires, solder joints, or different items.

Determine 2 The series-connected button-cell holder (within the highlighted oval): observe how the circumferential contact for the left-side battery additionally turns into the interconnection to the right-side battery and the contact for its backside facet as effectively. (The yellow-white areas will not be corrosion or discoloration however are a mirrored image from the sunshine.) (Picture supply: writer)

Even nicer, the bottom-side connector finish had tiny prongs which attain up and make contact with the battery, and might presumably pierce by way of any floor oil from the person’s pores and skin, oxidation, movie, or comparable. To me, this appeared higher than the flat tab of most button/coin cell holders, which gives comparatively giant floor space (good) however typically doesn’t make full contact (unhealthy)resulting from insufficient stress.

Since utilizing two cells in sequence will not be an uncommon configuration, I assumed that this straightforward hybrid-role holder with sequence connection was a regular merchandise. It could be, however I didn’t see it within the related catalog pages of the “go to” reference supply I exploit when researching small however important items that full a system (Keystone Electronics Corp.). After all, this can be a regular merchandise at different distributors, however my curiosity was overcome by the point the analysis would take.

Have you ever ever seen or used a battery connector – whether or not small, medium, or giant – that impressed you with its cleverness past its fundamental performance? Conversely, have you ever ever been pissed off looking for a mate for a battery connector of undetermined mannequin or vendor, and even needed to improvise one?  

Invoice Schweber is an EE who has written three textbooks, a whole lot of technical articles, opinion columns, and product options.

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