any battery techs that WOULD be cheaper except for degradation/defects of cells?

dariusroberts · March 2019

I've been reading about cell-balancing systems for batteries. https://www.analog.com/en/technical-articles/active-battery-cell-balancing.html

They don't really seem to explore the flip side -- which is that perhaps battery manufacturing standards could be relaxed for some applications, if balancing circuits can ignore "bad" cells.

does anyone do this? Are any technology families better suited for this?

I don't see these sorts of chips on car batteries, so I feel that active balancing must be fairly rare.

BB. · March 2019

Welcome to the forum DR,

Active balancing (moving energy between cells) is a "relatively" expensive per cell "isolated" power supply. You have expense, size, and things that can still go wrong (typically the magnets are what "resist" miniaturization and cost reduction).

And, in general, battery management systems have relatively low power transfers between cells (or balancing cells). So you are not really looking at a system that allows the engineer to "ignore or bypass bad cells".

Generally series connected cells are protected against over or under charging, and will disconnect a bad cell from the string (and because everything is series connected, a "badly behaving single cell" simply kills the entire string until the situation is fixed (over charged, over discharged) or until the cell/string has been mechanically replaced.

In general, electronics (and large Tesla type battery packs that use lots of 18650 (or slightly larger batteries--Size of 2x C or 2x D cells). are "working" because of high quality design and manufacturing. I.e., "no cell" fails before its time, and they all charge/discharge at relatively the same rate/no high self discharge/no opens/no shorts/etc.).

If you have to design "oversized/overly complex" Battery Monitoring/Balancing Systems, that saves cost, and wasted space.

Here, for example, is a "high energy" battery balancing system. Use for 12/24 volt RV Bus, Truck, Military vehicles that need to run both 12 volts and 24 volts from the same battery bank. An explanation and an example of a largish balancer/equalizer supply:

http://all-about-lead-acid-batteries.capnfatz.com/all-about-lead-acid-batteries/lead-acid-battery-management/how-battery-equalizers-work/

http://www.eaton.com/Eaton/ProductsServices/Electrical/ProductsandServices/Transportationsolutions/PowerConversion/Equalizers/24Vto12VBatteryEqualizers/index.htm

This allows a person to draw or charge the "low" 12 volt battery bank and share energy with the "high" 12 volt battery bank in a 24 volt overall system.

So--Not to say something cannot be done--Just to say is it not always a cost effective solution (and that may change in the future).

If you are talking about large prismatic Li Ion batteries, then the larger Amp*Hour cells are all in parallel, so you only need "one BMS" system per battery, not one BMS per string of "small cells".

-BIll

mcgivor · March 2019

The practice is used for lithium batteries and would probably be useful on lead acid, particularly in off grid deep cycle applications where a large portion of the capacity is used on a daily basis. Cell drift is a common phenomenon in lead acid where a cell or cells become weaker then their series mates become overcharged to make up the deficit, this is why maintenance is important.

Such a device wouldn't work in monoblock batteries without modification but better suited to single cells, having something like a BMS which not only monitors cell voltages but has the ability to disconnect charge and discharge would be better. Then again lead acid batteries are extremely robust, able to accept a fair amount of abuse, especially flooded type. Lithium batteries by contrast are not tollerant of voltage over or under very specific values which can render them useless, or even explode with some chemistries, so it's best to have a BMS.

Automotive batteries generally don't work that hard, quick discharge, immediate recharge

dariusroberts · March 2019

Thanks, both of you. I'm going to dig in and educate myself more. Maybe make a silly prototype, to understand better.

BB. · March 2019

By the way, one of the (in my humble opinion) big issues with BMS is that each cell (2 to 4 volt chemistry) needs its own pair of wires back to the BMS (48 volt battery with 24x 2 volt lead acid cells, needs, at least, 25 wires back to the BMS) to both "sense" the remote voltages, and in active equalization, need to carry some amount of current. And each of these wires is "hot" and needs some sort of over current protection (pure sense wires can use high value resistors. Active equalization needs true fuses, breakers, or fusible links).

It all ends up with a "rats nest" of sense wires for larger battery banks (typically high voltage and/or highly paralleled strings of isolated cells). Each wire is a connection that can fail. Ends up being like the old 2 wire copper based telephone central office (10,000 telephone lines = 10,000 pairs of small gauge copper wires all in a locked room to prevent people "playing" with the wires).

-Bill

Dave Angelini · March 2019

They do make PC boards and pre wired cell holders Bill😅

I had the key also to the locked door. Ours was not quite as bad as the one you are talking about but I agree rats nest is accurate.

BB. · March 2019

It gets to the point where the "support" equipment costs more than the batteries themselves.

But we are already there with Wind Turbines and Solar panels... The balance of the system (towers, racking, wiring, labor, etc.) can dwarf the costs of the thing that generates the power you are harvesting...

I have seen guys that can make beautiful wiring harness in the field. And aircraft wiring looms are amazing.

-Bill

Dave Angelini · March 2019

There was a woman at HP in the 80's who still wire wrapped (an old form of wiring before PCB) an ancient spectrum analyzer for the military. The aircraft wiring was amazing. My brother flew the FA 18, one of the first fly by wire and no more looms.

BB. · March 2019

I spent a summer (partially) on a USGS research ship, the S.P. Lee that had a wire wrap digital signal processing computer to record mutli-channel seismic sounding (about a 1 mile long towed array).

https://en.wikipedia.org/wiki/USNS_S._P._Lee_(T-AGS-31)

-Bill

Ralph Day · March 2019

Dave, I hate to whinge, but the first successful "fly by wire" was in the Avro Arrow...1956-1959. The Conservative government in Canada cancelled the program outright and destroyed all the built units, tooling, plans, engines, 30,000 jobs gone. But great for the American Military Industrial Complex (brain drain southwards) Sorry, still upsets me. Google it if you don't have enough projects for rant development.

any battery techs that WOULD be cheaper except for degradation/defects of cells?

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