Comments on: Design Considerations For Good Battery Pack Design & Integration http://www.cleancartalk.com/battery-technology-hybrid-electric-cars/design-considerations-for-good-battery-pack-design-integration/ Hybrid, Electric, Plug-in, Clean Diesel Cars for the Responsible Consumers. Thu, 09 Feb 2012 13:27:45 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: Tom Bartley http://www.cleancartalk.com/battery-technology-hybrid-electric-cars/design-considerations-for-good-battery-pack-design-integration/#comment-630 Tom Bartley Thu, 11 Mar 2010 22:03:50 +0000 http://www.cleancartalk.com/?p=1284#comment-630 Hi Ed, Parallel paths divide the current, I, according to the resistance, R, in each path according to I=V/R. The voltage, V, is a constant for each path. Tom Hi Ed,
Parallel paths divide the current, I, according to the resistance, R, in each path according to I=V/R. The voltage, V, is a constant for each path.
Tom

]]> By: E.A. Baker http://www.cleancartalk.com/battery-technology-hybrid-electric-cars/design-considerations-for-good-battery-pack-design-integration/#comment-629 E.A. Baker Thu, 11 Mar 2010 14:59:52 +0000 http://www.cleancartalk.com/?p=1284#comment-629 Tom, Back to ampacity. My question regards the ability of a single small cell to conduct large currents. If we think of the cell simply as a conducting element (with a resistance) in a complex circuit, we must then concern ourselves with the current that must flow thru that conductor (cell). My understanding of the"law of current" is that the current in a series (complex) circuit is the same everywhere in the circuit. Thus, it seems to me, that a battery pack along with it's load (a circuit) requires that all of the current in the circuit must flow thru all of the conductors in that circuit. While parallel configurations divide resistances, they do not divide current. If my interpretation of theory is incorrect, then my conclusions are probably not correct. I'd appreciate your opinion. Ed Tom,
Back to ampacity. My question regards the ability of a single small cell to conduct large currents. If we think of the cell simply as a conducting element (with a resistance) in a complex circuit, we must then concern ourselves with the current that must flow thru that conductor (cell). My understanding of the”law of current” is that the current in a series (complex) circuit is the same everywhere in the circuit. Thus, it seems to me, that a battery pack along with it’s load (a
circuit) requires that all of the current in the circuit must flow thru all of the conductors in that circuit. While parallel configurations divide resistances, they do not divide current.
If my interpretation of theory is incorrect, then my conclusions are probably not correct. I’d appreciate your opinion.
Ed

]]> By: Tom Bartley http://www.cleancartalk.com/battery-technology-hybrid-electric-cars/design-considerations-for-good-battery-pack-design-integration/#comment-628 Tom Bartley Thu, 11 Mar 2010 02:28:07 +0000 http://www.cleancartalk.com/?p=1284#comment-628 Hi Ed, Thanks for the response. Individual cell balancing and equalization is a major challenge for any transportation pack design, especially one that incorporates the frequent rapid charging from braking regeneration. The massive parallelism in the Tesla pack is one way to do this while adding some level of failure tolerance. Individual cell manufacturing and aging differences, even failures, can be averaged out in the parallel connections of the layers. Also, the many parallel connections creates many parallel current paths, thus reducing the current in each path and minmizing the effects of resistance in the connections. This approach is typically rejected because of the assembly cost of making all those connections. The other design considerations are structural integrity and cooling. The structure has to support each cell in an automotive shock and vibration environment with out affecting the electrical connections or cooling system. The cooling strategy has to consider hot spots like the middle of the pack and the downwind edge of the cooling air flow. It is also useful to know that cylindrical cells dissipate most of the heat through the ends and prismatic (flat) cells dissipate most of the heat through the sides. Another curious effect is that individual cells expand at certain states of charge enough to destroy the cell unless the packaging structure keeps it compressed. So, it "ain't" quite as simple as it first appears. Getting back to the Tesla, rumor has some owners complaining about the cost of haviing to run the battery pack cooling system after the car is fully charged sitting quietly in the garage. It's like adding two refrigerators in the garage. More rumors express investors' concerns about the thermal runaway potential of that early Lithuim ion chemistry. The Tesla reps I've talked with plead ignorance. Addressing battery pack current levels, most packs are designed for 200 Amps or less with occassional spikes up to 300 Amps. Looking at the available cables and connectors, this seems reasonable. Other interesting topics are the Magna Steyr/A123 pack for the Daimler hybrid; and the cell parameters changes with temperature and charge/discharge "C" rate. Your turn, Tom Hi Ed,
Thanks for the response. Individual cell balancing and equalization is a major challenge for any transportation pack design, especially one that incorporates the frequent rapid charging from braking regeneration. The massive parallelism in the Tesla pack is one way to do this while adding some level of failure tolerance. Individual cell manufacturing and aging differences, even failures, can be averaged out in the parallel connections of the layers. Also, the many parallel connections creates many parallel current paths, thus reducing the current in each path and minmizing the effects of resistance in the connections. This approach is typically rejected because of the assembly cost of making all those connections.

The other design considerations are structural integrity and cooling. The structure has to support each cell in an automotive shock and vibration environment with out affecting the electrical connections or cooling system. The cooling strategy has to consider hot spots like the middle of the pack and the downwind edge of the cooling air flow. It is also useful to know that cylindrical cells dissipate most of the heat through the ends and prismatic (flat) cells dissipate most of the heat through the sides. Another curious effect is that individual cells expand at certain states of charge enough to destroy the cell unless the packaging structure keeps it compressed.

So, it “ain’t” quite as simple as it first appears.

Getting back to the Tesla, rumor has some owners complaining about the cost of haviing to run the battery pack cooling system after the car is fully charged sitting quietly in the garage. It’s like adding two refrigerators in the garage. More rumors express investors’ concerns about the thermal runaway potential of that early Lithuim ion chemistry. The Tesla reps I’ve talked with plead ignorance.

Addressing battery pack current levels, most packs are designed for 200 Amps or less with occassional spikes up to 300 Amps. Looking at the available cables and connectors, this seems reasonable.

Other interesting topics are the Magna Steyr/A123 pack for the Daimler hybrid; and the cell parameters changes with temperature and charge/discharge “C” rate.

Your turn,
Tom

]]> By: E.A. Baker http://www.cleancartalk.com/battery-technology-hybrid-electric-cars/design-considerations-for-good-battery-pack-design-integration/#comment-627 E.A. Baker Wed, 10 Mar 2010 17:01:07 +0000 http://www.cleancartalk.com/?p=1284#comment-627 Dear Mr. Bartley, Again, I agree with you, debate is good. As a matter of fact, our dialog has led me to reexamine my investigations of the smalll cell/large battery concept. I have recently learned more about the "state" of battery pack and cell design, causing me to question further the heat "problem" apparently prevelant in all EV battteries. All battery manufacturers and/or EV manufacturers have the same goals (low battery pack weight, high stored energy capacity. Tesla is a good case to examine. They have done more to further the small cell/large battery concept than any other single entity. They have more real experience than any other entity. There is more literature available on the Tesla battery/vehicle than all other projects combined. All making their design a good candidate for investigation. There are 2 possible sources of excessive heat, the conductors or connectors and the individual cells themselves. The conductors were discussed previously. Is it reasonable to presume that the high current levels in the Tesla battery (or any other battery made up of many small cells) simply cannot be tolerated by the 18650(or other small) cells employed in the design? The question seems to merit consideration. I don't know the answer. By the way my name is Ed. Dear Mr. Bartley,
Again, I agree with you, debate is good. As a matter of fact, our dialog has led me to reexamine my investigations of the smalll cell/large battery concept. I have recently learned more about the “state” of battery pack and cell design, causing
me to question further the heat “problem” apparently prevelant in all EV battteries. All battery manufacturers and/or EV
manufacturers have the same goals (low battery pack weight, high stored energy capacity. Tesla is a good case to examine. They have done more to further the small cell/large battery concept than any other single entity. They have more real experience than any other entity. There is more literature available on the Tesla battery/vehicle than all other projects combined. All making their design a good candidate for investigation.
There are 2 possible sources of excessive heat, the conductors or connectors and the individual cells themselves. The
conductors were discussed previously. Is it reasonable to presume that the high current levels in the Tesla battery (or any other battery made up of many small cells) simply cannot be tolerated by the 18650(or other small) cells employed in the design? The question seems to merit consideration. I don’t know the answer.
By the way my name is Ed.

]]> By: Tom Bartley http://www.cleancartalk.com/battery-technology-hybrid-electric-cars/design-considerations-for-good-battery-pack-design-integration/#comment-626 Tom Bartley Tue, 09 Mar 2010 07:13:21 +0000 http://www.cleancartalk.com/?p=1284#comment-626 Dear E. A. Baker, While not wanting to be confrontational, I believe public debate is good to increase interest and spread information. Ah yes, the Tesla battery - the devil is in the details. If I remember correctly the pack voltage is about 340 volts. Doubling the voltage would half the required current for the same power and even if the equivalent series resistance (ESR) doubled the net heat loss would be half because of I**2 and the battery pack efficiency would double. Why didn't Tesla do this and why can't two of their packs be put in series to double the voltage? i believe the answer is in how the grounds are handled to reject the waste heat that is generated boith during charging and discharging. Last time I looked there were over a dozen patents in this area and even more if you look at the required balancing and equalization. Dear E. A. Baker,
While not wanting to be confrontational, I believe public debate is good to increase interest and spread information.
Ah yes, the Tesla battery – the devil is in the details. If I remember correctly the pack voltage is about 340 volts. Doubling the voltage would half the required current for the same power and even if the equivalent series resistance (ESR) doubled the net heat loss would be half because of I**2 and the battery pack efficiency would double. Why didn’t Tesla do this and why can’t two of their packs be put in series to double the voltage? i believe the answer is in how the grounds are handled to reject the waste heat that is generated boith during charging and discharging.
Last time I looked there were over a dozen patents in this area and even more if you look at the required balancing and equalization.

]]> By: E.A. Baker http://www.cleancartalk.com/battery-technology-hybrid-electric-cars/design-considerations-for-good-battery-pack-design-integration/#comment-625 E.A. Baker Wed, 03 Mar 2010 16:11:03 +0000 http://www.cleancartalk.com/?p=1284#comment-625 Dear Mr. Bartley, When I commented on your origional post, it was not my intention to open a debate. I concur that heat is a primary problem in large scale/high capacity battery packs. I also concur that inadequate conductors/connectors are generally the cause of these problems. A conductor's current carrying capacity is governed by two different qualities, the resistivity of the material and the size of the material (cross sectional area) generally collectively referred to as "ampacity". I can only presume that Tesla's battery pack design has the 69_18650 cells (brick) connected in parallel using light metal strips welded to the terminals of each individual cell to produce a supercell. 99 of these supercells are then connected in series to produce a high voltage battery pack. According to Kirchhof's law of current, the current is the same everywhere in a series circuit, thus the current levels in the Tesla battery would calculate to be about 150 amps. Far to high for the metal strips typically used in resistance welded connections. Dear Mr. Bartley,
When I commented on your origional post, it was not my intention to open a debate. I concur that heat is a primary problem in large scale/high capacity battery packs. I also concur that inadequate conductors/connectors are generally the cause of these problems. A conductor’s current carrying capacity is governed by two different qualities, the resistivity of the material and the size of the material (cross sectional area) generally collectively referred to as “ampacity”. I can only presume that Tesla’s battery pack design has the 69_18650 cells (brick) connected in parallel using light metal strips welded to the terminals of each individual cell to produce a supercell. 99 of these supercells are then connected in series to produce a high voltage battery pack.
According to Kirchhof’s law of current, the current is the same everywhere in a series circuit, thus the current levels in the Tesla battery would calculate to be about 150 amps. Far to high for the metal strips typically used in resistance welded connections.

]]> By: Tom Bartley http://www.cleancartalk.com/battery-technology-hybrid-electric-cars/design-considerations-for-good-battery-pack-design-integration/#comment-624 Tom Bartley Wed, 03 Mar 2010 06:43:46 +0000 http://www.cleancartalk.com/?p=1284#comment-624 Dear E.A. Baker, If you really want "to protect the methodology described in the application from being advanced as a proprietary product of someone elses work," just publish it for peer review. I don'r know what you mean by "the ampacity considerations or lack there of that can and do cause excessive heating and the wasting of the stored energy." If you are referring to high currents for charging and discharging, Ohm's Law, I**2 R, still holds where I is the current and R is the equivalent series resistance. The result is heat and loss of energy. if you haven't looked already, I refer you to the Lithium titanate battery chemistry that, in some points of operation actually absorbs heat. The real trick in pack designs is to consider all sources of heat, including new and aged or corroded interconnections, and reject that heat before it can raise the temperature enough to damage the pack. Ofcourse, storage efficiency is enhanced if you don't generate the heat in the first place. Tom Dear E.A. Baker,
If you really want “to protect the methodology described in the application from being advanced as a proprietary product of someone elses work,” just publish it for peer review. I don’r know what you mean by “the ampacity considerations or lack there of that can and do cause excessive heating and the wasting of the stored energy.” If you are referring to high currents for charging and discharging, Ohm’s Law, I**2 R, still holds where I is the current and R is the equivalent series resistance. The result is heat and loss of energy. if you haven’t looked already, I refer you to the Lithium titanate battery chemistry that, in some points of operation actually absorbs heat. The real trick in pack designs is to consider all sources of heat, including new and aged or corroded interconnections, and reject that heat before it can raise the temperature enough to damage the pack. Ofcourse, storage efficiency is enhanced if you don’t generate the heat in the first place.
Tom

]]> By: E.A. Baker http://www.cleancartalk.com/battery-technology-hybrid-electric-cars/design-considerations-for-good-battery-pack-design-integration/#comment-623 E.A. Baker Tue, 02 Mar 2010 18:40:17 +0000 http://www.cleancartalk.com/?p=1284#comment-623 E.A.Baker A great amount of research has been and is being conducted on cell and battery pack design. Most of the work that I am aware of is being carried on by "for profit enterprises". I assume that many if not all of them hope to profit from their investment. My purpose in applying for a patent is simply the best way I know of to protect the methodology described in the application from being advanced as a proprietary product of someone elses work. The primary product of my research pertains generally to the ampacity considerations or lack there of that can and do cause excessive heating and the wasting of the stored energy. You cite the "Tesla Battery" as an example. Therefore my origional comment. E.A.Baker
A great amount of research has been and is being conducted on cell and battery pack design. Most of the work that I am aware of is being carried on by “for profit enterprises”. I assume that many if not all of them hope to profit from their investment. My purpose in applying for a patent is simply the best way I know of to protect the methodology described in the application from being advanced as a proprietary product of someone elses work. The primary product of my research pertains generally to the ampacity considerations or lack there of that can and do cause excessive heating and the wasting of the stored energy. You cite the “Tesla Battery” as an example. Therefore my origional comment.

]]> By: Tom Bartley http://www.cleancartalk.com/battery-technology-hybrid-electric-cars/design-considerations-for-good-battery-pack-design-integration/#comment-622 Tom Bartley Tue, 02 Mar 2010 07:08:53 +0000 http://www.cleancartalk.com/?p=1284#comment-622 I am more interested in advancing the technology through the synergy and collaboration of open applied research rather than unknown proprietary intellectual property. Tom Bartley I am more interested in advancing the technology through the synergy and collaboration of open applied research rather than unknown proprietary intellectual property.
Tom Bartley

]]> By: E.A. Baker http://www.cleancartalk.com/battery-technology-hybrid-electric-cars/design-considerations-for-good-battery-pack-design-integration/#comment-621 E.A. Baker Thu, 18 Feb 2010 17:29:09 +0000 http://www.cleancartalk.com/?p=1284#comment-621 To the best of my knowledge, no one has yet produced a battery pack that provides all of the qualities Mr Bartley suggests are desirable (even necessary). However, this commenter has an invention that comes close. A patent has been applied for and is presently pending. A limited amount of prototypeing and testing has been completed. Further work is required. The inventor is seeking a partnership with an entity interested in advancing a proprietary design that could be highly profitable and quickly brought to a welcoming market. If any party has such an interest, I can be contacted via email (jlebcodes@gmail.com) E.A.Baker To the best of my knowledge, no one has yet produced a battery pack that provides all of the qualities Mr Bartley suggests are desirable (even necessary). However, this commenter has an invention that comes close. A patent has been applied for and is presently pending. A limited amount of prototypeing and testing has been completed. Further work is required. The inventor is seeking a partnership with an entity interested in advancing a proprietary design that could be highly profitable and quickly brought to a welcoming market. If any party has such an interest, I can be contacted via email (jlebcodes@gmail.com)
E.A.Baker

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