# New Headway 38120HP Cell



## Rational (Nov 26, 2011)

3.2v/(<0.003 ohms) = >1100 A, at least in principle. 
Some serious amps.

It's a theorem that max power transfer occurs when the load resistor equals Rint. In principle this would 0.003[3.2/.006]^2 = 850 w, but probably nobody safely loads batteries that heavily.


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## madmike8 (Jun 16, 2011)

So 225 cells 45s5p would get you a 144v pack that can pull 1000a for 10s, and weigh around 164 pounds. Make a good drag pack?


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## powerhouse (Apr 1, 2011)

Currently having some 'talks' with Headway


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## drgrieve (Apr 14, 2011)

Powerful but heavy @ 75 Wh/kg


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## sokon (Sep 15, 2011)

I agree, this battery looks interesting. The thing that really bothers me as well is its energy density of way below 100wh/kg...


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## frodus (Apr 12, 2008)

is the main difference between this and the 38120P cells just the lower IR?

Seems like the C rates are similar if not the same.



energy density sucks though......


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## Outtasight (Dec 8, 2011)

The C rate of a cell is more dependent on the chemical properties of the cell than the electronic properties. The so called "internal resistance" of any cell is only an apparent resistance. Some real resistance is made up of the electrode material (how conductive it is and how good the other connections to the outside world are). But most of the internal "resistance" of a cell is down to how good it is at doing it's chemical reactions very fast. Two cells with the same capacity can have very different internal resistances if the electrodes physical interface to the electrolyte and the ability of the ions to move from one place to another and react with other atoms is better - typically how much surface area the electrodes can present by making them ever more spongy and porus.

So the cell does not have electrical resistance in the sense of a resistor. It is a current source that has a limited ability to push electrons out of one electrode and pull them in from the other that is a function of how many atoms can come into contact with other atoms and react in a short time.

The pulse C rating is much higher because that is the instantaneous current that the cell can push given a starting point of the electrode surface being rested and just waiting to react with all the material floating in the electrolyte just next to it. But after that time of initial very high reactivity, some atoms have to move from A to B to get close to the electrode material and react with it some more... and that can't happen so fast, so the continuous current the cell can put out falls off to the speed at which that migration from A to B can happen.

The continous current rating is also limited by thermal considerations. The passing of 200A through a smallish electrode collector will cause it to heat up and a balance between how much of that heat can escape (through the innards of the cell which is spiral wound) will limit the safe current delivery. 

The manufacturer may also overestimate the continuous current based on a single cell in free air running at that current. It's a different ball game when you pack a couple of hundred of these hot things tightly together in a box and then run it at 200A...


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## Rational (Nov 26, 2011)

madmike8 said:


> a good drag pack?


When milliseconds count you might want to look into the transient response of your batteries. If it's long you could permanently parallel the batteries with a supercap but that is assuming the transient response of the supercap is close to the ideal of 0 mS.
Good luck trying to get these specs. . .


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## sokon (Sep 15, 2011)

also consider that for two cells (of the same chemistry) with the same C ratings, the more energy dense cell will always be be more power dense (gravimetrically) as well!
As an example, given a cell of the same weight as the headway cell but with say 140Wh/kg, then the the latter cell is around 15Ah and therefore only has to output 11C in order to pull out the same current as the headway cell at 20C.

Edit: For this reason the proper way to classify cells is power density rather than C ratings (you can even compare batteries, or energy storage of any kind for that matter, of different types (e.g. chemistries) in a usefull sense that way), at least if one likes to compare apples to apples. C rstings probably is more something for the RC crowd I think.


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## mizlplix (May 1, 2011)

OK, All of this hair splitting aside....{and it is hair splitting to us non-tech consumers]....

The only real distinct advantage I can see to the many small/build your own pack VS the few large/already built batteries is the ability to adapt them into your fixed car structure more easily and a less obvious way. Every time I add up the costs of each method, I still get sticker shock.

A few tenths of a volt, a few charge cycles, a slightly different "C" curve is no indication of a radical industry wide battery milestone. 

It is just interesting reading, like the guy that made his own strap spot welder. 

Some real improvements would be to *build in* the over/undercharge protection like in the power tool batteries. OR have a signal tap on each battery to be used to hook to a simple monitor to indicate a potential cell out-of-balance condition so we knew when to re-balance them. BOTH built into the battery.....Both seem do-able to me.

The battery industry as a whole seems just like OPEC. It is keeping the prices up while squeezing out their investment in the present manufacturing infrastructure and tickling us with trivial "Industry milestones" to keep us interested. 

Just my opinion, Miz


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