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  #1  
Old 12-08-2011, 05:05 PM
powerhouse powerhouse is offline
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Default New Headway 38120HP Cell

Forum member Yabert showed me this today...
Now the internal resistance is lower, and its red!
I am inquiring about the prices as I speak!
Take a look at the specs

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  #2  
Old 12-08-2011, 07:37 PM
Rational Rational is offline
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Default Re: New Headway 38120HP Cell

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.

Last edited by Rational; 12-08-2011 at 07:44 PM.
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Old 12-08-2011, 07:54 PM
madmike8 madmike8 is offline
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Default Re: New Headway 38120HP Cell

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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Old 12-08-2011, 08:02 PM
powerhouse powerhouse is offline
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Default Re: New Headway 38120HP Cell

Currently having some 'talks' with Headway

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Old 12-08-2011, 10:21 PM
drgrieve drgrieve is offline
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Default Re: New Headway 38120HP Cell

Powerful but heavy @ 75 Wh/kg
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Old 12-09-2011, 01:50 AM
sokon sokon is offline
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Default Re: New Headway 38120HP Cell

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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Old 12-09-2011, 09:49 AM
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Default Re: New Headway 38120HP Cell

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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Old 12-09-2011, 10:49 AM
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Default Re: New Headway 38120HP Cell

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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Old 12-09-2011, 11:55 AM
Rational Rational is offline
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Default Re: New Headway 38120HP Cell

Quote:
Originally Posted by madmike8 View Post
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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Old 12-10-2011, 05:22 AM
sokon sokon is offline
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Default Re: New Headway 38120HP Cell

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.

Last edited by sokon; 12-10-2011 at 05:27 AM.
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