Doctorbass
100 GW
post about:
-Internal resistance of a cell
-max load a single cell can hold
-explanations
I'm planning to construct a load able to hold 100A continuous for any cell voltages.
I can buy many single 0.2ohm 25W resistor for 0.99$ at my local electronic surplus store.
I plan to build a 700W 0.025ohm load.
I will use this configuration : 7p(2p2s) for a total of 28 resistors.... And for sure a biiiiiiiiiig 5" alot CFM fan!!
It will have constant resistor and not constant current because it would be too complicated and not necessary to regulate current at 100A continuously for that use.
You need to know that 100A passing thru a cell like the A123 that have around 0.01ohm internal resistance mean that it will dissipate 100W !!! and that's the reason why they specify that it can only take it for 10 sec. In the case of the killacycle, they often crank the current to 150A !! and that's 225W per cells!!! actally they have 1210 cells ...and that mean during each race they dissipate 225W x 1210 =272250W during 7.82sec that's 2.129 megajoules!!
eeee....ok let's go back to the subject
:lol:
What that limit each cell max current allowable is for sur is the temperature. The capability of a cell to dissipate its heat and the capability of its chemistry to be not negatively being affected by that heat.
the A123 specify that they can hold 120A during 10 sec... what does it mean..? why? let understand what happen:
p= the power a cell will dissipate
ir = internal resistor and A123 - 10 miliohm
I= the current that travel thru the cell A123 =max 120A
p=ir x I^2
=0.01 x 120^2
= 144Watts
144W during 10 sec = 1440 joules (1.44kJ)
That amount of energy is the max that an A123 cell can get without being damaged.
Do you remember the problem that happened with the COBALT li-ion cell that exploded?
One of the problem was that they have a high internal resistance...that mean a big heat dissipation for a given current passing thru it. Also because with the cobalt material, these chemistry was not stable and the themerature rise affect easily this stability.
Doc
-Internal resistance of a cell
-max load a single cell can hold
-explanations
I'm planning to construct a load able to hold 100A continuous for any cell voltages.
I can buy many single 0.2ohm 25W resistor for 0.99$ at my local electronic surplus store.
I plan to build a 700W 0.025ohm load.
I will use this configuration : 7p(2p2s) for a total of 28 resistors.... And for sure a biiiiiiiiiig 5" alot CFM fan!!
It will have constant resistor and not constant current because it would be too complicated and not necessary to regulate current at 100A continuously for that use.
You need to know that 100A passing thru a cell like the A123 that have around 0.01ohm internal resistance mean that it will dissipate 100W !!! and that's the reason why they specify that it can only take it for 10 sec. In the case of the killacycle, they often crank the current to 150A !! and that's 225W per cells!!! actally they have 1210 cells ...and that mean during each race they dissipate 225W x 1210 =272250W during 7.82sec that's 2.129 megajoules!!
eeee....ok let's go back to the subject
:lol:
What that limit each cell max current allowable is for sur is the temperature. The capability of a cell to dissipate its heat and the capability of its chemistry to be not negatively being affected by that heat.
the A123 specify that they can hold 120A during 10 sec... what does it mean..? why? let understand what happen:
p= the power a cell will dissipate
ir = internal resistor and A123 - 10 miliohm
I= the current that travel thru the cell A123 =max 120A
p=ir x I^2
=0.01 x 120^2
= 144Watts
144W during 10 sec = 1440 joules (1.44kJ)
That amount of energy is the max that an A123 cell can get without being damaged.
Do you remember the problem that happened with the COBALT li-ion cell that exploded?
One of the problem was that they have a high internal resistance...that mean a big heat dissipation for a given current passing thru it. Also because with the cobalt material, these chemistry was not stable and the themerature rise affect easily this stability.
Doc
