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Old 12-04-2005, 08:10 AM   #31
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Well, you haven't defined "ENDOTHERMIC" in your response, although you used the term over 5 times.

Endothermic I belive means a chemical reaction that takes place that produces heat (or cold) by means of a chemical reaction. Batteries make heat but not by just the chemical reaction alone. The energy created BY the chemical reaction passing through the cells produce heat in acordance to the amount of resistance in the cell. If there we 0 resistance, the heat would also be 0.

Higher load means more current passing through cells, means more heat.
Hi Mark,

I appreciate your response but please allow me to elaborate because there is a misunderstanding again about how batteries operate...

This is not a physics or chemistry forum and I will not go into details as to explain the actual endothermic reaction that occurs within a cell....its outside the scope of this answer and it will give away lots of information on how to enhance the performance of the cell. I used that term because that is the most accurate definition of what happens inside a cell. If you know enough chemistry and physics you can take the cell equation, figure it out, calculate the actual electric potential (the open cell voltage) and see what happens inside the cell.
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If there we 0 resistance, the heat would also be 0.
WRONG!!!!

The main reason for HEAT build up in a cell is not because of internal resistance. YOu are assuming that ohms law takes precedence but it does not.
The MAIN CAUSE FOR HEATBUILD UP HAS TO DO WITH THE TERM I USED...ENDOTHERMIC REACTION.... The main factor for heat build up is not INTERNAL RESISTANCE but inner cell pressure caused by excesssive oxygen build up in the inner core of the cell.

You are thinking of a battery as a resistor and it is not...there is a chemical reaction taking place regardless of IR.

Once the battery gets to around 2300+mahr it can only absorb X% of the current that is being supplied by the charger. Since that current cannot be absorbed at the same efficiency rate, oxygen buildup from the chemical reaction starts to take place inside the cell, thus increased pressure and the exponential rise in HEAT. Something very similar occurs while dischrging. Internal resistance is a factor, but minimal...PRESSURE is the main cause for heat build up, not resistance... that's why cells VENT and POP as they are charged. or DISCHARGED..
Have you ever heard that hissing sound while discharging a cell, that is due to the ENDOTHERMIC reaction that causes an increase in oxygen build up and pressure. This is typical of NiMh batteries because of their chemical compounds.

WOW, I wonder how many times I mentioned endothermic this time?

But a cell is an endothermic device and the chemical reaction is ENDOTHERMIC in principle.

I will be more than glad to explain this in more detail to you if you email me, but I will not spend 45 minutes deriving chemical equations that most readers do not care to see nor will they understand them.

Our r/c batteries have actual IRs in the range of .007 ohms or less (.00625...-) so the actual heat generated by the IR is in the range of 6.3 Watts @ 30A. As you can see the REAL factor that creates all that HEAT is PRESSURE...and that is a bi-product of the ENDOTHERMIC REACTION.... Batteries reach temperatures in excess of 160*F while being discharged at high current rates...and 160*f does not equate to a few watts.

Do yu remeber the formula PV=nRT n=avogadros number 6.02214199 x 10 (-23)

The main cause for heat build up in a cell is not the IR of the cell.
The differnce between discharging at 30 or 35 amps only creates a difference of around 2.27 Watts, not much when you look at the overall picture.
Now use the abovementioned formula and you might be able to see the consequences of pressure v temp.

Isaac

Last edited by BATT_MAN; 12-04-2005 at 11:00 AM.
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Old 12-04-2005, 11:42 PM   #32
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Cool.

Did you miss this in my post:

Endothermic I belive means a chemical reaction that takes place that produces heat (or cold) by means of a chemical reaction.

I am curious. Shouldn't hydrogen also be a by product of the "endothermic" process, as oxygen is? Especially during the charge cycle?

I only have about an average joe's understanding of how rechargable batteries operate...
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Old 12-05-2005, 12:48 AM   #33
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Mark,

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I am curious. Shouldn't hydrogen also be a by product of the "endothermic" process, as oxygen is? Especially during the charge cycle?
You are correct, the main chemical element for the anode is hydrogen. However, the newer cell designs utilize alloys at the electrodes that do a much better job at absorbing and transfering the hydrogen build up throughout the cell. I should have added to my answer the hydrogen since it is the MAIN compound. We are now talikng both endothermic and exothermic reactions when the hydrogen is taken into consideration.

However, it has been noticed that the main compound that causes the increase in pressure is oxygen and I will explain...

The principle behind a NiMh batery is to have the electrodes store the hydrogen atoms, thus generating power. although hydrogen has wonderful anodic qualities, it requires cell pressurization, and I believe this is why the oxygen plays such a role.

The anodes used in these cells are complex alloys containing many metals, such as an alloy of V, Ti, Zr, Ni, Cr, Co, and Fe. The underlying chemistry of these alloys and reasons for superior performance are not yet clearly understood by many of us, and the compositions are determined by empirical testing methods. IB has done a great job at finding the right metals (elements) to get higher voltages.

A very interesting fact about these alloys is that some metals absorb heat when absorbiong hydrogen, and some give off heat when absorbing hydrogen. Both of these are bad for a battery, since we would like the hydregen to move easily in and out without any energy transfer. The successful alloys are all mixtures of exothermic and endothermic metals in order to achieve this. A bi-product of this reaction because of the alloys is the excess molecules that end up reacting and producing oxygen thus the additional inner cell pressure. Both, hydrogen and oxygen play a very important role. The hydrogen GIVES energy and the oxygen bi-product creates excees inner cell pressure thus adding to the heat build up.

We have also noticed on some cells that when trickle charged (or charged at low current rates) there is an excess of oxygen being created thus an increase in pressure and temperature rise. It must be because of the alloys used for the electrodes tend to process and disperse the hydrogen much faster.

The main thing is that we are able to prove that the IR of a battery is negligent when it comes to temperature. Whether companies discharge at 20, 30, 35, or 40 amps we know that heat is bad and it can damage cells.

I am glad you brough the hydrogen factor to my attention... I just forgot to mention it in the heat of passion
GOOD CALL!!!!!

I like exchanging info with persons like you. I am the first person to admit when I miss something or I do not know it.

THANKS,

Isaac K
Axxis Racing

Last edited by BATT_MAN; 12-05-2005 at 01:21 AM.
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Old 12-05-2005, 01:31 AM   #34
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Quote:
Originally Posted by BATT_MAN
Hi Mark,

I appreciate your response but please allow me to elaborate because there is a misunderstanding again about how batteries operate...

This is not a physics or chemistry forum and I will not go into details as to explain the actual endothermic reaction that occurs within a cell....its outside the scope of this answer and it will give away lots of information on how to enhance the performance of the cell. I used that term because that is the most accurate definition of what happens inside a cell. If you know enough chemistry and physics you can take the cell equation, figure it out, calculate the actual electric potential (the open cell voltage) and see what happens inside the cell.

WRONG!!!!

The main reason for HEAT build up in a cell is not because of internal resistance. YOu are assuming that ohms law takes precedence but it does not.
The MAIN CAUSE FOR HEATBUILD UP HAS TO DO WITH THE TERM I USED...ENDOTHERMIC REACTION.... The main factor for heat build up is not INTERNAL RESISTANCE but inner cell pressure caused by excesssive oxygen build up in the inner core of the cell.

You are thinking of a battery as a resistor and it is not...there is a chemical reaction taking place regardless of IR.

Once the battery gets to around 2300+mahr it can only absorb X% of the current that is being supplied by the charger. Since that current cannot be absorbed at the same efficiency rate, oxygen buildup from the chemical reaction starts to take place inside the cell, thus increased pressure and the exponential rise in HEAT. Something very similar occurs while dischrging. Internal resistance is a factor, but minimal...PRESSURE is the main cause for heat build up, not resistance... that's why cells VENT and POP as they are charged. or DISCHARGED..
Have you ever heard that hissing sound while discharging a cell, that is due to the ENDOTHERMIC reaction that causes an increase in oxygen build up and pressure. This is typical of NiMh batteries because of their chemical compounds.

WOW, I wonder how many times I mentioned endothermic this time?

But a cell is an endothermic device and the chemical reaction is ENDOTHERMIC in principle.

I will be more than glad to explain this in more detail to you if you email me, but I will not spend 45 minutes deriving chemical equations that most readers do not care to see nor will they understand them.

Our r/c batteries have actual IRs in the range of .007 ohms or less (.00625...-) so the actual heat generated by the IR is in the range of 6.3 Watts @ 30A. As you can see the REAL factor that creates all that HEAT is PRESSURE...and that is a bi-product of the ENDOTHERMIC REACTION.... Batteries reach temperatures in excess of 160*F while being discharged at high current rates...and 160*f does not equate to a few watts.

Do yu remeber the formula PV=nRT n=avogadros number 6.02214199 x 10 (-23)

The main cause for heat build up in a cell is not the IR of the cell.
The differnce between discharging at 30 or 35 amps only creates a difference of around 2.27 Watts, not much when you look at the overall picture.
Now use the abovementioned formula and you might be able to see the consequences of pressure v temp.

Isaac

I'm calling you out Isaac. You obviously have zero clue what an endothermic reaction is, because if you did you wouldn't use that term. If our batteries reactions while running on our cars were ENDOTHERMIC, then that would mean we would be pumping heat INTO the battery from an outside source. I don't think we need to heat our batteries with a burner to produce electricity.

1. An endothermic process is one in which heat has to be supplied to the system from the surroundings.

2. An exothermic process is one that gives off heat. This heat is transferred to the surroundings.

BTW...while you're sitting there trying to sound like a college professor, why don't you enlighten us as to what Enthalpy means!?! (Hint: First law of thermodynamics )
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Old 12-05-2005, 01:46 AM   #35
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1. An endothermic process is one in which heat has to be supplied to the system from the surroundings.

2. An exothermic process is one that gives off heat. This heat is transferred to the surroundings.


WOW!!!!! YOU IMPRESS ME WITH YOUR VOCABULARY!!!!

1. What happens when you charge a battery?

2. What happens when you discharge a battery?

3. What happens inside a battery?


Quote:
The principle behind a NiMh batery is to have the electrodes store the hydrogen atoms, thus generating power. although hydrogen has wonderful anodic qualities, it requires cell pressurization, and I believe this is why the oxygen plays such a role.

The anodes used in these cells are complex alloys containing many metals, such as an alloy of V, Ti, Zr, Ni, Cr, Co, and Fe. The underlying chemistry of these alloys and reasons for superior performance are not yet clearly understood by many of us, and the compositions are determined by empirical testing methods. IB has done a great job at finding the right metals (elements) to get higher voltages.

A very interesting fact about these alloys is that some metals absorb heat when absorbiong hydrogen, and some give off heat when absorbing hydrogen. Both of these are bad for a battery, since we would like the hydregen to move easily in and out without any energy transfer. The successful alloys are all mixtures of exothermic and endothermic metals in order to achieve this. A bi-product of this reaction because of the alloys is the excess molecules that end up reacting and producing oxygen thus the additional inner cell pressure. Both, hydrogen and oxygen play a very important role. The hydrogen GIVES energy and the oxygen bi-product creates excees inner cell pressure thus adding to the heat build up.
YOu may know thermodynamics, but think.... and apply your knowledge to the way a battery operates. Look at the BIG picture, not at a dictionary definition.

Enthalpy has to do with gases and I was nottrying tio impress persons with BIG WORDS...

Enthalpy H=E+p*V

or do you want specific enthalpy h2 - h1 = Cp (T2 - T1)

Do you want me to elaborate more, how deep into the equations do you want me to go... do you want to start with the first law of thermodynamics...

I don't thionk thereaders care...but if you want lets go at it...
Ask any battery engineer or phycisist if this explanation is incorrect...then ....
PROVE ME WRONG!!!!

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Old 12-05-2005, 01:54 AM   #36
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My head hurts...
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Old 12-05-2005, 01:57 AM   #37
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Quote:
Originally Posted by BATT_MAN


WOW!!!!! YOU IMPRESS ME WITH YOUR VOCABULARY!!!!

1. What happens when you charge a battery?

2. What happens when you discharge a battery?

3. What happens inside a battery?




YOu may know thermodynamics, but think.... and apply your knowledge to the way a battery operates. Look at the BIG picture, not at a dictionary definition.

PROVE ME WRONG!!!!

Dude...face it...you didn't understand what endothermic meant. Don't use 50 cent words when all you've got is a dime.
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Old 12-05-2005, 01:58 AM   #38
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BTW...the proper term would be exothermic.
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Old 12-05-2005, 01:58 AM   #39
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...and I like cheese.
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Old 12-05-2005, 02:12 AM   #40
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I don't think we need to heat our batteries with a burner to produce electricity.
BUT YOU DO NEED TO CHARGE THEM...and what happens inside ....DUDE....
What happens at the electrodes...YOU ARE WAY OFF



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Old 12-05-2005, 02:20 AM   #41
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Originally Posted by BATT_MAN
I am not going to waist my time...

EAT YOUR CHEESE.... do you do get it endo or exo...
Eating food is exothermic, since the human body uses food to produce energy. Body heat being one of the by-products.

A "cold-pack" chemical pack to treat sprained ankles utilizes an endothermic reaction. Since the reaction of the chemicals within the cold-pack removes heat from the surrounding environment.

In the 23 times you used the term "endothermic" you never once utilized it properly.
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Old 12-05-2005, 02:23 AM   #42
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Quote:
Originally Posted by BATT_MAN

This is the EXPERT!!!!

Birthday: December 28, 1978
Biography: Human, male, functional reproductive system.
Location: Escaped the lab @ Penn State. (NC)
Interests: RC, PCs, MTBs, LMNOP's
Occupation: I'm a fucking mutant...Like radioactive and shit..

EAT YOUR CHEESE....
because I am not going to waist my time...
Yup...thats me. You have something against radioactivity?!?!?

BTW...you mean waste...not "waist." We're not talking female attributes here.
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Last edited by Soviet; 12-05-2005 at 12:06 PM.
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