# Battery spacing???



## helluvaengineer96 (Oct 8, 2010)

By looking at the various conversions on this forum it appears that everyone packs their lead-acids or Li batteries in as closely as possible. 

I always thought excessive heat was a batteries worst enemy and spacing or heat sinking the batteries would be a good practice. Right now I am leaning more towards spacing with air and using a fan to generate air flow during the charging phase.

Are folks packing their batteries to save as much space as possible, relying on the charger to stop during over temp?

Has anyone spaced or placed heat sinks between batteries with positive results. If so can you provide link to there conversion? I know in telco cabinet applications, spacing lead-acids will greatly increase life span.

Thanks in advance for any input.


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## MN Driver (Sep 29, 2009)

If the battery pack is sized with enough capacity to handle the load they shouldn't produce enough heat to damage them and in cold weather the warmer they are the better they perform so you want more heat in those cases, easier to heat the cells if they are closer together.

Another thing to keep in mind, the prismatic cells will be hotter inside than what will reach the outside of the case so even if you cool the outside of the case the built up heat inside will not be leaving fast enough if you are subjecting them to severe conditions causing them to rapidly heat up in the first place.


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## BMI/LiFeTech (Aug 12, 2009)

helluvaengineer96 said:


> Has anyone spaced or placed heat sinks between batteries with positive results. If so can you provide link to there conversion? I know in telco cabinet applications, spacing lead-acids will greatly increase life span.
> 
> Thanks in advance for any input.


LiFeTech Energy is the only company which has designed a cell with heatsink fins built into the cell to directly address the cooling issues at high rates of discharge. This will greatly increase the performance AND longevity of the cell.
This is an area where all of the major cell manufacturers have totally neglected.

LiFeTech Energy will be releasing the new 20Ah and 25Ah HEHC professional manufacturer's cells in 2011.


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## helluvaengineer96 (Oct 8, 2010)

Given your font I take it you are from Minnesota? I'm in SC so our environment is definitely impacting our view of the world . I plan on putting a cabinet heating element under the batteries, powering it via AC... During charging is the only time I think temp should be a problem, given my sunny climate. Telco cabinet battery trays come with great battery heating pads if you are looking for something that is light and designed to have batteries sit on them.

Honestly, since this is my first EC it was not thinking about the heat thrown off during discharge... All the applications I've ever worked on were pretty low draw affairs. I was planning to derate the controller configuration by about 20% to stay well in the safety range so this should help here.... Wonder if I should have fans available during discharge too? Originally planning to have the fans only powered by AC (since I was only worried about the charging phase).

My bigger concern with spacing is during the charging process: thermal run-a-way / overall battery life. I guess BMS and charger can help compensate but, 50 C on a sunny day with batteries charging is not that hard to hit.. Plus there will be non uniform battery temps, the ones in the middle will be significantly hotter, while charging. 

You make a good point the bag on in the inside will get warmer than the casing... *Maybe the prismatic cells are designed with internal spacing to provide insulation from other cells next to them... and the designers intended all the heat to be dissipated out the terminals?*

In which case I should not worry about spacing but adding non conductive heat sinks to the terminals?

Thanks for the input.



MN Driver said:


> If the battery pack is sized with enough capacity to handle the load they shouldn't produce enough heat to damage them and in cold weather the warmer they are the better they perform so you want more heat in those cases, easier to heat the cells if they are closer together.
> 
> Another thing to keep in mind, the prismatic cells will be hotter inside than what will reach the outside of the case so even if you cool the outside of the case the built up heat inside will not be leaving fast enough if you are subjecting them to severe conditions causing them to rapidly heat up in the first place.


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## helluvaengineer96 (Oct 8, 2010)

Hi,
I was not considering radial battery packages since the prismatic (brick form factor) seems so much easier to work with and it seemed like the radial technology was being abandoned (keep in mind I just started looking at this about 3 months ago).....

But I really like the thumbnail you attached... rather then insulating the reactives in a brick you are allowing the reactives to dissipate heat out their body (heat sink). Clearly there are thermal advantages to this... but I wonder what this does to overall density and weight?

Can you send me a data sheet on the new units.. So I can build a model and see if they meet my physical space requirements?

Also, do you know when you will be GA in 2011? Samples available date?

Other than EV, I am also looking to use Li for battery backup for work related deployments.

Thanks



BMI/LiFeTech said:


> LiFeTech Energy is the only company which has designed a cell with heatsink fins built into the cell to directly address the cooling issues at high rates of discharge. This will greatly increase the performance AND longevity of the cell.
> This is an area where all of the major cell manufacturers have totally neglected.
> 
> LiFeTech Energy will be releasing the new 20Ah and 25Ah HEHC professional manufacturer's cells in 2011.


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## DavidDymaxion (Dec 1, 2008)

I like it! I have been doing some torture testing of another brand of Lithium cells. At high currents they get too hot, the cell heat sinks seem like a good idea. Can you share any data on how much cooler the cells stay? Have you tested doing heatsink connections on the terminals?


BMI/LiFeTech said:


> LiFeTech Energy is the only company which has designed a cell with heatsink fins built into the cell to directly address the cooling issues at high rates of discharge. This will greatly increase the performance AND longevity of the cell.
> This is an area where all of the major cell manufacturers have totally neglected.
> 
> LiFeTech Energy will be releasing the new 20Ah and 25Ah HEHC professional manufacturer's cells in 2011.


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## Bottomfeeder (Jun 13, 2008)

BMI/LiFeTech said:


> LiFeTech Energy is the only company which has designed a cell with heatsink fins built into the cell to directly address the cooling issues at high rates of discharge. This will greatly increase the performance AND longevity of the cell.
> This is an area where all of the major cell manufacturers have totally neglected.
> 
> LiFeTech Energy will be releasing the new 20Ah and 25Ah HEHC professional manufacturer's cells in 2011.


Any links where we can learn more and stay informed? Any rough guess as to the price schedule for these things?


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## Jimdear2 (Oct 12, 2008)

DavidDymaxion said:


> I like it! I have been doing some torture testing of another brand of Lithium cells. At high currents they get too hot, the cell heat sinks seem like a good idea. Can you share any data on how much cooler the cells stay? Have you tested doing heatsink connections on the terminals?


David,

We are going to be using 30126P headways in such a way we will probably pull 150 amps ramping to 200 amps over a period of 15 -20 seconds. The cells are on their way so I haven't done any testing yet.

Do you have any data you would care to share. 

I've been thinking about various cooling methods. I've thought of everything from just thermal cycle (heat rises) air cooling to adding finned jackets and fan cooling to forced air through dry ice to fire extingusher type CO2. From what I can see the snap together blocks hold the cells too close together for our needs so I was thinking of polycarbonate seperators with holes to support the cells, something like Crodriver did.

What are your thoughts on cooling?


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## tomofreno (Mar 3, 2009)

> When performance and quality is all that matters.


 I think that is a hint on the cost.


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## DavidDymaxion (Dec 1, 2008)

I'm planning to do a big write up with all the data, but here's a quick snap of what I've done so far:

China High Power 42110 cylindrical cells 10 Ahr LiFe

I got mine from:
http://www.evequipmentsupply.com/

I got them long enough ago I forgot the exact price, but I think they are significantly cheaper than Headways.

I pulled 250 A very briefly on cool, freshly charged batteries. Note this is not a short circuit, just what my tester could go down to in resistance.

After they were thoroughly warmed up (50A or higher for minutes), uncomfortably hot to touch, I could pull 150A, but a battery or batteries made a frying bacon sound.

My best run with no drama was 100A for over 4 minutes. I terminated the test because the batteries hit 73C, the voltage was at or above 10.0 V for four in series almost the whole time.

I killed a battery with a 110A run for over 4 minutes. It went to over 88C (I had been monitoring a middle battery that went to 66C) and it dripped out some electrolyte. Amazingly it still reads 2.7V. I had put some pressure on the button, and was going copper to aluminum, and had a small contact spot, so those things might have been a problem.

Anyway, it looks like heat is the enemy for these cells. I have been thinking about heat sink tricks. I'd like to do some tests with fans on the cells, or immersing them in liquid, to see how much difference that makes.

I'm planning to do futher tests with the remaining 3 batteries. Once I've extracted all the knowlege I can, I have some 200 Ahr cells to test. That's going to be fun doing 1000+ A tests! The goal is to torture test them, too.

My interest is land speed and possibly some track racing, hence the longer test times than drag racers would do.

For drag racer time scales, A123 batteries are certainly better, and I think Headways are better from what I've read, but these look like they could be an excellent compromise for cost and performance for my racing needs.

Disclaimer: I have no financial interest in the success or failure of China High Power, A123, Headway, or EVEquipmentSupply.


Jimdear2 said:


> David,
> 
> We are going to be using 30126P headways in such a way we will probably pull 150 amps ramping to 200 amps over a period of 15 -20 seconds. The cells are on their way so I haven't done any testing yet.
> 
> ...


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## BMI/LiFeTech (Aug 12, 2009)

helluvaengineer96 said:


> Hi,
> I was not considering radial battery packages since the prismatic (brick form factor) seems so much easier to work with and it seemed like the radial technology was being abandoned (keep in mind I just started looking at this about 3 months ago).....
> 
> But I really like the thumbnail you attached... rather then insulating the reactives in a brick you are allowing the reactives to dissipate heat out their body (heat sink). Clearly there are thermal advantages to this... but I wonder what this does to overall density and weight?
> ...


I have replied to your email questions directly. Thankyou

The final cell data sheets are not available as yet since the cells are still in the final stages of testing.

We are busy setting up the cell assembly lines in our factory at the present time. These cells will be manufactured on the latest state of the art Japanese cell manufacturing machinery (completely automated/computer controlled manufacturing environment for consistent high quality product).


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## BMI/LiFeTech (Aug 12, 2009)

DavidDymaxion said:


> I like it! I have been doing some torture testing of another brand of Lithium cells. At high currents they get too hot, the cell heat sinks seem like a good idea. Can you share any data on how much cooler the cells stay? Have you tested doing heatsink connections on the terminals?


Yes poor cooling/hot cells leads to premature cell death. This is why our cell design engineers have spent many hours developing this cell so as to overcome the cooling issues which all other cell manufacturers have failed to address.
I will post more information when the final cell specification is released.


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## BMI/LiFeTech (Aug 12, 2009)

Bottomfeeder said:


> Any links where we can learn more and stay informed? Any rough guess as to the price schedule for these things?


I will start a new thread so I can post new information as it becomes available.
For direct answers to any questions you may have feel free to call me at anytime. My direct contact details are below.
Although I am the LiFeTech Energy sales representative I am primarily one of the electrical engineers involved with product development so I should be able to answer any technical questions raised.

Armin Pauza
General Manager and Principal Electrical Engineer
LiFeTech Lithium Energy & Lithium Batteries Australia
Ph. Int. 61 4 20948757
[email protected]


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## Jimdear2 (Oct 12, 2008)

DavidDymaxion said:


> I'm planning to do a big write up with all the data, but here's a quick snap of what I've done so far:
> 
> China High Power 42110 cylindrical cells 10 Ahr LiFe
> <snip>
> ...


David,

Thanks for the information. It pretty much confirms a lot of my guesses. 

I won't know how the batteries I have coming will react to the loads I plan until I get a chance to test them, but gut tells me that the higher capacity (Bigger Diameter/Length) cells are going to have a serious problem shedding internal heat so the 38mm diameter cells I have comming should perform better at heat shedding then the 40+mm cells. It will just take more of them for the same performance.

I would guess one reason is that the extended film length of the larger batteries is going to generate more heat and the larger diameter is going to slow down migration of heat from the core. I'm sure that part of the film used internally is a dielectric and probably a heat insulator as well

The above is probably just recovering the ground you already have, sorry about that.

It appears that the smaller cells do have a superior heat shedding ability, I assume just because of the smaller radius. I agree this probably explains a lot of the superior performance of the A123 in high performance. it also helps explain why why the A123s are the performance choice, even with the difficulty in building a pack.

With the heat buildup problem in mind I had been doing a bit of looking around and came up with this site

http://www.robfin.com/Products/PlainFin/tabid/85/Default.aspx

If testing shows that I'll have a heating problem in my Headways with the loads I intend, I had planned on taking a battery down to them to see if they couldn't come up with a cover, possibly self adhesive ot treated with thermal grease, that could wrap either a battery or stick of batteries. They can make this material in up to 24 inch lengths. Something that would allow us to come up with a reasonable cost alternative to the Life Tech. A fan placed at the end of a battery/stick of batteries and blowing down the channels formed by a wrapped folded fin heat sink should do a lot to control temperatures.

If you look at their spec sheet for the plain folded fins you will see that their is a large variation of what they can do. I'm sure some of the engineering types can help with thermal specifications on various configurations. They may have some generic material on hand that we can use for testing purposes.

You might try contacting them before you test your remaining three batteries and see if the have something you could use during your testing to see if they would help.

Those of us using the spiral wound cylinder type batteries will probably always run into a heating problem at one time or another If not during discharging then maybe during charging. If this is a viable, reasonably priced, method of battery cooling, we should all know about it.

Since you are looking at severe heating problems in your chosen use, I hope this helps. I would really like to see your name on an EV speed record.

Just a thought, for your land speed attempts, think about CO2 expansion cooling or even a dry ice cold box.

Jim


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## helluvaengineer96 (Oct 8, 2010)

Jim,
The phenomena you are seeing is related to surface area of a sphere vs internal volume. An amoeba has the same problem.. the greater the diameter the worst the volume to surface area ratio becomes... from a 2D look 2*3.14*R / 3.14*R^2 == 2/R... the bigger R gets the worse the ratio is.

Like the link you found... This is a great idea.. However keep in mind you want as much of the outer shell to come in contact with the heat sink as possible. It will be more expensive but an extruded aluminum shell will provide greater surface area contact. Expansion and contraction rates could be different between the battery and the aluminum so this will have to be considered. You don't want the battery contents expanding faster then the aluminum, creating internal pressure and a possible rupture. 

If you want to be really inexpensive... might be able to find electric aluminum conduit that is the same diameter of the cell you are working with, then attach fins.... This would give you a prototype to base your tests on. If the results are good enough then have it machined. The machined part would of course have better performance than the prototype.

For the prototype....if you can find conduit thick enough your could even machine valleys into it to provide a little more surface area and easier than attaching fins.

Here is link for extruded Al vender... http://www.argylein.com/extruded_shapes_search.php?profile=Pipe
for 30 mm 
160 1.500 1.900 0.281 1.681 would give 0.16" of space
80 1.250 1.660 0.191 1.037 would give 0.10" of space but thinner walls.

for 40 mm
40 1.500 1.900 0.145 0.940 would give 0.040" of space with thin walls
160 2.000 2.375 0.343 2.628 would give 0.120" of space

Think you will want less than 0.025" of space.....





Jimdear2 said:


> David,
> 
> It appears that the smaller cells do have a superior heat shedding ability, I assume just because of the smaller radius. I agree this probably explains a lot of the superior performance of the A123 in high performance. it also helps explain why why the A123s are the performance choice, even with the difficulty in building a pack.
> 
> ...


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## Jimdear2 (Oct 12, 2008)

helluvaengineer96 said:


> Jim,
> The phenomena you are seeing is related to surface area of a sphere vs internal volume. An amoeba has the same problem.. the greater the diameter the worst the volume to surface area ratio becomes... from a 2D look 2*3.14*R / 3.14*R^2 == 2/R... the bigger R gets the worse the ratio is.


'engineer',

Thanks for the formula, I am one of those unfortunate cripples that math makes go catonic. Help like this is always a plus.



helluvaengineer96 said:


> Like the link you found... This is a great idea.. However keep in mind you want as much of the outer shell to come in contact with the heat sink as possible. It will be more expensive but an extruded aluminum shell will provide greater surface area contact. Expansion and contraction rates could be different between the battery and the aluminum so this will have to be considered.
> 
> If you want to be really inexpensive... might be able to find electric aluminum conduit that is the same diameter of the cell you are working with, then attach fins.... This would give you a prototype to base your tests on. If the results are good enough then have it machined. The machined part would of course have better performance than the prototype.
> 
> For the prototype....if you can find conduit thick enough your could even machine valleys into it to provide a little more surface area and easier than attaching fins.


Without contacting them I don't know if they have any "stock" shapes on hand, but I would bet they do, or at least have some production overruns we all could play with to get a workable shape. If you look on the site it appears they have or can make shapes designed to give 100% surface contact once it is wrapped.

Your conduit idea got me to thinking of a combination. First wrap the battery, with say 1/4 or 1/2 inch fin material, then slip a thin piece of split tubing of slightly smaller ID than the OD of the finning. Might make a nice ducted heat sink.

Any machined heat sink in quantity would probably be much more expensive then this folded fin stuff, otherwise there wouldn't be a market for it.

Keep throwing out ideas.

Jim


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## helluvaengineer96 (Oct 8, 2010)

I like your idea for ducting.. controlled air flow and pressure is always better. 

Extruded will definitely be more expensive. 

I've done zero research on the cylinder Li batteries.. Do you have a good link that shows who the venders are and what the standard dimensions are (if there are any standards). Thought I was done picking my battery plant but this opens a whole new avenue.




Jimdear2 said:


> Your conduit idea got me to thinking of a combination. First wrap the battery, with say 1/4 or 1/2 inch fin material, then slip a thin piece of split tubing of slightly smaller ID then the OD of the finning. Might make a nice ducted heat sink.
> 
> Any machined heat sink in quantity would probably be much more expensive then this folded fin stuff, otherwise there wouldn't be a market for it.
> 
> ...


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## Jimdear2 (Oct 12, 2008)

helluvaengineer96 said:


> I like your idea for ducting.. controlled air flow and pressure is always better.
> 
> Extruded will definitely be more expensive.
> 
> I've done zero research on the cylinder Li batteries.. Do you have a good link that shows who the venders are and what the standard dimensions are (if there are any standards). Thought I was done picking my battery plant but this opens a whole new avenue.


'engineer'

I haven't done any formal documents, nor have I seen any sites or reports that list them.

In knocking around the sites I have seen that just about all of the major LiPo manufactures make some form of cylinder type cell in some size. 

My decision for Headways from Manzanita Micro is based on support, US availabilty, reasonable price and a no nonsence attitude.

Manzanita lists the specs for the batteries they sell on their site, most other resellers do also. You can also go to the major Chinese manufacturers sites for information. 

The US outfits like A123 are not interested in small orders from individuals so their information is harder to get but available.

Look up CroDrivers threads, He built a KILLER Headway pack, over 500HP available.

The spiral wound cells, because of their continious film, allow higher C draw then the prizmatic's stacked assemblies, I believe because of lower internal resistance. Size and weight for capacity in the smaller cells is a trade off. I haven't seen any 200 ah spiral wound cells either. Heat would most likly be a killer.

The end result is you can build a prizmatic or cylinder battery. The prismatic will be more compact and may be heavier but you are limited in the rate of draw to 3 or 4 C. The cylinders will require a higher count (cost) to reach the same capacity and will allow MUCH higher C rates.

Basically a family car battery (prizmatics) or a sport car battery (cylinders)

That's my take on it, others may differ.

Jim


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## DavidDymaxion (Dec 1, 2008)

Agree, smaller sheds heat faster. I am trying to think of ways to cool batteries -- CO2 and dry ice are good ideas. Another thought is immersing the pack in a liquid.



Jimdear2 said:


> David,
> 
> Thanks for the information. It pretty much confirms a lot of my guesses.
> 
> ...


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## helluvaengineer96 (Oct 8, 2010)

Jim,
Thanks for the input. I've got to run the numbers but I think the cylinders can be a cure for my problems.

I''m converting a Fiero into and AC50 EV. Have only a two block commute to work and only want the car to experiment with. So I need 550 Amps of continuous current available, derating puts me at ~660 Amps..but not a whole lot of Ahrs. Max charge V must stay under 130V.

My other goal it to fit all the batteries where the gas tank use to go, hump between the two seats. 

Going to be using solar for the AUX battery and converting all lighting over to LED.

Anyway appreciate the help think it will send me down a better battery path.

One more question.... Do folks really use BMS with so many darn cells? Guess the centralized BMS makes a lot more sense when using the cylinders....



Jimdear2 said:


> 'engineer'
> 
> I haven't done any formal documents, nor have I seen any sites or reports that list them.
> 
> ...


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## helluvaengineer96 (Oct 8, 2010)

David,
Where are you located? Air density makes a surprisingly big impact when it comes to cooling...Do you know how watts (in heat) you want to remove from each battery? 
Servers remove a lot of heat from procs with just forced air. However, when I was @ Intel the chip validation folks used a company that used liquid to cool the chips... I'll check over the week to get the name of the company and what liquid they used in the cooling process.




DavidDymaxion said:


> Agree, smaller sheds heat faster. I am trying to think of ways to cool batteries -- CO2 and dry ice are good ideas. Another thought is immersing the pack in a liquid.


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