Battery cooling idea - heatsink tape and heatsink

[Jestronix]

So, I'm building a long thin 18650 battery - 660mm x 65mm x 54mm ,it will run down the bottom bar of my bike and get lots of airflow. So could I build a battery box that uses heatsink tape or paste with an aluminium face plate " heat sink" my pack is heat glued together so heat should transfer easier.

How much of a difference is the question, is it worth it. I'd love to reduce stress on the batteries and heat is a big killer.

These are new cells and will run only bursts at their continuous rated output. But it nets hot here in summer.

 

[amberwolf]

If the air is hot, and the heatsinks connect cells to air, then cells will get hot because of the air, rather than cooling them off.

If the cells themselves don't heat much from usage, then you'd be better off insulating the pack against the heated air. Make it so you can take this insulation off, if you need to cool the pack once air temperatures are less than the cells. Add a temperature sensor inside with a display on the bars (old BBQ thermometer, etc), so you know if it's getting hot inside (either from heat getting thru insulation, or higher-power-usage).

 

[redilast]

So, I'm building a long thin 18650 battery - 660mm x 65mm x 54mm ,it will run down the bottom bar of my bike and get lots of airflow. So could I build a battery box that uses heatsink tape or paste with an aluminium face plate " heat sink" my pack is heat glued together so heat should transfer easier.

How much of a difference is the question, is it worth it. I'd love to reduce stress on the batteries and heat is a big killer.

These are new cells and will run only bursts at their continuous rated output. But it nets hot here in summer.

What cells are they? Many cells can get very hot at their continuous rated output. I know you said bursts, but are we talking a few seconds or a few minutes? Take the Sony VTC5 and VTC6 for example. Even though Sony says they can discharge at 30A continuous, they actually also say don't exceed 80C, which is very hot. Put multiple cells together side by side in a pack with little to no airflow and discharge at 30A and they are going to hit 80C and beyond easily.

I think what you could do is make the battery box so it has a little window or something that you can slide open or closed to allow air to flow into the pack when its not blistering hot in the summer and that will help cool it down. In the summer depending on the ambient temperature vs cell temperature you would then decide if you want to open the window or close it. 30C air will still cool 50C cells.

By heatsink tape are you referring to like thermally conductive pads often used on computers to transfer heat from a chip to an aluminum heatsink? If so I could see that as working a bit, however the inside cells wouldn't get much benefit.

I think the best way to reduce heat is to reduce load on the cells. Either via a smaller load, or more or lower resistance cells which produce less heat.

 

[Monstarr]

Add liquid cooling, a radiator, a fan and possibly a heat-exchanger for your all-season battery solution 8)

 

[Jestronix]

Add liquid cooling, a radiator, a fan and possibly a heat-exchanger for your all-season battery solution 8)

Or strap a couple peltiers to them turns out there's a patent for it ancillary systems like this are to parasitic and overly complex but have a kool factor bad pun

http://www.google.com/patents/US20080268333

 

[Syonyk]

Or design your pack so the cells run cool and don't need active cooling...

 

[koco]

Add liquid cooling, a radiator, a fan and possibly a heat-exchanger for your all-season battery solution 8)

Or strap a couple peltiers to them turns out there's a patent for it ancillary systems like this are to parasitic and overly complex but have a kool factor bad pun

http://www.google.com/patents/US20080268333

I like Peltier cooling, but condensation may collect on them if they get cold enough. Care must be taken so that water doesn't drip down onto components.

 

[Jestronix]

Or design your pack so the cells run cool and don't need active cooling...

Pretty much it, then again tesla and co wouldn't need cooling systems if they ran in spec, but they ain't building a Camry it has a place for performance and taking care of batts, not necessarily murdering them as such. Dunno I can see active battery cooling having its place and use cases.

 

[Overclocker]

54mm like 3 cells deep? sounds viable.

 

[Chalo]

To me, there's no question that if you're overheating your batteries, you have fundamental system design problems that you should address directly rather than by trying to remedy the symptom of the underlying problem.

If you have enough battery to serve your motor and controller combination, heat in the battery won't be a problem. If you screw it up, of course it will be all screwed up.

 

[dogman dan]

The real solution is to run more battery. Why not run less and cool em? Because when you do it that way, they still sag under load like grannies tits.

The sag is the real problem you can't live with. So run them cool.

 

[Jestronix]

The real solution is to run more battery. Why not run less and cool em? Because when you do it that way, they still sag under load like grannies tits.

The sag is the real problem you can't live with. So run them cool.

I'd love to know what tesla is doing around saggy tits , they still cool their bats, or is tesla more interested in keeping temperature just right for maximum life? I guess it's to do with the way they pack them with so manny so close. Even under normal operation I dare say temps still rise and would cut battery life.

 

[Overclocker]

heat is a real battery killer. electric car batts can be exposed to much more heat than ebike's e.g. driving down hot pavement, parked in the sun, etc. see how well the nissan leaf batteries did in hot AZ weather

i've been to the hotter parts of arizona which are hotter than here in philippines but not by much. that's why i'm not in too much of a hurry to do an electric car conversion. apparently you need chilled-water cooling for this kind of weather here.

 

[Jestronix]

heat is a real battery killer. electric car batts can be exposed to much more heat than ebike's e.g. driving down hot pavement, parked in the sun, etc. see how well the nissan leaf batteries did in hot AZ weather

i've been to the hotter parts of arizona which are hotter than here in philippines but not by much. that's why i'm not in too much of a hurry to do an electric car conversion. apparently you need chilled-water cooling for this kind of weather here.

So even with lots of battery and very little in the way of abuse, hot weather climates work their magic and deal an early death. Here in Brisbane Australia we see weeks in summer in the high 30c even breaking into midge 40s , so hot it stings your face. Batteries simply sitting on an ebike in these temps surely have their life shortened ?

I often think about storing my batts in the fridge when not in use lol , imagine the surprise when the misses opens the fridge.

Anyone have any good data on storage temps vs life cycle ?

 

[Syonyk]

Or design your pack so the cells run cool and don't need active cooling...

Pretty much it, then again tesla and co wouldn't need cooling systems if they ran in spec, but they ain't building a Camry it has a place for performance and taking care of batts, not necessarily murdering them as such. Dunno I can see active battery cooling having its place and use cases.

Tesla's cooling system is mostly for removing the heat from supercharging at 120-150kW (a 2C charge rate), and for bringing the batteries up to temperature before charging them. It's in use on the road, and you can warm things up a good bit if you're repeatedly drag racing, but as far as I know, the cells don't generate much heat under normal driving.

 

[dogman dan]

I had a suspicion that the tesla car did not sag that much. Makes sense to have cooling so you can charge faster though. Makes sense to warm the pack before charging it if it's sitting in frozen weather too. That car needs to be able to adjust it's battery temp to stand it being out in the weather on both charge and discharge.

Parked in the desert southwest where I live,, it will be siting on a parking lot with a 140f temperature at the surface, so yeah,, it's not ideal to own an electric car in the desert if you don't have shaded parking at work. In the shade, a mere 110F, which really,, is not so hot for a battery to stand it. Similarly while rolling, it won't be above ambient temp just from the roads asphalt temp.

However, at work your car won't be at full charge. ( full and hot is the thing to really try to avoid) At home, if your garage is not insulated, has a tin door facing south, you can have pretty darn hot temps all day in there. My garage hits 120f pretty regular in summer. And at home, it might be sitting there fully charged.

In any case,, the battery can be warm in use and still last reasonably well. But if your discharge makes it really hot,, that is when you need a larger battery, or better cells, regardless of what the battery spec says. If your battery gets hotter than ambient when it's 110,, it's time to lower the rate, or increase the size.

 

[cell_man]

How long do you think a tesla pack sees it's full discharge current. Not very long, i can assure you, not when the highest spec cars hit 60 in less than 3 seconds.

How long will a tesla typically take to fully discharge it pack, in normal conditions (continuous usage)? My guess would be at least 3hrs, but typically much longer. So maybe 0.33C or less discharge rate (average). My guess is that there is no need to actively cool a tesla pack when its being used normally and at a moderate ambient temperature.

A tesla pack has very stringent requirements, it must be able to work correctly and reliably over a huge range of operating conditions (both hot and cold, plus super charging).it is also such a large battery, so the complexity of acive temperature control is worthwhile economically and necessary to meet the numerous requirements.

In an ebike application, where you often don't have this huge surplus of power, you will see full curent to the kit, every time you give it some reasonable twist and a discharge time of maybe 1hr, or even 30mins. So 1C average, or 2C respectively. So this means a far higher average discharge rate and high current bursts that can be for a much longer duration, than in a Tesla.

My personal recomendation is to use cells at maybe half their rated c rate or a little more (max current rating of controller). You can get away with a bit more than this, if you don't use the kit to it's full potential, baby it most of the time, or if you have some awareness of the limitations of the battery snd use it accordingly. If I'm selling a battery to someone, I need to be confident the battery is fit for purpose, for all usage (not just for those that stick to pas level 5, or don't have too many hills...).

If someone thinks they are killing it on their rides, yet they can get a couple of hours ride time (as I've heard), then i can assure them, the pack is not being used hard at all. A pack is being used hard when it been run flat in 10-20mins, then you know it is being used hard, continuously, so there is no time to dissipate the heat generated in the cells during those short bursts of power.

I guess a fan blowing in and another blowing out of a pack will help to cool it, if there is some gsp between the cells, so the air can flow between them.

 

[TheBeastie]

heat is a real battery killer. electric car batts can be exposed to much more heat than ebike's e.g. driving down hot pavement, parked in the sun, etc. see how well the nissan leaf batteries did in hot AZ weather

i've been to the hotter parts of arizona which are hotter than here in philippines but not by much. that's why i'm not in too much of a hurry to do an electric car conversion. apparently you need chilled-water cooling for this kind of weather here.

So even with lots of battery and very little in the way of abuse, hot weather climates work their magic and deal an early death. Here in Brisbane Australia we see weeks in summer in the high 30c even breaking into midge 40s , so hot it stings your face. Batteries simply sitting on an ebike in these temps surely have their life shortened ?

I often think about storing my batts in the fridge when not in use lol , imagine the surprise when the misses opens the fridge.

Anyone have any good data on storage temps vs life cycle ?

Was just looking on average temperature in Arizona vs Brisbane and Arizona is a fair bit hotter on average..
https://en.wikipedia.org/wiki/Brisbane#Climate
Average high °C 30.2
https://en.wikipedia.org/wiki/Phoenix,_Arizona#Climate
Average high °C 41.2
And Arizona has multiple months over 40c average.

I think if you're afraid your cells are going to get too hot it's because you just haven't built a big enough pack.. not enough in parallel or your controller/motor is just way too big.
The official spec 'rated' for 18650s seem to me to be high amps promise on that they won't burst into flames, but little to do with a lot of cycles in a long lasting battery pack, same with the very new 20700 cells as well. Sure you can beat the shit out of them but they wont last long.

 

[GoldenCO]

I use a backpack for my battery mount so of course not very good for heat dissipation being enclosed and not in wind path. after first couple of rides i noticed decreased perfromance in heat of mid day as opposed to early morning. my solution was putting a frozen blue ice pack about size of battery footprint in the backpack between my back and the battery. this seems to work great and keeps me cooler, stays frozen longer than the battery life. After that worked i did similar for my 2000 honda insight hybrid by placing the freezer pack over the battery and under some foam and it did help my battery performance. Now that it is cooling off in the morning, live in colorado, i see a negative impact to battery performance similar to what I normally see in the winter. so yea, I think there is a happy ideal cool temperature that seems to be around 60 or 65F and between storing battery at room temp and using ice pack i can get close with very little effort. I know the honda insight also uses vents to force air around the battery after the air passes through the cabin (looking for room temp), forums say make sure you keep up on changing the cabin air filter.