Battery pack_high temperature safety issue

Batteries, Chargers, and Battery Management Systems.
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pratikdas87   10 mW

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Battery pack_high temperature safety issue

Post by pratikdas87 » May 16 2017 2:26am

Dear All,
I am designing a 48V 100Ah lithium ion battery pack (NMC chemistry) for mobility application. The battery pack will be used in a hot weather conditions. Average temperature in summer greater than 43 °C. I need some advice regarding the safety issues. My BMS has a high temperature protection of 60 °C. Do I definitely need cooling for the pack? What can happen if i do not have a cooling in terms of safety (I am aware of the ageing issues at high temperature cycling).

If someone can guide me for a cheap and easy cooling design, or share some information, that would be great. Thanks in advance.

With kind regards,
Pratik

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amberwolf   100 GW

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Re: Battery pack_high temperature safety issue

Post by amberwolf » May 16 2017 2:54am

What are the manufacturer's temperature ratings for the cells?

What does the manufacturer say will happen if they are exceeded?

You'll need to know things like that to determine pack limitations.


If the cell specs are greater than the temperatures they'll actually experience, I don't see what the problem would be.

I don't imagine any cells that are designed for EV use that can't handle the temperatures you're expecting. (it's not uncommon for cars here in Arizona, especially in the summer sun, to get to >150F or higher inside, for example).

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dogman dan   100 GW

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Re: Battery pack_high temperature safety issue

Post by dogman dan » May 16 2017 5:42am

Like AW,, I live in the western desert, where a 110F/43c day is common. Worst I ever saw here, where its a bit cooler than Phoenix, was 118f. We still have EV's and don't cook our batteries in one season.

As long as the vehicle is moving, temps like these should not be a problem at all for your cells. Bottom line, if your body can stand it, your battery can too.

HOWEVER,,, park on the sunny side of a building in the sun, and you can have your wheels on concrete or asphalt that is easily 60c, 140F. The ol fry an egg on the sidewalk conditions. Those temps can be harsh on your cells, so step one is to think about where you park. You couldn't stand it there long either. Shade if at all possible, if not, at least not up against that reflecting sun facing wall of a building. Middle of the parking lot may be a much cooler 120f or so, which is still in the quite tolerable range for most batteries.

So I really see no safety issues with the battery, just from ambient temps. But if you melt your pack discharging it, that of course is a big safety problem. That is the situation to avoid, either by improving the c rate of the cells, increasing the size of the pack, reducing the load, or doing some kind of active cooling.

My personal rule of thumb on bikes is, if when you finish a ride, if you can't hold that pack comfortably in your hand, you are killing the cells, which then increases the hazard. Again, about the max you can stand, 45c or so, should not be exceeded inside the pack, in my opinion. A happy battery is not melting the shrink wrap on it.

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Overclocker   10 kW

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Re: Battery pack_high temperature safety issue

Post by Overclocker » May 16 2017 7:49am

Image

well 48v 100ah isn't a small cheap pack that you could afford to replace every couple of years. perhaps you should think about active cooling

the cells would certainly "work" at elevated temperatures but the calendar life might not be satisfactory

i'm not too sure but i think NCA chemistry fares better at higher temps than NMC

pratikdas87   10 mW

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Re: Battery pack_high temperature safety issue

Post by pratikdas87 » May 17 2017 6:10am

amberwolf wrote:What are the manufacturer's temperature ratings for the cells?

What does the manufacturer say will happen if they are exceeded?

You'll need to know things like that to determine pack limitations.


If the cell specs are greater than the temperatures they'll actually experience, I don't see what the problem would be.

I don't imagine any cells that are designed for EV use that can't handle the temperatures you're expecting. (it's not uncommon for cars here in Arizona, especially in the summer sun, to get to >150F or higher inside, for example).
Hey amberwolf,
Thank you very much for the reply. really appriciated.
the manufacturer guideline is 60 °C during discharge. i do not know what they say if i exceed the limit (something to cross check). thanks.

pratikdas87   10 mW

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Re: Battery pack_high temperature safety issue

Post by pratikdas87 » May 17 2017 6:14am

dogman dan wrote:Like AW,, I live in the western desert, where a 110F/43c day is common. Worst I ever saw here, where its a bit cooler than Phoenix, was 118f. We still have EV's and don't cook our batteries in one season.

As long as the vehicle is moving, temps like these should not be a problem at all for your cells. Bottom line, if your body can stand it, your battery can too.

HOWEVER,,, park on the sunny side of a building in the sun, and you can have your wheels on concrete or asphalt that is easily 60c, 140F. The ol fry an egg on the sidewalk conditions. Those temps can be harsh on your cells, so step one is to think about where you park. You couldn't stand it there long either. Shade if at all possible, if not, at least not up against that reflecting sun facing wall of a building. Middle of the parking lot may be a much cooler 120f or so, which is still in the quite tolerable range for most batteries.

So I really see no safety issues with the battery, just from ambient temps. But if you melt your pack discharging it, that of course is a big safety problem. That is the situation to avoid, either by improving the c rate of the cells, increasing the size of the pack, reducing the load, or doing some kind of active cooling.

My personal rule of thumb on bikes is, if when you finish a ride, if you can't hold that pack comfortably in your hand, you are killing the cells, which then increases the hazard. Again, about the max you can stand, 45c or so, should not be exceeded inside the pack, in my opinion. A happy battery is not melting the shrink wrap on it.
Hey DAn,
Thank you very much for the reply. yes you are absolutely right about the user awareness about the battery for safety. I think your point of melting the battery is something i can keep a look during operation.

regards,
Pratik

pratikdas87   10 mW

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Re: Battery pack_high temperature safety issue

Post by pratikdas87 » May 17 2017 6:16am

Overclocker wrote:Image

well 48v 100ah isn't a small cheap pack that you could afford to replace every couple of years. perhaps you should think about active cooling

the cells would certainly "work" at elevated temperatures but the calendar life might not be satisfactory

i'm not too sure but i think NCA chemistry fares better at higher temps than NMC
Thank you for the advice. yes, it is not that cheap to be honest. do you have some detail of the cooling design you have posted?
Have you used these kind of cooling before?

With regards,
Pratik

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Overclocker   10 kW

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Re: Battery pack_high temperature safety issue

Post by Overclocker » May 17 2017 6:46am

i just found that mini chiller while browsing aliexpress. it's powered by DC so it does seem very interesting for solar or EV applications. but i haven't personally used one

so far all my ebike batteries have no active cooling because they don't really need it. they're not parked in the sun and they're not very expensive to replace. but i've been fantasizing about building an electric dune buggy of sorts which would require a sizable investment in batteries therefore the motivation to make them last as long as possible would be strong.

i have now one pack which i've designed to have a lower thermal resistance to its aluminum outer shell, by bonding with zinc oxide-filled silicone.

Image

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