Question about "Maximum Momentary Pulse" for an 18650 cell

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Question about "Maximum Momentary Pulse" for an 18650 cell

Post by garolittle » Sep 27 2020 9:06pm

The spec sheet for the INR Samsung 25R cell (rated at 20A continuous) shows a "Maximum Momentary Pulse" of 100A. This may be a dumb question but would 100A be the "moment of death" for this cell? In other words, would hitting 100A kill the cell completely? Just curious. In practice I would never exceed 20A per cell (probably not even 15A per cell). That seems like a crazy high current level. Thanks for any comments. Gary

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by Balmorhea » Sep 27 2020 10:33pm

It will probably just put out 100A for an instant before the voltage collapses and current drops accordingly. No way I'm aware of that you can connect to an 18650 will tolerate that kind of current for more than an eyeblink anyway.

I wouldn't trouble myself about it.

If you want big currents, you're definitely looking at the wrong size cell.
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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by garolittle » Sep 27 2020 11:25pm

Balmorhea wrote:
Sep 27 2020 10:33pm
It will probably just put out 100A for an instant before the voltage collapses and current drops accordingly. No way I'm aware of that you can connect to an 18650 will tolerate that kind of current for more than an eyeblink anyway.

I wouldn't trouble myself about it.

If you want big currents, you're definitely looking at the wrong size cell.
Thanks. Appreciate the feedback. Was also interested in how to “size” the cell level fusing that I will use. Basically want to protect the driver (electric go kart) in unlikely event of a dead short situation. Max amps per cell will only be about 10 A. However I’m trying to figure out the ideal current level it which the fuse will “pop”. 100 A is clearly too high but is there a certain current level I should be aiming for regarding the fuse even though it is unlikely I will ever hit that level?

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by 999zip999 » Sep 27 2020 11:32pm

What buss bar ? Most would melt So a pack of 10p for a cart would be 1,000 amps. What controller do you have ?
Kart what kart no pics ???
1,000a 72v 72,000 watts what kind of rubber you use ? On 10in tires. Ok enough.

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by john61ct » Sep 28 2020 12:49am

Current / power output (or input) rating, peak or continuous, 0.01sec vs 10sec

needs to be converted to C-rate up front in any such discussion, in proportion to Ah / mAh energy capacity

whether on a per cell basis, or a 10P pack, whatever

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by john61ct » Sep 28 2020 12:52am

LG M36 aka MJ1 would be a better choice for longevity

1C continuous, 3C peak

Samsung 35E, SONY VC7 pretty close if you find them cheaper

Do not use Sanyo GA, too inconsistent

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by serious_sam » Sep 28 2020 4:31am

garolittle wrote:
Sep 27 2020 9:06pm
This may be a dumb question but would 100A be the "moment of death" for this cell? In other words, would hitting 100A kill the cell completely?
No. It'll be fine. That 100A spec is for 1 second bursts. Remember, it's mostly about heat. If the duty cycle is low enough to minimise heat production, then damage is minimised.
This graph is from the datasheet too. Lot of cycles of bursts of high currents. Deep discharge too. The cells can handle a decent amount of "abuse":
Screenshot_20200928-192454.jpg
Screenshot_20200928-192454.jpg (142.56 KiB) Viewed 299 times
The cell initial DCIR spec is 22mOhm. So maximum short circuit current is 190A.

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by Pajda » Sep 28 2020 4:47am

It is always a good approach to do a simple math with DCIR. From the presentation sheet it should be about 20mR for Samsung 25R. This DCIR value gives an instantaneous voltage drop of 2.2V at 100A load. If you use simple BMS with instantaneous 3V cut-off voltage, you can get only up to 60A from fully charged cell to 4.2V before BMS will react. So your BMS must be aware of this and allowing to go lower than common 2.5V cut-off voltage.

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by serious_sam » Sep 28 2020 6:07am

Pajda wrote:
Sep 28 2020 4:47am
So your BMS must be aware of this and allowing to go lower than common 2.5V cut-off voltage.
Good advice.

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by garolittle » Sep 28 2020 7:29am

999zip999 wrote:
Sep 27 2020 11:32pm
What buss bar ? Most would melt So a pack of 10p for a cart would be 1,000 amps. What controller do you have ?
Kart what kart no pics ???
1,000a 72v 72,000 watts what kind of rubber you use ? On 10in tires. Ok enough.
Sorry about that. Pictures attached. The busbar for the prototype battery pack is a SigmaCLAD material that is approximately 40% copper. The rest is mostly pure nickel. The pack will be 22S/20P and the maximum current expected is 200A (so 10A) per cell. The cell level fuses will be designed to pop at about 50A-60A to protect against a dead short. The cells used will be the INR Samsung 25R. Controller will be the Curtis 1234SE which is rated for 300+ A (max).
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Re: Question about

Post by garolittle » Sep 28 2020 7:31am

john61ct wrote:
Sep 28 2020 12:49am
Current / power output (or input) rating, peak or continuous, 0.01sec vs 10sec

needs to be converted to C-rate up front in any such discussion, in proportion to Ah / mAh energy capacity

whether on a per cell basis, or a 10P pack, whatever
Roger that and thanks. The C-rate for the INR Samsung 25R cells is "8C". The pack will be a 22S/20P pack of these cells with a maximum current of 200A (probably about 175A continuous). Using cell-level fuses so just want to protect the driver (ie. give time to get away from the kart) if there is a dead short situation.

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Re: Question about

Post by garolittle » Sep 28 2020 7:33am

john61ct wrote:
Sep 28 2020 12:52am
LG M36 aka MJ1 would be a better choice for longevity

1C continuous, 3C peak

Samsung 35E, SONY VC7 pretty close if you find them cheaper

Do not use Sanyo GA, too inconsistent
Really like the MJ1 cells. Have not used them recently but may do so in the future. Thanks for the idea. May also try a 21700 size cell at some point.

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by garolittle » Sep 28 2020 7:36am

serious_sam wrote:
Sep 28 2020 4:31am
garolittle wrote:
Sep 27 2020 9:06pm
This may be a dumb question but would 100A be the "moment of death" for this cell? In other words, would hitting 100A kill the cell completely?
No. It'll be fine. That 100A spec is for 1 second bursts. Remember, it's mostly about heat. If the duty cycle is low enough to minimise heat production, then damage is minimised.
This graph is from the datasheet too. Lot of cycles of bursts of high currents. Deep discharge too. The cells can handle a decent amount of "abuse":
Screenshot_20200928-192454.jpg
The cell initial DCIR spec is 22mOhm. So maximum short circuit current is 190A.
Thank you! Really good response. The cell-level fuses are designed to pop at about 50-60A. I have tested this many times by creating a "dead short" with a single 25R cell and measuring the time it takes for the fuse to pop (about 1/2 of a second). It sounds like I am on the right track as far as the fuse is concerned but your feedback above is great information. Really appreciate that!
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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by garolittle » Sep 28 2020 7:45am

Pajda wrote:
Sep 28 2020 4:47am
It is always a good approach to do a simple math with DCIR. From the presentation sheet it should be about 20mR for Samsung 25R. This DCIR value gives an instantaneous voltage drop of 2.2V at 100A load. If you use simple BMS with instantaneous 3V cut-off voltage, you can get only up to 60A from fully charged cell to 4.2V before BMS will react. So your BMS must be aware of this and allowing to go lower than common 2.5V cut-off voltage.
Really good point. Thanks! :thumb:

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by garolittle » Sep 28 2020 7:51am

Pajda wrote:
Sep 28 2020 4:47am
It is always a good approach to do a simple math with DCIR. From the presentation sheet it should be about 20mR for Samsung 25R. This DCIR value gives an instantaneous voltage drop of 2.2V at 100A load. If you use simple BMS with instantaneous 3V cut-off voltage, you can get only up to 60A from fully charged cell to 4.2V before BMS will react. So your BMS must be aware of this and allowing to go lower than common 2.5V cut-off voltage.
So this would create two layers of protection? 1) the BMS shuts cuts off at 60A (in the scenario above) and 2) the cell-level fuse (assuming it is sized correctly) will "pop" at 60A. Correct? Thanks for the comment.

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by 999zip999 » Sep 28 2020 9:51am

Great garolittle Lot of learning here. I would love to see that. Cart live.

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by garolittle » Sep 28 2020 10:52am

999zip999 wrote:
Sep 28 2020 9:51am
Great garolittle Lot of learning here. I would love to see that. Cart live.
Yes Sir and thanks. I really like ES. This forum is a great resource for learning and for sharing ideas. Building a second prototype kart now. The first one was a blast. Check it out ...

https://youtu.be/b_kEQsOaJGc

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by john61ct » Sep 28 2020 11:40am

A howto thread aimed at beginners, with links

on your cell-level fusing and

the other pack building details

would I think be a great resource for the community.

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Re: Question about

Post by garolittle » Sep 28 2020 12:41pm

john61ct wrote:
Sep 28 2020 11:40am
A howto thread aimed at beginners, with links

on your cell-level fusing and

the other pack building details

would I think be a great resource for the community.
Yes Sir. It has been a long process and trial and error. Lacking high end equipment, I have performed fairly simple tests involving intentional dead shorting of a single cell (at a distance for safety). The goal is to determine the best size of the fuse "cross section" so that heat is minimized at max amps (10-15A per cell) but "pops" at a level that protects the pack (about 60-80A per cell). Willing to sacrifice a cell to improve safety. Still running lots of tests but will post more data once we settle on a final fuse design. Really appreciate all the help from this forum. Gary

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by 999zip999 » Sep 28 2020 12:53pm

Four-wheel drive next for electric motors one on each wheel

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by garolittle » Sep 28 2020 10:41pm

999zip999 wrote:
Sep 28 2020 12:53pm
Four-wheel drive next for electric motors one on each wheel
Definitely would make for an impressive performance. Beyond my expertise at this point but would love to try it one day.

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by 999zip999 » Sep 29 2020 6:53am

Lots of love. Me 43mph on bicycle tires moped speed ratie. Oh no 7yrs 26,000 miles same batteries.

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by 999zip999 » Sep 29 2020 6:54am

I'm trying to say all my batteries can be a life-long experience like when you buy a parrot and last 100 years. So what batteries do you want and what weight you have to carry around.
Last edited by 999zip999 on Sep 29 2020 5:20pm, edited 1 time in total.

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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by Balmorhea » Sep 29 2020 2:38pm

999zip999 wrote:
Sep 29 2020 6:54am
I'm trying to say call me batteries can be a life-long experience like when you buy a parrot in last 100 years.
https://en.wikipedia.org/wiki/Nickel%E2 ... on_battery

Great for stationary electric vehicles.
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Re: Question about "Maximum Momentary Pulse" for an 18650 cell

Post by 999zip999 » Sep 29 2020 5:22pm

Sorry I was in the field when I talk to text that but my lifepo4 are still going strong. 7 yrs 30,000 miles Yes heavy.

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