Looking at building a new pack with Samsung 50E

Batteries, Chargers, and Battery Management Systems.
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pwd   1 kW

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Re: Looking at building a new pack with Samsung 50E

Post by pwd » Jul 17 2019 3:37pm

Great, thanks for the information Pajda!
Commuter/Street Build viewtopic.php?f=6&t=98286:
Rocky Mountain Element
Magic Pie 4 front + Leafmotor 1500 rear w/ WCEC 18fet
em3ev 14S5P 30Q + 14S6P 25R pack

Offroad Build viewtopic.php?f=6&t=102195:
2019 Rocky Mountain Blizzard 20
Cyclone "3kw" 13T motor to 36T chain ring then 32T chain ring to 11T-46T Cassette
em3ev 14S5P 30Q or 14S6P 25R pack

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Allex   1 GW

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Re: Looking at building a new pack with Samsung 50E

Post by Allex » Jul 20 2019 3:41pm

Pajda wrote:
Jun 26 2019 9:57am

If we talk about a specific cells. 40T and 30Q definitelly belongs to the 2. category. They lose their capacity almost regardless on load. Both are designed for continuous operation at 1.3C charge and 5C discharge and so the are best suited for powertools. 30Q has shitty cycle life (only ca 400cycles no matter when discharged at 1C or 3C continuous, there is also no benefit when the 30Q is charged to 4.1V, the capacity loss is the same as for 4.2V charging) 40T is significntly better than 30Q and can do 1000cycles with 63% of initial capacity at 100% DoD.

But for the comparison 50E will do 1000cycles with 85% of its initial capacity and so it totally outperform 40T at 100% DoD in the cycle life if your average load is lower than 1C and you do not need faster charging that 0.5C. So I can only repeat that 50E is actually the best cell for traction application in 21700 size. LG cells excells in 18650 size, but in 21700 their actual production has poor cycle life and I still did not find reason why.
Did you have the chance to test Sanyo NCR2070C 20700 3500mAh - 30A?

I have a 6p 30q pack that sees 90A currents and start to get unbalanced. I need a new set of cells and looking at sanyos or 40Ts. I am after the most light weight pack so I do not want to add a lot of cells in P. 18Ah is plenty fine for my needs.


Pajda   1 kW

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Re: Looking at building a new pack with Samsung 50E

Post by Pajda » Jul 21 2019 4:45am

Allex wrote:
Jul 20 2019 3:41pm
Did you have the chance to test Sanyo NCR2070C 20700 3500mAh - 30A?

I have a 6p 30q pack that sees 90A currents and start to get unbalanced. I need a new set of cells and looking at sanyos or 40Ts. I am after the most light weight pack so I do not want to add a lot of cells in P. 18Ah is plenty fine for my needs.
No, I have only tested NCR20700B 4200mAh some time ago aka High Energy density cell, when this new format was available on the market.But it took only few months to find, that this particular format will not have shiny future and will be replaced by 21700 and so I lost interest. I have tested 40T and it will work for you well, even with your 90A peaks at 6p, much better than 30Q in terms of cycle life.

dukestar   1 mW

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Re: Looking at building a new pack with Samsung 50E

Post by dukestar » Jul 26 2019 4:43pm

Ok, so after going back and forth between 40T and 50E I built my battery with the 50E because of the cycle life rating of >80% after 500 cycles. The 40T had same rating as 30Q which is what my current pack used.

Here's the build details.

20s7p - due to space constraints I hot glued 16s7p on the bottom and laid 4s7p flat on top. Fish paper between 16s7p cells and 4s7p. Large copper bus bars at positive and negative battery ends. Used 8mm strip of .15 nickel and one wide strip of .125 copper utilizing the sandwich spot welding technique to connect the cells. Embedded thermistor in center of 16s7p part of pack. 90A BMS.

Charged it to 81.6V so just under 4.1V.

Did a test run and here are my observations.

Did a 20 mile run with some pretty steep hills. In 50.5 minutes used 11.4A so that averages 13.54Ah - approx .4C. Max A reached was 48.89 - approx 1.4C. Used 847.75wh - 41.1 wh/mi. Battery voltage at end of ride was 74.8V. Min voltage reached was 68.9V.

Pack temp started at 20.3°C and ended at 34.4°C. Half hour later pack temp decreased to 33.9°C so it does not cool off quickly. I imagine it is a heat sink and with no active cooling takes a lot of time to cool.

Not sure what to make of the pack temperature. Problem with my setup is I have no easy way to cool the pack and am wondering if that is going to be a problem. I don't doubt if I continued riding that the pack would have continually increased in temp.

The 50E data sheet has temperature rating of:
3.16 Operating Temperature(*2) Charge: 0 to 45°C
(Cell Surface Temperature) Discharge : -20 to 60°C
Does this mean I can get close to 60°C and not be concerned? At what temp will the pack start to be damaged?

Note that when charging at 2.4A the pack temp reached 35°C so if I took the battery off charge and immediately started riding the temps would start at 35°C. Not sure if that is an issue or not. My last pack did not have an embedded thermistor so I'm wondering if I had heat issues with my old pack and that helped it degrade.

Thanks for any comments/feedback.

Edit: must've misread the temperature when charging. Pack doesn't get to 35°C when charging at 2.4A, appears to stay at ambient room temp which was mid 20s.
Last edited by dukestar on Jul 29 2019 3:52pm, edited 2 times in total.

DjSpaceGhost   100 mW

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Re: Looking at building a new pack with Samsung 50E

Post by DjSpaceGhost » Jul 26 2019 7:15pm

At a constant 30 ° C , the cycle life can drop up to around 20% vs a constant 20°C , but ambient temperature in a lot of places can stay at that level for long stretches of time, so I wouldn't stress over it. If it gets to say, 45°C, I'd take a break for a while if possible.

Pajda   1 kW

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Re: Looking at building a new pack with Samsung 50E

Post by Pajda » Jul 28 2019 7:30am

dukestar wrote:
Jul 26 2019 4:43pm
Ok, so after going back and forth between 40T and 50E I built my battery with the 50E because of the cycle life rating of >80% after 500 cycles. The 40T had same rating as 30Q which is what my current pack used.
40T has signifiantly lower DCIR than 30Q. ("LG" 10sec 0.5C load DCIR test method at 50% DoD): New 40T has ca 16 mOhms, new 30Q has ca 25 mOhm, new 50E has ca 34 mOhms at 27°C. But as I mentioned many times before, almost all modern cells with low DCIR does not have good cycle life! In fact there only few cells on the market with low DCIR and great cycle life.
dukestar wrote:
Jul 26 2019 4:43pm
Did a test run and here are my observations.

Did a 20 mile run with some pretty steep hills. In 50.5 minutes used 11.4A so that averages 13.54Ah - approx .4C. Max A reached was 48.89 - approx 1.4C. Used 847.75wh - 41.1 wh/mi. Battery voltage at end of ride was 74.8V. Min voltage reached was 68.9V.

Pack temp started at 20.3°C and ended at 34.4°C. Half hour later pack temp decreased to 33.9°C so it does not cool off quickly. I imagine it is a heat sink and with no active cooling takes a lot of time to cool.
This is exactly example what I am talking about. If you are able to design a battery, where the average load is lower than ca 1C, you will not have problem with heating even when used HE cells with higher DCIR. 40°C is absolutelly ok as operating temperature in traction app. It is also because you are not able to hold this temperature during use for longer period of time (days) instead of stationary app.

dukestar wrote:
Jul 26 2019 4:43pm
Not sure what to make of the pack temperature. Problem with my setup is I have no easy way to cool the pack and am wondering if that is going to be a problem. I don't doubt if I continued riding that the pack would have continually increased in temp.

The 50E data sheet has temperature rating of:
3.16 Operating Temperature(*2) Charge: 0 to 45°C
(Cell Surface Temperature) Discharge : -20 to 60°C
Does this mean I can get close to 60°C and not be concerned? At what temp will the pack start to be damaged?

Note that when charging at 2.4A the pack temp reached 35°C so if I took the battery off charge and immediately started riding the temps would start at 35°C. Not sure if that is an issue or not. My last pack did not have an embedded thermistor so I'm wondering if I had heat issues with my old pack and that helped it degrade.
The effect of temperature on the cell wear is much related to the length of exposure. Exponential dependence can be expected.
Even 60°C continuous discharge temperature should be completely safe for operation, but it will of course affect cycle life. The temperature where you can expect instant internal cell damage is above ca 90°C, but this differs from cell to cell. It should be noted that to pass UL tests cells must withstand hot oven test of 130-140°C with no explosion, no fire, only leak is allowed.

john61ct   1.21 GW

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Re: Looking at building a new pack with Samsung 50E

Post by john61ct » Jul 28 2019 12:32pm

Pajda, thanks so much for doing this work.
Pajda wrote:40T has signifiantly lower DCIR than 30Q. ("LG" 10sec 0.5C load DCIR test method at 50% DoD): New 40T has ca 16 mOhms, new 30Q has ca 25 mOhm, new 50E has ca 34 mOhms at 27°C. But as I mentioned many times before, almost all modern cells with low DCIR does not have good cycle life! In fact there only few cells on the market with low DCIR and great cycle life.
Could please you specify them?

My use case is low C-rate, no temp concerns, lower density either way is no problem, don't care about DCIR.

So really the only "quality" factors left are Ah capacity and cycle count longevity

dukestar   1 mW

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Re: Looking at building a new pack with Samsung 50E

Post by dukestar » Jul 28 2019 4:29pm

Pajda, thanks for your input much appreciated. Your comments about pack temps is reassuring. Do you think if I max the pack temp at around 40°C - 45°C that I will be ok with regards to preventing pack cycle life degradation due to excessive heat? I think I can manage that without active cooling. If not, I'll look at adding a fan to my battery case to get some airflow over it.

Thanks again...
Last edited by dukestar on Jul 28 2019 4:39pm, edited 1 time in total.

dukestar   1 mW

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Re: Looking at building a new pack with Samsung 50E

Post by dukestar » Jul 28 2019 4:38pm

john61ct wrote:
Jul 28 2019 12:32pm
So really the only "quality" factors left are Ah capacity and cycle count longevity
john61ct, based on your quote the 50E may be a good option for you but note the datasheet has a recommended charge current of 2.45A for pack longevity, max 4.9A (not for cycle life). If you need a fast charge it may not be the cell for you.

HTH

john61ct   1.21 GW

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Re: Looking at building a new pack with Samsung 50E

Post by john61ct » Jul 31 2019 9:07am


dukestar wrote:
john61ct wrote:
Jul 28 2019 12:32pm
So really the only "quality" factors left are Ah capacity and cycle count longevity
john61ct, based on your quote the 50E may be a good option for you but note the datasheet has a recommended charge current of 2.45A for pack longevity, max 4.9A (not for cycle life). If you need a fast charge it may not be the cell for you.
Thanks, discharge and fast charge might approach 0.6C occasionally, but usually both kept under 0.3C

As stated not a propulsion use case.


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