Need help for decision between two different cells

[DasDouble]

Hey guys, Im thinking about building my own battery pack.

I have calculated all cells I could find on nkon.nl. I made a list with their prices, their real capacity, their data-sheet capacity, c-rates, nominal voltage, range in kilometers etc etc..


I have now two cells which are the best for my use. The Samsung 30Q and the Samsung -35E.

I want to build a 240 cells pack, or a 300 cells pack.

I will talk about the one with 300 cells for now.

The Samsung 30Q Pack will have a real world capacity of 2833Wh and a possible, save output of 16650 Watts (15A).

The Samsung -35E Pack will have a rwc of 3424Wh and an output of 11.655 Watts(10,5A).

I run a QS 205 V3 with a Max-E Adaptto Controller (14kW).

With middle hard offroad riding (30Wh/km) and the 30Q Pack I will get a range of 140km and with the 35E ones 167 (+27km)

But on the other hand I will have 5kW of theoretically possible output more with the 30Q, then with the 35E.

The price for both packs are pretty much the same. So I only have to decide between power (3kW) Experts will know why 3, and not 5kW and range (+27km).


For what would you decide

Also the question is what is better for the battery?

Is it better to
-squeeze less possible power out of the battery but for that disscharge it more
-or is better squeeze more possible power out of it, but uncharge it less?



Regards

 

[Ianhill]

The 35e pack will be around 0.6kilo heavier too.
When your ride doesn't use a lot of the batterys energy and it doesn't go below half discharge its not to good for the pack if its left at that state, ideally after each ride storage charge should be reached around %20 remaining but real world a few trips around the block may be required best be over capacity and have to use it up than cut it too fine and stress the battery beyond 80% capacity usage as capacity fluctuates with temperature on a very cold day u may get as low as 2/3's of nominal capacity.

 

[cell_man]

It depends what current you intend to pull from the pack. Generally, I'd personally suggest a high Energy cell (~3C in the case of the 35E) be ran at about ~1.5C max and you'll be very happy with the performance and they should last a long time. You could exceed this figure a little, if full power is only used occasionally, but my rule of thumb is to suggest 50% of the rated discharge rate is used for all cell types.

In your case, the 30Q would likely be best for your aplication. If you beat on the 35E cells, they will deliver less Ah than you might expect (LVC dependent) and the Whr figure will be worse again, as the reduced Ah will be compounded by the sag (reduced nominal voltage). High energy cells that are worked hard tend to degrade quickly (high power cells too, but they have higher limits). Even when new, the 30Q cell will likely deliver within ~10% of the energy/Whr that the 35E delivers (assuming the 35E are being worked pretty hard and the 30Q are being used well within their limits). Additionally, that high energy cell that is being worked hard will perform quite poorly below maybe 20% SOC.

If range is a priority and you will rarely use high power, then the high Energy cells should be fine. High energy cells can work ok on a too powerful kit, so long as they are babied most of the time. This is evident by the number of people that run inadequite batteries, with no proper way to monitor usage (such as a CA) and think it's working great.

By no means am I knocking high energy cells, that would be ridiculous, I'm only knocking their usage when a high power cell would be the better choice. In fact, I would always suggest a high energy cell be used rather than a power cell, when the application means they will be operating wthin their reasonable limits (according to my ~50% rule).

 

[cell_man]

.

 

[999zip999]

Wow love letters.

 

[Ianhill]

The spec sheets are there for you to read how you digest the information is down to you but I would just like to add that a 300 cell 18650 pack compared to a less paralleled prismatic cell pack like used in the Nissan leaf will not cycle as well and takes up a lot less space cylinder's don't stack well Tesla only use them because its easier to cool/heat them evenly and increase cycling life if you plan on a cooled pack then pick 18650 if not go with a large limn prismatic.

 

[tomjasz]

Wow love letters.

A nice change from the vitriolic attacks. Yeah the attacks with no sense or data are far more entertaining.