Safe Sodium Batteries battery pack - Page 1
Forum section: electronics / general

author: federico
author_rank: Contributor
timestamp: November 11, 2024, 12:36:21 pm
content: Hi Everyone.I would like to create the battery pack for the electric longboard that i am designing,but I am very afraid of using a lithium pack, I would like to create my pack with the new sodium batteriesI know it's not very convenient because they have a low capacity compared to lithium, but I prefer to sleep safe knowing that it will never catch fire..I found these batteries:https://hakadibattery.com/products/hakadi-sodium-ion-3v-26700-battery-3500mah-brand-new-rechargeable-cell-for-e-bike-diy-12v-24v-48v-battery-pack?variant=41884768141517https://srikobatteries.com/product/sodium-ion-26700-3-0v-3-2ah-9-60wh-3c-rechargeable-battery/My brushless engine is the following:https://flipsky.net/collections/e-skateboard/products/flipsky-bldc-belt-motor-6354-140kv-2450w-for-electric-skateboardWhich absorbs max: 65Amp...The motor controller (ESC) works from 14 to 60Volts.With these batteries I was thinking of creating a pack like this: 13S 2PRow of 13 batteries in series, put in parallel with another row of 13 batteries in series.What should I have about 48Volt and about 6AH?I'm not so interested in the range, (I don't travel much) as that the engine has the energy to work at its full power,.Is my pack ok with these sodium batteries? do you think with these batteries i will have the necessary power in terms of current discharge, etc..?I'm confused, Before I waste time/money I ask for help from you who surely understand more than me...

author: Sniper1
author_rank: Regular Contributor
timestamp: November 20, 2024, 06:01:48 pm
content: Quote from: federico on November 11, 2024, 12:36:21 pmSimple answer: NO not even closeLong: cells have 0.5C rating so 1.75A per cell , in practice u should be fine with 3A from what i understandFor your rated 65A max current u will need like 20 strings or 6-7 strings if you go with absolute max ratingAs for cells in series 13 is ok tho u can add a few more BUT i would not go over 16-17Questions?

author: Hydrochloride
author_rank: Contributor
timestamp: November 21, 2024, 01:35:10 pm
content: Surely I must be missing something. With 26 cells, it seems like you're going to have very little runtime.I imagine you’re not asking for the maximum power of the motor, but doing the calculations just to request 1/4(constant) of what the specifications state: 2450/4 = 613W (rounded).-----------------------------------Load : Flipsky BLDC Belt Motor → 613WCells : HAKADI Sodium ion 3.0V 26700 Battery 3500mAh → 1cell. 3.1V*3.5Ah = 10.85WhIf you want to hold this load for 2 hours : you need (613*2)/10.85 = 112.99 cells. → 113 cells minimumIf you want to deliver 48V with nominal voltage, that will be 48/3.1 = 15.48 → 16 cells series.But the cells maximum operating voltage is 4V. So 16x4 = 64V. Better remove 1 to be within ESC limits.Pack voltage that way will be from 22.5V to 60V.Other cells in parallel strings, so that is 113/15 = 7.53 strings → 8 strings15*8 = 120 cells1 cell is 2.64cm diameter x 7.1cm length.120 cells will be like a box of length x wide x height → 26.40cmx31.68cmx7.10cm. Without counting tabs for spot welding and other materials to finish the pack.Edit : Fixed with max voltage

author: Sniper1
author_rank: Regular Contributor
timestamp: November 21, 2024, 04:57:24 pm
content: Quote from: Hydrochloride on November 21, 2024, 01:35:10 pmThose numbers now look way more reasonable , you can increase the string number later , if you want more powerAs for series cells yea 15 is a good call 16 might also work IF you slightly undercharge or use some devices that have static loses along the ESC power patch like some IGBT still like that that control the on/of power of a IGBT it is like 1.5V drop and with large currents u can get some good drop on cables and such but yea 15 is the safe route

author: janoc
author_rank: Super Contributor
timestamp: November 21, 2024, 05:39:26 pm
content: Quote from: federico on November 11, 2024, 12:36:21 pmDon't land in the trap thinking that since you have replaced perceived dangerous liquid lithium chemistry with solid sodium and thinking you are safe. You aren't, unless you really know what you are doing. This is a high energy device and e.g. your BMS failing or battery developing an internal short e.g. because of a manufacturing defect will have exactly the same devastating effects, namely a major fire. Lead acid batteries don't catch fire either - but you wouldn't want to short a charged one!It isn't the lithium that causes the batteries to catch fire but most often either manufacturing defects, operational abuse (over charge/discharge, short circuits) and things like dendrite growth that could cause a short circuit over a time. These things apply even for sodium batteries. The only major advantage you have with sodium is that you won't have a thermal runaway in most cases. But thermal runaway is usually only the consequence of some other problem (e.g. a short circuit), not what starts the fire unless you seriously overheat the battery.So even with sodium batteries it is a very prudent idea to observe the standard safety precautions - never leave the batteries charge unattended, make sure there is nothing flammable around, don't abuse your battery, have fuses/BMS in place, etc.And the most important one -buy batteries from reputable manufacturers, not some random Chinese reseller from Shenzen packaging who knows what. Poor quality batteries are the #1 reason for battery fires.

author: federico
author_rank: Contributor
timestamp: November 26, 2024, 07:41:02 pm
content: Quote from: Sniper1 on November 20, 2024, 06:01:48 pmThanks for your quick reply, sorry I disappeared, I left for work and came back yesterday.Ok, so the safe discharge is 1C. Let's say that I would like to use the maximum current only in case of starting from a standstill/slight climb, I read that they have a maximum discharge of 3C, so I thought I would use that for the "peaks".Quote from: Hydrochloride on November 21, 2024, 01:35:10 pmThanks for your detailed explanation, I think I understand well how to do all the calculations now..the only thing where i have no problem is in calculating the space of the cells, I am a 3d CAD designer, I put them on Autodesk InventorIn theory yes, I had calculated 1/4 or anyway 1/2 Throttle for most of the time (I'm on the plain), but the autonomy does not interest me because I want to build a scooter as light/small as possible to make a short trip from home/work, it's like 5 minutes round trip 4 times a day, so when I have an autonomy of an hour I'm more than satisfied.So if I were to create my package consisting of: 15*4I should get an hour of autonomy at 1/4,But if I were to push at full power for a few seconds, therefore consuming 3C, I could have 1980 Watts right?maybe I could buy a less powerful motor, and use a gear ratio for less speed and more power.Quote from: janoc on November 21, 2024, 05:39:26 pmThanks for the advice, I would like to make a proper electrical system, fortunately these battery manufacturers also provide the relative BMS suitable for the voltages of these batteries, I would add fuses and additional thermal protections.I did a lot of research and found users who have done stress tests to the limit, and no fire,. let's say that I would feel safer than with Lithium.

author: Sniper1
author_rank: Regular Contributor
timestamp: November 26, 2024, 08:43:23 pm
content: Quote from: federico on November 26, 2024, 07:41:02 pmMostly yesSo at 3C u are at 10A/ cell peack so if u go 15*4 that is 40A* 3V6*15 W so 2160W abs max more then your motor can handle but fine for the ESC ( at full charge)As for the normal use if we go for 1.5A /cell then you are at 350-400W or double if you go for 1C rate

author: Hydrochloride
author_rank: Contributor
timestamp: November 27, 2024, 08:12:03 am
content: As Sniper1 said you should be ok with those requirements.I got similar answers with a different approach :--------------------------------------------------------------------Pack: 15S4P. 60 cells, 1 hour runtime for 613W → 1/4 of full throttle.Pack working voltage : 22.5V to 60VCells : 3500mAh → 1CIf you want to ask 3C to each cell maximum, that's 3.5*3 = 10.5A.There are 4 strings, then the pack maximum discharge current will be 10.5*4 = 42ANow output power :Fully charged level : 60*42 = 2520W.** But it will surely be lower, because the value of 60V (4*15) given in the datasheets is when thecurrent demand is low (likely OCV - open circuit voltage). You will experience a voltage sag due to theinternal resistance of the cells. No way to know how much, unless you order 1 cell and apply 10.5A toit. Then scale to your pack. I would stick to the average value as a maximum, 46.5V (3.1*15).Thus maximum output power will be 46.5*42 = 1953WLike 1953/2452 = 0.79 → 79% of full throttle maximum.Almost empty charge level : 22.5*42 = 945WLike 945/2452 = 0.38 → 38% of full throttle.Regarding weight. The pack will weight 81g*60 = 5kg (rounded)