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batterisystem

3.2 kWh cells packs
Batteriet på en elektrisk cykel eller trike er muligvis den vigtigste del af køretøjet. Følgende vil vise, hvordan VELOKS-batteriet er designet og konstrueret

CELLER

Anvendte litiumceller 
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DESIGN

Litiumbatteri design
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MEKANIK

Konstruktion af litiumbatteri
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OPLADNING

Opladning af litiumbatteri
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REGENERATION

Energi Regeneration
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Levetid

Lithium-batteriets levetid
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CELLER

As for most electric bikes and trikes today, VELOKS make use of lithium cells in its batteries. Today, there are only a handful of Lithium cells producers. Key producers are Panasonic, Samsung, LG, SONY and SANYO. Most other brands are based on OEM versions produced by these manufacturers.

Lithiumceller findes i mange former og størrelser, men mest almindeligt for elektriske cykler er den cylinderformede 18650-celle og mere sjældent den cylinderformede 21700-celle. De første to cifre henviser til diameteren (henholdsvis 18 mm og 21 mm, mens de 3 sidste cifre henviser til højden (henholdsvis 65 mm og 70 mm).

Each of these types of cells has a nominal voltage of 3.7 volts, while the energy (expressed in Ah = amperage hours) varies depending on chemistry and size. Similarly, the continuous maximal discharge current and maximal change current will vary deepening upon chemistry and size. Cell types that VELOKS uses or have used are:

TypeSpændingKapacitet [Ah]Udledningsstrøm [A]Opladningsstrøm [A]Opladningscykler [80%]Densitet [W / Kg]
Panasonic NCR18650PF3,72,9101,45500227
Sony US18650VTC63,73,1305300242
LG INR18650MH13,73,2101,6500250
Samsung INR18650-35E3,73,5101,8500273
Samsung INR21700-50E 3,75102,5500272


Kritiske kriterier for valg af disse celletyper var: kapacitet (> = 2,9Ah), energitæthed (> = 240 W / Kg), pris, kvalitetsproducent, tilgængelighed, ladestrøm (> = 0,5C), udladningsstrøm (> = 10A ) og ladecyklusser (> = 500).

VELOKS producerer sine batterier fra bunden, hvilket gør det muligt for os at gøre brug af de bedste battericeller på markedet og foretage hurtige ændringer, når teknologien udvikler sig.

Da vi startede i 2015, brugte vi Panasonic NCR18650PF, da disse var og er meget gode celler til prisen. Derefter skiftede vi til LG INR18650MH1, som er ens i pris, men har mere kapacitet. Siden foråret 2019 har vi brugt INR18650-35E og INR21700-50E cellerne fra Samsung, da disse nu er prisbillige og har større kapacitet. Den seneste tid har vi tilføjet celler med høj strøm for at understøtte vores nye 4000w og 6000w MK3 modeller. 

DESIGN

Creating batteries from individual lithium cells is done by connecting X number of equal lithium cells in parallel, creating an “aggregate battery cell”, with an X * cell capacity,  then connecting Y number of these “aggregate battery cells” in series until the desired nominal voltage is reached..

This type battery configuration is specified as for example 16S17P, meaning 16 aggregate cells in series (16 x S), where each aggregate cell has 17 lithium cells in parallel (17 x P).

De konfigurationer, vi bruger, er altid 16 "samlede battericeller" i serie for at skabe et 60 V nominelt batteri (faktisk 59 Volt mere præcist, men dette kaldes normalt 60V). Til de forskellige batterikapaciteter bruger vi følgende konfigurationer:

Kapacitet [kWh]Config.Celle #Vægt [KG]Udledningsstrøm [A]Densitet [W / Kg]
1,316S07P1125,4210242
2,416S13P20810,0390242
2,716S13P20810.0130273
3,316S11P17612,1110272
3,716S20P32015,4600242
4,216S14P22415,4140272
5,116S17P27218,8170272

Once a given configuration has been established, it is important to validate that the characteristics of the battery meets the requirements.

For our trike and motor design, we need a battery this is capable of delivering from 250 watts up to 6000 watts continuously, and are able to handle regeneration and charging requirements.

The voltage of lithium cells varies from 4.2 V fully charged to 3.0 V fully discharged, so the actual voltage of the battery will charge from 67.2 volt fully changed down to 49 volts fully discharged. So, in order to generate for example 3000w continuously  at any state of charge, the current required will vary from 3000 / 67.2 = 45A to 3000 / 49 = 61A continuous current.

The lithium cells that we use are all able to generate 10A continues discharge current each, so for the smallest capacity of 1.5 kWh we have 7 of these is parallel, which gives a maximum continuous current of 7 * 10A = 70A, which is sufficient to fulfill this requirement. If we take the largest battery of 5.1 kWh of capacity, this is 17 * 10A = 170A, or more than 2.8 times more than required at 3000 Watt.

Batteristyringssystemet (BMS) installeret i VELOKS-batterier giver beskyttelse for:

    - Maks. udledningsstrøm
    - Maks. opladning (Regen) nuværende
    - Min. og Max. spænding til batteri
    - Min. og Max. spænding for hver celle
    - Kortslutning til batteri
    - Min. og Max. ladetemperatur
    - Min. og Max. udledningstemperatur
    - Forkert cellebalance


Standardkonfigurationen er som følger:

    - For standardstrømbatteriet er det maks. udledningskur. 60A.
    - For højstrømbatteriet er det maks. udledningskur. 120A.
    - Maks. opladning (regen) cur. er afhængig af batteritype.
    - Min. og Max. Batterispændingsbeskyttelse er indstillet til henholdsvis 68V og 46V.
    - Min. og Max. Cellespændingsbeskyttelse er indstillet til henholdsvis 4,25V og 2,85V.
    - Min. og Max. udløbstemperatur henholdsvis 20 grader celsius og plus 60 grader celsius
    - Min. og Max. opladningstemperatur henholdsvis 0 grader celsius og plus 60 grader celsius
    - Når der er mere end 0,005v celle diff, sker der balance mellem 65,6 volt og 67,36 volt.

BMS kan overvåges og konfigureres trådløst via Bluetooth af VELOKS.

MEKANIK

Now let’s talk about how to actually put the battery together, and let’s discuss how to do this in an optimal way. The areas to consider are:

      - Batteriets størrelse og form
      - Celleforbindelse
      - Nuværende strøm
      - Montering af celler og batteri
      - Design af batteriboks

Size & Shape of the battery

Den nemmeste og mest optimale form på et batteri er en rektangulær form, hvor cellerne er parallelle i en retning, og i serie i den ortogonale retning. Dette skyldes, at denne form muliggør den mest optimale strømning mellem cellerne og det mest kompakte design.

Spørgsmålet med denne form er, at det kan være vanskeligt at rumme for visse typer cykler, hvor pladsen er begrænset eller begrænset på andre måder.

VELOKS er designet fra grunden til elektrisk drev, og batteriets form og placering var et vigtigt designkriterium. Dette har gjort det muligt for os at bruge den optimale rektangelform og har endda gjort det muligt for os at variere bredden på formen i vid udstrækning uden nogen negativ påvirkning.

Mere på vej....

OPLADNING

Charging lithium ion cells is quite simple and requires a charger that can handle constant current (CC) during the initial stage and constant voltage (CV) during the final stage of the charging cycle.

During charging, the maximum charge current must not normally exceed 0.5C (which corresponds to the current needed to discharge a fully charged battery in two hours).

Charging beyond 0.5C is possible, but cooling of the battery is required. Examples of this is the so-called super charging used by TESLA for their electric cars, but this is obviously beyond the scope for e-bikes and e-trikes.

Når man begynder at oplade, vil opladeren være i CC-tilstand, og når spændingen når 4,2 volt for cellen, skifter opladeren til CV-tilstand, og CV-tilstanden holdes, mens strømmen reduceres, indtil den når 0,1C, og hvilken punkt cellen er fuldt opladet (se graf nedenfor)


Lithium battery Charge Profile

The charger must not exceed the maximum allowed charge current of the battery.

Also charging at temperatures below zero degrees celsius must be avoided as this will destroy the lithium ion cells. This protection is handled by the Battery Management System (BMS) which is described later.

For lithium ion cells, the maximum voltage is always 4.2 V per cells. For the VELOKS batteries, where 16 cells are connected in series, the max. charge voltage is 16 X 4.2 volt = 67.2 volt.

Tilsvarende er vi nødt til at bestemme den maksimale opladningsstrøm for batteriet. For de konfigurationer, vi bruger, kan vi beregne den maksimale ladestrøm som:

Kapacitet [kWh]Config.CalcOpladningsstrøm [A]Celletype
1,316S07P7 * 535Sony US18650VTC6
2,416S13P13* 565Sony US18650VTC6
2,716S13P13 * 1,823Samsung INR18650-35E
3,316S17P17 * 2,528Samsung INR21700-50E
3,716S20P20 * 5100Sony US18650VTC6
4,216S14P14 * 2,535Samsung INR21700-50E
5,116S17P17 * 2,543Samsung INR21700-50E

As can be seen, the standard charger of 8A that we provide is a safe choice for all batteries. For all but the smallest battery the 18A is also a good choice.

For maximum charging speed we provide a charger of 27A, which is well suited for the 3 largest batteries.

REGENERATION

Regeneration is similar to charging and must follow the same rules as charging. The difference is that the voltage and current originates from the motor, which through the motor controller charges the battery, while at the same time providing mechanical resistance (braking) to the wheel in relation to the regeneration (charging) current

Motorstyringen styrer spænding og strøm til batteri, så det ikke for VELOKS-batterier overskrider 67,2 volt, og strømmen er begrænset afhængigt af batterikapaciteten og ladningstilstanden.

Den maksimale regenereringsstrøm som funktion af batterikapaciteten og spændingen er specificeret for hvert batteri med hensyn til maks. regenereringskraft:

Kapacitet [kWh]Config.CalcRegen Power [kW]Celletype
1,316S07P60 * 352,0Sony US18650VTC6
2,416S13P60 * 653,8Sony US18650VTC6
2,716S13P60 * 231,4Samsung INR18650-35E
3,316S11P60 * 281,6Samsung INR21700-50E
3,716S20P60 * 1006.0Sony US18650VTC6
4,216S14P60 * 352,1Samsung INR21700-50E
5,116S17P60 * 432,5Samsung INR21700-50E

I praksis er den maksimale regeneffekt konfigureret til ikke at overstige 1500W for baghjulsdrevversionen af MK3 for ikke at miste trækkraft. For forhjulstrækningen og alle hjulversioner er der ingen problemer med trækkraft, og de kan have den maksimale regenereringseffekt.

Controlleren skal også begrænse den strøm, der sendes til batteriet, når batteriet er tæt på fuldt opladet. Dette gøres ved at starte rampe ned af regenereringsstrømmen ved 66,5 volt batterispænding og rampe ned til nul ved 67,2 volt batterispænding.


Levetid

Each of the selected lithium cells are designed to retain 80% of their capacity after 500 charging cycles. But this requires that each are not treated outside of their specifications, i.e. we must not exceed: max. discharge current, max. charge current, min and max operating temperatures, and storing batteries long term only between 80% and 50% SOC.

One charging cycle is defined as a complete discharge from full to empty followed by a charge to full again. If you discharge your battery from full to 50% empty and then recharge to 100%, that counts as half a charge cycle.

The lifespan of 500 cycles is valid when charging the battery to 100% capacity every time.

If you always charge the capacity to only 80%, then the number of cycles doubles (i.e. 1000 cycles) before capacity is reduced to 80%.

But charging to 80% is not so easy with most of today's chargers as they are configured to stop charging at 100%. The only charger that I am aware of that currently supports charging to 80% (or to any level) is the GRIN Satiator. Unfortunately this can only deliver a max charging current of 5A. A "hack"  for the other chargers, is to manually abort charging by removing the charge plug when capacity has reached 80% or approx. 63 volt (for a 60V Nominal battery).

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