Accumulators of Electric Charge
How and What
The NCM cells have at nominal value data, a “difference of electrical potential” or “voltage” of 3.7 V and a field of operation amounted to 4.25 to 2.70 V about.
For the LFP, the nominal voltage is 3.2 V and the operation in the field from 3.90 to 2.50 V about.
The nominal “capacity” of the NCM in the format 18650, varies in the range 1800-3000 mAh.
The charging method, requires both charging voltage (V) and current intensity (I) constant and limited, for times of about 3 hours for the standard cycle and approx 2.5 hours to the rapid cycle.
As it is for each chemical, the data from the technical sheets, should be carefully studied and understood bearing in mind that always and however – necessarily and conveniently – the producer declares laboratory values said just nominal, in the sense that they are real in the test phase condition and for more almost always only valid within a certain period of time from the date of construction for which, “cells never used” can realistically be already “old” even if bought as new.
An important parameter of the rechargeable batteries is also the factor “C”, which specifies the multiplier to be considered for a certain performance with reference to the nominal homologous on an hourly basis.
In relation to the nominal values reported for 1 hour then, just as many data are expressed such as: discharge current or charging current “maximum”, “life cycles”, “charging times” and so on, so for example, indicated 1 C for the maximum permissible charging current for a fully empty cell of 3 Ah, you want to indicate that the phase of full charge can take place in a minimum of one hour providing 3 A maximum at the rated voltage.
Similarly, for the same cell, a C ratio of 0.1, which was declared as the maximum continuous discharge capacity, it means that the maximum value of discharge bearable and therefore usable without prejudice and limits of time is 0.3 A at the rated voltage discharge.
The lack of knowledge of these aspects creates illusions and very serious damages because the realistic performances of the power unit are not ends in themselves but depend from the accumulator and the BMS which is coupled.
Exemplifying a maximum discharge rate of 1C, is therefore entirely illusory to think that a motor torque corresponding to 16A can be available continuously in a vehicle equipped with a battery pack with a nominal capacity of less than 16Ah because in NCM normally, the maximum discharge current is twice the nominal or continuous one but must be considered usable for the transient of 14-20 milliseconds corresponding to the default set-up time setting in BMS.
The “energy content”, as seen depends from the chemical and from the format of the cell hence from its the size, but it is however impossible to configure batteries having voltage and capacity sufficient for electric traction also minimal, without adequately connect “multiple cells” in “series” to reach the “nominal voltage” required, and in “parallel” to ensure the “energy capacity” or the “electric power” requested.
The electric tanks thus obtained are called “battery packs” or “electric accumulators” or “accumulators of the electric charge “.
A battery pack of nominal voltage of 48 V requires a connection in series of 13-14 cells NCM or 16 if LFP cells are used , called string and abbreviated 13S – 14S or 16S.
If to this pack is required a total capacity of 8.8 to 9 Ah, using elements of unit capacity of 2200-2250 mAh, it is necessary to realize the parallel connection of 4 serial strings, abbreviated 4P.
The battery pack thus assembled called 13-16S4P, will have a reserve of the electrical energy equal to 422-432 Wh respectively, and will consist of 52 or 64 cells NCM or LFP of the chosen format, such as 18650, which correspond to a precise dimensioning, weight and volume.
To ensure adequate stability, durability and heat dissipation which is a function of the C rates of the typical use, the cells must be well-positioned, often retained by a plastic containment flanges appropriately configured and further wrapped in a sheet of PVC shrink, to be finally placed in an structural external sturdy container.
The cycles of charge and discharge, as it is for all transfers and energy transformations, also occur in this specific with efficiency less than one and the energy lost has thermal nature; the optimal duration of this electric machine can therefore also require its eventual climatization, as in the cases where it is designed to provide transient power much higher than the nominal power, employing it as injector of the additional power, time-limited.
Accumulators of Electric Charge Table by Minimal Powertrain AG
|Part Code||Chemistry Format||Nominal Voltage||Nominal Capacity||Assembling||Numero Celle||Cells Number||Total Capacity/Total Voltage||Cells Weight|
|BP36_331||NCM 18650||3,7V||2,30 Ah||10S4P||40||9,2 Ah-36 V||331,2 Wh||1,78 Kg|
|BP36_418||NCM 18650||3,7V||2,30 Ah||10S5P||50||11,5 Ah-36 V||417,6 Wh||2,23 Kg|
|BP36_486||NCM 18650||3,7V||2,25 Ah||10S6P||60||13,5 Ah-36 V||486,0 Wh||2,68 Kg|
|BP48_432||NCM 18650||3,7V||2,25 Ah||13S4P||52||9,0 Ah-48 V||432,0 Wh||2,32 Kg|
|BP48_499||NCM 18650||3,7V||2,60 Ah||13S4P||52||10,4 Ah-48 V||499,2 Wh||2,45 Kg|
|BP48_547||NCM 18650||3,7V||2,85 Ah||13S4P||52||11,4 Ah-48 V||547,2 Wh||2,50 Kg|
|BP48_648||NCM 18650||3,7V||2,25 Ah||13S6P||78||13,5 Ah-48 V||648,0 Wh||3,48 Kg|
|BP48_749||NCM 18650||3,7V||2,60 Ah||13S6P||78||15,6 Ah-48 V||748.8 Wh||3,67 Kg|
|BP48_821||NCM 18650||3,7V||2,85 Ah||13S6P||78||17,1 Ah-48 V||820.8 Wh||3,75 Kg|
|BP48_4992||NCM 18650||3,7V||2,60 Ah||13S40P||520||104 Ah-48 V||4992,0 Wh||24,47 Kg|
A good battery should be sized for the type of service that will be burdened (peak, continuous and transient) and for the other performances required like the recharging time, must have first quality cells newly produced or properly maintained, be well assembled and managed by a good BMS.
The cost of each component is so important to the economy of the vehicle that it is often the object of saving, to the detriment of performance, safety and durability really sometimes very different from that declared.
rechargeable battery pack for lightweight quadricycle L6e class by 2002 24 CE norm, produced with high performance 18650 NMC cells 3.7V – 2.6Ah with layout 13S40P to achieve an output of 48V and 104Ah.
Smart BMS with telemetry function
Tested before delivery
R&D Minimal Powertrain Center in Ronchis (UD), Italia