BESS 20-ft DC Cable Current Distribution

Series / parallel arrangement

Switch design here, or fine-tune racks / strings-per-rack / packs on the Input tab. The whole network re-solves instantly.

Engineering dashboard

calculated user input datasheet assumption limit

Engineering checks

Automatic warnings compare calculated results against the engineering limits you set on the Input tab.

Current distribution by HV Box

Current imbalance

Cable route & current loading

Branch line weight and colour scale with branch current. Hover a branch for full detail.

Input data

Everything below is editable. Fields marked assumption or carrying a required-input note must be confirmed against the UL3932 2/0 AWG datasheet and the installation conditions before the results are used for design.

⤓ Import Excel

Data source: built-in defaults. Put an inputs.xlsx next to this page (or Import one) to drive it from Excel.

Series / parallel arrangement ›

Design presetinput

D1 = 12 racks × 1 string × 8 packs. D2 = 6 racks × 2 strings × 4 packs (dual-string HV box). A preset sets the rack count, strings/rack, packs/string, string cabling and feeder schedule — then edit any field below.

Racks (HV boxes)input

= number of feeders; one feeder per HV box

Strings per rack (k)input

1 = single-string HV box, 2 = dual-string

Packs in series / stringinput

sets string voltage & cabling hops

Cells in series / packinput

104 for a 104S1P pack

Nominal cell voltageassumption

V/cell — ~3.2 for LFP (informational)

Total stringscalculated

racks × strings/rack, all in parallel

The feeder from the combine cabinet runs to each rack's HV box and is shared by every string in that rack, so it carries their combined current. The strings inside a rack are in parallel; the racks are in parallel at the DC bus. Changing k here re-solves the whole two-level network.

Operating point ›

DC bus voltageinput

V — nominal pack-string / bus voltage

Total DC current sourceinput

PCS DC powerinput

kW — total DC power drawn through the combine cabinet. I_total = P / V_bus

Conductor resistance model ›

UL3932 · 2/0 AWG · DC1500V · cable duct

Resistance source

DC resistance at reference temp.required input

Ω/km — REQUIRED. Enter the UL3932 2/0 AWG value from the cable datasheet. Placeholder shown is an assumption only.

Datasheet reference temperaturerequired input

°C — temperature at which the Ω/km value is quoted (commonly 20 °C)

Operating conductor temperaturerequired input

°C — resistance is corrected to this temperature. R(T)=R_ref·[1+α(T−T_ref)]

Temperature coefficient αassumption

1/°C — copper ≈ 0.00393

Parallel cables per poleinput

divides conductor resistance (1 = single cable per pole)

Return-conductor factor (feeder)input

×2 counts positive + negative feeder of equal length as the current loop. Set 1 if the schedule length already is the loop.

Connector & string internals (per string) ›

All values below are for one string (one series stack of packs). The tool applies them to every string and parallels the strings inside each rack.

Contact / connector resistance (each)required input

Ω per connector — enter the measured/datasheet value (0 = ignore)

Connectors in series per stringinput

String internal resistance (one string)required input

Ω — DC resistance of one series pack-string. In reality this dominates and equalises current sharing. 0 isolates the cable-only effect (worst case for imbalance). For k strings in a rack the parallel value is this ÷ k.

String internal cabling segmentsinput

mm, comma-separated — one string's series loop HV Box→P1→…→Pn→HV Box. For 4 packs: 5 values (e.g. 1600,500,500,500,800); for 8 packs: 9 values. Replace pack-to-pack values with your real schedule — defaults use 500 mm spacing.

Engineering limits ›

Cable ampacity (per pole)limit

A — required. Rated current for UL3932 2/0 AWG at the installed method & ambient, after derating. Verify on datasheet.

Allowable feeder voltage droplimit

% of DC bus voltage

Allowable current imbalancelimit

% (Max−Min)/Average

Max physical routing lengthlimit

mm — flags any feeder longer than the routing allows

Combine Cabinet → HV Box feeder lengths

One feeder per rack. Set the rack count under Series / parallel arrangement above; edit each feeder length here.

HV Box	Feeder length (mm)	R feeder (mΩ)	R rack (mΩ)	Share	Feeder I (A)

Cable calculation — complete DC network solution

Each branch is a series resistance from the common DC bus node to the common return. Current divides by conductance: I_i = I_total · G_i / ΣG, with G_i = 1/R_branch,i. This is the exact network result for equal-EMF parallel sources — never a proportional-to-length approximation.

R / metre (per pole, @T)

Feeder loop R / metre

String cabling R (per string)

Connector R / string

Parallel-network R

Total DC current

R(section)

ρ·L / A

Rack R

R_feeder + R_string/k

Rack I

I_tot·G_i/ΣG

String I

I_rack / k

Feeder V-drop

I_rack·R_feeder

Cable loss

I_rack²R_f + k·I_str²R_str

Average current

Max current

Min current

Imbalance

Total cable loss

Max feeder V-drop

HV Box	Length (mm)	R feeder (mΩ)	R branch (mΩ)	Feeder I (A)	Share (%)	Feeder V-drop (V / %)	Cable loss (W)	Deviation (%)

The feeder carries the combined current of every string in its rack (×k), so with a dual-string HV box it sees roughly twice a single string — this is the binding figure for feeder ampacity and voltage drop. The per-string current (shown in parentheses when k>1) is what flows in the string cable and the pack. Node-to-node voltage drop (bus → string) is equal for every string by construction; the feeder-cable portion shown here varies with routing.

Cable length vs branch current

Shorter feeder → lower resistance → higher current share. The relationship is inverse-resistance, not linear.

Cable resistance vs length

Branch resistance rises linearly with feeder length (plus the fixed rack / connector / pack terms).

Feeder voltage drop by branch

Cable power loss by branch

Current balancing analysis

HV Box	Length (mm)	Resistance (mΩ)	Current (A)	Share (%)	V-drop (V)	Loss (W)	Deviation (%)

Scenario comparison

Scenario A is the current design (locked to your input lengths). Edit B and C to test alternative routing. All other parameters are shared from the Input tab.

HV Box	A · Existing (mm)	B · Optimised (mm)	C · User-defined (mm)

Results & difference from baseline (A)

Current distribution — all scenarios

Imbalance-reduction study

Imbalance is driven by the spread in branch resistance. Mathematically it is minimised by bringing every branch resistance toward the highest branch — achieved by padding shorter feeders. This is an analysis scenario only; it does not alter the engineering design, and physical routing/EMI/length limits always govern.

Min feeder lengthlimit

mm

Max feeder lengthlimit

mm — padding is capped here

Target imbalancelimit

% — padding stops once reached

Method: raise each branch R toward R_max by adding feeder length, within [min,max].

20-ft container — isometric layout

Combine cabinet plus each rack's HV box (holding its strings in parallel), cable duct and pos/neg feeders. Rack height/colour shows feeder-current loading. Reflects the arrangement set on the dashboard.

Cable route diagram

Combine Cabinet branching to every HV Box, with actual feeder length and a current arrow per branch — arrow weight and colour scale with branch current. Hover for cable length, resistance, current, voltage drop and loss.

Sensitivity analysis

Sweep one parameter and watch the key metrics move. Uniformly scaling every length (or changing cable size) preserves the resistance ratios, so imbalance holds while loss and voltage drop scale — scaling an individual length is what changes the distribution.

Parameter to vary

Sweep points (× / factor)input

comma-separated multipliers of the current value

Factor	Varied value	I total (A)	Max I (A)	Min I (A)	Imbalance (%)	Total loss (W)	Max V-drop (V)

Model & assumptions

Topology (configurable). Two-level parallel network: N rack feeders in parallel at the combine-cabinet DC± nodes, and within each rack k strings in parallel sharing that rack's feeder. Each string is a series stack of packs (e.g. 104S1P packs, 4 or 8 in series). Switch between the two designs on the dashboard — Design 1 (12 racks × 1 string, single-string HV box) and Design 2 (6 racks × 2 strings, dual-string HV box) — or set racks, strings/rack and packs/string directly on the Input tab. With k = 1 this reduces exactly to the flat 12-branch current-divider.
Feeder carries combined string current. Because both strings in a dual-string rack share one feeder, that feeder carries k× a single string's current. Feeder ampacity and voltage drop are checked against the combined (feeder) current; the string cable and pack see the per-string current. The string-to-string current imbalance is driven by the feeder-length spread across racks; strings within a rack split evenly when identical.
Equal-EMF assumption. All strings are taken at the same open-circuit voltage (balanced SOC). Under this assumption the exact network solution is the conductance current-divider I_i=I_tot·G_i/ΣG. Unequal SOC would add circulating currents not modelled here.
Steady-state, resistive. DC only; inductance, skin/proximity effect and transient sharing are not modelled.
Feeder loop. Positive and negative feeders of equal length ⇒ loop resistance = factor × ρL/A (default factor 2).
Equal branch V-drop. Node-to-node drop is identical across branches by construction; the reported per-branch drop is the feeder-cable portion, which varies.
Pack internal resistance dominates reality. With a realistic string resistance the cable-driven imbalance shrinks markedly. Default 0 shows the cable-only worst case the brief asks to expose.

Value-type legend

calculatedDerived by the model from your inputs.

user inputEntered directly by you.

datasheetTo be taken from the UL3932 2/0 AWG cable datasheet.

assumptionPlaceholder / generic value — confirm before design use.

limitEngineering acceptance limit you define.

Required inputs not to be invented: DC resistance of UL3932 2/0 AWG (Ω/km), conductor temperature, connector resistance, pack resistance, ampacity, allowable voltage drop, allowable current imbalance. Each has an editable field above and is flagged accordingly.

Disclaimer

Results are engineering calculations based on user-entered electrical parameters and cable resistance. Final design shall be verified against the applicable cable datasheet, installation method, temperature derating, protection settings and applicable standards.