12, 24 or 48 volts? — choosing a system voltage

The calculator compares all three voltages on current, required conductor size and cost. It recommends not the electrically superior option but the one with the lowest total cost: if you already own 12 V appliances such as a compressor fridge, water pump and lighting, a 24 or 48 V bus forces a DC-DC converter, whose cost is set against the cable savings.

Cross-section scales with 1/U², not 1/U: the current falls with 1/U, and at the same time the permissible absolute voltage drop grows with U because it is specified as a percentage of system voltage. From 12 V to 48 V that is a factor of 16. In the reference case — 1200 W over 4 m at 3 % — the requirements are 44.2 mm² at 12 V, 11.1 mm² at 24 V and 2.77 mm² at 48 V.

No — it checks voltage drop only, and it explicitly flags that ampacity is a separate check. Also outside its scope are the availability and price of specific appliances, DC-DC converter efficiency, battery block granularity, and national limits on DC voltages.

Because two effects combine: at four times the voltage, a quarter of the current flows — AND the permissible absolute voltage drop (3% of U) is four times larger. Cross-section therefore scales with 1/U². In the spec test case (1,200 W, 4 m, 3%): 44.2 mm² at 12 V, 11.1 mm² at 24 V, 2.77 mm² at 48 V — exactly 16:4:1. The area-true circles in the chart make this physically visible.

When the device balance says so: compressor coolers, water pumps and lighting are cheapest and most varied as 12 V devices. Going to 24/48 V requires a DC-DC converter for them — whose cost and losses enter the comparison. For small systems with short cables and many 12 V loads, 12 V wins the total-cost calculation despite thicker cables.

As a rule of thumb via current: from about 100 A continuous (≈ 1,200 W at 12 V) cables, fuses and terminals become unwieldy and expensive, and every joint becomes a heat source. A 3,000 W inverter at 12 V means over 250 A of peak current — there, 24 or 48 V is no longer a matter of taste. The calculator shows the currents per candidate directly in the columns.

It is a visible assumption with a market anchor: in August 2026, fine-stranded H07V-K copper cable retails around €0.26 per mm² and metre at 25 mm² and €0.19 at 50 mm² — larger sections are cheaper per mm². The default of €0.25 sits inside that range. Previously the value was fixed at €0.35 and unreachable through the form, although it decides half the recommendation.

When existing 12 V appliances would require a DC-DC converter. In the reference case (1,200 W, 4 m) the cables cost €100 at 12 V and €8 at 48 V — but 240 W of legacy 12 V loads plus a €150 converter flip the total: €100 versus €158. Exactly this counter-calculation is missing from rule-of-thumb articles that blanket-recommend 48 V.

Because two things change at once: current falls with 1/U, and the permissible absolute voltage drop rises with U, since it is defined as a percentage of system voltage. From 12 to 48 V that is a factor of 4 × 4 = 16 — 44.2 mm² versus 2.77 mm² in the reference case. Looking at current alone, you expect a factor of 4 and are surprised.

No, deliberately not — it calculates voltage drop and says so in its own warning. Ampacity depends on installation method, grouping and ambient temperature and has its own calculator. Both checks must pass; the stricter one wins. At 12 V and 111 A, ampacity is almost always the tighter limit.

Yes: if you entered continuous and peak load there, both arrive pre-filled here — the chaining hands them over via the follow-on link. Conductor material (copper or aluminium), conductor temperature and efficiency are also adjustable since 5 August 2026; before that they existed in the calculation schema but were unreachable through the form.