DC-DC Charger Cable Size Calculator
Use this calculator to estimate the correct cable size for a DC-DC charger wired from an alternator or starter battery to a leisure battery. It helps you choose a practical cable size based on charger current, cable run length, system voltage and allowed voltage drop for 12V and 24V systems.
Enter your setup
Based on the values shown, 10mm² is a practical starting point for this DC-DC charger installation.
Recommended MKGT product paths
After choosing a cable size, move into the most relevant MKGT cable range for your installation.
Suitable for higher current DC circuits, leisure battery charging and inverter supply runs.
View battery cable →Useful for lower-current vehicle wiring, control circuits and general low-voltage installations.
View 2 core cable →You may also find these tools useful
DC-DC charger sizing often goes hand in hand with voltage drop checks, fuse selection and overall campervan power planning.
Frequently asked questions
What cable size for a 30A DC-DC charger?
For shorter runs, 10mm² is often suitable for a 30A DC-DC charger, but longer runs may require 16mm² to keep voltage drop within a sensible limit. Use the calculator above for a more specific recommendation.
Should I fuse both sides of a DC-DC charger?
Yes. It is generally good practice to fit one fuse close to the starter battery and another close to the leisure battery so the cable is protected on both sides of the installation.
Can I use the same cable size for positive and negative?
Yes. In most DC-DC charger installations, positive and negative conductors should be the same size.
Why does cable length matter so much on 12V systems?
Low-voltage systems are much more sensitive to voltage drop than higher-voltage systems. Longer cable runs increase resistance, which can reduce charger performance and waste power as heat.