Fridge, dual battery and solar

A cold drink and fresh food make a trip better, but a compressor fridge is the biggest power user in a Jimny camp. Plan the fridge, the battery and the solar together, and weigh them, because the payload is small.

These notes cover the 5-door Jimny in India, where the heat makes fridges work harder. Figures are typical and vary with the fridge, the weather and how you use it. Have electrical work done by a competent installer.

By Gypsy Overlanding Family ®

How power flows to a camping fridge The alternator charges an auxiliary battery through a DC to DC charger while you drive. A solar panel also charges the battery at camp. The battery runs the fridge. Alternatorwhile driving DC-DCcharger Solar panelat camp Auxiliarybattery Fridge via a charge controller
The usual setup: the car charges a second battery while you drive, solar tops it up at camp, and the fridge runs from that battery.

The short answer

A 40 to 50 litre compressor fridge typically uses about 30 to 60 amp-hours per day in moderate weather, and more in the heat. Run it from a separate auxiliary battery, charge that battery from the alternator through a DC-DC charger, and add solar if you camp for more than a night or two.

A sensible setup

  • A 40 to 50 litre compressor fridge
  • A separate auxiliary battery
  • A DC-DC charger, to charge it while driving
  • A portable solar panel for camp
  • Proper fusing and wiring

Watch out for

  • Flattening the starting battery
  • Heat, which makes the fridge run far more
  • Battery and panel weight eating payload
  • Poor wiring and missing fuses

How much power a fridge uses

A compressor fridge draws about 30 to 60 watts while the compressor runs, but it cycles on and off. Over a day, a typical 40 to 50 litre unit uses about 30 to 60 amp-hours at around 25 °C, according to fridge guides.

Rough daily use for a 40 to 50 litre fridge
ConditionsTypical use
Cool day, shaded, lightly usedabout 30 Ah per day
Moderate weather, around 25 °Cabout 30 to 60 Ah per day
Hot day, with frequent openingcan double, so 60 Ah or more
Run as a freezermuch more, and often runs almost all day

Heat is the big factor. A fridge in direct sun, or in a hot, unventilated boot, works much harder than one in the shade with good airflow. That matters in Indian summers.

Dual battery basics

A second battery keeps the fridge from draining the one that starts the car. It is charged from the alternator while you drive, and isolated when you park.

  • DC-DC charger. It charges the second battery properly from the alternator, and it protects the starting battery. It suits modern cars best.
  • Fuses. Fit a fuse close to each battery, sized for the cable. A short on a thick cable can start a fire.
  • Cable and connections. Use the right cable thickness for the current and the length, and make clean, tight connections.
  • Placement. Fix the battery down firmly and keep it low and central. Lead-acid types need ventilation.
  • Weight. A 100 Ah AGM battery typically weighs around 28 to 30 kg, and a lithium one of the same size around 11 to 13 kg. Weigh yours, because it comes out of your payload.
Battery types compared
TypeUsable capacityWeightNotes
AGM or lead-acidabout 50%heavyCheaper, tolerant, but you only use half of what you buy.
Lithiumabout 80% or moremuch lighterCosts more, but gives more usable power for less weight.

Solar

To size a panel, divide the fridge's daily energy by the hours of strong sun you get. A fridge using 45 Ah a day at 12 V is about 540 Wh. With five hours of good sun, and allowing for real-world losses of around a quarter, you need roughly 145 W of panel.

  • Use a portable panel. You can park the car in the shade and put the panel in the sun, and it adds nothing to roof weight.
  • Roof-mounted panels add weight where you can least afford it. See roof racks and rooftop tents.
  • Use a charge controller between the panel and the battery.
  • Plan for cloudy days. Monsoon cloud cuts solar output a lot, so carry more battery or drive more.

India: heat, rules and warranty

  • Heat. Hot weather can nearly double a fridge's use. Shade it, give it airflow, and pre-cool it at home.
  • Warranty and insurance. Electrical changes can affect your warranty. Ask Maruti what is allowed, and tell your insurer.
  • Roof panels. A fixed roof panel and its mounts add weight and may raise the same rule questions as a roof rack.
  • Quality parts. Use proper fuses, cable and connectors. Cheap parts are the usual cause of electrical failures.

Plan your power

Enter your fridge, battery and panel to see how long you can stay put. The figures are rough, so leave a margin.

Fridge use (3 to try)

Battery type

from the chips, or your own
nominal capacity
0 for none
fewer in monsoon

What it means

Usable battery
-
Battery alone lasts
-
Solar adds per day
-
Daily balance
-

Common mistakes

  • Running the fridge from the starting battery. One warm night can leave you unable to start.
  • Ignoring heat. A fridge in direct sun can use double the power.
  • Buying amp-hours you cannot use. AGM batteries only give about half their rating.
  • Skimping on fuses and cable. It is a fire risk.
  • Mounting heavy gear high. Batteries and panels belong low, and inside.
  • Forgetting the weight. A battery and fridge can add 50 kg or more.
  • Counting on solar in the monsoon. Cloud cuts output sharply.
A final word. Power figures here are typical and vary widely. Wiring a car carries fire and shock risks, and changes can affect your warranty and insurance. Have the work done by a competent installer, and use fused, correctly sized cable and quality parts.