Reefer Container Power: Gensets, Clip-Ons and Keeping the Box Cold on the Road

A refrigerated container is a fridge with no fridge power of its own. The refrigeration machine is built into one end of the box, but it needs a three-phase electrical feed to run. Everywhere that container goes — the terminal, the ship, the truck, your yard — something has to plug it in, and the cold chain breaks at every point where nothing does. Understanding where the power comes from at each stage is the difference between cargo that arrives at temperature and a claim.

This builds on our guides to reefer container shipping and refrigerated road transport.

What the reefer machine needs

A standard shipping-line reefer runs on a three-phase supply — commonly around 400 volts, 50 hertz in this region — drawing a heavy current on start-up and a steady load while it holds temperature, more when it is pulling a hot load down or running defrost. It does not carry batteries. If the supply is cut, the insulated box buys you some time — hours, not days, and far less in tropical heat with a frozen load — and then the cargo temperature starts to climb.

Where the power comes from at each stage

Follow one container from a China cold store to a Dhaka warehouse:

• Origin cold store / stuffing: plugged into the building supply while it is loaded and pre-cooled.
• Origin terminal: plugged into a reefer rack — a bank of powered sockets — and monitored by terminal staff who log temperatures.
• On the ship: plugged into the vessel’s reefer sockets; the crew monitors and records each box.
• Transhipment port: unplugged from one ship, moved, plugged into the terminal rack, later plugged into the next ship. Each unplug-replug is a gap and a risk point.
• Destination terminal (Chattogram): plugged into the reefer yard rack while it waits for clearance. Reefer plug points are limited, which is one reason cold cargo needs priority clearance.
• Road move inland: this is the leg with no fixed socket — and where the genset or clip-on comes in.
• Your yard / warehouse: plugged into your supply, or run on a genset, until it is unpacked.

Genset vs clip-on: the road-leg options

For the truck leg there are two ways to keep the reefer running:

• Underslung / clip-on diesel generator set (genset): a self-contained diesel generator that either hangs under the trailer chassis (underslung) or clips onto the front of the container (clip-on). It has its own fuel tank, starts and stops automatically to match the reefer’s demand, and typically runs many hours on a tank. This is the standard solution for moving a reefer container by road where there is no shore power.
• Generator truck / power pack: a larger generator mounted on the prime mover or a separate unit, used where one tractor pulls reefers all day.

The genset is not optional equipment on an inland reefer move — it is the refrigeration power for that leg. A booking that does not specify and confirm a genset for the road portion has a hole in it.

The failure points to design out

Reefer cold-chain breaks cluster around a few predictable moments:

• The gap between unplugging at the terminal and the genset starting for the road move — keep it to minutes, and confirm the genset has fuel before the container is unplugged.
• Genset running out of diesel mid-journey, especially in port or border queues — brief the driver to check the gauge and top up.
• Long clearance delays at Chattogram with the box on a terminal plug that may or may not be reliable — push for priority clearance of reefer cargo.
• Arrival at a warehouse with no three-phase point, so the container sits on a dying genset while someone finds a socket — arrange the connection before the truck leaves the port.
• Nobody reading the temperature log or the machine’s display at handover points, so a drift is discovered only at unpacking.

Set-point, pull-down, and fresh-air

A few operating basics that affect whether the cargo holds. The reefer maintains a set-point; it is sized to hold a pre-cooled load, not to chill a warm one quickly, so cargo must go in already at temperature. Frozen loads run with the fresh-air vent closed; chilled produce that respires — fruit, vegetables, flowers — needs the vent set open a defined amount to release carbon dioxide and heat, and the correct setting is cargo-specific. Defrost cycles briefly raise the coil temperature and are normal. If you are shipping produce, the vent setting and any controlled-atmosphere requirement should be written on the booking, not left to the terminal.

Monitoring and the paper trail

Modern reefers log temperature continuously and many transmit it live, but you still want an agreed record. Ask for the download or the monitoring report covering the whole journey, and have someone physically check and photograph the machine’s display and set-point at each handover — origin stuffing, port in, port out, and delivery. If a claim arises, a continuous log that shows exactly where and when the temperature drifted is worth more than any amount of argument about whose leg it happened on.

What to confirm before you book

For any reefer move into Bangladesh, get these in writing: the set-point and fresh-air / atmosphere settings for your specific cargo; that a genset is included and fuelled for the inland leg; who monitors and logs temperature at each stage; the plan for priority clearance at Chattogram; and that a three-phase connection or standby genset is ready at the delivery point. The cost of each of these depends on the lane, the container type, and the season, so ask us for a quote against your actual route and cargo.

Pre-trip inspection of a reefer

Before a reefer is accepted for stuffing it should pass a pre-trip inspection (PTI) — a self-test the machine runs plus a physical check. What matters to you as the cargo owner: the machine holds set-point on test, the evaporator and condenser coils are clean, the door gaskets seal, the interior is clean and odour-free, the drain holes are clear, and the T-bar floor is undamaged so air can move under the load. Ask the line or your forwarder for the PTI pass before the container comes to the factory. A reefer that fails PTI at the cold store is a delay; a reefer that was never PTI-tested and fails at sea is a claim.

Chilled versus frozen: different risk profiles

A frozen load at minus 18 °C has thermal inertia on its side — a short power gap moves the surface temperature but the core stays frozen for a while. A chilled load at, say, 2 °C has almost no margin: a few hours without cooling in tropical heat and respiring produce is into the danger zone, and produce also generates its own heat, so the reefer is fighting the cargo as well as the ambient. This is why chilled produce moves need tighter handling at every plug-in gap, an open fresh-air vent set correctly, and faster clearance than a frozen container of the same value.

Insurance and the temperature clause

Standard cargo insurance often excludes or limits loss from a refrigeration breakdown unless you specifically arrange cover for it. For reefer cargo, confirm the policy includes a machinery-breakdown or refrigeration clause, understand the deductible and any requirement that the breakdown exceed a set number of hours before it responds, and know what evidence the insurer wants — usually the continuous temperature log plus proof of correct stuffing temperature. A policy that pays only for physical accident to the ship will not help you when the cargo cooked because a genset ran dry in a port queue.

DE International helps Bangladeshi businesses source from China, move goods door to door by air and sea, clear customs, and set up storage — including cold rooms and warehousing. To talk through a project, contact our team, see the full service list, or start with our China sourcing and buying agent service. Stock lines are in our shop. Prices, capacities, temperatures, and timelines in this article depend on your product and site — ask us for figures built around your case.