People use “power distribution unit” for almost anything, from a basic fuse box upwards. On a specialist vehicle it has a narrower meaning. A PDU is the one place where incoming power is split up, protected and switched out to the vehicle’s loads, laid out so that someone can service it. If you know what a proper PDU does, and can tell when a build has outgrown a plain fuse board, you save yourself a lot of rework later.
The jobs it does
A PDU takes the main feed from the battery and charging system and handles several jobs in one box. It splits the supply into separate output circuits. It protects each of those circuits with the right fuse, or with electronic protection sized for the load. It switches the outputs, with relays in an older design or electronically in a modern one. If it is an intelligent unit, it also monitors current and output status.
The reason to put all of that in one place is serviceability. Plenty of conversions still have inline fuse holders cable-tied behind the dash, relays taped into the loom and a schematic that only exists in the head of the person who built it. A PDU puts the protection and switching where you can get at it, in a known layout that matches the drawings.
Why a fuse box is not the same thing
A fuse box protects circuits and does nothing else. A PDU protects, switches and often reports back as well. That difference starts to matter in four situations. The first is when loads need controlled switching, timed, interlocked or sequenced, rather than being fused and left live. The second is when you want diagnostics, such as which circuit tripped, what a load is drawing and what state each output is in. The third is when circuits have to be shed in priority order as battery voltage drops. The fourth is when there are simply too many circuits to manage scattered around the vehicle.
An intelligent PDU that switches electronically can protect itself and reset without a physical fuse. It can also pass faults to the vehicle system or to a remote platform. A fuse box cannot do either.
Signs a build has outgrown its fuse board
Circuit count is the obvious one. Once you are past a couple of dozen switched loads, a documented central unit is far quicker to build, test and fault-find than a spread of inline fuses.
Repeat builds are another. If you are converting twenty identical vans, a standard PDU makes each one the same, and an engineer who has fixed one fault has effectively fixed it on the whole fleet.
Then there is load management. A tail lift on a delivery truck is the classic example. Drivers use it all day with the engine off, and an evening of deliveries can leave the starter battery too flat to crank. If loads have to be prioritised and dropped to protect the battery, the distribution and switching need to be intelligent. For that particular case, the Battery Guard CD Tail Lift warns the operator after two minutes at low voltage and isolates the lift after four.
Weight is a consideration on longer vehicles. Centralising the distribution and pairing it with CAN switching takes a lot of heavy copper out of the run from cab to rear.
Finally, diagnostics. Fleet and OEM customers increasingly want fault reporting and remote visibility, and you only get that from an intelligent unit.
For a simple vehicle with half a dozen loads, a decent fuse box is still the right answer and the cheapest one. A PDU starts to justify its cost as the build gets more complex.
Intellitec’s approach
We do not sell one fixed box. Distribution and control are built from programmable modules sized to the vehicle.
iConnex is the CAN switching and control system for works vans, welfare vehicles and amber-light builds. Its ICX-MOD-PRO module gives ten FET outputs and two 30A relays on 12V or 24V, with CAN keypads for the driver, and it replaces the relay-and-fuse loom with outputs you can diagnose.
PMC Multiplex is for the bigger builds. Its CPU handles up to 320 channels, and you add relay modules, solid-state dimmers and mixed I/O boards as the vehicle needs them. The PMC 809 Load Manager feeds battery-voltage thresholds into the logic, so selected loads drop out as the voltage falls.
The IPLC is a rugged programmable controller. The K192 version carries 10 inputs, 20 outputs, two voltage monitors and an LCD screen, and Load Manager modules are available for high-current loads.
Battery Guards protect the supply feeding all of it against deep discharge.
Between them they split, protect, switch and monitor, which is everything a PDU does, and they add programmable logic and diagnostics that a passive box cannot offer.
Making the call
Start with what the vehicle has to do with its power, not just how to protect it. If the honest answer is a few circuits that need fusing, buy a fuse box. If the vehicle has to switch, sequence, prioritise, shed and diagnose, it needs intelligent distribution. Size it to the real loads, document the layout, and get the first vehicle right so the next nineteen copy it. Our distribution and control hardware is made in the UK at our Bromborough site.