Motorhome Issue: Smart Alternator
This article is positioned as an overview of “smart alternators, motorhomes and accessories”, describing basic principles.
It is meant for discussion, if you have any comments or suggestions please contact the author direct at:
oakleigh@bristolcaravans.com
Issue
Can incorrect accessory fitting damage the engine battery or engine battery charging?
Background
EU legislation was introduced to help reduce vehicle emissions. “Smart alternators” are part of the EU emissions initiative.
Smart alternators were introduced to the UK car market around 2015, some motorhome brands were slower to implement. We recommend that you check. Do not assume your motorhome or campervan has a smart alternator based on date.
What do smart alternators do in motorhomes?
Smart alternators switch off when they are not needed (ie a low 12v load). This reduces friction on the drive belts, which in turn reduces load on the engine. A lower load on the engine means better fuel consumption and less emissions.
How do smart alternators work in the modern motorhome?
A sensor or “shunt” is fitted to measure the load on the engine battery. This is usually fitted to the negative terminal of the engine battery. The sensor works with the engine’s ECU and switches the alternator Off & On. When the shunt senses the engine battery is full it switches the alternator off. When the shunt detects a load, the alternator is brought back into play.
The alternator is often switched off before the battery is 100% full, to allow capacity for surges and/or regenerative braking (if fitted).
What is the potential accessory install problem?
If the accessory is fitted with the negative cable attached direct to the negative terminal, it has bypassed the shut, which means the sensor will not read the load of the accessory. In turn the engine battery many not be charged correctly.
If fitting an accessory to a motorhome with a smart alternator, the negative termination should be the point where the batteries negative cable connects to the chassis (cab body).
Example A
Pre Smart Alternator
The negative connections to the engine battery looked similar to the image below:
2017, Fiat Ducato 2.3 Diesel, A Class Motorhome
Pre Smart Alternators, accessories were connected to the buzz bar built into the negative terminal clamp.
Example B
Early shunt attached to the negative terminal on the engine battery
In this case all accessories should be wired direct or via a correctly spec’ed buzz bar connected to the body where the negative battery lead is terminated.
2021, Fiat Ducato 2.3 Diesel, X250 Chassis Cab Motorhome
Example C
2023 Motorhome Smart Alternator sensor
Interestingly, the part label is date stamped 2019.
Again in this case, accessories should be wired direct to the vehicle body where the battery is connected, alternatively if the accessory load is light, via a buzz bar.
2023, Fiat Ducato 2.2 Diesel, X250 Chassis Cab Motorhome
Why wire direct to the vehicle body if a smart alternator is fitted?
If wired to the body negative battery point, the load from the accessory will be accurately measured by the sensor. Which means the alternator will be switched on when required and recharge the engine battery.
Notes:
1. Accessories that will be operated when the engine is switch off ie Levelling systems, could be wired direct to the engine battery. But to ensure consistency, it is recommended that all accessories fitted to vehicles with a smart alternator are wired in such a way as to ensure the smart alternator shunt (sensor) can read the load.
2. Do not connect accessories via the bolt-on AL-KO chassis. The joint between base vehicle and AL-KO chassis can sometimes cause poor electrical connection. Always connect wiring to base vehicle chassis (Fiat, Mercedes, Ford, etc).
3. How do you check to see if you have a smart alternator? Click here for information on the test.
Owner Actions
- When booking your next accessory install, ask for specific details regarding the installation process.
Read about our Motorhome, Caravan, Campervan accessory services here
If you have a question about accessories, or you would like to book in for a free assessment to obtain an estimate for your vehicle please email service@bristolcaravans.com or give us a call on 01454 612 893.
Bristol Caravans is an Approved installer of many accessory brands.
