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I have been receiving a lot of emails over the last two or three months from people reporting issues around charging their leisure batteries after changing tow vehicles and a similar number from people who are having problems with performance of the installation of the electrical harness on their new vehicle tow bar.

I’ve spent quite a bit of time answering emails and thought I’d try to sum up what is happening. A lot of this is also going to apply to Motor Homes, especially if they have a new Euro 6 engine.

When we bought our VW Amarok last year (2016) It took me a few days of research and an exchanging of emails with the technical people at Wolfsburg to make sure I had the correct VW approved OEM electrical tow package for the vehicle installed. (Read about it here: Choosing A New Tow Vehicle Pt3…) As the Amarok has a smart alternator with regenerative braking and stop start technology I started to do a bit of research on what this would mean for us towing. While looking in to it I started see a couple of things that I thought as potential issues not only for us but for anyone that tows a caravan or for motorhomes when it comes to charging the leisure batteries.

What exactly are ‘smart alternators’?

Well they are not really smart. They do what they have always done and that is convert mechanical energy into electrical energy. What is smart now is a central control unit (ECU, EMS) which controls them.

In order for vehicle manufacturers to produce more efficient engines with more power and fewer emissions they looked at ways of reducing other loads on the engine and one way is to control the alternator. When you put your foot down for acceleration, the Control unit senses this and reduces the field coil voltage and hence the mechanical load the alternator puts on the engine to maximise power available. Like wise when cruising along to reduce emissions the load on the alternator is reduced. However to make up for  all this the energy to charge the vehicle battery has to be found from somewhere and its done by using something called regenerative braking. When you take you foot off the accelerator and start to brake, the control units senses this and ramps up the field voltage to get the maximum output from the alternator using the excess energy from the braking action of the engine being driven by the road wheels.

That is a very quick and simplistic view but for me to sit and type a detailed explanation of what’s actually happening would probably take me a couple of days (with one finger typing and editing) and they say a picture… well in this case a video, is worth a thousand words.

If you are a regular reader to the blog, you will know I have been pointing people in the direction of Sterling Power products for a while for inverters and battery to battery charging and recently Sterling’s MD, Charles Sterling produced a video in which he explains some of the issues with smart alternators….

Other issues…

All vehicles now use a central control unit to manage systems, everything from engine tuning to controlling lights. Now when you turn on the heated rear window for example all you re doing is pushing a button that requests the central control unit to turn on the heating element. Like wise, when you connect your caravan electrics, the control unit detects this and changes a number of things, the abs and traction control systems, maybe the shift points in the automatic gearbox and it turns on power to pins 9 and 10 on the 13 pin towing socket. Traditionally a relay has turned on power to pin 10 (the fridge circuit) which in turn activates the habitation relay in the caravan allowing pin 9 to charge the leisure battery.

Now, the operation of pin 10 and pin 9 are controlled by the central control unit, so if it detects that the vehicle systems require more electrical power due to low alternator output, it can turn off both pin 9 and pin 10. Something else I have recently discovered is that with some vehicles, pin 10 becomes live as soon as the key is inserted without the engine running, powering up the caravan and activating the habitation relay, therefore putting a drain on the vehicle starter battery. This may or may not be an issue, but I don’t know if there is protection within the vehicle to stop any engine starting procedure from drawing current from the caravan leisure battery. This is particularly important for engines with stop start features.

Something else this now leads to. If the central control unit can turn off power to these pins at will, then turn it back on again if this happened while driving this could have implications for caravans fitted with the ALCO ATS system. One function of the ATS is when first powered up it goes through a self test procedure which involves operating the  caravan brakes and releasing them before confirming everything is OK by turning the indicator light to green. If the vehicle turns off the power then restores it, this could lead to the ATS applying the brakes while the vehicle is underway. I really don’t know if this is a possibility?

How to check if your vehicle has a smart alternator…

If you have any comments or experiences of issues with smart alternators or issues with towing electrics on the latest vehicles, please comment below. If you could include the vehicle manufacturer, model, year and caravan make, model and year it would help others and maybe we can build up a repository of information. I’ll try to answer questions or find out more information for you.