Just found this:

Quote:

MPORTANT NOTE: VSR relays are not suitable for vehicles with 'smart' or 'intelligent' alternators. As a guide this applies to vehicles having engines that comply with Euro5 emissions standards and onward, often also incorporating regenerative braking (if in doubt please consult your vehicle manufacturer to confirm). If your vehicle has a smart alternator then you will need to use a battery-to-battery charger instead of a VSR.

A simple VSR works fine with my MY12. The above statement sounds like marketing hype for DC to DC chargers.

Hi Graeme, ok that's very interesting. So what do you think about this, do you think from your experience/in practice this happens? :

Quote:

The difference between DC battery chargers and other split charge systems is that whereas a split charge relay is ruled by how the vehicle alternator senses the leisure battery charge the DC battery charger uses it's own micro-processor system to determine the actual level of charge in the leisure battery and tricks the alternator into providing extra charge for long periods in order that the leisure battery reaches full charge.

Confused? Let us explain further...

As stated previously a split charge relay is governed by what the vehicle alternator does. When the leisure battery voltage rises to a certain level (surface charge) the alternator will cut down it's charge rate to minimal amps because it thinks the battery is now charged; in most cases (i.e. light caravan and camping uses) where the leisure battery is not deeply discharged this would be acceptable. However, if the battery is deeply discharged the alternator will cut back too early because it cannot differentiate between what is just surface charge (i.e. the voltage has reached a level, but the battery actually needs much more charging) and what is full charge. This is where the DC battery charger comes in... Basically it reacts the same as a top quality mains battery charger, but instead of using mains electricity is uses power from the alternator instead and it will keep demanding that power until the leisure battery's actual full charge is reached.

So, to summarise, if you use a lot of leisure battery power and deep discharge the battery/batteries regularly then the DC battery charger should be your preferred option.

Our vehicles sense the drain from the main battery via a sensor in the battery's negative to earth connection. An auxiliary battery that has its negative connected directly to earth is seen as a load by the logic controlling the alternator rather than a battery so keeps supplying power whilst the battery is using power (charging), just like idling with headlights, a/c, seat coolers switched on. If the auxiliary battery's negative was connected to the main battery's negative then the auxiliary battery would only be charged to LR's 80% charged design criteria for the main battery.

....err not following you 100% but as per your earlier comment this is marketing hype and I can use a normal VSR? Cheers, Greg
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2011 Vogue SE 4.4 with lots of toys in Stornaway

My VSR is nothing special but gets the AGM aux battery back to fully-charged quite quickly.

Some vehicles, eg later model Toyotas, have a low voltage system that makes it difficult to properly charge aux batteries using a VSR because it can disconnect even with the engine running. DC to DC chargers are popular for these vehicles. LRs run a high voltage system, very close to 15V when needed but never low enough to cause the VSR to disconnect.

Ok thanks Graeme, great to know.

One question - if I sit parked with the tv running I get a low battery shutdown after around 15-20mins.

Does the VSR set up allow the second battery to add power or extend running the main system?

Thanks,
Greg Cheers, Greg
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2011 Vogue SE 4.4 with lots of toys in Stornaway

Not unless the VSR specifically provides this feature, which some do until the auz battery voltage drops below the cut-out level. I may fit one of this type if mine dies although that compromises the ability to use the aux if the main is too flat to start the engine due to it already having been run down somewhat, but perhaps the aux would still have enough reserve to do the job.

A small relay could be fitted to bridge the VSR that is switched in for those times when more usable time is desired from the main battery but you would then have to remember to turn it off.