12V Guru – can I charge breakaway battery from caravan house battery?

Question to 12V Guru

My Jayco van battery is charged with a Setec ST-III power supply when on mains power and a solar panel when in storage. The BrakeSafe battery is charged via a 220V plugpack when on mains power but is not charged at all when in storage for most of the year.

 After reading the answer about charging a BrakeSafe battery published in issue 591, I wondered whether it would be safe to connect the BrakeSafe battery charge input to my caravan house battery instead of the car 12v.  Would I need a diode between the house battery and the BrakeSafe battery to prevent discharging the BrakeSafe battery when free camping?

12V Guru answers:

Hi John,

Glad to see that you are one of the few who does pay attention to the safety devices installed on your van.  As mentioned in previous articles it does concern us when we observe out there in the “real” world that many caravanners do ensure that the battery on their Breaksafe is properly maintained.

Where these devices are legally required to be installed, care should be taken to ensure that they are properly maintained.  If you had a flat tyre on your van you would certainly fix it!  “Out of sight, out of mind” is no excuse. Your responsibility extends to other road users to whom this device could potentially be life saving for in the face of a decoupled oncoming caravan.

How to charge breakaway battery

In regard to charging this device it is recommended to either charge from the vehicle line or from a 240v charger. However, if you were to charge directly from the caravan house battery it would have the same effect as charging from the vehicle assuming the solar panels are keeping the voltage on the battery at the upper levels. 

As the Breaksafe has a built-in trickle charger you should be able to expect that it would not allow current to drain back to the larger caravan house battery and that the inbuilt circuit would have a reverse diode inbuilt or equivalent circuitry to prevent this. 

Trickle chargers are used to maintain batteries over a long period of time.  They do not charge a battery very quickly but are appropriate where you don’t want to be left with a flat battery after having you caravan in storage for a long period of time. They should switch off automatically once the battery is fully charged.

The Breaksafe contains a 12v lead acid battery which is only 7ahr in capacity.  Having it properly charged is critical as it needs to be fully charged to be able to operate effective in case of emergency. A dual axle caravan with 4 electric brakes drums will draw approximately 6amps for each pair of brakes.  By the time you include the brake lights as well it could be up to approximately 13-14 Amps.  This is twice the capacity of the actual battery so in the case of an emergency it will be extracting current at 2C (rated capacity/amps required).  To work effectively the batteries in these units must be carefully maintained and tested regularly.  If in doubt – replace with a new and fully charged battery.

In the Setec ST-III setup you will most likely have the Drifter display inside your van so you will need to ensure that you are wiring correctly through the shunt if you decide to wire directly to the battery.  The negative must be connected on the non-battery side of the shunt to measure all the current correctly.  This will be the same terminal where the solar is connected.

Stay safe on the roads!

In summary, it is great that you are managing this safety critical device properly. Don’t also forget to also check that the switch device on the drawbar is operational and not damaged, and that the battery is fully charged before you leave. 

In your case if you have wired this correctly it should be maintained but many RVers just plug it into their car and think that this will be fine.  The battery may have gone flat over winter (non-use period) and it will take several hours to trickle charge from the car AUX line – no good if you have a decoupling event 1 hour after leaving home.

Checking your safety devices should form part of all good trip preparation.

Safe travels – 12V Guru

The article is written for Caravan World Magazine.

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