Charging connections relative to Isolator switches

[JimC]

In a two battery installation with vsr controlled charging and a permanently connected mains charger, which side of the battery isolator switches should you put the vsr and the charger connections, the battery side or the load side?

 

[sailorman]

In a two battery installation with vsr controlled charging and a permanently connected mains charger, which side of the battery isolator switches should you put the vsr and the charger connections, the battery side or the load side?

if you intend leaving the charger "On" then the battery side

 

[VicS]

+1

Not only does it mean that you will be able to leave the battery charger operating while all the other circuits are safely isolated but it will eliminate the possibility of disconnecting the batteries from the alternator while the engine is running.

If you have or will be fitting a combining switch . Consider putting that on the load side of the switches rather than the battery side. Doing so will enable you to parallel the batteries when necessary but also to isolate a completely defunct battery and run all circuits from the good one

 

[JimC]

.... it will eliminate the possibility of disconnecting the batteries from the alternator while the engine is running.

VicS

I don't quite understand this part of your response. The thick wire from the starter motor & alternator goes straight to the engine battery terminal via that battery's isolator. Opening this isolator will always open-circuit the alternator so I'm careful not to do it, in fact I have considered dispensing with this isolator altogether like on a car. The quiescent current drain from the alternator is only 5ma.

My question related to the connections for the vsr and mains charger. At the moment both go to the battery side of the isolators. In the winter the engine battery gets virtually no use but the domestic battery gets plenty of use for the cabin lights and the Eberspacher. The vsr is a dual-sensing one and parallels both batteries when it senses the charge from the mains charger. The result is that the engine battery is always gassing and needs frequent topping up. My thought was that if I moved the mains charger and vsr connections to the load side of the isolators I could charge the domestic battery in isolation, something I can't currently do.

 

[VicS]

I assumed that if you have, or were fitting, a VSR you would also be using it to split the charge from the alternator by taking the alternator output directly to one of the batteries and employing the VSR to charge the other.

By choosing the right VSR you can even wire it so that the alternator charges the starter battery preferentially and the battery charger , or other charging systems, charge the domestic battery preferentially.

 

[JimC]

I assumed that if you have, or were fitting, a VSR you would also be using it to split the charge from the alternator by taking the alternator output directly to one of the batteries and employing the VSR to charge the other.

The charging current from the alternator and the starting current to the starter motor both go along the same heavy cable to the engine battery (like on a car). The engine battery +ve is linked to the domestice battery +ve by a vsr. This connects the domestic battery to the engine battery when the voltage of the latter indicates it is near fully charged. At the moment the vsr, and also the mains charger connections, are on the battery sides of the respective battery isolators. This makes it impossible to charge the batteries independently of one another using the mains charger.

 

[VicS]

The charging current from the alternator and the starting current to the starter motor both go along the same heavy cable to the engine battery (like on a car). The engine battery +ve is linked to the domestice battery +ve by a vsr. This connects the domestic battery to the engine battery when the voltage of the latter indicates it is near fully charged. At the moment the vsr, and also the mains charger connections, are on the battery sides of the respective battery isolators. This makes it impossible to charge the batteries independently of one another using the mains charger.

If the alternator output was re-routed to the engine battery directly, by passing the isolator, it would eliminate the risks of disconnection while the engine is running.

The down side is of course is that the alternator is not isolated by the isolator switch and you would have to remember to disconnect the battery while working on the engine if there was any risk of shorting the alternator output terminal to earth

 

[pvb]

At the moment the vsr, and also the mains charger connections, are on the battery sides of the respective battery isolators. This makes it impossible to charge the batteries independently of one another using the mains charger.

If you simply move the VSR connection from the battery side of the engine isolator to the load side of the engine isolator, you'd be able to disconnect the engine battery when using the mains charger.

 

[JimC]

If you simply move the VSR connection from the battery side of the engine isolator to the load side of the engine isolator, you'd be able to disconnect the engine battery when using the mains charger.

That's what I had in mind. Was just concerned in case doing so might raise other unforeseen issues. Presumably could do same with domestic battery isolator to cover opposite situation? Should I leave mains charger wires going direct to battery terminals? Mains charger is Dolphin type dual output, but outputs aren't truly independent: engine battery feed is just split off from domestic battery feed via a diode.