Can I connect the battery charger directly to the VSR?

[Colvic Watson]

We have three battery 'banks' - house which will be 330ah, starter 110ah and bowthruster/windlass at 110ah. This winter the thruster battery got quite low because I forgot to isolate it. I thought about connecting the Cetek 25ah charger direct to the VSR (one of the newer type with almost no voltage loss). That way like the alternator it will send the juice to wherever needs it most. But is there a problem I haven't forseen?

 

[JumbleDuck]

We have three battery 'banks' - house which will be 330ah, starter 110ah and bowthruster/windlass at 110ah. This winter the thruster battery got quite low because I forgot to isolate it. I thought about connecting the Cetek 25ah charger direct to the VSR (one of the newer type with almost no voltage loss). That way like the alternator it will send the juice to wherever needs it most. But is there a problem I haven't forseen?

Yup. Most VSRs are dual sensing for just this purpose: you connect the alternator to one battery and the charger to the other and the VSR connects them whenever incoming current pushes either battery high enough.

 

[nigelmercier]

That way like the alternator it will send the juice to wherever needs it most...

It doesn't work like that, it is a common misconception that a VSR "decides" what to charge. The VSR will switch and simply connect all the batteries together. If you only have one shore power charger, this is what you want. However, with three banks, you need more than one VSR.

 

[pampas]

Not so mine has 3 studs for each battery.

In reply to the question "Can I connect to the vsr"( At the alternator input connection) yes provided you disconnect prior to starting your engine,

 

[halcyon]

We have three battery 'banks' - house which will be 330ah, starter 110ah and bowthruster/windlass at 110ah. This winter the thruster battery got quite low because I forgot to isolate it. I thought about connecting the Cetek 25ah charger direct to the VSR (one of the newer type with almost no voltage loss). That way like the alternator it will send the juice to wherever needs it most. But is there a problem I haven't forseen?

All VSR's are virtually zero volt drop, are you talking solid state ?

Assume a single output charger ? you need a twin relay VSR, with mains charger connected to service battery. This allows charging from engine or mains charger to all three battery banks.


Brian

 

[halcyon]

It doesn't work like that, it is a common misconception that a VSR "decides" what to charge. The VSR will switch and simply connect all the batteries together. If you only have one shore power charger, this is what you want. However, with three banks, you need more than one VSR.

The batteries decide what is charged, the VSR only provides the means. As the engine battery is normally at a higher capacity than the service battery when the relay engages, charge will go to the service bank until the service approaches engine battery level, least line of resistance. Today with high capacity alternators, this does not work as well due to surface charging of service battery, faster you charge a battery the lower the charge it excepts.

 

[Colvic Watson]

I hope I've used the right terminology.

The VSR has four studs, alternator and three positive output studs, one for each of the three 'banks'. The whole boat uses a common 12v negative. I assumed that if I connected the positive lead from the battery charger to the alternator stud and the negative to the house bank then it would be as if the alternator was feeding the VSR. What would happen if I forgot to switch off the charger before I started the engine?

 

[VicS]

I hope I've used the right terminology.

The VSR has four studs, alternator and three positive output studs, one for each of the three 'banks'. The whole boat uses a common 12v negative. I assumed that if I connected the positive lead from the battery charger to the alternator stud and the negative to the house bank then it would be as if the alternator was feeding the VSR. What would happen if I forgot to switch off the charger before I started the engine?

Are you sure you are describing a VSR ..... not a 3way diode splitter?

What is it exactly ...... make and other marks/ name/ numbers

is there a negative connection as well as the 4 connections you already mention..... if not its not a VSR

 

[halcyon]

Are you sure you are describing a VSR ..... not a 3way diode splitter?

He's describing a diode type splitter.

It depends on the mains charger electronics, they may need to see the battery voltage to regulate, so the solid state splitter may not work, or may need some fiddling.

Brian

 

[nigelmercier]

The VSR has four studs, alternator and three positive output studs ...

Sounds like a diode splitter to me, not a VSR. A VSR has just two battery studs, one (or both) of them will also sense the voltage, there is no stud for an alternator. In addition there is a low current negative terminal. When activated, it joins the two studs together. An alternate charging source can be sensed in the same way.

 

[Colvic Watson]

Crikey - it sounds like a diode splitter - will it work with that?

 

[VicS]

Crikey - it sounds like a diode splitter - will it work with that?

The snag with diode splitters is the volts drop across them.

It can be overcome as far as the alternator is concerned if it is battery sensed. It will then deliver the correct voltage at the batteries.

Probably the most satisfactory solution as far as a battery charger is concerned is to use one with three outputs.

For other charging sources eg solar or wind to use a regulator or regulators with three outputs

Alternatively of course change to a VSR controlled system

 

[Colvic Watson]

When it was installed the engineer said it was the new type with less than 0.2 volts drop.

 

[nigelmercier]

Crikey - it sounds like a diode splitter - will it work with that?

Yes, just connect the charger to the alternator terminal.