Dual Batteries - VSR & Charger Advice

[machineage]

Hello all

I just wanted to pose a question about the above...

Proposed system:

Dual Batteries - one start - one house
BEP VSR or VSS
On-board Charger (one or two)

Now when underway I understand that when the start battery voltage reaches a preset level the VSR will activate and parallel the batteries.
What if the house battery is quite depleted - will the charge from the start battery dissipate into the house battery causing a lack of charge in both?
Also - when I am at shore and connect my battery charger - how would this work in the above system? Again if it's a dual sensing VSR then I understand when one battery reaches a preset level the VSR will activate with possibly a similar situation to above?
How would a battery charger deal with this situation - don't they detect and charge batteries individually in the case of a dual bank charger?
I note that CTEK supply a larger charger (M300) for the house batteries and a smaller charger for the start as a package. How would I wire these up with the VSR or VSS?

Thanks!

 

[VicS]

What if the house battery is quite depleted - will the charge from the start battery dissipate into the house battery causing a lack of charge in both?

It can be a problem if a large house battery is well dischaged.

The starter battery charges, when the set voltage is reached the VSR operates to parallel the banks. If this drops the voltage below the point at which it opens again it does so but then the volts quickly recover and the relay closes again. You then have situation in which the relay is repeatedly opening and closing until the house bank gets enough charge in it to stop the cycle.
Its minimised by not having a vast house battery along with a tiny starter battery ... but that is probably what you want!

It won,t actually discharge the starter battery because the relay opens before that can happen.

Similar thing will happen with a battery charger BUT if you use a dual sensing VSR and connect the large house bank to the charger that will cahrge first and then the small starter battery will be connected . The small battery , which, should have been charged from the engine anyway, wont cause the same problems.

Not sure what will happen to a dual output charger if the outputs are individually connected to the two batteries. Perhaps better to common the outputs and just connect to the house bank or use a single output charger.

I think one would similarly just use a single charger connected to the house bank rather than two chargers.

 

[Hoolie]

... ... Not sure what will happen to a dual output charger if the outputs are individually connected to the two batteries. Perhaps better to common the outputs and just connect to the house bank or use a single output charger.

I think one would similarly just use a single charger connected to the house bank rather than two chargers.

In principle that's correct, but I'm in the process of re-vamping my charging system and I will use a multiple output charger connected directly to each of the batteries (3 in my case) bypassing the battery isolator switches. This allows float charge even when the batteries are turned off. Of course the charger outputs are individually fused.

 

[Tranona]

Agree with above. I have the VSR and the independent isolator switches as supplied in the BEP switch cluster. This keeps the two banks independent but charged correctly from the engine. The mains battery charger has dual (in fact 3) outputs directly and independently to each bank. Works well.

 

[machineage]

Agree with above. I have the VSR and the independent isolator switches as supplied in the BEP switch cluster. This keeps the two banks independent but charged correctly from the engine. The mains battery charger has dual (in fact 3) outputs directly and independently to each bank. Works well.

Thanks for the answers people

I only require a small house battery - I have few house requirements as such and wanted a second battery mainly to isolate electronics etc from cranking currents and for redundancy. In fact it could well be the same as the start - I am considering two Optima dual purpose blue tops.

So in the above situation where you have a dual bank charger - once the house battery connected to the sense wire has has reached it's voltage then the VSR will activate and parallel the batteries. I assume it doesn't cause a problem then for the charger if at that point the batteries are of differing stages of charge for whatever reason - as I see some chargers have up to 8 steps of charge output?

Thanks again

 

[nigelmercier]

So in the above situation where you have a dual bank charger - once the house battery connected to the sense wire has has reached it's voltage then the VSR will activate and parallel the batteries. I assume it doesn't cause a problem then for the charger if at that point the batteries are of differing stages of charge for whatever reason - as I see some chargers have up to 8 steps of charge output?

It is for this very reason that I have fitted a relay in the negative line of my VSR so it only activates when the engine is running. Although the VSR specifications say they operate when the battery reaches a certain voltage, in practice this means they operate fairly soon after the charging begins. At this point they parallel the split feeds from shore-power chargers, totally negating their purpose.

 

[machineage]

It is for this very reason that I have fitted a relay in the negative line of my VSR so it only activates when the engine is running. Although the VSR specifications say they operate when the battery reaches a certain voltage, in practice this means they operate fairly soon after the charging begins. At this point they parallel the split feeds from shore-power chargers, totally negating their purpose.

Hi Nigel

Yes I can see that is a good solution!

OK so -
Two Optima Dual Purpose Batteries
BEP Single Sense VSS
Two BEP Isolators
Dual Bank Charger directly attached to Batteries
Relay in VSS Neutral with sense cable attached to engine side of start isolator.

Where did you decide to take your coil feed for the Relay?

Thanks again

Chris.