Manually open a VSR?

[Simon_and_Tanja]

In process of re-wiring the boat and upgrading from single to dual (start and domestic) 12v batteries. In trying to keep things relatively simple and cheap and have opted to install a VSR between the two batteries. I have a 140A dual sensing VSR already for the task.
I also have a panel battery meter (analogue voltmeter) which I would like to use. I envisage wiring this to display charge on either battery via a Momentary 3-position SPDT Centre Off toggle switch. For this to work the VSR would need to be open whilst the meter is engaged. So how can I force the VSR to open even if the batteries are charging?

Is this as simple as lifting the VSR ground wire to +12v ?
Would letting it float have the same effect ?

Never seen a schematic of VSR circuitry so hard to work out if this will work but I'm guessing it should ?
Has anybody any idea what the sense circuit current is likely to be ?

I could (of course) put a 12v 70A NC relay in series with the VSR and drive this from the voltmeter input but this solution hardly aligns with the keeping it simple brief.

 

[jamie N]

I reckon that if you were to use the relay to momentarily halt the charge, and then to reinstate it, it could cause damage.
Could it be that you'd have a workable solution by monitoring the charging amps, to gain an idea of the charge, and the battery condition over a period of time?

 

[Keith-i]

Is there much point trying to take a voltage reading on either bank if they are being, or have just been, charged? More meaningful would be a reading at rest some time after being charged. During or just after charge they would both read fairly similarly and be above 12v.

 

[prv]

I reckon that if you were to use the relay to momentarily halt the charge, and then to reinstate it, could cause damage.

I don't see why. The VSR goes between batteries, so the alternator still has one battery connected when the relay is opened.

That said, this still doesn't seem like a very good idea. The meter on the battery that remains connected will simply report the alternator charging voltage, and the voltage of the other battery when taken off charge for a few seconds won't show anything meaningful.

Pete

 

[Danny]

One possible snag: a lot of VSRs have a delay of several seconds before they drop out. Would this be a problem for you?

 

[Lon nan Gruagach]

In process of re-wiring the boat and upgrading from single to dual (start and domestic) 12v batteries. In trying to keep things relatively simple and cheap and have opted to install a VSR between the two batteries. I have a 140A dual sensing VSR already for the task.
I also have a panel battery meter (analogue voltmeter) which I would like to use. I envisage wiring this to display charge on either battery via a Momentary 3-position SPDT Centre Off toggle switch. For this to work the VSR would need to be open whilst the meter is engaged. So how can I force the VSR to open even if the batteries are charging?

Is this as simple as lifting the VSR ground wire to +12v ?
Would letting it float have the same effect ?

Never seen a schematic of VSR circuitry so hard to work out if this will work but I'm guessing it should ?
Has anybody any idea what the sense circuit current is likely to be ?

I could (of course) put a 12v 70A NC relay in series with the VSR and drive this from the voltmeter input but this solution hardly aligns with the keeping it simple brief.

I think it might not be possible.
Without opening the box you cannot tell how its built. If I were to design one I would compare the 2 battery voltages and use a change over relay to select which one to charge. If yours is built this way then one battery will always be connected even if there is no power in the circuit at all. To use 2 separate relays make no commercial sense at all.
My vote is with jamie N measure the curent.

 

[Simon_and_Tanja]

Is there much point trying to take a voltage reading on either bank if they are being, or have just been, charged? More meaningful would be a reading at rest some time after being charged. During or just after charge they would both read fairly similarly and be above 12v.

That's a fair point Keith. I suppose the meter would tell me what the alternator/regulator is doing but not much help for indicating battery status when either battery is charging. (Not sure, for that matter, static battery voltage is much of a status indication either, but the meter looks pretty!). I'll keep the wiring simple. If not charging then the VSR will be open and I can select battery volts on either battery independently. If it is charging (and VSR is closed) then either switch position will give the same reading and I should see a nice healthy 14.5v alternator output.

I might clamp an ammeter on the domestic circuit if I can find a matching meter .

 

[PaulRainbow]

That said, this still doesn't seem like a very good idea. The meter on the battery that remains connected will simply report the alternator charging voltage, and the voltage of the other battery when taken off charge for a few seconds won't show anything meaningful.

Pete

I agree with Pete, taking reading of batteries on charge, or freshly charged is pointless. I have a dual bank setup, with dual output mains charger, solar panels to the domestic bank and the alternator to the engine bank, with a Victron dual sensing VSR and my voltmeter is wired via a mom on-off-mon on switch. Taking voltage readings is a waste of time under certain conditions, like if the VSR is closed or the batteries have just been charged. However, keeping an eye on voltages in the evening, when the solar panels and engine aren't charging is useful as it allows me to switch the mains charger on as needed.

In summary, fit the voltmeter and VSR as planned but forget about interfering with the state of the VSR, only take voltage readings when the batteries are off charge.

 

[VicS]

In process of re-wiring the boat and upgrading from single to dual (start and domestic) 12v batteries. In trying to keep things relatively simple and cheap and have opted to install a VSR between the two batteries. I have a 140A dual sensing VSR already for the task.
I also have a panel battery meter (analogue voltmeter) which I would like to use. I envisage wiring this to display charge on either battery via a Momentary 3-position SPDT Centre Off toggle switch. For this to work the VSR would need to be open whilst the meter is engaged. So how can I force the VSR to open even if the batteries are charging?

Is this as simple as lifting the VSR ground wire to +12v ?
Would letting it float have the same effect ?

Never seen a schematic of VSR circuitry so hard to work out if this will work but I'm guessing it should ?
Has anybody any idea what the sense circuit current is likely to be ?

I could (of course) put a 12v 70A NC relay in series with the VSR and drive this from the voltmeter input but this solution hardly aligns with the keeping it simple brief.

Interrupting the ground wire connection to 12 volt negative will cause the VSR to open but as others have said one battery will remain on charge and the volts reading on the other will be pretty meaningless as it will probably have just been on charge.

 

[nigelmercier]

Interrupting the ground wire connection to 12 volt negative will cause the VSR to open but as others have said one battery will remain on charge and the volts reading on the other will be pretty meaningless as it will probably have just been on charge.

My VSR is wired with the negative reference going via a relay which operates when the ignition is on, so the concept of disengagement is OK. The result however would be meaningless as Vic says.

 

[Mistroma]

Vics is correct and I also think it wouldn't be a particularly useful feature to implement. If you fit a toggle to allow you to switch the meter between each battery then you can get useful readings for each when discharging. Of course the VSR means they'll read the same when charging but it will indicate the charge voltage. A momentary disconnect during charging wouldn't tell you much about each battery as they'd still read much higher than at their actual resting state (and even that is not a definitive indication of battery state).

EDIT: Just noticed that our Nigel has already agreed as well .

 

[ghostlymoron]

This seems unnecessarily complicated and won't produce any useful data. Fit a dual sensing VSR and a NASA BM1.

 

[prv]

Fit a dual sensing VSR and a NASA BM1.

Yep, or SmartGauge monitor together with its SmartBank relay. Fitted this combination to two boats now and very happy - it just works.

Pete