Risk of using a VSR with a failing / very discharged battery

[MattS]

I'm considering installing a VSR as the first step to moving away from the 1-2-Both setup currently installed.

Initially I want to just remove that risk of forgetting to switch the batteries over when I'm out in that exciting wind and have turned off the engine to enjoy it....

I've read through some previous threads (e.g. VSR and solar inter-working question) and there is lots of talk of 'VSR chatter' and whether or not solar charging can keep the voltage high enough to trigger the VSR.

Am I right in understanding that if you had a battery that was failing being charged by solar, and the VSR engaged (e.g. from a solar charge), it shouldn't be possible for it to drain the good battery given that the voltage across the failing battery would be higher? And then if the charging voltage fell, the VSR would open again anyway.

At worse, you might find that the VSR would close the circuit when the good battery starts charging, and the majority of the charging current would then be directed to the discharged battery therefore not adding much charge to the good one.

Which I presume could eventually lead to the good battery being depleted if you're just charging from short engine runs?

I'm basically trying to work out what risk still remains that you could deplete a good battery with a VSR in place...

 

[pvb]

You might consider using a low-loss splitter instead. Batteries remain electrically isolated. Look at Victron ArgoFET perhaps.

 

[JumbleDuck]

I have a dual-battery solar controller and a VSR which only works when the engine is running.

 

[BabaYaga]

From your other thread it seems you have a 30 W solar panel. With such a modest amount of solar, a VSR, when closed, might eat a considerable portion of the solar output, perhaps 15 percent. For what purpose, one might ask? The starter battery is likely already fully charged, by the alternator.

 

[PaulRainbow]

If you only have a 30W panel, don't bother with a VSR. If you want to maintain the battery (if you leave the boat without mains charging for long periods) you could fit another small panel to look after the engine battery.

 

[VicS]

I'm considering installing a VSR as the first step to moving away from the 1-2-Both setup currently installed.
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At worse, you might find that the VSR would close the circuit when the good battery starts charging, and the majority of the charging current would then be directed to the discharged battery therefore not adding much charge to the good one.

Which I presume could eventually lead to the good battery being depleted if you're just charging from short engine runs?

I'm basically trying to work out what risk still remains that you could deplete a good battery with a VSR in place...

This, as I see it, is a potential drawback of a vsr even when isolators and emergency crossover switch are wired as usually recommended.

The problem can be overcome by fitting a switch in the negative connection to the vsr. Opening the switch will disable the vsr. OK it needs manual intervention but it's a whole ,lot easier than disconnecting a failed battery..

 

[Jamie Dundee]

and whether or not solar charging can keep the voltage high enough to trigger the VSR.

Mine does, solar charges engine battery through vsr and engine charges house through vsr. I do have 150w of panels although my last boat did the same with a 50w panel.

 

[JumbleDuck]

If you only have a 30W panel, don't bother with a VSR. If you want to maintain the battery )(if you leave the boat without mains charging for long periods) you could fit another small panel to look after the engine battery.

Or even let the engine look after the engine battery?

 

[PaulRainbow]

Or even let the engine look after the engine battery?

That was my point, if the boat is in regular use. If left unattended for long periods a small panel would keep the battery safe.

But taking this thread along with the OPs other thread, he still needs to consider how the alternator will charge the domestic battery.

 

[JumbleDuck]

That was my point, if the boat is in regular use. If left unattended for long periods a small panel would keep the battery safe.

i was agreeing! My regulator is set to send 1/10 of its output to the engine, which is probably a complete waste of time in the summer but I hope keeps it topped up over the winter. If even that is necessary.

 

[ithet]

I have a dual-battery solar controller and a VSR which only works when the engine is running.

Interested in how you arranged for the VSR to only work with the engine?

 

[halcyon]

I'm considering installing a VSR as the first step to moving away from the 1-2-Both setup currently installed.

Initially I want to just remove that risk of forgetting to switch the batteries over when I'm out in that exciting wind and have turned off the engine to enjoy it....

I've read through some previous threads (e.g. VSR and solar inter-working question) and there is lots of talk of 'VSR chatter' and whether or not solar charging can keep the voltage high enough to trigger the VSR.

Am I right in understanding that if you had a battery that was failing being charged by solar, and the VSR engaged (e.g. from a solar charge), it shouldn't be possible for it to drain the good battery given that the voltage across the failing battery would be higher? And then if the charging voltage fell, the VSR would open again anyway.

At worse, you might find that the VSR would close the circuit when the good battery starts charging, and the majority of the charging current would then be directed to the discharged battery therefore not adding much charge to the good one.

Which I presume could eventually lead to the good battery being depleted if you're just charging from short engine runs?

I'm basically trying to work out what risk still remains that you could deplete a good battery with a VSR in place...,

If you plan to change from 1,2,B to VSR, keep the rotory switch and fit a single isolator to supply engine start. Little extra work, but you still can use the rotory in emergancy, and have seperate battery dedicated to engine.

Now as one battery only starts engine, it should not be normally low catacity. So if you have a low service battery and solar cells are charging it, due to low current from small cell the volatage will rise slowly. So let us say the solar reaches 13.8 volt and VSR cuts in, engine is at say 70% capacity. We have two factors, To charge a flat battery you need about 13.0 volt, to charge our 70% engine battery you need about 14.0 volt. So the VSR closes, engine battery has 13.8 volt applied, a very small charge will take place and the volatage will rise very fast to 13.8v, engine battery will take no charge now as it needs more tham 13.8 volt to except charge, in fact around 14.0 volt. So until the solar gets the domestic upto 14.0 all charge goes to the domestic and VSR relay.

Part one.

Brian

 

[MattS]

From your other thread it seems you have a 30 W solar panel. With such a modest amount of solar, a VSR, when closed, might eat a considerable portion of the solar output, perhaps 15 percent. For what purpose, one might ask? The starter battery is likely already fully charged, by the alternator.

The main reason was actually to ensure that the engine battery was always charged first by the alternator, and then would automatically start charging the house (rather than me having to remember to switch onto Both when under power, and then remember to switch back to House Only when sailing).

I guess to achieve this I could just use a one-way VSR, which would ensure that it only ever closes when the alternator is providing power...? I guess @ithet that's how @JumbleDuck got the VSR to only work when the engine is running (and alternator is charging)?

 

[MattS]

If you plan to change from 1,2,B to VSR, keep the rotory switch and fit a single isolator to supply engine start. Little extra work, but you still can use the rotory in emergancy, and have seperate battery dedicated to engine.

So to do this, I'd have to slightly re-wire the starter motor so that it's fed (also?) only from the new single isolator? And then put a connection from the 1-2-BOTH switch to after the new isolator, so that I could use that original switch to bridge the service battery to the starter motor in an emergency?

I'd also have to re-wire the alternator so that it didn't charge through the 1-2-BOTH switch, but rather charged directly to the starter battery?

So the VSR closes, engine battery has 13.8 volt applied, a very small charge will take place and the volatage will rise very fast to 13.8v, engine battery will take no charge now as it needs more tham 13.8 volt to except charge, in fact around 14.0 volt. So until the solar gets the domestic upto 14.0 all charge goes to the domestic and VSR relay.

Thanks - that's useful to understand!

 

[JumbleDuck]

Interested in how you arranged for the VSR to only work with the engine?

I dug around the engine control panel until I found I spare wire which came live with "ignition" and use that to actuate a relay in the earth line of the VSR, so when the engine is on the earth is connected and the VSR does its stuff. It's a bit kludgy, but it works fine.

 

[MattS]

I dug around the engine control panel until I found I spare wire which came live with "ignition" and use that to actuate a relay in the earth line of the VSR, so when the engine is on the earth is connected and the VSR does its stuff. It's a bit kludgy, but it works fine.

Out of interest, what situation were you trying to protect against with that approach @JumbleDuck?

 

[JumbleDuck]

Out of interest, what situation were you trying to protect against with that approach @JumbleDuck?

The dreaded VSR chatter, and allowing the dual-battery controller to do its thing without getting confused.

In retrospect, I think it may be over-elaborate and if I was doing this again I would probably use a single battery solar controller and let the engine look after its own battery.

 

[Stemar]

On Jissel, I had a simple system that worked well. 40W of solar power managed by a dual battery controller set up to charge the engine battery until it was full, then do the domestic. The output from the controller was permanently connected to the batteries. I also had a 1-2-both switch that allowed me to use the starter battery alone until I had a problem, but switch to the domestic one or both in parallel if needed, which it almost never was. Split charging was managed by a cheap headlamp relay fed from the alternator's warning light terminal because VSRs were silly money when I set it up, but now I'd use a VSR.

With a twin engined cat, that I do need to sort out, only real difference I can see needing to that setup would be to have a VSR for each alternator.

 

[halcyon]

So to do this, I'd have to slightly re-wire the starter motor so that it's fed (also?) only from the new single isolator? And then put a connection from the 1-2-BOTH switch to after the new isolator, so that I could use that original switch to bridge the service battery to the starter motor in an emergency?

I'd also have to re-wire the alternator so that it didn't charge through the 1-2-BOTH switch, but rather charged directly to the starter battery?



Thanks - that's useful to understand!

Depends on boat wiring, normally alternator feeds starter motor, then common on 1,2,B via starter cable.
So you would take the starter cable from the 12B output and fit to isolator out, say batt 1 cable from the 12B batt 1 input and fit to isolator input.
Leave domestic loads and batt 2 as before on 12B, leaving one new cable from 12B to isolator output, allowing emergency feed in both position.

Brian

 

[ithet]

I dug around the engine control panel until I found I spare wire which came live with "ignition" and use that to actuate a relay in the earth line of the VSR, so when the engine is on the earth is connected and the VSR does its stuff. It's a bit kludgy, but it works fine.

Out of interest, what situation were you trying to protect against with that approach @JumbleDuck?

The reason I asked about this, is not because of chatter (which I think is not a problem with the hysteresis curves of modern VSRs) but because I do not like my VSR being already closed due to solar when I start the engine - but because I am worried about start voltage spikes damaging my electronics. Obviously JumbleDuck's solution will not work for this as I need to have the VSR off until after the engine is running. I had wondered about a 'normally closed' relay wired to the starter circuit. Or maybe I am looking for a solution to a non-existent problem?