What exactly does a battery isolator isolate - and from what?

[Kantara]

I thought I knew the answer to this question, because it seems kind of obvious, but when I switched off my domestic battery isolators today (and the starter battery and the bowthruster battery isolators too) I found I still had domestic battery power available in the boat - the lights could be switched on. What's wrong here, anyone - please??

[Chris Pink]

It's not the domestic isolator (obviously). You need to trace the main battery wiring to understand why. Or why not.

Edited November 26, 2012 by Chris Pink

[Paul C]

We can't tell you how your boat is wired, but on my boat the battery isolator isolates everything except three things:

 

alternator

solar panel (fused)

voltmeter (fused)

 

The first two generate power, they don't consume it; and the voltmeter is connected as directly to the battery as possible, so it reads true.

[davidg]

I thought I knew the answer to this question, because it seems kind of obvious, but when I switched off my domestic battery isolators today (and the starter battery and the bowthruster battery isolators too) I found I still had domestic battery power available in the boat - the lights could be switched on. What's wrong here, anyone - please??

 

Do you have a battery charger and was it on at the time?

[matty40s]

I have three isolators, engine, fridge, and lights/water.

Once these are all off, there is nothing connected.

 

The only variation to this I would expect normally is where a bilge pump is wired outside the isolator circuits so it kicks in whenever it is needed to.

 

I would suggest there is another isolator, or some lights have been wired from where they shouldn;t have been.

[gazza]

Do you have a battery charger and was it on at the time?

 

I reckon you are on the money here.....

Edited November 26, 2012 by gazza

[Smelly]

The red key isolators have been known to stick closed.

[Guest]

Second guessing is not this forums strong point....

 

but I'd go with smelly

Edited November 26, 2012 by The Dog House

[Grace and Favour]

Second guessing is not this forums strong point....

 

but I'd go with smelly

 

I guess you may be right.........

[The Bagdad Boatman (waits)]

Correct wiring of isolation switches is one pole to battery positive terminal, the other to all services (alternator, starter etc) and same for domestic battery one pole to positive terminal other pole to charger, domestic supply etc. Only if you want to have a bilge pump live all the time then link it direct to the leisure battery positive terminal.

Edited November 26, 2012 by The Bagdad Boatman (waits)

[by'eck]

I would go with davidg as well, but put us out of misery and confirm charger(s) not powered.

[Keeping Up]

One other possibility is that something could be providing an unexpected path around the isolator. For example if the negative is unintentionally connected to the hull on both sides of the isolator (I've seen it happen)

[PaulJ]

Ive seen this happen in a boat fitted with led lights.We thought we had discovered magic 12v but turned out to be caused by the capacitor in the (largish)inverter.

[Kantara]

It's not the domestic isolator (obviously). You need to trace the main battery wiring to understand why. Or why not.

 

No, sorry, but it is - I have no doubt about that.

 

We can't tell you how your boat is wired, but on my boat the battery isolator isolates everything except three things:

 

alternator

solar panel (fused)

voltmeter (fused)

 

The first two generate power, they don't consume it; and the voltmeter is connected as directly to the battery as possible, so it reads true.

 

Ahh! It could be my solar panels! Thanks for that!

 

Do you have a battery charger and was it on at the time?

 

Thanks, battery charger was off - landline disconnected.

[RLWP]

No, sorry, but it is - I have no doubt about that.

 

Actually, he's right. It isn't isolating the circuits as you have proved, so it can't be the isolator. It may have been designed to be in the first place, but it is no longer doing what it was supposed to. You need to do some wire following to see what is going on

 

Richard

[Kantara]

I have three isolators, engine, fridge, and lights/water.

Once these are all off, there is nothing connected.

 

The only variation to this I would expect normally is where a bilge pump is wired outside the isolator circuits so it kicks in whenever it is needed to.

 

I would suggest there is another isolator, or some lights have been wired from where they shouldn;t have been.

 

I have three as well - domestic, engine, bowthruster. All were turned off at the time.

 

The red key isolators have been known to stick closed.

 

I'll check that - thanks.

 

One other possibility is that something could be providing an unexpected path around the isolator. For example if the negative is unintentionally connected to the hull on both sides of the isolator (I've seen it happen)

 

I'll check that, thanks, but my money is on the solar panels now - see above.

[Tony Brooks]

I have three as well - domestic, engine, bowthruster. All were turned off at the time.

 

 

 

I'll check that - thanks.

 

 

 

I'll check that, thanks, but my money is on the solar panels now - see above.

 

 

Except for solar to charge while you are away from the boat they should be wired to the battery side of the master switch so turning the switch off should isolated them from the boat but not from the batteries.

 

It may help to know if the isolators is in the positive or negative.

[Timleech]

 

 

 

I'll check that, thanks, but my money is on the solar panels now - see above.

 

I wired in a Voltage Sensitive relay exactly as per the instructions supplied, without giving it too much thought.

It was actually on the battery side of the main isolators, I then found that the (quite modest) solar panel was causing the relay to drop in and out, creating some strange effects. Probably nothing to do with what you are seeing, but another indication that things don't always do what you expect them to.

 

Don't you have your panels wired to the battery side of the isolator (via a fuse)? It seems the logical way to me.

 

Tim

[Paul C]

The easy check to do would be to see if the lights/etc come on when its dark (no solar panel power output).

[RLWP]

The easy check to do would be to see if the lights/etc come on when its dark (no solar panel power output).

 

Clever! Or throw your coat over the panel and save the wait

 

Richard

[Paul C]

I wired in a Voltage Sensitive relay exactly as per the instructions supplied, without giving it too much thought.

It was actually on the battery side of the main isolators, I then found that the (quite modest) solar panel was causing the relay to drop in and out, creating some strange effects. Probably nothing to do with what you are seeing, but another indication that things don't always do what you expect them to.

 

Don't you have your panels wired to the battery side of the isolator (via a fuse)? It seems the logical way to me.

 

Tim

 

What did the voltage sensitive relay control? If it were to split or join the battery banks, surely the only 'strange effect' should be to charge the starter battery when its sunny, which is what you'd want?

[bottle]

irrelevant now.

Edited November 27, 2012 by bottle

[Gibbo]

What did the voltage sensitive relay control? If it were to split or join the battery banks, surely the only 'strange effect' should be to charge the starter battery when its sunny, which is what you'd want?

 

Yes, but with such a small charger (a solar panel) they usually connect, then the other battery drags the voltage down because the small charger can't keep up, so the VSR disconnects. Now the voltage rises, so it connects again, then the voltage collapses, so it disconnects, etc.

[Paul C]

Yes, but with such a small charger (a solar panel) they usually connect, then the other battery drags the voltage down because the small charger can't keep up, so the VSR disconnects. Now the voltage rises, so it connects again, then the voltage collapses, so it disconnects, etc.

 

I did suspect it might be this but I'd assumed they'd be more clever than simply allowing this to happen, eg by having a turn-on and turn-off voltage which are significantly different. Otherwise any relay, with any size of charger, and any difference in the state-of-charge of batteries, would potentially do this???

Edited November 27, 2012 by Paul C

[Gibbo]

I did suspect it might be this but I'd assumed they'd be more clever than simply allowing this to happen, eg by having a turn-on and turn-off voltage which are significantly different. Otherwise any relay, with any size of charger, and any difference in the state-of-charge of batteries, would potentially do this???

 

They do have turn on and turn off voltages that are different, but you have to remember that a VSR is the base model. The pits if you like. The bottom rung.

 

Moving up market to full battery combiners etc they incorporate more tricks and features to reduce this effect such as timers and delays, voltage filtering etc. But that can then lead to problems where very high power, very intermittent loads, can fool it and still discharge all the batteries, so they need further tricks to get round that. Which is why people buy low end VSRs because they're cheaper because they don't have the bells and whistles.