Electrics - tell me what's wrong

[frahkn]

Came back to the boat yesterday after about a month away. We are in a marina on shore power at the moment.

We had been having some work done and the fitter had switched the leisure bank off. Good or bad, I never do and so didn't spot this.

We turned the fridge on and the water pumps (all 12 volt) and went out for a meal. When we got back we needed some light and it wasn't long before the lights started dimming as the fridge or water pump came on.

A bit late in the day we spotted our error and un-isolated the leisure batteries - all was well and the starter battery even started the engine this morning.

My question is: surely nothing (except the bilge pump) should have worked with the leisure batteries isolated? Is this a wiring error - in which case where should I start looking - or are some boats wired like this.

Or have I misunderstood the position for years?

 

Frank.

 

[Neil2]

Well there's plenty of expertise on here I'm sure someone will be along soon but my reaction would be there's something amiss with your isolator switch.  Are you saying that turning it to the "on" position stopped the lights dimming? 

 

[frahkn]

Sorry, I wasn't clear.

We have two isolator switches, 1 for the leisure bank and a separate one for the starter battery (which is itself located about 8 feet from the 5 leisure batteries). The fitter had left the starter battery switch "on" but had switched off the leisure batteries. We never switch off either and didn't notice at first.

 

Frank.

[Rob-M]

Is it possible that the isolator that was on is actually joining the leisure and starter batteries together, this was how our electrics were configured when we purchased our boat so each time i turned one isolator on I wasn't aware I was potentially draining the starter battery.

[WotEver]

The short answer is that anything is possible.

Turn off both isolators. Is anything still on?

Turn them on one at a time. What works?

The above will give you a starting point. 

[Richard10002]

I was going to say that turning our leisure isolator off turns all the leisure stuff off. However, I realised that I have never turned only the leisure isolator off on its own... I've always turned both off.

Out of interest I'll try turning them off separately next time I'm down there, and see what happens.

[nicknorman]

The leisure battery isolator isolates the leisure batteries from everything else. Including quite probably (though not necessarily), the shore power charger. The shore power charger is thus still connected to the boat's leisure services and it will have been supplying the services you switched on, up to the point where it reached its maximum output, then with more things turned on the system voltage will droop and things start to go dim. So probably nothing wrong except isolator turned off.

[Sir Nibble]

35 minutes ago, nicknorman said:

The leisure battery isolator isolates the leisure batteries from everything else. Including quite probably (though not necessarily), the shore power charger. The shore power charger is thus still connected to the boat's leisure services and it will have been supplying the services you switched on, up to the point where it reached its maximum output, then with more things turned on the system voltage will droop and things start to go dim. So probably nothing wrong except isolator turned off.

This ^^^

[WotEver]

37 minutes ago, nicknorman said:

The leisure battery isolator isolates the leisure batteries from everything else. Including quite probably (though not necessarily), the shore power charger. The shore power charger is thus still connected to the boat's leisure services and it will have been supplying the services you switched on, up to the point where it reached its maximum output, then with more things turned on the system voltage will droop and things start to go dim. So probably nothing wrong except isolator turned off.

Sounds very likely. 

Charger is one of the things that needn't (and probably shouldn't) be wired via the isolator.  

[frahkn]

Nicknormam, Sir Nibble and WotEver,

Are you saying that the 16 amp shore power would have difficulty with some led lights, the fridge and the water pumps? If so, why was this difficulty not apparent from the outset but only appeared gradually?

I do not know enough to argue with any of you but I have difficulty understanding this.

 

Frank.

[WotEver]

5 hours ago, frahkn said:

Nicknormam, Sir Nibble and WotEver,

Are you saying that the 16 amp shore power would have difficulty with some led lights, the fridge and the water pumps? If so, why was this difficulty not apparent from the outset but only appeared gradually?

I do not know enough to argue with any of you but I have difficulty understanding this.

 

Frank.

But the 16A shore supply isn't powering those things. They are 12V items, not mains. With the isolator switched off their only source of power was the charger. The charger has a finite current capacity and when that was reached its output voltage would have drooped, which is what you witnessed with the lights dimming. 

The charger should be rewired to bypass the isolator. That way the batteries will still be charged with the isolator switched off plus the isolator will achieve what it's supposed to - isolate the 12V systems. 

[frangar]

2 hours ago, WotEver said:

 

The charger should be rewired to bypass the isolator. That way the batteries will still be charged with the isolator switched off plus the isolator will achieve what it's supposed to - isolate the 12V systems. 

Please think before you do this. If it's a combined inverter/charger you won't have any way of isolating the unit which is a BSS fail not to mention terrible practice. 

[WotEver]

50 minutes ago, frangar said:

Please think before you do this. If it's a combined inverter/charger you won't have any way of isolating the unit which is a BSS fail not to mention terrible practice. 

If it's an inverter/charger then it should have its own dedicated isolator.

It is neither a BSS fail, nor is it 'terrible practice' to wire a charger correctly. It is listed as one of the exceptions within the guide for very obvious and sensible reasons.  

[frangar]

10 minutes ago, WotEver said:

If it's an inverter/charger then it should have its own dedicated isolator.

It is neither a BSS fail, nor is it 'terrible practice' to wire a charger correctly. It is listed as one of the exceptions within the guide for very obvious and sensible reasons.  

So that's another switch to forget to turn on and potentially cause more problems. I'd much rather see that the batteries be able to be totally & quickly isolated from all loads/inputs. One master switch does this job rather well. 

[MtB]

On 10/04/2017 at 05:57, WotEver said:

But the 16A shore supply isn't powering those things. They are 12V items, not mains. With the isolator switched off their only source of power was the charger. The charger has a finite current capacity and when that was reached its output voltage would have drooped, which is what you witnessed with the lights dimming. 

The charger should be rewired to bypass the isolator. That way the batteries will still be charged with the isolator switched off plus the isolator will achieve what it's supposed to - isolate the 12V systems. 

 

Is that really what it's for? I've always felt it should be to isolate the batteries from everything. A tool for convenience when working on the boat electrics.

I've always been faintly surprised a battery isolator is a requirement for the BSS. What exactly IS it's purpose, and why?

 

[WotEver]

13 minutes ago, frangar said:

So that's another switch to forget to turn on and potentially cause more problems. I'd much rather see that the batteries be able to be totally & quickly isolated from all loads/inputs. One master switch does this job rather well. 

That's your opinion. I'm of the opinion that it's 'terrible practice' to disconnect the charger from that which it's supposed to be charging. It would appear that the BSS agrees with me as they list a charger as one of the exceptions which may be connected directly. 

As for 'forgetting to switch it on' in the case of a combi, why would you ever switch it off unless performing some maintenance?

6 minutes ago, Mike the Boilerman said:

Is that really what it's for? I've always felt it should be to isolate the batteries from everything.

Yes, that's what 'isolate the 12V systems' means

[cereal tiller]

5 minutes ago, Mike the Boilerman said:

 

Is that really what it's for? I've always felt it should be to isolate the batteries from everything. A tool for convenience when working on the boat electrics.

I've always been faintly surprised a battery isolator is a requirement for the BSS. What exactly IS it's purpose, and why?

 

A good quality Master Switch is rather handy should a Starter Motor Solenoid stay closed(have seen the results if the Current cannot be Switched off)

[WotEver]

7 minutes ago, Mike the Boilerman said:

What exactly IS it's purpose, and why?

For that you'd have to ask the BSS. If someone had a catastrophic fault causing hundreds of amps to be flowing and making cables glow in the dark I can't imagine too many boaters saying 'oh, I must turn off the isolator'. I find isolators convenient for when performing maintenance, as you do, but I don't know if that's their intended purpose. 

3 minutes ago, cereal tiller said:

A good quality Master Switch is rather handy should a Starter Motor Solenoid stay closed(have seen the results if the Current cannot be Switched off)

Yup, the starter master switch would be good for that if it's easily accessible. 

[MtB]

On 10/04/2017 at 09:30, cereal tiller said:

A good quality Master Switch is rather handy should a Starter Motor Solenoid stay closed(have seen the results if the Current cannot be Switched off)

 

Is that it?!

Any other reasons?

[MtB]

On 10/04/2017 at 09:33, WotEver said:

For that you'd have to ask the BSS. If someone had a catastrophic fault causing hundreds of amps to be flowing and making cables glow in the dark I can't imagine too many boaters saying 'oh, I must turn off the isolator'. I find isolators convenient for when performing maintenance, as you do, but I don't know if that's their intended purpose. 

Yup, the starter master switch would be good for that if it's easily accessible. 

 

Same applies to gas isolators. When an LPG fire is raging on a boat, most people are inclined to call the fire brigade rather than hunt around for a label saying "Gas Isolator Below".

[nicknorman]

1 minute ago, cereal tiller said:

A good quality Master Switch is rather handy should a Starter Motor Solenoid stay closed(have seen the results if the Current cannot be Switched off)

Yeabut that's for the engine battery!

Anyway, the domestic isolator is to isolate a source of near-unlimited current (the batteries) from everything else, so that that source of current can be turned off should there be a major short circuit or should maintenance /repairs/wiring be being carried out in order to eliminate the risk of a worker-induced short circuit.

It is also  convenient way to make sure everything is turned off when one leaves the boat, but that is not its primary purpose.

There is nothing wrong with, in fact it is standard practice, to have the charger connected directly to the batteries (via a fuse) such that the batteries get charged when the isolator is off. This also means that when the isolator is open, the boat's services are completely unpowered and not still potentially powered by the charger. This is the batter way of doing it IMO, although connecting the charger to the services-side of the isolator is allowed.

Our Combi is connected directly to the batteries (via a fuse). There are arguments for and against fitting an additional isolator just for the Combi, I choose not to since it is just another source of voltage drop for a device that can pull 200A or more.

 

[frahkn]

24 minutes ago, nicknorman said:

Yeabut that's for the engine battery!

Anyway, the domestic isolator is to isolate a source of near-unlimited current (the batteries) from everything else, so that that source of current can be turned off should there be a major short circuit or should maintenance /repairs/wiring be being carried out in order to eliminate the risk of a worker-induced short circuit.

It is also  convenient way to make sure everything is turned off when one leaves the boat, but that is not its primary purpose.

There is nothing wrong with, in fact it is standard practice, to have the charger connected directly to the batteries (via a fuse) such that the batteries get charged when the isolator is off. This also means that when the isolator is open, the boat's services are completely unpowered and not still potentially powered by the charger. This is the batter way of doing it IMO, although connecting the charger to the services-side of the isolator is allowed.

Our Combi is connected directly to the batteries (via a fuse). There are arguments for and against fitting an additional isolator just for the Combi, I choose not to since it is just another source of voltage drop for a device that can pull 200A or more.

 

OK, I go to sleep and wake to find that the conversation has reached heights way above my head.

It is a Mastervolt combi and by the time I switched on the leisure batteries, the 'low battery' warning light was flashing.

 

[WotEver]

17 minutes ago, frahkn said:

OK, I go to sleep and wake to find that the conversation has reached heights way above my head.

I refer you to my previous reply:

 

[WotEver]

2 hours ago, frangar said:

If it's a combined inverter/charger you won't have any way of isolating the unit which is a BSS fail not to mention terrible practice. 

Not only unwarranted scaremongering but also completely incorrect. I suggest you read the BSS Guide. 

[cuthound]

Not sure about isolators on boats, but in the real world they are to isolate equipment so that it can be worked on, not to break a fault current (circuit breakers are for interrupting a fault current).

Can't see why it should be any different, just coz it is on a boat.