Alternator wiring direct to Battery

[Rob Dean]

Hi Folks,

Busy planning a wiring upgrade in the charging circuit. Read a really useful technical article on the Smartgauge website which has me convinced I should run a heavy duty line direct from the alternator to the leisure battery bank. The article warns of the risk of engine starting with the leisure bank switch off and suggests some ways to reduce that risk.

 

Now the silly question . . . why not run the cable direct to the battery? Why does it need to be switched? And if so, why not give its own switch (which could generally be left on?

 

Is the answer that cables must always be switched close to the battery? BSS?

 

Rob

nb Pukeko

K&A

[springy]

Single or Twin Alternator setup ?

 

If Single then in the absence of any switching you would effectively connect the leisure bank

to the starter battery through this cable (and the terminal stud on the back of the alternator) -

resulting either in a flat starter battery having run the tv, lights, etc all night or some of the

starter current being drawn through the charging cable from the leisure bank.

 

With Twin alternators, one dedicated to each system, then there are good logical reasons

for doing as you suggest - any switch, junction etc. is a potential problem spot - high

resistance contacts etc., and this is indeed the practice commonly used in automotive

single alternator + single battery bank setup. However BSS requires that battery banks

can be isolated from their associated systems so AIUI you must have a switch somewhere

in the system between the battery and any attached equipment.

 

springy

[Gibbo]

The BSS says you have to have isolators "capable of disconnecting the entire system". The alternator is part of the system, therefore you have to have an isolator that will disconnect it.

[WotEver]

The BSS says you have to have isolators "capable of disconnecting the entire system". The alternator is part of the system, therefore you have to have an isolator that will disconnect it.

But if you didn't, would they notice?

 

I never said that.

 

Tony

[Gibbo]

But if you didn't, would they notice?

 

I never said that.

 

Tony

 

Half of them wouldn't notice if you had a 1mm cable feeding a 3000 watt inverter.

[luctor et emergo]

Half of them wouldn't notice if you had a 1mm cable feeding a 3000 watt inverter.

 

 

I don't know how true that is, but I'm of to get a screen wipe...

 

[Arnot]

Hi Folks,

Busy planning a wiring upgrade in the charging circuit. Read a really useful technical article on the Smartgauge website which has me convinced I should run a heavy duty line direct from the alternator to the leisure battery bank. The article warns of the risk of engine starting with the leisure bank switch off and suggests some ways to reduce that risk.

 

Now the silly question . . . why not run the cable direct to the battery? Why does it need to be switched? And if so, why not give its own switch (which could generally be left on?

 

Is the answer that cables must always be switched close to the battery? BSS?

 

Rob

nb Pukeko

K&A

It's a thorny one this...

 

The BSS manual says that a battery master switch must be fitted - and then goes on to say that there are a variety of circuits that can circumvent this providing they are fused.

 

For my part, I tend to wire domestic alternators directly to the battery but is it a bit af a balance of risks as follows;

 

1) If the alternator is connected through the master switch.

If it is inadvertently operated whilst the engine is running (or fails) there are two scenarios. In the case of a simple alternator it will possibly fubar it and probably not even down power the domestic circuits. In the case of a battery sensed alternator, it will probably fubar it and at the same time generate immense voltages and fubar almost anything else connected to the domestic circuit, there are some systems though that anticipate this possibility and have safety circuits buit in to prevent over voltage. However the safety element is that the switch can be operated and make the complete system safe to work on if the engine is off.

 

2) If the alternator is not connected through the master switch.

There is little possibility of the problems oulined above - but - the casual owner may thnk that when the switch was in the "off" position the alternator wiring was safe and short circuit it whilst working in the engine. The current path for charging is more direct and has fewer connections which results in better reliability and better charging. Also, if the master switch is operated in case of an emergency then it really does kill the domestic circuits immediately.

 

All that I can say is that acknowledging the BSS intention to promote boat safety, technically I have reservations about wiring the domestic alternator through a master switch. I have aften seen catastrophic failure and a lot of consequential damage as a result. The idea is that the operation of the master switch allows disconnection of the power from the system immediately but of course if the engine is running, the alternator just keeps on pumping it in.

 

Finally, ask youself, if this is such an important safety issue, why don't they fit master switches to cars? Some vehicles do have a master switch but these tend to have auxilary contacts to switch off the alternator when it is operated.

 

Regards

 

Arnot

Edited September 14, 2010 by Arnot

[FORTUNATA]

"There is little possibility of the problems oulined above - but - the casual owner may thnk that when the switch was in the "off" position the alternator wiring was safe and short circuit it whilst working in the engine."

 

I always prefer to actually disconnect the batteries if I can. I also sometimes wonder how my inverter/charger is wired around the alternator. To find out, I'd have to get to the wires behind boards and so on. I do know my batteries get charged via the alternator when the engine runs but also whenever I hook up to mains via trickle charge.

 

 

It's a thorny one this...

 

The BSS manual says that a battery master switch must be fitted - and then goes on to say that there are a variety of circuits that can circumvent this providing they are fused.

 

For my part, I tend to wire domestic alternators directly to the battery but is it a bit af a balance of risks as follows;

 

1) If the alternator is connected through the master switch.

If it is inadvertently operated whilst the engine is running (or fails) there are two scenarios. In the case of a simple alternator it will possibly fubar it and probably not even down power the domestic circuits. In the case of a battery sensed alternator, it will probably fubar it and at the same time generate immense voltages and fubar almost anything else connected to the domestic circuit, there are some systems though that anticipate this possibility and have safety circuits buit in to prevent over voltage. However the safety element is that the switch can be operated and make the complete system safe to work on if the engine is off.

 

2) If the alternator is not connected through the master switch.

There is little possibility of the problems oulined above - but - the casual owner may thnk that when the switch was in the "off" position the alternator wiring was safe and short circuit it whilst working in the engine. The current path for charging is more direct and has fewer connections which results in better reliability and better charging. Also, if the master switch is operated in case of an emergency then it really does kill the domestic circuits immediately.

 

All that I can say is that acknowledging the BSS intention to promote boat safety, technically I have reservations about wiring the domestic alternator through a master switch. I have aften seen catastrophic failure and a lot of consequential damage as a result. The idea is that the operation of the master switch allows disconnection of the power from the system immediately but of course if the engine is running, the alternator just keeps on pumping it in.

 

Finally, ask youself, if this is such an important safety issue, why don't they fit master switches to cars? Some vehicles do have a master switch but these tend to have auxilary contacts to switch off the alternator when it is operated.

 

Regards

 

Arnot

[Gibbo]

It's a thorny one this...

 

The BSS manual says that a battery master switch must be fitted - and then goes on to say that there are a variety of circuits that can circumvent this providing they are fused.

 

 

Correct but, unfortunately, the alternator isn't one of the possible exceptions.

 

I agree it's stupid, the rule shouldn't be there, and it was clearly drawn up by retarded pen pushers who haven't got a clue what they're talking about but it is indeed what the BSS says.

[Arnot]

It's a thorny one this...

 

The BSS manual says that a battery master switch must be fitted - and then goes on to say that there are a variety of circuits that can circumvent this providing they are fused.

 

1) If the alternator is connected through the master switch.

If it is inadvertently operated whilst the engine is running (or fails) there are two scenarios. In the case of a simple alternator it will possibly fubar it and probably not even down power the domestic circuits. In the case of a battery sensed alternator, it will probably fubar it and at the same time generate immense voltages and fubar almost anything else connected to the domestic circuit, there are some systems though that anticipate this possibility and have safety circuits buit in to prevent over voltage. However the safety element is that the switch can be operated and make the complete system safe to work on if the engine is off.

Well.. what a coincidence. I have just been out to a boat that exactly this has happened.

 

The boat in question has a Beta 43 installed with the optional 160A alternator fitted. This morning, their dog accidentally knocked the domestic master switch off just as they were about to go into the Harecastle tunnel. Shortly after entering it, the smoke started to escape from the alternator in reasonably large quantities accompanied by the dreaded smell of burning insulation. Fortunately the owner was a seasoned boater with reasonable technical ability and had a friend on board who could rapidly take the helm whilst he made it safe, heaven only knows what would have happened otherwise...

 

The alternator is badly damaged, possibly beyond repair, quite a few of the lights have been blown and there is still a lot of stuff to try.

 

Come on BSS, how about a revision on the Boat Safety Manual? The risks in this instance well outweighed the alternatives.

 

Regards

 

Arnot

[Rob Dean]

Well.. what a coincidence. I have just been out to a boat that exactly this has happened.

 

Thank you Arnot, Gibbo and others for the clear advice on this subject.

 

It's pretty clear to me that, in general use, the alternator is best and most safely wired direct to the leisure battery. Arnot's example illustrates that well. The BSS requirement makes sense only if one takes a narrow view of the risks involved with batteries, large currents and fire. Nevertheless it is a requirement.

 

There are of course 2 ways to isolate a battery. At the moment my boat takes the second route which is a single switch in the negative line. I can see that there are risks in that (if working with 12v lines I tend to disconnect the positive battery line). It's passed BSS every time though.

 

I think I've decided to:

1. Wire the alternator direct to the leisure battery (and not to engine battery). It will actually connect via an ammeter shunt.

2. Fit a master switch between battery and DC panel that will isolate all the domestic wiring but not impact the alternator.

3. Leave the switch in the negative line. It's in the engine compartment, well out of the way and generally will never need touching. But at least it provides BSS compliance.

 

I'd welcome any tweaks on that (or corrections if I'm plain wrong).

 

The alternator of course also has a negative line. At present it's a weedy 6mm2 wire about 6 inches long connecting to the body of the starter motor. Does anyone think it worth a direct line all the way back to the (negative) battery switch? Or just a decent wire to the starter body?

 

Thanks all

 

Rob

[steelaway]

The alternator need not be isolated IMO

The alternator and batterys are connected together on one side of the isolating switch, so that if it is turned off, the alternators are not going to burn out as they are still charging the batterys.

The switchs only isolates the power to the the domestic circiuts or the engine.

 

Alex

[Gibbo]

Come on BSS, how about a revision on the Boat Safety Manual? The risks in this instance well outweighed the alternatives.

 

I was in considerable correspondence with the BSS some years ago. Actually on two separate occasions.

 

I argued that the battery isolator switches should have several further exceptions (alternators, battery chargers, inverters etc) for three main reasons:-

 

1. The majority of battery isolators (ie those found on the shelf in the chandlers) simply aren't up to the task of dealing with this equipment.

2. Inadvertent operation of the switch was likely to cause considerable damage and mess.

3. A faulty switch (a high possibility considering the current through them) is likely to cause considerable damage.

 

Their reply, on both occasions was:-

 

1. That's down to incorrect component specification not the actual presence of the switch.

2. That's down to operator error not the actual presence of the switch.

3. That's down to a faulty switch not the actual presence of the switch.

 

Pointing out that not having the switch in the first place would cure all three possible problems fell on completely deaf ears.

 

After realising I was banging my head against a wall I gave up.

 

They did however have the sense to recommend switches are not in the negative.

[Arnot]

After realising I was banging my head against a wall I gave up.

Thanks for the warning, I will avoid the wall if I can and concentrate on making boats safe and reliable.

 

A reasonable demonstration that a little bit of knowledge...

 

I'm off to fix the two alternators that are fubar'd (the builder had managed to connect the sensing wire on the starter alternator to the domestic batteries - nice one!)

 

Regards

 

Arnot

[MtB]

I was in considerable correspondence with the BSS some years ago. Actually on two separate occasions.

 

I argued that the battery isolator switches should have several further exceptions (alternators, battery chargers, inverters etc) for three main reasons:-

 

1. The majority of battery isolators (ie those found on the shelf in the chandlers) simply aren't up to the task of dealing with this equipment

 

Gibbo,

 

I imagine you mean the commonly seen Hella 'red flag' key switch in particular is not up to the task?

 

I ask because I'm just getting around to installing the alternator and wiring on my K1 and I need to install two battery isolator switches. As you say the majority of switches are not up to the task, this implies there are a few switches around that ARE. Which would they be please?

 

I'd like to get my installation right first time and it's easy at this stage to specify whichever switches meet with your (or the board's) approval.

 

Thanks,

 

Mike

[Timleech]

I was in considerable correspondence with the BSS some years ago. Actually on two separate occasions.

 

I argued that the battery isolator switches should have several further exceptions (alternators, battery chargers, inverters etc) for three main reasons:-

 

1. The majority of battery isolators (ie those found on the shelf in the chandlers) simply aren't up to the task of dealing with this equipment.

2. Inadvertent operation of the switch was likely to cause considerable damage and mess.

3. A faulty switch (a high possibility considering the current through them) is likely to cause considerable damage.

 

Their reply, on both occasions was:-

 

1. That's down to incorrect component specification not the actual presence of the switch.

2. That's down to operator error not the actual presence of the switch.

3. That's down to a faulty switch not the actual presence of the switch.

 

Pointing out that not having the switch in the first place would cure all three possible problems fell on completely deaf ears.

 

After realising I was banging my head against a wall I gave up.

 

They did however have the sense to recommend switches are not in the negative.

 

To the best of my recollection, when the original Certificate of Compliance came in which predates the BSS, they did recognise there were issues with isolating alternators and had a form of words which, IIRC, allowed a bit of discretion in that area.

Unfortunately the BSS was supposed to remove all room for discretion and seems to have come down on the wrong side.

 

Tim

[Gibbo]

I imagine you mean the commonly seen Hella 'red flag' key switch in particular is not up to the task?

 

Yes, they're rated at 100 amps. It's someone's ideas of humour.

 

 

I ask because I'm just getting around to installing the alternator and wiring on my K1 and I need to install two battery isolator switches. As you say the majority of switches are not up to the task, this implies there are a few switches around that ARE. Which would they be please?

 

I'd like to get my installation right first time and it's easy at this stage to specify whichever switches meet with your (or the board's) approval.

 

 

From another thread.........

 

Lucas 219SA is my favourite for these size installations. Durite do a clone which is almost as good but not quite.

 

The ones shown in the photos I have destroyed at 30 amps after a couple of hours. 100 amps in less than 5 minutes. They are utter shyte.

 

The "ones shown in the photos" were indeed the Hella type.

 

To the best of my recollection, when the original Certificate of Compliance came in which predates the BSS, they did recognise there were issues with isolating alternators and had a form of words which, IIRC, allowed a bit of discretion in that area.

Unfortunately the BSS was supposed to remove all room for discretion and seems to have come down on the wrong side.

 

Tim

 

Wouldn't surprise me.

 

The impression I got when in correspondence with them was that they were a bunch of desk dwellers with not an ounce of practical experience between the lot of them, despite their assertions to the contrary.

 

They also said they "regularly sought advice from professionals within the field". I can only assume they ignored all such advice.

[BEngo]

Yes, they're rated at 100 amps. It's someone's ideas of humour.

 

 

 

From another thread.........

 

 

 

The "ones shown in the photos" were indeed the Hella type.

 

 

 

Wouldn't surprise me.

 

The impression I got when in correspondence with them was that they were a bunch of desk dwellers with not an ounce of practical experience between the lot of them, despite their assertions to the contrary.

 

They also said they "regularly sought advice from professionals within the field". I can only assume they ignored all such advice.

 

 

The original BSS Manager was a zoologist by education, I believe.

 

As one who sat through innumerable meetings at the start of the BSS they most certainly did seek advice from professionals. BSS collected the bees in the bonnets of almost every surveyor active in the inland market at the time and codified the requirements around these. The requirements had to be rigid because there was no requirement for the examiners to have any previous competence in examing boats. BSS steadfastly refused to undertake any sort of risk analysis based on safety and struggled to recognise either historic installations, the impact of the RCD or even common industry practice at the time. The result was firstly a well publicised Ombudsman case over polystrene in contact with PVC (BW paid out quite a lot of money to people who had been forced unnecessarily to have re-wires) secondly to moving goal posts and frequent changes of interpretation then eventually to the more risk based re-write which took place after about 5 years and turned a lot of requirements into advisories for private craft.

 

The IWA, which could have pushed back hard, and would probably then have been supported by the RYA, throughout adopted a head in the sand, we can't do anything about it attitude and sent a non-professional to the meetings. BW as a result claimed that boaters were happy.

 

With some exceptions (like alternator wiring) the BSS generally represents a sound and safe way to build a canal boat. It is still not properly aligned with the RCD and sooner or later appeals will force a change but in the meantime most peo[ple find it best to stick to one examiner and go with the flow of his foibles.

 

N

[Chris Pink]

The BSS allows ;

 

Check that any electrical circuits bypassing the battery isolator supply

the following equipment....

 

....any other equipment where the manufacturer’s instructions indicate

or specifically require direct connection to a battery...

 

Could be read to include alternators.

 

 

 

On my first BSS inspection years ago I was told that an axe close by an exposed battery cable would satisfy that examiner as being a 'battery isolator'

[WotEver]

On my first BSS inspection years ago I was told that an axe close by an exposed battery cable would satisfy that examiner as being a 'battery isolator'

[MtB]

 

On my first BSS inspection years ago I was told that an axe close by an exposed battery cable would satisfy that examiner as being a 'battery isolator'

 

 

I was musing today on the reasons for battery isolator switches. I couldn't think of any safety reasons that aren't addressed better with the use of fuses. This is the Boat SAFETY Scheme specifying them after all.

 

So what ARE the safety reasons for demanding battery isolator switches? Can anybody explain please? Rob? Anybody?

 

Maybe I'm not thinking clearly.

 

Mike

Edited October 8, 2010 by Mike the Boilerman

[WotEver]

I was musing today on the reasons for battery isolator switches. I couldn't think of any safety reasons that aren't addressed better with the use of fuses. This is the Boat SAFETY Scheme specifying them after all.

 

So what ARE the safety reasons for demanding battery isolator switches? Can anybody explain please? Rob? Anybody?

 

Maybe I'm not thinking clearly.

 

Mike

My understanding of the reasoning behind this regulation is that if anyone is going to do any work on the electrics the isolation switch offers a simple and unambiguous method of ensuring that all circuits are dead. It therefore makes the boat electrics safe to deal with.

 

Tony

[n.b.Goldie]

I was in considerable correspondence with the BSS some years ago. Actually on two separate occasions.

 

I argued that the battery isolator switches should have several further exceptions (alternators, battery chargers, inverters etc) for three main reasons:-

 

1. The majority of battery isolators (ie those found on the shelf in the chandlers) simply aren't up to the task of dealing with this equipment.

2. Inadvertent operation of the switch was likely to cause considerable damage and mess.

3. A faulty switch (a high possibility considering the current through them) is likely to cause considerable damage.

 

Their reply, on both occasions was:-

 

1. That's down to incorrect component specification not the actual presence of the switch.

2. That's down to operator error not the actual presence of the switch.

3. That's down to a faulty switch not the actual presence of the switch.

 

Pointing out that not having the switch in the first place would cure all three possible problems fell on completely deaf ears.

 

After realising I was banging my head against a wall I gave up.

 

They did however have the sense to recommend switches are not in the negative.

 

Can I ask - does the sentence I have put into bold & italic mean that there should not be a switch in the negative line back to the batteries? My little ship has isolator switches in both the engine start and domestic batteries positive lines and a switch in the negative line back to all the batteries.

 

It has just passed boat safety (July).

 

Elektrickery makes my head hurt!

 

Thanks

Ditchdabbler

[MtB]

My understanding of the reasoning behind this regulation is that if anyone is going to do any work on the electrics the isolation switch offers a simple and unambiguous method of ensuring that all circuits are dead. It therefore makes the boat electrics safe to deal with.

 

Tony

 

Hmmm I wondered if it was something like that. In which case the battery isolator switch needs to be on the positive battery terminal, or the lead from the positive battery terminal to the master switch remains live/positive even when the battery isloator switch is OFF.

 

A battery isolator switch in the negative line is even less use if (like most boats) something somewhere is connecting negative to the hull.

 

I prefer to disconnect the positive battery terminal if I'm doing anything batteryside of a fuse.

 

Mike

[n.b.Goldie]

Hmmm I wondered if it was something like that. In which case the battery isolator switch needs to be on the positive battery terminal, or the lead from the positive battery terminal to the master switch remains live/positive even when the battery isloator switch is OFF.

 

A battery isolator switch in the negative line is even less use if (like most boats) something somewhere is connecting negative to the hull.

 

I prefer to disconnect the positive battery terminal if I'm doing anything batteryside of a fuse.

 

Mike

 

I still don't understand - if the switch in the negative line is 'the last thing before the battery' then, when it is switched off, surely no electrickery can get back to the batteries and therefore no circuit short or otherwise can be made regardless of what is earthed via the hull.

 

Though if the engine is running with the negative isolator switched off, I would think a circuit could be made between the alternator and whatever is earthed via the hull but not the batteries.

 

Yours confusedly

 

Ditchdabbler