Alternator & battery isolation switch

[Bro]

Is it better to connect the alternator to the battery via the isolation switch or direct to the battery terminal, or does it make no difference?

[Jrtm]

Do you mean the main electrics isolation switch or a 2+ battery isolation switch (split charging isolation switch normally for splitting the charging between starter and leasure batteries.)?

[Bro]

Do you mean the main electrics isolation switch or a 2+ battery isolation switch (split charging isolation switch normally for splitting the charging between starter and leasure batteries.)?

Not a split charging system!

Boat has two alternators, one for domestic batteries t'other for engine battery and each has isolation switch.

 

If the alternators were to be connected direct to the batteries (not via the switches) then with engine not running and switches open, the alternators would still be connected to the batteries. So, would that be a problem in any way? Effectively, could there be issues with batteries permanently connect to alternators?

[ditchcrawler]

Not a split charging system!

Boat has two alternators, one for domestic batteries t'other for engine battery and each has isolation switch.

 

If the alternators were to be connected direct to the batteries (not via the switches) then with engine not running and switches open, the alternators would still be connected to the batteries. So, would that be a problem in any way? Effectively, could there be issues with batteries permanently connect to alternators?

A lot depends how you interpreter the BSS requirements on isolation

[Bro]

A lot depends how you interpreter the BSS requirements on isolation

 

I don't understand your reply. Which is the best way to connect the alternators to the batteries, via the switch or not?

[Jrtm]

Most systems have the batteries connected to the alternator permanently.

 

But simple answer is no. there is no problems with the alternator charging wire permanently conected to the battery of that system as long as its fused at the correct fuse rating for the alternator and the wires are the correct size.

 

Just treat each alternator and battery bank as a separate system. I.e dont charge 1 battery from 2 alternators

 

You can if you need to go via a isolation switch but you must put the alternator wire on the battery side fused before the switch. not on the side the system you want to isolate.

 

The reason i say this is if you have to run the engine for any reason when the isolation switch key is out your electrics will still see power and you could then damage something

Edited November 2, 2016 by billybobbooth

[ditchcrawler]

 

I don't understand your reply. Which is the best way to connect the alternators to the batteries, via the switch or not?

People will advise you that both ways are best, but the Boat safety Scheme (BSS) has a bit to say about what should and shouldn't run via an isolation switch and depending on how you interpret that depends if you can do what you want to.

Mine are connected via the isolation switches so that switching them off everything except the bilge pump and solar panels are disconnected.

[Jrtm]

I have 2 isolation switches

1 is a high amp switch one side goes to the battery the other to a 4 way distribution block. Off that block comes the wire to fuse box for bildge pumps and 1 back cabin light, 1 to the solar pannel and 1 to the main electric power wire

 

The main electric power wire goes to another isolation switch.

 

If i turn off the 1st switch everything dies the lot nothing can get to the battery. Except the alternator.

 

If i turn only the second one off it kills my main electrics fuse box but not my fuses to bildge pumps and 1 rear cabin light and solar pannel.

 

This way i can leave the boat with the bildge pumps on and solar but the rest dead

Its 3 if you count the switch at the solar pannel.

Edited November 2, 2016 by billybobbooth

[by'eck]

Not a split charging system!

Boat has two alternators, one for domestic batteries t'other for engine battery and each has isolation switch.

 

If the alternators were to be connected direct to the batteries (not via the switches) then with engine not running and switches open, the alternators would still be connected to the batteries. So, would that be a problem in any way? Effectively, could there be issues with batteries permanently connect to alternators?

 

No issues as such, but to my mind a battery isolator should do just that, isolate the batteries completely. To do this effectively on a typical boat installation you need two. One to isolate batteries from main distribution panel and maybe used when boat left unattended. Another to isolate all other connections to batteries including mains chargers/combi's, alternators, bilge pumps etc, and typically left on except in emergency, when working on electrics or when changing batteries.

[Geo]

Is it better to connect the alternator to the battery via the isolation switch or direct to the battery terminal, or does it make no difference?

 

The BSS rules http://www.boatsafetyscheme.org/media/268789/ecp-private-boats-ed3_rev2_apr2015_public_final.pdf 3.6.2 allow for all charging source (Alternator) to be connected directly to the battery and not via an Isolation switch.

 

I my opinion it is better to connect alternator directly to the battery so that if the Isolation switch is switched off while the engine is running damage etc is not caused to the Alternator.

[Jrtm]

Thats the way i understood it.

[Geo]

Thats the way i understood it.

Good it just seemed there was a bit of confusion floating around the thread

[Tony Brooks]

Is it better to connect the alternator to the battery via the isolation switch or direct to the battery terminal, or does it make no difference?

 

The answer is to do what the BSS require and for many years that has been to put the alternator through the isolator.

 

Alternators are not specifically listed in 3.6.2 of the BSS document but it does list "battery chargers". I accept that you could construe "battery chargers" to include alternators but I suspect that is not what the BSS require. Suitable battery chargers can be left running 24/7 so would need to bypass the master switch if the owner turned the switch off when not on the boat. Alternators by their design can only be charging when the engine is running so I suspect they is not included.

 

In the past some/many BSS examiners have either turned a blind eye to alternators bypassing the master switch or have not inspected closely enough to find out.

 

My advice is not to take what you get told here as gospel UNLESS it is posted by more than one BSS examiner. Email or phone the BSS office and get the definitive answer. If you email you will get a written reply that might save problems at a future BSS examination.

 

.

PS - BSS 3.6.2 does NOT say "CHARGING SOURCE" it says "BATTERY CHARGER". That slight difference introduces ambiguity, especially in light of years of assertions from the BSS that alternators must go through the master switch.

Edited November 3, 2016 by Tony Brooks

[ditchcrawler]

 

I don't understand your reply. Which is the best way to connect the alternators to the batteries, via the switch or not?

Now do you see why my reply was what it was?

[Jrtm]

My issue with having the alternator on the isolation side is if you start your engine without the electrics on your still giving your system power via the alternator as its also earthed. If you have left anything on a light or tv ect or you have a exposed wire it all becomes live.

 

With the alt direct to the battery this cant happen the only way around this would be to fit 2 or 3 isolation switches. Depending on how your system is setup.

 

So you had a wire from battery to switch, switch to alternator, alt to switch, switch to bildge pumps ect, pumps to switch, switch to all other electrics.

 

Which i would find odd as you would have to turn off 2 kill switches to turn the system off not just 1. Why i cant see a prob with the alt being the only thing the battery side of the kill switch.

Edited November 3, 2016 by billybobbooth

[Tony Brooks]

Today most canal boats use two battery banks. If you are going to wire them for best practice that means two master switches. One in the engine battery positive and one in the domestic battery positive. I am sure that you know the reason why master switches ideally should be in the positives.

 

The items listed in the latest BSS 3.6.2 are allowed to bypass the master switch as long as they are adequately fused. The BSS do not envisage that these will ever be turned off. If the boater felt the need to isolate them then they would disconnect a battery lead.

 

The major arguments against putting the alternator output through the master switch are:

 

1. Each connection and the switch WILL introduce a little more voltdrop but with a decent installation and a quality switch this is unlikely to cause a practical charging problem (unlike if a cheap plastic key type master switch is used).

 

2. If the master switch is turned off with the alternator energised and running it might produce a voltage surge that could damage the alternator electronics. However the same would happen if a fuse blew.

 

Whatever any posters on here may think, including myself, the arbiter in all this is the BSS. This is why I advised the OP to contact them himself. Not so long ago we had BSS examiners contributing but if they do not contacting the BSS is the only way to get a definitive answer. Neither you or I can overrule the BSS whatever we think about their requirements.

 

The likelihood of the scenario you mention actually causing any damage is very slight indeed but as I do not understand your third paragraph I can not comment further.

 

 

 

[cereal tiller]

My issue with having the alternator on the isolation side is if you start your engine without the electrics on your still giving your system power via the alternator as its also earthed. If you have left anything on a light or tv ect or you have a exposed wire it all becomes live.

 

With the alt direct to the battery this cant happen the only way around this would be to fit 2 or 3 isolation switches. Depending on how your system is setup.

 

So you had a wire from battery to switch, switch to alternator, alt to switch, switch to bildge pumps ect, pumps to switch, switch to all other electrics.

 

Which i would find odd as you would have to turn off 2 kill switches to turn the system off not just 1. Why i cant see a prob with the alt being the only thing the battery side of the kill switch.

Have come across an Alternator draining Batteries more than once,due to faulty diodes,only an Amp. or so but enough to drain a bank of batteries in a week.

 

If the alternator were isolated by the Master switch this could not happen

 

CT

[WotEver]

The simple fact is that Rule 3.6.2 states:

 

 

All d.c. electrical circuits must pass through a battery isolator, except those which feed equipment requiring a continuous supply which must be protected by a suitable fuse or circuit‐breaker.

.

 

An alternator does not 'require a continuous supply' unlike solar, bilge pump, battery charger etc which are listed as specific exceptions.

 

Interpret it how you like, but unless BSS changes their rule on this, if you get a sharp inspector you'll fail the next inspection.

[Jrtm]

The simple fact is that Rule 3.6.2 states:.

 

An alternator does not 'require a continuous supply' unlike solar, bilge pump, battery charger etc which are listed as specific exceptions.

 

Interpret it how you like, but unless BSS changes their rule on this, if you get a sharp inspector you'll fail the next inspection.

I do agree its worth the op checking directly

 

An alternator does require a constant conection. As you cant isolate the alternator charge if running the engine. If you dont want to turn on any electrics but say just turned up to move the boat in or out of dock or something small like round the corner all your electrics would become live and the charge wouldnt be going anywhere.

 

+if you ran the alternator with out going anywhere youll damage the alternator.

 

I dont understand you coment that a solar required a constant conection but an alternator dosnt they do the same job a solar panel if there big enough can even replace you alternator if you really needed to. So in that way would you then isolate the solar?

 

I can see a good reason for doing it both ways but ive always been told to conect alt direct to battery with a sutable fuse.

 

Also i cant see a tester failing it as if you ask them to show you where it says alternator they cant. Its not a battery charger.

 

If anything i would put it under the same category as dynamos and starter motors. Do you isolate a starter motor from the system?

Have come across an Alternator draining Batteries more than once,due to faulty diodes,only an Amp. or so but enough to drain a bank of batteries in a week.

 

If the alternator were isolated by the Master switch this could not happen

 

CT

Thats down to a failed component any shorted out electrical item can do. Even a bildge pump or starter motor anything. Edited November 3, 2016 by billybobbooth

[Geo]

 

The answer is to do what the BSS require and for many years that has been to put the alternator through the isolator.

 

Alternators are not specifically listed in 3.6.2 of the BSS document but it does list "battery chargers". I accept that you could construe "battery chargers" to include alternators but I suspect that is not what the BSS require. Suitable battery chargers can be left running 24/7 so would need to bypass the master switch if the owner turned the switch off when not on the boat. Alternators by their design can only be charging when the engine is running so I suspect they is not included.

 

In the past some/many BSS examiners have either turned a blind eye to alternators bypassing the master switch or have not inspected closely enough to find out.

 

My advice is not to take what you get told here as gospel UNLESS it is posted by more than one BSS examiner. Email or phone the BSS office and get the definitive answer. If you email you will get a written reply that might save problems at a future BSS examination.

 

.

PS - BSS 3.6.2 does NOT say "CHARGING SOURCE" it says "BATTERY CHARGER". That slight difference introduces ambiguity, especially in light of years of assertions from the BSS that alternators must go through the master switch.

 

Several years ago I was advised by BSS that the exemption applied to all charging sources including alternators.

 

 

Have come across an Alternator draining Batteries more than once,due to faulty diodes,only an Amp. or so but enough to drain a bank of batteries in a week.

 

If the alternator were isolated by the Master switch this could not happen

 

CT

 

I find that interesting as there are big diode in the alternator that would block a positive flow into the alternator from the positive side of the battery. That is of course unless the alternator is faulty.

 

 

I think there is a problem with this circuit Tony Brooks

Should it not be like this

Edited November 3, 2016 by Geo

[Jrtm]

Several years ago I was advised by BSS that the expemption applied to all charging sources including alternators.

 

 

If they told you this they lied as a solar is a charging source and dosnt need isolating.

I think part of the prob is its a gray area as there not mentioned directly like other charging items are.

[Geo]

Several years ago I was advised by BSS that the expemption applied to all charging sources including alternators.

 

 

If they told you this they lied as a solar is a charging source and dosnt need isolating.

I think part of the prob is its a gray area as there not mentioned directly like other charging items are.

 

I think you have misunderstood. The exemption is not having to go through the isolator switch

[WotEver]

I don't see any grey in the rule. It's very clear. All d.c. electrical circuits must pass through a battery isolator, except those which feed equipment requiring a continuous supply which must be protected by a suitable fuse or circuit‐breaker.

 

An alternator does NOT require a continuous connection. It requires a connection when the engine is running but does not require one when it isn't. It's therefore not required to be continuous.

 

I personally think that the BSS is wrong on this and in the past several of us have argued with them about it. However, the rule as it stands appears to me to be unambiguous.

What some folk do is to fit a completely separate isolator just for the alternator. It satisfies BSS and if it's a quality isolator will probably be more reliable than a fuse which can age.

[Geo]

I don't see any grey in the rule. It's very clear. All d.c. electrical circuits must pass through a battery isolator, except those which feed equipment requiring a continuous supply which must be protected by a suitable fuse or circuit‐breaker.

 

An alternator does NOT require a continuous connection. It requires a connection when the engine is running but does not require one when it isn't. It's therefore not required to be continuous.

 

I personally think that the BSS is wrong on this and in the past several of us have argued with them about it. However, the rule as it stands appears to me to be unambiguous.

What some folk do is to fit a completely separate isolator just for the alternator. It satisfies BSS and if it's a quality isolator will probably be more reliable than a fuse which can age.

 

Well I have two boats which regularly go through BSS the last time three months ago and the inspector is hot as I want him to be, Both boats have hardwired (via fuse)x 2 Alternator connections and he agrees that is acceptable under the BSS rules.

[WotEver]

 

Well I have two boats which regularly go through BSS the last time three months ago and the inspector is hot as I want him to be, Both boats have hardwired (via fuse)x 2 Alternator connections and he agrees that is acceptable under the BSS rules.

Then he's wrong because that's not what the guide says.

 

Not unusual for a BSS inspector to be wrong.