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Master Switch Sizes


jddevel

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Well having completed a great deal of the "furniture" fit-out of my sailaway and having to wait three weeks to get the boat moved from Cornwall to the crane in point I`m going to spend this time coming to grips with the 12 volt installation. So be warned lots of what to many may seem silly questions but help is needed. To start with:

1) I have a bank of 620ah leisure batteries. A starter battery (unknown ah as installed by engine installer at Bourne Boats) and a bow thruster with 2x 100ah batteries. The bow thruster has its own isolater already installed however how do I size the Master switches for the leisure batteries and starter battery. I have a Victron 3600watt Inverter.

2) I see on a one particular narrowboat wiring diagram that I`m finding extremely helpful, the use of a 500amp shunt between the starter battery and leisure battery. Can the forum please explain it`s purpose and also whilst both starter and leisure batteries are immediately adjacent to each other if needed its ideal fitting location.

Thanks in anticipation BUT BEWARE THERE WILL BE MORE TO FOLLOW!!!!!

Incidentally am reading 12 volt bible and Tony Brooks very helpful website-pity his courses weren`t still running. 

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I’ve used BlueSea master switches, 500amp.  Don’t use those cheap crappy ones.  Unless you have some very high power dc equipment. 500 amp should be more than enough, I wouldn’t go less tho.

The shunt is the only thing connected to the negative main battery, everything else is on the other side of the shunt including negative to the starter and bow batteries.  It’s purpose is to accurately measure the amps going to/from the battery.  It connects up to a battery monitor/amp gauge.

Edited by Robbo
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8 minutes ago, Robbo said:

It connects up to a battery monitor/amp gauge.

I`ve a Victron battery monitor is there value in having a amp gauge as well. Possibly near the helm? Plus as my bow thruster batteries are forward as is the master switch for these would an additional shunt and amp. gauge be advisable in that location?

BlueSea it is then.

Thanks Robbo

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I have a combination of Blue sea and BEP marine isolation/changeover switches. Decidedly NOT cheap especialy when you have four but VASTLY superior to the usual pathetic narrowboat fitments with the red plastic toggle switch.

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16 minutes ago, jddevel said:

I`ve a Victron battery monitor is there value in having a amp gauge as well. Possibly near the helm? Plus as my bow thruster batteries are forward as is the master switch for these would an additional shunt and amp. gauge be advisable in that location?

BlueSea it is then.

Thanks Robbo

The BMV has an amp gauge on it.   The BMV has a long cable to the shunt so you can pretty much mount anywhere you like.  If it’s not at the helm having a separate amp gauge just for the alternator can be handy, although like a voltage meter here, they are hardly used in reality.

i wouldn’t bother with a shunt for the bow batteries myself.   Bit like a starter battery, they hardly get used and should be near enough fully charged all the time.

Your setup is near enough like mine so I’ll dig out my diagram.   I only have 1 alternator, and my inverter is a Combi.

Other good tips are to wire the alternator separately to the main batteries and use voltage sensitive relays to go to starter and now batteries.

If you going BlueSea and wiring the alternator to the main batteries as recommended the Bluesea do a dual switch to turn off/on both main and starter at the same time (it also has a combine option).  This is the one I have.

Edited by Robbo
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Another vote for Blue Sea 500A.  I have two, one for the inverter and one for the rest of the 12V electrics.  I also have a Blue Sea digital volt/amp meter.  The shunt goes in the negative side and absolutely everything goes through it.  Blue Sea kit is not cheap, but it will outlast just about everything else on your boat.

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3 minutes ago, jddevel said:

Have 2 x 650 amp bus bars from Furneaux Riddall. Thanks again Robbo and all. Keep going!!! 

If you list all your main dc equipment like solar, charger, inverter, alternators.  I can draw up a quick diagram during next week if ya fancy.

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9 minutes ago, dor said:

outlast just about everything else on your boat

Certainly probably me!!!! Thanks for the BlueSea tip. Searching a suitable source as I type before out to lunch with the family. It`s why I`ve time today to do more research.

2 minutes ago, Robbo said:

I can draw up a quick diagram during next week if ya fancy.

Fantastic. Will try and do so later today- if not to much falling down water consumed over lunch. Thank you assistance appreciated.

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1 hour ago, jddevel said:

Certainly probably me!!!! Thanks for the BlueSea tip. Searching a suitable source as I type before out to lunch with the family. It`s why I`ve time today to do more research.

Fantastic. Will try and do so later today- if not to much falling down water consumed over lunch. Thank you assistance appreciated.

Bluesea do a voltage sensitive relay and the dual battery switch as a kit if you want/need both.

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4 hours ago, Robbo said:

Bluesea do a voltage sensitive relay and the dual battery switch as a kit if you want/need both.

Searching the advised by BlueSea online supplier but unable to find this item. Have you a link please? Will obviously help me decide. Logically sounds a good idea.

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8 hours ago, jddevel said:

Well having completed a great deal of the "furniture" fit-out of my sailaway and having to wait three weeks to get the boat moved from Cornwall to the crane in point I`m going to spend this time coming to grips with the 12 volt installation. So be warned lots of what to many may seem silly questions but help is needed. To start with:

1) I have a bank of 620ah leisure batteries. A starter battery (unknown ah as installed by engine installer at Bourne Boats) and a bow thruster with 2x 100ah batteries. The bow thruster has its own isolater already installed however how do I size the Master switches for the leisure batteries and starter battery. I have a Victron 3600watt Inverter.

2) I see on a one particular narrowboat wiring diagram that I`m finding extremely helpful, the use of a 500amp shunt between the starter battery and leisure battery. Can the forum please explain it`s purpose and also whilst both starter and leisure batteries are immediately adjacent to each other if needed its ideal fitting location.

Thanks in anticipation BUT BEWARE THERE WILL BE MORE TO FOLLOW!!!!!

Incidentally am reading 12 volt bible and Tony Brooks very helpful website-pity his courses weren`t still running. 

1) The master switches (normally called Battery Isolators) are sized depending on the maximum current they have to pass. Not the battery capacity. The maximum current for the domestic isolator is likely to come either from the alternator(s) rating, or the Inverter rating. If you have a Combi I'd suggest not powering that through the domestic battery isolator since you want be able to turn that off when you leave the boat, whilst allowing the Combi to still trickle charge the battery from shore power.

For the engine battery, the max current is from the starter motor. Maybe 400A surge?

Note that isolators normally have several different ratings, e.g. continuous, peak, and surge.

 

2) A shunt is used to measure large currents, typically for an amps display (in and out of the batteries) and/or for an amphour-counting State of Charge meter. There are two possible configurations, one is to have the shunt between the engine and starter battery negatives with the main negative lead from the engine going to the starter battery negative. Alternatively, have no local connection between the two banks' negatives, but separate negative wires from engine to starter battery negative and engine to non-battery side of the shunt. The latter would be appropriate if there were two seperate alternators with insulated negatives. Otherwise, these configurations are topologically identical.

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18 minutes ago, nicknorman said:

two seperate alternators with insulated negatives

Yes my Beta 38 has two alternators. I`m trying to ascertain their sizes. Robbo who has offered to assist I feel may need this information.

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1 minute ago, jddevel said:

Yes my Beta 38 has two alternators. I`m trying to ascertain their sizes. Robbo who has offered to assist I feel may need this information.

Beta canal engines normally seem to have the alternator negatives connected to the case and hence to the engine block. If it's anything like my Beta 43 there are studs for positive and negative connection for both alternators mounted near the bottom of the engine frame, one pair on each side. But of course the negatives are connected together via the engine casing, so it is not strictly necessary to run two cables. I do though, one to each of the domestic battery -ve and the starter battery -ve. And thus there is no connection between these two points local to the batteries.

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Hi Daniel,

Hmmmm.... a steam master switch? Quite amazing considering the walk in fridge freezer, dish washer, aircon, mood lighting and jacuzzi :-)

Seriously though, one reason for the longevity of your master switch is the use of a 24v system. For a given power loading this reduces the current by 50% and correspondingly the heat generated losses by 75% and its usually heat that kills master switches.

Another, I suspect, is the lack of inverter. Even when switched off, when these are powered up they create a significant arc on connection.

My take on master switches is to use the big metal jobbies, all the aesthetic appeal of a brick outhouse but I never remember changing one in 40 years of sorting boat electrics. 

For the OP, I would suggest the aforementioned metal jobbies, readily available from the swindlers especially given the 3.6kW inverter although the Mastervolt ones tend to be more gentle on connection surge.

The shunt you refer to may be a master switch installed to use as an emergency link between batteries in case of unexpected failure. Not a bad idea on an offshore boat but not so relevant when you are unlikely to be stranded more than ten feet from the bank. I’ve seen these before but suspect that  when needed, years of oxidisation on the internal contacts due to lack of use may mean they wouldn’t work. My suggestion to folk is to carry a spare jump lead to join battery banks in extremis.

Arnot

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1 hour ago, Arnot said:

given the 3.6kW inverter

As the OP on this topic just checked the specification of my inverter it`s 3000 not 3600 as stated earlier. I was away from the unit when I typed the enquiry and my memory had failed me again!!! My apologies.

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11 hours ago, Arnot said:

Hmmmm.... a steam master switch? 

We call the steam.master switch the 'crown valve' but it's all the same. I expect that could do 300amps to, but in terms of being an isolator it's much better at 300psi!

11 hours ago, Arnot said:

Seriously though, one reason for the longevity of your master switch is the use of a 24v system. For a given power loading this reduces the current by 50% and correspondingly the heat generated losses by 75% and its usually heat that kills master switches.

Another, I suspect, is the lack of inverter. Even when switched off, when these are powered up they create a significant arc on connection.

Oh indeed. Hence including the information.

11 hours ago, Arnot said:

My take on master switches is to use the big metal jobbies, all the aesthetic appeal of a brick outhouse but I never remember changing one in 40 years of sorting boat electrics. 

Do you refer to the key based ones, like the red plastic key type but larger? Or a knife based type.

Daniel

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Thanks Robbo. The link you showed listed was obviously helpful however is the a system which incorporates three sets of batteries? I`ve a starter, leisure and bow thrusters. Is there a system that can accommodate this please?

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5 minutes ago, jddevel said:

Thanks Robbo. The link you showed listed was obviously helpful however is the a system which incorporates three sets of batteries? I`ve a starter, leisure and bow thrusters. Is there a system that can accommodate this please?

There are several ways to deal with this, none of them very complex :)

To help I guess we need to know the answer to "How are you intending to charge the BT batts?"

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1 minute ago, WotEver said:

"How are you intending to charge the BT batts?"

That I`ve yet to answer in that I`m still looking for advice on the subject. I`m very much a novice with the whole 12 volt world and gradually trying to accumulate enough knowledge to complete a rudimentary system that`s safe, secure and fulfills  the BSS obligations. In Cornwall as I`ve previously stated and experience has proved little professional tradesmen other than automotive engineers are familiar with 12 volt systems. I`ve to wait until the end of August for the boat to be moved northwards and get proper help. In the meantime I`m trying to get as much as possible completed much with the forums experience and help.

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