1 2 both off switch.....just checking

[Matata]

Our boat has a simple 1 2 both off switch and generally happy with the set up. I'm replacing the original cable from the batteries to the engine with new tinned 35mm cable. I'd like to confirm I understand the wiring before I launch in!
The negatives from the batteries both go to the earth /negative on the engine. The positives from the batteries go to the 12 off switch, one to 1, another to 2, then ONE positive goes from the switch to the starter. I presume the panel/circuit breakers gets its positive from the 12 switch. It obviously doesnt need to be as heavy wiring as the currents are a lot less. The negative for the power panel is taken from the common negative that meets at the engine. Again this doesn't have to be super heavy gauge either.
Have I got it right! Ta as ever Nik

 

[VicS]

You have it figured out.
Dont make the other wiring too light esp if you have much domestic stuff to support or nav lights etc. Surprising how the amps can add up on 12 volt stuff when you are having a good time

 

[Matata]

Cheers Vic. Please find enclosed a very nice pint of Guinness, Ta Nik

 

[Stu Jackson]

That's correct. It appears, although unsaid, that your alternator output goes directly to your house bank.

 

[Maine Sail]

The only...

You have it right. The only change I would consider would be a ground bus bar. This is a point where all the grounds are tied to, then one wire, the same gauge as the battery cables, goes over to the engine ground point.

As Stu said the alt would be best served by being wired directly to the house bank so you avoid the potential for human error and fried alternator diodes by accidentally flipping it to OFF with the engine running. If you have a diode type battery isolator this has, in a sense, already been done.

 

[VicS]

As Stu said the alt would be best served by being wired directly to the house bank

Disagree. Stick to the conventional arrangement with all charging and power supply via the common terminal. You have one battery or the other (or both) selected for use/charging.

Select battery no 1 and start engine.

When battery recharged select battery no2 via the both position

If the system is to be improved fit separate isolators, separate the engine and domestic electrics, fit VSR to automatically switch in domestic battery when engine start is recharged.
Better still a combined VSR and switch panel from KDDPowercentre or a BEP Marine one from Merlin Powerstore.

However OP is happy with the basic set up, cant say I blame him BUT he should make the rule that he alone switches battery banks!

 

[Stu Jackson]

AO

Having the alternator output go directly to the house bank is, as you mention Vic, a choice.

I recommend it for two reasons.

1) The brother-in-law syndrome; avoids inadvertent interruption of alternator output forever

2) wire sizing: most older 1-2-B installations had #4 wiring for alternator to switch and switch to and from batteries. If a higher output alternator were installed, the #4 wiring could well become questionable for 3% voltage drop in a place where as little voltage drop as possible is preferred. So, when charging the #4 wiring from the alternator to the banks could be too small for the 50 A that would be seen for a reasonably long period of time from a 100 A high output alternator when charging a 50% depleted reasonably sized house bank, of, say, 400 AH. The #4s would. of course, be fine for power FROM the banks to the distribution panel.

Understanding how your boat is wired is extremely important because it determines how to properly use the 1-2-B switch and how to charge your banks from the alternator and whatever other sources you may have.

 

[VicS]

wire sizing: most older 1-2-B installations had #4 wiring for alternator to switch and switch to and from batteries.

Id take 35mm² cable (or heavier) from the batteries to the switch and from the common terminal of the switch to the starter solenoid.
I'd wire the alternator output to the same terminal of the solenoid.
In many case that would be a very short connection.

Its how VP engines I've looked at are wired .. my car too.

Have not looked up a cable size. 10mm² more than adequate. Hopefully too short to need to allow for volts drop.

Would have to be altered though if an ammeter were to be fitted.

 

[halcyon]

Yes, though the alternator size and battery bank size would be useful.

Re ammeter, if bank 2 is the service bank, then a shunt can be fitted to the battery terminal, thus no need to change any large size wiring.

http://www.kddpowercentre.com/kddpowercentre2/page9.html


Brian

 

[willie4646]

If you have not bought your cable I would reccommend using 50mm welding cable, It is nice and flexible and easier to fit but most of all it keeps voltage drop to the very minimum.
Willie

 

[ghostlymoron]

Not this AGAIN

How many times does this subject need to be re-aired? I've raised it several times I must admit. Surely there must be a definitive solution to the battery wiring/charging question but I've never found it there seem to be as many ways of doing it as there are boats. When you compare with Automotive wiring there only seems to be one way of doing it. My preference is the idiot proof solution involving a VSR but a good friend of mine who has 2 circumnavigations under his belt as well as 40yrs sailing round Britain/Mediterranean/European coasts prefers the fully manual approach. He is undoubtably more experience than me but DID leave a switch in the wrong position and flattened all his batteries recently. My reasoning with the VSR is that if you can start your engine you can charge your leisure batteries.
Will someone please publish the definitive solution for battery wiring/charging?
End of rant.

 

[rosssavage]

It gets re-aired cos there's a lot of different ways of doing it depending on age / use of boat, number of battery banks etc... To add to the mix, mine is again different... Princess have used two alternators with diode-seperated twin outputs, so four outputs in total. One on each alt is parralleled to the other alt and fed to the engine batteries, the others are parralleled and fed to the house banks. No switching or VSR involved, all done within the alternator regulators. Possibly not great for retrofitting due cost of modifying alternators, but a very simple (and so far..) effective system.

 

[halcyon]

Princess have used two alternators with diode-seperated twin outputs, so four outputs in total. One on each alt is parralleled to the other alt and fed to the engine batteries, the others are parralleled and fed to the house banks. No switching or VSR involved, all done within the alternator regulators. .

That was a standard system fitted by Volvo, there was a lot of problems when it came out, as it had battery sensing for alternator regulation. If it compensated for diode drop to service bank it over charged the engine battery, regulating to suit the engine battery lead to low charge to service battery.

Equally Sealine used to fit a VSR system to twin engine boats were each engine charged it's battery, then the service battery. If say you lost the port alternator, the system charged the port battery from starboard alternator. It also interfaced with the multi-stage mains charger, allowing the service battery to be charged before engine batteries, avoiding over charging the engine batteries and water lose.

The end of the day, all systems have a problem, it's just minimising them.

Though the OP was about cable size

Brian

 

[rosssavage]

Brian, yes it was, but where's the fun without a bit of thread drift! Cheers, Ross

 

[Matata]

Thanks for all the help/advice. I'm a big fan in adding simplicity. So I've moved the engine battery beside the engine ie 2 feet away. It was originally 12' ! So I think between that and upping the cable from a pretty miserable size to 35mm it will be fine. Ta Nik ps I'm not buying pints for all of you!

 

[Stu Jackson]

Surely there must be a definitive solution to the battery wiring/charging question but I've never found it there seem to be as many ways of doing it as there are boats.

Not quite, but close!

The 1-2-B switch has been around, and has been misunderstood and misused for decades.

A description of how and why I summarized here in Reply #11: http://c34.org/bbs/index.php/topic,4949.0.html

Recently, manufacturers were trying to sell more switches, so they came up with the stupid dual circuit switch. Comments here: http://c34.org/bbs/index.php/topic,4623.15.html

And the relatively newer relays are helpful in automatically switching to allow charging of a reserve (service) bank, if you're severely (mentally) limited when it comes to switching.

The only downside to this simplistic design is that when the engine is started electronics could reboot, so you'll need a way around that. I use handheld electronics and turn my autopilot off before I start the engine, and then just turn the ap on again once the engine is going. I helped a friend design his system which always started his engine on the reserve bank to avoid this issue. It required more switches, which he'd already purchased. I also insisted that he wire it so that the reserve bank could serve limited house loads (like the VHF) in an emergency situation. Many people neglect this important feature.

Your boat, your choice, that's why there are so many ways to do it!!!

My personal approach has been to understand how the 1-2-B switches work (four positions but only three posts to land a wire!) and KISS.

A good summary discussion can also be found here: http://forums.catalina.sailboatowners.com/showthread.php?t=104505&page=2

Both Maine Sail and I contributed to that discussion, which raised pretty much the same questions you have aired here.

Do the simple 1-2-B design and run your entire boat on the house bank, and keep the reserve for a reserve. Simple, no switching required during the day.

...but DID leave a switch in the wrong position and flattened all his batteries recently.

That's exactly why getting the alternator output off the switch is the best thing you can do for your electrical system.