12v electrical system

[Col_T]

I've spent a bit of time trying to trace the 12v electrics on the boat, which has resulted in the diagram below . . . . .  and a number of questions!

 

The domestic batteries are low maintenance, sealed lead acids and the motor battery is an open cell lead acid battery e.g. gets topped-up as and when required.

The motor is a twin alternator Beta BV 1505.

There are two connections onto a metal engine bearer [Metal Engine Bearer (1) and MEB2 in the diagram above]. These connections are onto the same physical engine bearer, though not the same physical connection point being separated by about 6 inches.

Questions:-

1. This relates to the left alternator / starter motor circuit.  My interpretation is that the circuit goes from the starter motor to the -ves of the battery marked as 'Dom 4' => 'Dom 5' => Motor Battery and then continues from the +ve of the Motor Battery through the Isolator Switch and thence back to the starter motor. This seems a little odd, as I would expect the -ve from the starter motor to go straight to the Motor Battery, so I plan to alter this part of the wiring but is there any reason why I shouldn't?
2. This relates to the Mikuni water heater circuit. My interpretation is that the circuit goes from the +ve of the battery marked as 'Dom 3' => the Mikuni to the -ve of the Motor Battery and then back along the -ves of 'Dom 5' => 'Dom 4' => 'Dom 3'. I'm not convinced this is best practice, so I  plan to alter the wiring so that the -ve goes direct from the Mikuni to 'Dom 3', so that both connections for the Mikuni are to the same battery. I also plan to move the existing connection, to the 12v distribution panel, from 'Dom 3' to 'Dom 4' to reduce the number of connections on the 'Dom 3' -ve, just so that there are not too many connections on any single terminal. Does all of this sound sensible?
3. Not shown on the diagram is a connection that goes from a hull earth bonding point to the Inverter / Charger (a Sterling Pro-Combi 1500w modified sine-wave affair), and another connection that goes from the  hull earth bonding point to the boat side of a Galvanic Isolator . I have yet to find any DC connection to a hull earth bonding point, or is this adequately dealt by the connections from the battery DC to the metal engine bearer?

All / any comments welcomed, and apologies for the basic nature of some of this but I'm trying to understand this electrickery stuff, and, with the first two questions at least, and trying to check my understanding.

 

Thanks in advance.

[Tony Brooks]

Apart from the fact MEB 2 would (if I am reading your text correctly )be a dead short I think that and MEB 1 are the bond points for the 12V system.

The left alternator (engine alternator) is not connected to the starter a shown. I probably uses a terminal on the starter solenoid as a junction to feed the master switch and battery.

Ideally ALL 12V domestic negatives will run to one end of the battery bank (say Dom1) and ALL positives to the other end (Dom5). This helps make each battery do equal work.

 

 

[Col_T]

Thanks for this, Tony.

I've redrawn the diagram as you suggested, which comes out as below:

In all honesty, this just makes me realise that I'm not entirely sure how the battery charging circuit, from the Inverter / Charger, works as originally drawn or, indeed, as drawn in this revised version! Any comments would be much appreciated.

I've attached a photo showing the two -ve connections to the metal engine bearer which will, hopefully, make things a little more clear. I'm also hoping this will confirm that MEB 2 is not a dead short though, again, comments would appreciated. Oh, the separated by about 6 inches, in the OP, is well wrong; probably not even 6cm!!

Thanks for your help.

[Tony Brooks]

The connection with the red wire on it looks very much like a positive "bus bar" and is insulated from the metal it is fixed to.

The one below it (just a bolt) is the negative bond to the hull.

The engine and domestic negatives are all connected together so the negative cable, although attached to the engine battery is in reality connected to the domestic negatives. The positive is as it should be. As drawn it is only charging the domestic bank so it may have a pair of spare terminals to allow it to also charge the engine battery. If not don't worry because engine batteries are almost always fully charged and last for years.

 

 

[WotEver]

31 minutes ago, Tony Brooks said:

As drawn it is only charging the domestic bank so it may have a pair of spare terminals to allow it to also charge the engine battery.

If you take another look Tony there is another alt ("Left"), which charges the starter batt. As drawn it's connection is via the starter motor. 

[Alan de Enfield]

43 minutes ago, Tony Brooks said:

The connection with the red wire on it looks very much like a positive "bus bar" and is insulated from the metal it is fixed to.

Looks like it is using 'wooden washers' as insulators.

Col - if they are indeed -ve cables then it is not a good idea to have them colour 'red'.

Someone with less electrical 'savvy' than your self could easily mistake them for +ve cables.

[Jen-in-Wellies]

1 hour ago, Tony Brooks said:

The connection with the red wire on it looks very much like a positive "bus bar" and is insulated from the metal it is fixed to.

 

It is indeed a positive common connection point, insulated from the engine bearer. Standard Beta Marine way of doing things. The insulation is white plastic under the grime. On my boats Beta 43 there are two, one to connect the wires to the starter motor, starter battery and engine alternator, the other to connect a wire from the house alternator and to the house batteries.

Jen

[Tony Brooks]

1 hour ago, WotEver said:

If you take another look Tony there is another alt ("Left"), which charges the starter batt. As drawn it's connection is via the starter motor. 

I know but I was talking about charge from the combi-unit, not the alternators. I may have misse3d something but I can see no way for the combi to charge the engine battery and doubt that it does.

[Col_T]

Many thanks for the replies, chaps.

11 minutes ago, Tony Brooks said:

I know but I was talking about charge from the combi-unit, not the alternators. I may have misse3d something but I can see no way for the combi to charge the engine battery and doubt that it does.

Thanks for confirming this, Tony. I've checked the original scraps of paper which I used when drawing this out on the boat, and I can see no obvious mistakes, but I'll check again next time I'm on board. In a perverse kind of way, this is good news as it suggests that I am starting to get some kind of idea about this electrickery stuff! Who said the age of miracles had passed?!

1 hour ago, Alan de Enfield said:

Looks like it is using 'wooden washers' as insulators.

Col - if they are indeed -ve cables then it is not a good idea to have them colour 'red'.

Someone with less electrical 'savvy' than your self could easily mistake them for +ve cables.

A sound comment, Alan, though I fear my drawing has led you astray somewhat. The 'red' cables you refer to are shown, in the photo, at the point MEB 2 on the diagram (top left corner). From there the circuit goes via Isolator Switch (R) => 12v Distribution Panel => the -ve side of Dom 1. Typing this on a laptop, it's easy to see where the circuit goes though, having previewed it in tablet and phone mode, I can see that it is far from clear.

 

Another question - I've read in a number of threads that the AC and DC hull bonding points should be in close proximity to each, though not use the same physical point - what is the reasoning this, please? I ask as the AC hull bonding is a good couple of feet away from the DC bonding point on the engine bearer and I wonder whether there is any advantage to moving it closer.

[Tony Brooks]

If both were fixed together and however that point was fixed to the hull fell off any mains faults would put mains voltage on the 12V circuits, far from idea,

The BMEA code says the close together bit and I expect the BS/ISOs do as well but I have yet to work out an overriding reason for this. The best I can come up with is if they are close together and properly colour coded its easy to locate them when working on the systems. Electrically I can see no reason and as long as they are obvious and colour codes I would not bother.

 

[Col_T]

Thanks for that, Tony, and for all the other help you've given me both directly (answering my questions) and indirectly (answering other people's questions).

Much appreciated.

 

Over and out.

[Alan de Enfield]

14 minutes ago, Col_T said:

Over and out.

You have been watching too many American war films :

Over & Out literally means "I am handing back over to you but I am 'out' and will not be listening to anything you say"

[bizzard]

Roger Rog over and out...........  Why dya keep callin me Roger when me names Bert.

Edited August 6, 2017 by bizzard

[Col_T]

2 hours ago, Alan de Enfield said:

You have been watching too many American war films :

Over & Out literally means "I am handing back over to you but I am 'out' and will not be listening to anything you say"

Thanks for that, Alan, which confirms that I, almost, understood it correctly. I used it in the sense "I don't have anything further to add, but may still pop-in to see if anyone has made a comment that improves my understanding a tad".

On that basis, I'll say ta-ra for now, and y'all have a good day, now!

[WotEver]

5 hours ago, Col_T said:

I've read in a number of threads that the AC and DC hull bonding points should be in close proximity to each, though not use the same physical point - what is the reasoning this, please?

As Tony B points out, it's purely for convenience and logic. No electrical reason. 

5 hours ago, Tony Brooks said:

I know but I was talking about charge from the combi-unit, not the alternators. I may have misse3d something but I can see no way for the combi to charge the engine battery and doubt that it does.

Ahh yes, you're quite right

[Col_T]

Chaps,

Given the second diagram as a starting point, I'm trying to come up with options that will allow the inverter / charger to charge both the domestics and the engine battery. 

The only thing that I can come up with is a new +ve connection from Dom 5 to the Motor Battery, but this would result in a single battery bank which isn't what I want. So, I could put an isolator switch into the new connection between the domestics and the motor - 'on' allowing current to flow between domestics and motor, for when the boat is on shore-line, 'off' separating them, for when we're not. I'm not terribly keen on that idea as it just complicates things, and I can practically guarantee it'll get left in the wrong position at some point.

Other options, of course, include adding a new charger specifically for motor battery, and fitting solar to the boat. Given that the boat spends most of it's life in a marina connected to a shore-line this doesn't seem wholly appropriate.

Any suggestions?

[WotEver]

1 hour ago, Col_T said:

Any suggestions?

A VSR would do it

[Tony Brooks]

This ^^^^^^^

Connected between the engine and domestic battery positives by suitably heavy cables. It will also send solar to both batteries when charging and parallel the two alternators once a certain degree of charge has been reached.

Edited August 6, 2017 by Tony Brooks

[stegra]

Split charge relay used in vehicles with leisure batteries:

http://m.ebay.co.uk/itm/160477-0-727-10-EQUIV-12V-100A-100-AMP-HEAVY-DUTY-SPLIT-CHARGE-RELAY-CAMPER-VAN-/201605769301?epid=1226699295&hash=item2ef0a3e855%3Ag%3ApqoAAOSwU-pXqbR0&_trkparms=pageci%3Aa27d01cb-7ada-11e7-92b7-74dbd1803b4b%7Cparentrq%3Ab8f2ddc015d0a88f59565b71fffffc81%7Ciid%3A15

[Col_T]

Thanks for further info, chaps.

13 hours ago, Tony Brooks said:

This ^^^^^^^

Connected between the engine and domestic battery positives by suitably heavy cables. It will also send solar to both batteries when charging and parallel the two alternators once a certain degree of charge has been reached.

The manual for the Inverter / Charger specifies 35mm^2, so I anticipate using that for the connections to the VSR. I've come across a manual and wiring diagram for a VSR that shows the negative going to a 'common ground', shown as the -ve bus-bar in the diagram. I'm thinking of mounting the VSR in the battery bay, and making the VSR -ve connection to one of the battery -ve posts, purely on the grounds of convenience. Would this be bad practice or otherwise frowned upon for some reason?

Also, would either of the new connections to the VSR need to be fused?

Finally, solar is something for the future but . . . presumably the idea would be to connect the output from the charge controller direct into the VSR?

 

[Tony Brooks]

Practically it will be fine as the VSR only draws a few mA although purists would advise connecting with all the other negatives to the end of the battery chain.

That 35 sq mm CCSA is almost certainly dictated by the maximum inverter current, not the charging current. In my view a CCSA of 25 sq mm would be ample. In fact if it were mine I would probably go for 8.5 sq mm because it will be far easier to attach suitable terminals. That's good for 60 or 70 amps in very short runs depending upon type of cable.

Solar goes to the domestic bank. I would use the battery side of the master switch for the positive and the negative end of the battery chain for the negative. However that's an extra 2 negative connections on the battery post so for that a bus bar is looking increasingly better practice so there is only 1 connection on the battery terminal. You will need a suitable fuse as close as is reasonably possible to the battery positive end of the solar wiring as it will bypass the master switches etc. Normally you would connect the solar to the domestic bank so make sure if the VSR is not bi-directional the sensing side is connected to the domestic bank as well. Whenever any charge source raises the domestic bank voltage to above about 13.6 the VSR will connect both banks. When the charging voltage falls below about 13.6 the relay drops out and isolates both banks from each other.

Fusing the VSR. In a perfect world probably yes but practically as long as you have short well protected cable runs I would say  no, but its at your risk which in my view would be vanishingly low as long as the cable protection is good. I bet you battery cables and main charging positives are not fused. Well protected     does not necessarily mean running in trunking etc. It could mean them being well supported and secured away from any significant danger of damage.

[WotEver]

With regard to 'well protected', take a look at the installation and ask yourself if vibration could cause problems. Could it be accidentally stepped on? Could anything drop on it and damage it?  It's all pretty much common sense as Tony says.  

[Col_T]

Okay, that's me sorted, so thanks very much for your help and advice.

Colin T

[Col_T]

Well, back again.

I got one of these, http://www.12voltplanet.co.uk/voltage-sensitive-relay-12v-140a.html, and have fitted it so that the 'sensed battery' is the starter, which also means that the -ve connects to the starter battery -ve, and I am now having second thoughts about whether I have fitted it the right way round!

The domestic bank comprises 5 maintenance free batteries, and the Sterling inverter charger is set for those. The starter battery is a wet lead acid which, I think, requires a higher charge rate that the domestics. The logic was that when the boat is on shore power, about 48 weeks a year, the starter battery will get charged first, and the domestics second. However, thinking about it more, when cruising the domestics will want much more charge from the alternators (starter has a 40 amp alternator, domestics a 70 amp) than the starter battery and I am now starting to wonder whether the starter battery will be charged enough to divert charge current to the domestics. My guess is that we cruise 4 or 5 hours a day. 

We don't have television or 240v appliances on-board; we do have a 12v fridge, most of the lighting is LED and phones only get charged whethe engine is running.

Given the above, any comments on whether I should alter how the VSR is fitted would be welcomed!

 

 

[WotEver]

As a general rule you should connect a VSR sense input to the domestics so that when it parallels up the batteries it will only be passing a small current to charge up the starter battery. The logic here is that starting the engine takes only a tiny bit of energy, so the engine battery will take very little charging. As you have twin Alternators then I'd suggest that you don't actually need a VSR anyway. By the time the domestics reach the switching voltage the engine battery will be fully recharged by the 40A alternator.