Rewiring small boat, have I got this right?

S

steve yates

Well-Known Member
Joined
16 Oct 2014
Messages
4,106
Location
Benfleet, Essex/Keswick, Cumbria
Visit site
My plan is to rip out all existing wiring in bethfran and start from scratch.

I have one 85a/hr leasure battery in her, and am adding more instruments during her current refurb.

She will have, 2 cabin lights (I will switch to led bulbs),
a tricolour nav light (not led)
a garmin 158 satnav,
a nasa depth sounder
an illuminated compass,
a vhf radio, (with external antennae)
a garmin chart plotter (old one)
an autohelm 1000 (the thing I'm most excited about having)
a 20 watt solar panel.
a cigarette lighter socket and a dual usb charging point
and thats it.


Been trying to get my head round all this,

As I see it I need to buy 2m of 16mm sq tinned battery cable, +ve and -ve.

I run the +ve from the battery to the isolator switch (a simple red wing shaped item thats currently installed), and then from there run it to the fuse/switchbox.
I run the -ve battery cable from the battery to the negative busbar.

I then buy something like 1.5mm sq tinned twin core cable to connect the instruments & other loads. The +ve & -ve in the twin core connects to the instrument, and the cable is run back to the switch box where the +ve twin core attaches to the relevant switch/fuse and the -ve twin core attaches to the busbar.

The batteries are charged via a battery charger on shore power when on a berth. When sailing, I have a 20w rigid solar panel I will mount on the hatch, with the cable through a gland on the coachroof, running to a controller, and then run the +ve and -ve wires from the controller to the respective battery terminals.

There is no engine charging to consider.

I will fit two 6gang switches units and 2-ve busbars so everything can have its own on/off switch & fuse.

I expect the wiring cost to be about £40 for the cabling and the price of an extra busbar/fusebox.

Questions...

I assume I should have a -ve cable running from the battery -ve to the isolator switch also?

Are my wire dimensions appropriate for the job? (I realise the vhf ariel is a coaxial cable and runs straight to the vhf unit and is not part of this circuit as such)

What sort of fuse sizes should I be using for the loads? And I read somewhere the fuse protects the cable, not the unit, so if I used 1.5mm cable for everything should the fuses then all be the same size?

Am I missing anything that could make this a better job, am I doing anything materially wrong or is my understanding wrong in any points?

Given the wiring is not exactly extensive & complicated, rather than have it hidden behind ceiling panels etc, is there a simple low profile trunking system I could just screw against a bulkhead below the roof to make access easier?

Thanks.
 
steve yates said:
.....

Questions...

I assume I should have a -ve cable running from the battery -ve to the isolator switch also?
.....

Am I missing anything that could make this a better job, am I doing anything materially wrong or is my understanding wrong in any points?
...

Thanks.
Click to expand...

You are giving the impression of not understanding the basics of electric circuits.
That impression might be wrong. Or not?
There are lots of people out there who know nothing about circuits and there is no shame in that, but it isn't a great idea for them to do this sort of work without help. Real help, not online help.

A circuit is a loop. Current flows around the loop. The switch breaks that loop to stop current flowing. It has two terminals one to the battery and one to the loads.
Why would you want to connect battery - to either of these points?
Or does the switch have a 3rd terminal such as a -ve for the bulb in an illuminated switch?
 
Nope, I don't understand how it works, so I have read up on it and am asking here to check what I THINK I have learned so far.

Then folk like you can point out what I have wrong or don't know, thank you :)

I was wondering what went to the -ve terminal of the switch, hence my question. So if not the battery -ve then the busbar? You told me what was wrong, but not what is right.

I haven't looked inside the switch by the way, I had assumed that up and down it made a connection, and when turned at right angles, that connection was broken and no current could flow. I am also open to changing the type of isolator if this type is seen as a problem?

This is not a job I will pay someone to do, it's a job I intend to do myself to learn about all this stuff, so I can sort it when it goes wrong.

But thats a different topic, so lets not thread drift into that :)
 
I find it very dangerous to attempt to explain stuff over the internet, when you don't know if the person on the other end even understands the language used to talk about the problem.
The last thing I want to do is mislead you into thinking it's all simple, resulting in you damaging all the electronics or something.
I freely admit to not being very good at teaching the basics of this sort of thing, I've been wiring things up for 50+ years and can't remember what it's like not to have a basic grasp of it all. Is there nobody who can help face to face, or maybe recommend a good book?
 
I know the feeling of not knowing how to explain basics at a level you cease to even think about, it can be really difficult!

Don't worry about it, I have books, but I find it more useful to check the knowledge I think I have gained with folk on here. Someone else will be along soon enough to explain it.

Just to be sure though, you would NOT connect your battery -ve to an isolator switch?

For anyone else reading, I will prob add a car stereo into the mix, but that will just be another load going to an empty switch and busbar terminal.

Another question would be, I think I should have a battery monitor in this set up. I have a little circular one that seems straightforward enough, but could I connect it to a switch/busbar like everything else? or should it be connected directly to the battery? In which case should I add some kind of inline fuse?

Thx
 
steve yates said:
The battery isolator switch is this kind of gadget, https://www.amazon.co.uk/Qiorange-Battery-Master-Isolator-12V-24V/dp/B015VTQ6P2/ref=asc_df_B015VTQ6P2/?tag=googshopuk-21&linkCode=df0&hvadid=310822128238&hvpos=1o10&hvnetw=g&hvrand=13866167230279588438&hvpone=&hvptwo=&hvqmt=&hvdev=t&hvdvcmdl=&hvlocint=&hvlocphy=9045016&hvtargid=pla-563006682380&psc=1
Click to expand...

That has two terminals, which is as one would expect for a simple isolator in the positive line.

Where on earth did you imagine "the -ve terminal of the switch" is on there? :confused:

Pete
 
Wrong terminology, I knew there would be two terminals, presumed one was for a -ve feed, hence called it a -ve terminal.

Regardless, for a simpleton, can someone enlighten me as to what does connect to the second terminal of the isolator switch? Something obviously does, otherwise there is no circuit.

Every wiring diagram I can find online has feeds coming from engines etc, none of which apply in my case.
 
Last edited:
steve yates said:
Wrong terminology, I knew there would be two terminals, presumed one was for a -ve feed, hence called it a -ve terminal.
Click to expand...

Steve, you've done some impressive sailing and are obviously a sharp guy. I refuse to believe that you're stupid enough to connect one side of a simple switch to the positive pole of a battery and the other side of the switch to the negative pole. Dropping a spanner across the terminals is bad enough, but at least that's generally only there for a moment, not firmly bolted into place.

This is a wind-up, isn't it.

Pete
 
steve yates said:
Wrong terminology, I knew there would be two terminals, presumed one was for a -ve feed, hence called it a -ve terminal.

Regardless, for a simpleton, can someone enlighten me as to what does connect to the second terminal of the isolator switch? Something obviously does, otherwise there is no circuit.

Every wiring diagram I can find online has feeds coming from engines etc, none of which apply in my case.
Click to expand...

A switch, when switched off, breaks the flow of current. When switched on it completes the circuit, allowing the positive electrons to flow to the positive terminal of the "load" e.g. your VHF or plotter. The wire attached to the -ve terminal of the item allows the electrons to continue their journey back to the -ve terminal of the battery. The isolator switch, therefore has both terminals connected to the +ve wire, one in, one out allowing the switch to make or break the circuit.
In the wiring diagrams you refer to, the power will be depicted as coming from the alternator on the engine, but in your case you need to imagine just the battery providing the power.
Looking at the list of equipment you intend to run from your 85Ah battery I think you may need to calculate the total load, compare that to the attainable recharging effort from your solar panel and think again about the size or quantity of batteries required. Someone will undoubtedly be along shortly to explain Ohm's Law etc and how you can make these calculations.
 
Nope, no wind up. I've already said I don't get it in answer to lw35, and he has already told me not to connect the -be battery cable to the switch. I'm getting the message that it's a very bad idea.

I posted to find out if what I had in mind would work, and see if any of it was wrong. I asked about the switch connection specifically because I realised I didn't really know what came back to the second terminal ( my -Ve one )
I keep getting told don't connect the -ve battery terminal to this. Ok, I hear you. ( and your example of the spanner was perfect imagery too help me grasp why :) )
But I really really want to know what I should connect to the other terminal of the isolator.
I'd also like to know if the rest of my post works or if there are any other major screw ups in there?
 
Last edited:
Spirit (of Glenans) said:
A switch, when switched off, breaks the flow of current. When switched on it completes the circuit, allowing the positive electrons to flow to the positive terminal of the "load" e.g. your VHF or plotter. The wire attached to the -ve terminal of the item allows the electrons to continue their journey back to the -ve terminal of the battery. The isolator switch, therefore has both terminals connected to the +ve wire, one in, one out allowing the switch to make or break the circuit.
In the wiring diagrams you refer to, the power will be depicted as coming from the alternator on the engine, but in your case you need to imagine just the battery providing the power.
Looking at the list of equipment you intend to run from your 85Ah battery I think you may need to calculate the total load, compare that to the attainable recharging effort from your solar panel and think again about the size or quantity of batteries required. Someone will undoubtedly be along shortly to explain Ohm's Law etc and how you can make these calculations.
Click to expand...

THANK YOU!
So I should connect both terminals of the switch with red battery cable to the positive battery terminal? (Not run red cable from the 2nd switch terminal to the switching box?)

I actually know ohms law and how to work out my power requirements, and I will do that once I figure out the power rating of all the items. I'm saying 20 v panel ad I have one in the garage, but I may well increase it if I find I need to.
( tho if anyone already knows the current draw of my items, feel free to tell me :) )
 
It's a switch. It goes between the battery positive terminal and the load. You'll also need a fuse as close to the battery as possible. You might find that drawing a circuit diagram would help clarify your thinking about how stuff is connected.
 
Actually, your first post was OK. There was just some later confusion about the switch and the negative.

1.5mm cable will be fine for those devices, perhaps 1mm would do for some.

As to power draw, it will obviously be variable depending on whether you have chart plotter on all the time, how hard the autohelm is working etc. Maybe 1-4 Amps at any time with a potential max of 8A with everything on, so work on 4A average for comfort. But could be just depth and VHF on a day sail using <1A. In good condition, the 85Ah battery will give you around 10-15 hours running (assuming 50% max discharge but you'd want to be getting it on charge pronto).

You might get 10-12Ah from from the solar panel on a good day. Whether that and shore power will be enough depends on your pattern of use. Assuming day sails around a home shore power berth, you'll likely be fine. If you're on a mooring then you'd want 2-3 days to recharge from panel.
 
This battery switch seems to be causing a lot of confusion! Connect the thick wire from battery + to one terminal on the switch. Connect the other terminal of the switch to the distribution panel for the various circuits. DONT whatever you do connect battery minus to the switch. It will go bang and set fire to your boat when you switch on!
 
oldharry said:
This battery switch seems to be causing a lot of confusion! Connect the thick wire from battery + to one terminal on the switch. Connect the other terminal of the switch to the distribution panel for the various circuits. DONT whatever you do connect battery minus to the switch. It will go bang and set fire to your boat when you switch on!
Click to expand...
Perfect, thank you!
 
steve yates said:
I run the +ve from the battery to the isolator switch (a simple red wing shaped item thats currently installed), and then from there run it to the fuse/switchbox.
I run the -ve battery cable from the battery to the negative busbar.
Click to expand...

That's correct Steve.

I then buy something like 1.5mm sq tinned twin core cable to connect the instruments & other loads. The +ve & -ve in the twin core connects to the instrument, and the cable is run back to the switch box where the +ve twin core attaches to the relevant switch/fuse and the -ve twin core attaches to the busbar.
Click to expand...

Generally speaking, twin core is more expensive and pretty bulky when several runs are used. It's normal to use mostly single core cable for a job like this. Obviously things like the mast light should be 2 core.

I assume I should have a -ve cable running from the battery -ve to the isolator switch also?
Click to expand...

There is no -VE connection to the isolator switch, you nailed it in the first paragraph above.
 
MikeCC said:
Actually, your first post was OK. There was just some later confusion about the switch and the negative.

1.5mm cable will be fine for those devices, perhaps 1mm would do for some.

As to power draw, it will obviously be variable depending on whether you have chart plotter on all the time, how hard the autohelm is working etc. Maybe 1-4 Amps at any time with a potential max of 8A with everything on, so work on 4A average for comfort. But could be just depth and VHF on a day sail using <1A. In good condition, the 85Ah battery will give you around 10-15 hours running (assuming 50% max discharge but you'd want to be getting it on charge pronto).

You might get 10-12Ah from from the solar panel on a good day. Whether that and shore power will be enough depends on your pattern of use. Assuming day sails around a home shore power berth, you'll likely be fine. If you're on a mooring then you'd want 2-3 days to recharge from panel.
Click to expand...

Thx, 1mm for depth, gps, compass, and USB chargers? All will have short cable runs. Tho might be as cheap to get 30 m of the 1.5mm, I have my longbow to rewire later once I have experimented on this.

I don't do day sails, just trips. I will want power for up to 3 days at a time before plugging into mains.

If I make a rough estimate of .5a p/hr each for gps, depth, vhf, and both USB charger slots On a typical trip these could run for 10 hrs, so 25amps. The chart plotter would be off, I use an iPad, it is just a back up.
The auto pilot might run for about half that time, at 2a? So another 10amps.

Then cabin lights for 4 hours, and USB points charging devices overnight and that's another 5 amps brings me to 40 amos in 24 hrs.

So to stay out for 3 days at this consumption I prob need to look at 80 watts, prob a 100 realistically?

I can of course manage my use significantly, I only ever used to have compass, gps and a USB charger. The iPad ran off a battery bank during the day and I used a handheld vhf, no plotter and no autohelm.
That would reduce my daytime use to 10a and the 5 at night gives me 15a.

My problem is space for a bigger panel on an 18ft boat. Anyway, use and supply can be worked out by trial and error.

First I need to wire it all up :)
 
You must log in or register to reply here.

Other threads that may be of interest

P
Adding fuses to my batteries
2 3 4
Replies
61
Views
2K
AngusMcDoon
AngusMcDoon

Share this page

Top