# What size Cable?



## Tallpaul (Jan 15, 2018)

I am fitting a new 12v fuse box and 100A split relay for charging leisure battery. Ripping out and updating the old faulty Nordelettronica NE13 12v distribution unit with integrated relays 40A split charge, with a 5 metre length of blue coloured 6mm2 cable running from starter battery to the unit. and then all the way back upto  the leisure battery in the engine compartment. On my 1997 Fiat Ducato AutoRoller Motorhome, I'm sure when they built it 21 years ago this cable and relays etc were adequate for what motorhomes had fitted inside but with modern technology, more things to charge, more things to have as standard in your motorhome, they are not.

I have already re positioned the leisure battery from underneath the front cross member, to the left of the radiator, where it was getting wet and covered in road crud all the time, not to mention been outside when the temperature drops affecting it's performance. To underneath my dining area seating, it is fastened down securely and properly vented. I have recently purchased a 140A M-Power volt sensing relay by Merlin as part of a complete kit off ebay. But been advised not to use this type of relay as they come with there own problems. Now thinking of fitting a standard type of split charge relay (100A) using my 12v ignition fed switch cable as the trigger. 

Just not sure what size cable to use instead of the old 6mm2 blue cable present. Go for 16mm2 110A rated or just 10mm2 70A rated. A lot of people install these large 16mm2 heavy duty cable from starter battery to leisure battery but it's my understanding that the alternator only really pushes around 20-30A to leisure battery for charging. Obviously there is a much larger current on initial start up, but does this warrant the need for such large cables?

I have both sizes of cables and reading all the mixed advise with regards with what size cable to use, I'm a little confused. My original plan was to run a 5 metre length of 16mm2 cable from starter battery with 100A fuse fitted close as possible to starter battery, to leisure battery via the 140A  M-Power volt sensing relay with another 100A fuse before it. Along with a 16mm2 earth cable from negative to Earth on chassis (no more than 500mm) from leisure battery.

I planned to then run a 10mm2 70A tri rated cable from leisure battery to my new 12v fuse box via a 60A fuse and master isolation switch. Does this sound all about right?

Please any comments, ideas and advice are very welcome and appreciated. 
Paul


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## oppy (Jan 15, 2018)

I'll probably be shot down in flames for this, but-----------------------I have used standard 13a cable for all the connections within the 'van on the premise, that if it works in the house, it's bound to work in the 'van. The lovely Channa concurs with this as it was his advice.


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## colinm (Jan 15, 2018)

Well I've got my popcorn, unfortunately I'm still not allowed alcohol for another 4 weeks, but don't let that stop the fun.


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## Fazerloz (Jan 15, 2018)

oppy said:


> I'll probably be shot down in flames for this, but-----------------------I have used standard 13a cable for all the connections within the 'van on the premise, that if it works in the house, it's bound to work in the 'van. The lovely Channa concurs with this as it was his advice.



 Gives the advise then blames Channa  :lol-049::lol-049: :lol-049: I can't fault you.   Just kidding oppy.  :cheers:


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## Admin (Jan 15, 2018)

Tallpaul said:


> I am fitting a new 12v fuse box and 100A split relay for charging leisure battery. Ripping out and updating the old faulty Nordelettronica NE13 12v distribution unit with integrated relays 40A split charge, with a 5 metre length of blue coloured 6mm2 cable running from starter battery to the unit. and then all the way back upto  the leisure battery in the engine compartment. On my 1997 Fiat Ducato AutoRoller Motorhome, I'm sure when they built it 21 years ago this cable and relays etc were adequate for what motorhomes had fitted inside but with modern technology, more things to charge, more things to have as standard in your motorhome, they are not.
> 
> I have already re positioned the leisure battery from underneath the front cross member, to the left of the radiator, where it was getting wet and covered in road crud all the time, not to mention been outside when the temperature drops affecting it's performance. To underneath my dining area seating, it is fastened down securely and properly vented. I have recently purchased a 140A M-Power volt sensing relay by Merlin as part of a complete kit off ebay. But been advised not to use this type of relay as they come with there own problems. Now thinking of fitting a standard type of split charge relay (100A) using my 12v ignition fed switch cable as the trigger.
> 
> ...


Use 16mm, make sure that you fuse the cable at both batteries. Thicker cable gives a lower voltage drop. Lower voltage drop means a higher voltage at the habitation battery. Higher voltage means more energy stored in the battery. The lights stay on a little bit longer


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## oppy (Jan 15, 2018)

Fazerloz said:


> Gives the advise then blames Channa  :lol-049::lol-049: :lol-049: I can't fault you.   Just kidding oppy.  :cheers:



Y'know, I've just realised why I hate you!!!!!!!!:lol-049::lol-049::lol-049::lol-049::lol-049::lol-049:


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## trevskoda (Jan 15, 2018)

oppy said:


> I'll probably be shot down in flames for this, but-----------------------I have used standard 13a cable for all the connections within the 'van on the premise, that if it works in the house, it's bound to work in the 'van. The lovely Channa concurs with this as it was his advice.



No ,house cable works at high voltage low amps so can be thin,vans work at low voltage but very high ampage so a very thick cable as in starter cable must be used.
For relays 200ah with big battery screw on terms rather than spades are best,on ebay £6.


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## stonedaddy (Jan 15, 2018)

As above, and also house cable is quiet rigid and tends to start breaking down after a while. Auto cable is very flexible and takes the traveling vibration a lot better.
.... Tom ....


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## frankrose (Jan 15, 2018)

*cable*



stonedaddy said:


> As above, and also house cable is quiet rigid and tends to start breaking down after a while. Auto cable is very flexible and takes the traveling vibration a lot better.
> .... Tom ....



If you a cable that is multi stranded  you get a much higher though current at lower voltage ( also applies to 240v) which also gives a flexsble insulation. I have used 6mm speaker cable from solars to regulator, reduces volt drop.


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## malagaoth (Jan 16, 2018)

> house cable works at high voltage low amps



Trev, firstly I dont think that this was a serious suggestion secondly the cable doesnt care what  the voltage is, 13A rated cable will carry 13A at any voltage.

IF (and only if ) you are using it to carry a 13A load - and at 12V that isnt a whole load of watts (150) then 13A household cable would be perfectly safe - because it is double insulated it will be physically bigger than auto cable and harder to get a neat job and you will be paying for three conductors (the expensive bits) when you only need two .




> Auto cable is very flexible



Tell that to Peugeot! the wiring loom on mine is largely made up of a couple of strands of very stiff quite brittle copper which seems to be extremely prone to corrosion


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## Tallpaul (Jan 16, 2018)

trevskoda said:


> No ,house cable works at high voltage low amps so can be thin,vans work at low voltage but very high ampage so a very thick cable as in starter cable must be used.
> For relays 200ah with big battery screw on terms rather than spades are best,on ebay £6.



Hi yes not stupid to use domestic cable in my motorhome, who ever owned it before me, had 2.5mm twin and earth domestic cable connected via an inline fuse to the electric step. One of the first things I done was to rip it out. 

Domestic cable with solid copper is fine in a domestic situation with no movement, but in a motorhome it is likely to break, that's why you use thinwall, tri rated cable.

Yes the relay you have shown is the one I have ordered off ebay with screw on terminals. And will be using 16mm2 cable with 100A fuses either end. 

Thanks for your advice.


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## Deleted user 48797 (Jan 16, 2018)

hairydog said:


> You are making changes without understanding the effects. The reason the cable to the aux battery was "too thin" was not the builder's cheapness. It was for a good reason.
> When the alternator cuts in and starts charging the starter battery, the SCR also connects the leisure battery.
> Quite often, the LB will be much more discharged than the starter battery.
> With a hefty cable joining them, a large current will flow from the starter battery to the LB. Probably not enough to damage the starter battery, but very likely to be far too much for the LB.
> ...



Not sure of the theory behind your suggestion here. I've never known an installation where current flow is controlled by the cable size. While voltage is present current flow is dependent on load, or demand, - no load = no current flow - the cable is blind to this until it's capacity is exceeded it then heats up and melts if a controlling fuse has not broken the circuit.  The fuse is there only to protect the cable.


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## Tallpaul (Jan 16, 2018)

hairydog said:


> You are making changes without understanding the effects. The reason the cable to the aux battery was "too thin" was not the builder's cheapness. It was for a good reason.
> When the alternator cuts in and starts charging the starter battery, the SCR also connects the leisure battery.
> Quite often, the LB will be much more discharged than the starter battery.
> With a hefty cable joining them, a large current will flow from the starter battery to the LB. Probably not enough to damage the starter battery, but very likely to be far too much for the LB.
> ...



Why I appreciate your comment and advice, I do not agree with you I'm afraid. Firstly the route that I explained in the original post from Starter battery with 4mm cable with a not a 20 or 30A fuse fitted but rather a 50A strip link type fuse in engine bay. This cable ran a distance of 5m to the middle of my motorhome where it was fed to my original 12v distribution power unit. To the split charge relay, then via a 15A fuse, before making it's way another 5m back to engine bay to LB. Talk about voltage drop, that is some distance. 

I don't mean to sound rude but I'm not sure what your background is or expertise in this field, but in one of the other forums outandaboutllive - motorhome matters, I have had advice from Allan from aandncaravans, who actually repair all makes of motorhome 12v distribution units and 12v electrics and he informed me that the majority of faults and melted connectors on the 12v units are down to people not using the correct size cable. And at no point did I say it was down to the builders cheapness, but most likely due to my motorhome been 21 years old,back then all motorhome had were lights, pump, heaters. There were no tv on board, no laptops or smart phones to be charged. So a small leisure battery was adequate and the cable that was originally installed was probably efficient enough. But with modern times motorhome users require more and more power, solar panels, dual LB's, inverters etc. And so the old cable needs to be uprated, along with the 12v units usually. 

The more modern units by Sargent, CBE and Nordelettronica are built to accompany more adequate cable, replacing the old plastic connectors with spade terminals for stud like terminals where you can crimp a heavy duty copper ring lug on to cable and then bolt it down inside the unit there are 3 of these studs, one for starter +, one for LB + and Earth.


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## harrow (Jan 16, 2018)

Bigusdickus said:


> Not sure of the theory behind your suggestion here. I've never known an installation where current flow is controlled by the cable size. While voltage is present current flow is dependent on load, or demand, - no load = no current flow - the cable is blind to this until it's capacity is exceeded it then heats up and melts if a controlling fuse has not broken the circuit.  The fuse is there only to protect the cable.


Keeping it simple.

A higher voltage will flow towards a lower voltage. Fact.

If the engine is running and the alternator is charging then the voltage could be say 14.5 volts.

If the leisure battery is part discharged then the voltage could be 12 volts.

When the leisure battery charge commences, in this example relay contact closing then the only thing that limits the current is the physical link,

being the relay contacts, the cable and the connectors,

in theory the amount of current flowing is infinite...

until the leisure battery voltage rises and the flow of current reduces. 

:bow::bow::bow:


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## trevskoda (Jan 16, 2018)

malagaoth said:


> Trev, firstly I dont think that this was a serious suggestion secondly the cable doesnt care what  the voltage is, 13A rated cable will carry 13A at any voltage.
> 
> IF (and only if ) you are using it to carry a 13A load - and at 12V that isnt a whole load of watts (150) then 13A household cable would be perfectly safe - because it is double insulated it will be physically bigger than auto cable and harder to get a neat job and you will be paying for three conductors (the expensive bits) when you only need two .
> 
> ...



Almost correct,do remember that when the relay opens there is a fair chance of 20/50 amps being drawn down it,thine cable will overheat hence best to use starter cable every time,my bus came from factory cabled this way from a split diode unit rather than a relay.


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## Deleted user 48797 (Jan 16, 2018)

harrow said:


> Keeping it simple.
> 
> A higher voltage will flow towards a lower voltage. Fact.
> 
> ...



I agree with your comment about voltage - fact. 
I don't agree that a cable, relay or connectors will limit current unless incorrectly installed. Excess current will manifest itself as heat and that is dangerous in any installation.

Edit. Advising anyone to limit current flow using thin cables is reckless, cable size is dependent on load only.


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## trevskoda (Jan 16, 2018)

hairydog said:


> You are making changes without understanding the effects. The reason the cable to the aux battery was "too thin" was not the builder's cheapness. It was for a good reason.
> When the alternator cuts in and starts charging the starter battery, the SCR also connects the leisure battery.
> Quite often, the LB will be much more discharged than the starter battery.
> With a hefty cable joining them, a large current will flow from the starter battery to the LB. Probably not enough to damage the starter battery, but very likely to be far too much for the LB.
> ...



Get a grip,if you use thin wire to restrict current it will glow like a firefly at night,i have just before xmas rewired a van because of this,and beleave me just about all was burnt or melted from relay to hab battery.
The thinking from makers is batterys will always be full and on hook up at a site so the alt will almost never have to shunt so much current,but we wilders know better as are batterys some time get half discharged.


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## Deleted user 48797 (Jan 16, 2018)

hairydog said:


> Sorry, you are simply wrong.



Ok, try limiting current flow to a 3kw heater using bell wire and see what happens....
Your principles are deeply flawed and your advice should be retracted.


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## trevskoda (Jan 16, 2018)

hairydog said:


> Sorry, you are simply wrong.



That is your opinion but most of us here disagree ,then we all could be incorrect and you right,im over 45 years working on autos and never heard of cable being used as a current choke.:scared:
Try putting your hand on a old wire wound resister ,it may burn or be quite hot,hence most were mounted on a heat dissapation pad and sheilded.


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## hextal (Jan 16, 2018)

When I wired my van up I back worked everything from the maximum loads specified (or likely) at each bit of kit, put a fuse in just above that rating then used wire that was usually rated at about 4X that, cos it didn't cost that much more to do.

Not saying that's how to do it, just that that was what I did.

All multi-core. 

I'd imagine that, all other things aside, road vibration and 'bounce' would make any kind of screw connections loosen/fatigue faster if single core. Plus I reckon it's easier to get a good crimp connection on a multi-core.


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## trevskoda (Jan 16, 2018)

hairydog said:


> I hadn't realised that it was a referendum. The trouble is that physics doesn't work that way.
> 
> The fact is that I know about these things, and clearly many people (seemingly including you) only have a sketchy understanding.
> If you don't think they use thin wire to limit the current, what do you think is limiting it? After all, the fuse is only 20a or 30a and it doesn't blow, so something is limiting it.
> ...


That is what a wire wound resistor is and on a heatsink,not a open wire running round a van,and yes i know some makers did this but it can start a fire,i always remove and fit thick cable,thats the way my van was fitted to from new and the italians invented elictrickery.


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## Mul (Jan 16, 2018)

Crikes, this is turning into a proper old fashioned Wints.... style thead. Anyone else missing the old Bugger, he'd have a thousand authoritative opinions on this. Sorry,  nothing to add, just reminiscing about the good (is there summit wrong with me ????!????) ol' days. I'll get my coat.

Chrz Mul


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## Deleted user 48797 (Jan 16, 2018)

hairydog said:


> Sorry, I can't help you if you really won't try to understand. What you describe is not relevant.



What I am trying to tell you are known electrical principles not assumption, hearsay or guesswork. This is derived from a lifetime as an electrician working on domestic, commercial and industrial installations culminating in the post of maintenance supervisor during 18 years at a major oil storage terminal - I think I know what I'm talking about. With this in mind I would never do what you are suggesting, to limit current flow using small cables, nor would I advise anyone else to do it either, however you may do as you wish.


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## colinm (Jan 16, 2018)

Mul said:


> Crikes, this is turning into a proper old fashioned Wints.... style thead. Anyone else missing the old Bugger, he'd have a thousand authoritative opinions on this. Sorry,  nothing to add, just reminiscing about the good (is there summit wrong with me ????!????) ol' days. I'll get my coat.
> 
> Chrz Mul



See post 3, didn't ya just know this was going to be an entertaining thread.


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## Deleted user 48797 (Jan 16, 2018)

Mul said:


> Crikes, this is turning into a proper old fashioned Wints.... style thead. Anyone else missing the old Bugger, he'd have a thousand authoritative opinions on this. Sorry,  nothing to add, just reminiscing about the good (is there summit wrong with me ????!????) ol' days. I'll get my coat.
> 
> Chrz Mul



Sorry it wasn't meant to be like that. However, when incorrect advice is posted the outcome could be dangerous.


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## maingate (Jan 17, 2018)

Without a definitive declaration from our former French based colleague we will never know the answer.


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## wildebus (Jan 17, 2018)

maingate said:


> Without a definitive declaration from our former French based colleague we will never know the answer.


Or instead of The David, we could tweet The Donald. He will know which tremendous cable to use


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## st3v3 (Jan 17, 2018)

I think Hairydog is right. I'd never do it, would never advise it and would replace it if it were mine but a thin cable will limit current in this situation and be safe* if fused correctly.

If the leisure batt is part discharged connecting it to the main batt will result in current flowing through the wire, because there is a voltage difference between the two.

When current flows through a wire, as it's effectively a resistor, it will have a voltage drop from one end to the other.

Now that the voltage at the leisure batt is lower, not so much current will flow.

Wire sizes have published voltage drops per metre, so this can be calculated to cover the expected maximum difference between the two ends and make sure the current never exceeds the limits for the cable.

* The problem comes when lots of items in the van are turned on, presenting more of a load than just the battery, therefore more current could be drawn though the wire. In this situation the fuse comes in to play, and breaks the circuit. Annoying, but not necessarily dangerous - AS LONG AS it's all been calculated correctly. That's why the sledgehammer to crack a walnut approach sits better with me.


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## Admin (Jan 17, 2018)

A 3 metre length of 4mm2 cable has a resistance of 0.013 ohms.
Let us assume that we have a charging battery at 13.8v and a discharged battery at 10.8v. This gives us a potential difference of 3v.

Ohms law.

I = v/r

Amps = voltage / resistance

Amps = 3 /0.013

Answer 230 amps

*So the cable will limit the current to 230 amps on a cable rated at about 25 amps.*

If you increase the voltage drop then you increase the amps.


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## maingate (Jan 17, 2018)

From the opening post, there only appears to be a single Leisure battery. If we assume that it is a 100 Ah battery then the accepted maximum charge rate (in Amps) of 10% of the battery Ah rating is 10 Amps. Anything over this by a substantial amount will shorten the battery life if consistently discharged to a low level.

I think that what the OP wants is unrealistic.

Whatever he ends up with, I think his fuse rating is critical. Suppose his battery fails and demands a huge output from the alternator. It happens.


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## Admin (Jan 17, 2018)

hairydog said:


> Three metres seems unrealistically short. I'd assume more like double that, by the time the wire has run to the control unit  and back. And then there is the resistance of the negative return. You also have to allow for the internal resistance of the batteries, which is about 50 milliohms each, I think.



Ok,

I will recalculate, but I would like to point out that the additional variables that you have suggested will be the same for 4mm2 and 16mm2 cable which is why I omitted them.

A 6 metre length of 4mm2 cable has a resistance of 0.013 ohms.
Each battery has an internal resistance of 0.05 ohms (0.1 ohms total)
The earth straps are:
1 metre of 16mm2 at the starter battery  0.001 ohms
1metre of 10mm2 at the hab battery 0.002 ohms

Total circuit resistance of 0.116 ohms


Let us assume that we have a charging battery at 14.0v and a discharged battery at 11.0v. This gives us a potential difference of 3v.

Ohms law.

I = v/r

Amps = voltage / resistance

Amps = 3 /0.116

*Answer 25.8 amps*
*

Now let us  do the same with 16mm2 cable


*A 6 metre length of 16mm2 cable has a resistance of 0.006 ohms.
Each battery has an internal resistance of 0.05 ohms (0.1 ohms total)
The earth straps are:
1 metre of 16mm2 at the starter battery  0.001 ohms
1metre of 10mm2 at the hab battery 0.002 ohms

Total circuit resistance of 0.109 ohms


Let us assume that we have a charging battery at 14.0v and a discharged battery at 11.0v. This gives us a potential difference of 3v.

Ohms law.

I = v/r

Amps = voltage / resistance

Amps = 3 /0.109

Answer 27.09 amps*

-----------*
But the voltage drop is different.

On the 4mm2 cable it approx 0.50v
On the 16mm2 cable it approx 0.12v

So with the 4mm2 cable, the charge voltage at the hab battery is reduced to 13.5v or less.


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## trevskoda (Jan 17, 2018)

Phil knows his stuff.:bow::wave:


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## st3v3 (Jan 17, 2018)

Admin said:


> .....4mm2 cable .....Answer 25.8 amps
> 
> 
> ...... 16mm2 cable..... Answer 27.09 amps



So, the thinner cable is reducing the current.

Caravans have been using 1.5mm, maybe even 1.0mm for ever on the split charge wiring from the towing socket, and it's because of this volt drop/battery pulls less current that the wiring isn't catching fire all of the time. It's a sh1t charging system of course, because of the low voltage presented to the LB.


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## Admin (Jan 17, 2018)

hairydog said:


> You've got it wrong (or I'm misreading you). The voltage drop will be more or less the same whatever thickness of cable. What will vary is the current that causes that voltage drop.
> The batteries internal resistance makes a bigger difference if you use thick wire. It needs to be in the calculations. I



Just saying to everyone that they are wrong and you are right is not helpful. 
Please provide proof as to why this is wrong.


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## Admin (Jan 17, 2018)

st3v3 said:


> So, the thinner cable is reducing the current.
> 
> Caravans have been using 1.5mm, maybe even 1.0mm for ever on the split charge wiring from the towing socket, and it's because of this volt drop/battery pulls less current that the wiring isn't catching fire all of the time. It's a sh1t charging system of course, because of the low voltage presented to the LB.



Yes Steve, the difference between 4mm2 and 16mm2 is 1.29 amps. So the cable size has little effect on the current in the circuit.


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## iampatman (Jan 17, 2018)

Wow! I’m learning so much from this thread; which is what it’s all about eh? 

Pat


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## Deleted member 58274 (Jan 17, 2018)

*What to use*

....by eck...I hope that all the posters here arrive at a compromise !!! The 6m length is what I will be needing....so, when you folks sort it out I want a set up that doesn't toast my standard boxer alternator...doesn't blow my fridge up....and charges the LB's.....along with solar.....but then it's not just that simple is it lol .  Not doing off-grid set up till March so much to learn yet !!! Maja07


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## Tallpaul (Jan 17, 2018)

hairydog said:


> Admin's calculatons are getting to look right, but they're based on a misapprehension.
> 
> When you are doing the calculation, there are not two things to consider, but three.
> 
> ...



That is what fuses are for are they not? I have installed a 50A strip link type fuse on either end. One just after the starter battery and one just before the Leisure battery. I only have one Leisure battery which is 88Ah but as I'm not sure how old it is, I will be updating it to either one or two new batteries with a higher capacity.


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## Tallpaul (Jan 17, 2018)

Tallpaul said:


> I am fitting a new 12v fuse box and 100A split relay for charging leisure battery. Ripping out and updating the old faulty Nordelettronica NE13 12v distribution unit with integrated relays 40A split charge, with a 5 metre length of blue coloured 6mm2 cable running from starter battery to the unit. and then all the way back upto  the leisure battery in the engine compartment. On my 1997 Fiat Ducato AutoRoller Motorhome, I'm sure when they built it 21 years ago this cable and relays etc were adequate for what motorhomes had fitted inside but with modern technology, more things to charge, more things to have as standard in your motorhome, they are not.
> 
> I have already re positioned the leisure battery from underneath the front cross member, to the left of the radiator, where it was getting wet and covered in road crud all the time, not to mention been outside when the temperature drops affecting it's performance. To underneath my dining area seating, it is fastened down securely and properly vented. I have recently purchased a 140A M-Power volt sensing relay by Merlin as part of a complete kit off ebay. But been advised not to use this type of relay as they come with there own problems. Now thinking of fitting a standard type of split charge relay (100A) using my 12v ignition fed switch cable as the trigger.
> 
> ...



I never knew when I started this post that it would be so controversial, If you read my post above I did say that I wasn't sure which cable to use as there are so many people who claim to be experts who are offering mixed advice and opinions. And after reading all these replies I am no more informed and just as confused then why I first written it. The kit I bought off ebay came supplied with 16mm2 110A rated cable, already made up. 

6mtr Split Charge Kit 12V 140a M-Power Intelligent VSR 110a Ready Made Leads  | eBay

Is states that this kit is suitable for charging Leisure batteries from 85A to 220A. 

I also received lots of advice from Allan from aandncaravans, who are based in conwy who repair motorhome, caravans and camper electrics and 12v power distribution units. 
How to Wire your Camper Conversion the Professional way and save money




Here are a few pictures of my 21 year old motorhome not long after I bought it, and what I was faced with regarding the wiring.


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## Tallpaul (Jan 17, 2018)

hairydog said:


> Those pictures look like the result of somone replacing the thin wires with fatter ones, just as I am advising against.
> 
> Note that in picture 1, the label says the battery lead fuse should be 15A. The unit and its connectors are not designed for fat wires carrying high currents.



You are obviously not listening to anyone else on here, you have a thing in your head and bending stories to fit your ideology, quite sad really. Very narrow minded. 

The above pictures were a result of nothing been added (fatter cables) like your suggesting, the blue cable in the photo's is the original factory fitted one by Autoroller 21 years ago, you can tell this one by the colour, two by the size and three by when I removed it today it was very badly corroded in places, crumbling exterior sleeve exposing the copper wire which as a result suffered oxidization. This wasn't visible as it was in a plastic outer conduit.  And as I said the cable route was very indirect route. Cable run from starter battery to unit in the middle of my motorhome 6m away, then through the unit via the SCR and like you say 15A fuse before making it's way back 6m to engine bay to charge Leisure Battery. 

You are implying that that this faults were caused by someone adding wrong size cables, these were taken well before I was even considering fitting the new kit with 16mm2 cable. 

You are wrong


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## Admin (Jan 17, 2018)

hairydog said:


> I'm sorry. I was wrong. Admin's resistance figures were not correct.
> 
> I should have checked, but they did look about right, so I took them on trust.
> 
> ...



Your right, my data was wrong. I used an online calculator for the data and it appears to be wrong.

ePanorama.net | Audio | Video | Circuits | Electronics Design

I will get some cable data sheets from manufacturers tomorrow to get some real world figures. I will then recalculate.


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## trevskoda (Jan 17, 2018)

hairydog said:


> Oh and for the people suggesting that the wires will glow, the heat dissipated per metre for the three wire sizes are:
> 1.5mm wire: 3 x 0.09 x 32.09 / 6 = 1.445 watts per metre
> 4mm wire: 3 x 0.03375 x 80.54 / 6 = 1.359 watts per metre
> 16mm wire: 3 x 0.0084375 x 251.26 / 6 = 1.06 watts per metre



I am the those person and the last van i rewired did burn the cable slightly,when charging from either mains or alt heat was quite warm to the hand,and yes the end connections were clean.
I replaced with starter battery cable and 200ah relay,the voltage at cab display unit went up from around 12.7-13.2 to a healthy 13.7-14.2 and also brought the 100ah les battery up to a good charge much faster without gassing.
My van is wired as so from new using a big 3 way split diode divider,one take of for les battery and one for rear lift,this is factory iveco iris bus setup.


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## trevskoda (Jan 17, 2018)

Tallpaul said:


> I never knew when I started this post that it would be so controversial, If you read my post above I did say that I wasn't sure which cable to use as there are so many people who claim to be experts who are offering mixed advice and opinions. And after reading all these replies I am no more informed and just as confused then why I first written it. The kit I bought off ebay came supplied with 16mm2 110A rated cable, already made up.
> 
> 6mtr Split Charge Kit 12V 140a M-Power Intelligent VSR 110a Ready Made Leads  | eBay
> 
> ...



Thanks for links,crap wiring looks burnt as the van i rewired.


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## Tallpaul (Jan 17, 2018)

Here is a useful link to 12v planet and information regarding cable sizing and voltage drop calculator.


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## trevskoda (Jan 17, 2018)

Tallpaul said:


> Here is a useful link to 12v planet and information regarding cable sizing and voltage drop calculator.



No link posted.:rolleyes2:and im the wildest person on the planet:scared:


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## Tallpaul (Jan 17, 2018)

trevskoda said:


> No link posted.:rolleyes2:and im the wildest person on the planet:scared:




Oh yes, sorry forgot to add it, here you go

Cable sizing and selection | 12 volt planet


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## Admin (Jan 20, 2018)

hairydog said:


> Did you get anywhere with this? It would be interesting to know what resistance values cable specsheets give.




No sorry, I haven't had time, I am at Stonehenge at the moment with some members. I will try and get back into this when I return.


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## Fletch6 (Jan 20, 2018)

hairydog said:


> And as others have said, use multicore flex, not single core cable. It has nothing to do with voltage: it's because of vibration.



Also electrons only travel along the outer edge of the copper so many strands will have a bigger area and higher current carrying capacity.


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## jagmanx (Jan 20, 2018)

*Given the no of replies*

I think it is now safe to say

Ask VINCE !


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## Fletch6 (Jan 20, 2018)

hairydog said:


> What you say is simply not correct. Utter and complete piffle.



Oh. It's just something I read. Just shows what nonsense is peddled on forums 


Edit: Reading more again, It's the skin effect and only applicable to high frequency AC... I'll get me coat.


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## st3v3 (Jan 20, 2018)

hairydog said:


> What you say is simply not correct. Utter and complete piffle.



Do you mean for DC conductors or always?


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## st3v3 (Jan 20, 2018)

Fletch6 said:


> Oh. It's just something I read. Just shows what nonsense is peddled on forums
> 
> 
> Edit: Reading more again, It's the skin effect and only applicable to high frequency AC... I'll get me coat.



It's applicable to any ac cable, but the effect increases with frequency.


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## harrow (Jan 21, 2018)

The real deciding factor is,

what you can steal from work or,

what you can find at the boot sale !

:hammer:


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## dozukime (Aug 2, 2018)

*M system probs*

Hi can you tell me as to what problems you have heard about the "M" split charge relay set up, i was just going to order one.


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