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Discussion Starter #1
Hi all.
I am shortly going to be putting my cabinets into my van. The question of what size of power cable to run between my split charge diode & the leisure battery has popped into my head. The battery will be placed somewhere around the drivers side rear wheel arch & the diode will be placed in the engine bay, near the starter battery. I think that the total cable run will be about 5m & include one of those quick disconnect pull switches you see on racing cars. I have found a websupplier battery cable that does different cables & I am not sure which size to buy.
The starter battery is a 70ah & the leisure battery is a 113ah.
Can anybody help?
 

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Discussion Starter #3
The diode pack I have just bought is a Sterling split charge diode 130A from midland chandlers It is a 1 in 2 out jobbie & should be good enough. One thing I have forgotten is the fuse. Any Idea of capacity?
 

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I dont exactly know how a diode differs from a relay, but would assume you should really be looking at 130A cable, but that said i dont know what the alternator output on a T4 is? and your battery will not be capable of drawing more that 113 Amps even if its totally flat.
The last time I installed a split relay although I used a 100Amp relay, I used 80Amp cable with a 60Amp fuse on the basis that the system was not likely to draw more that 60 amps for long, and if it did it would only blow a fuse.
 

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Discussion Starter #6
I dont exactly know how a diode differs from a relay, but would assume you should really be looking at 130A cable, but that said i dont know what the alternator output on a T4 is? and your battery will not be capable of drawing more that 113 Amps even if its totally flat.
The last time I installed a split relay although I used a 100Amp relay, I used 80Amp cable with a 60Amp fuse on the basis that the system was not likely to draw more that 60 amps for long, and if it did it would only blow a fuse.
According to my brooklands (lightweight) manual, the T4 was fitted with 60, 90 or 120 amp alternator.
It also says about 5 different batteries were fitted, up to about 60ah. My battery is 70ah, so I am confused about the battery/alternator combination on my van.
Can anybody tell me how to verify what the output is on my alternator, without taking it out?
Still no idea about the size of fuse for the leisure battery. Also, where to get a large fuse (& holder that can be clamped to the 130a wiring) from?
:confused::confused::confused::confused:
 

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130Amp wire is going to be massively thick - the 80 Amp wire I used is 10mm2 and is about on the limit of a 'midi' fuse holder. Also you may need to get hold of heavy duty cable crimps and crimping pliers.
Vehicle wiring supplies sell everything you need, but if you need to start getting hold of crimping pliers etc it gets a bit expensive.
 

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If you want to use the pliers for a couple of cables go to a CEF city electrical factors or the like and ask if you can borrow theirs to the cables.
 

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Vehicle wiring products will crimp the terminals and heatshrink them for you if you ask, you'll just need to know how long you want the cable. Where are you intending to put your leisure battery?

The Mega Fuse holder fuses they do except 8mm terminals and the fuses start at 100amp. You could go for for something like 25mm2 cable (170amp) to reduce your voltage drop as you'll already be getting a drop over your diode pack.
 

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130Amp wire is going to be massively thick - the 80 Amp wire I used is 10mm2 and is about on the limit of a 'midi' fuse holder. Also you may need to get hold of heavy duty cable crimps and crimping pliers.
Vehicle wiring supplies sell everything you need, but if you need to start getting hold of crimping pliers etc it gets a bit expensive.
they do hex screw fittings save on the crimping nightmares and makes for a better joint, unless you have a air crimper.
 

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also different suppliers will call the cable different names to add even more muddle into the sums, car audio folk call there cable 4awg which = 20mmsq and so on.
 

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hi mate, even if you have a 90amp alternator it won't actually kick out 90amps, so go with 10sqmm cable rated at around 70 amps should be fine, i work on electrical systems on boats and trust me this will be fine:)
 

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hi mate, even if you have a 90amp alternator it won't actually kick out 90amps, so go with 10sqmm cable rated at around 70 amps should be fine, i work on electrical systems on boats and trust me this will be fine:)
I agree - 10mm2 cable is pretty serious and shoud handle anything except for starting engines.
 

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Thanks all.
10mm2 cable it is.T:T:
I personally disagree, I think your going to be pretty disatisfied with your leisure battery charging if you use cable of only 10mm2.

The reason being is that the sterling diode blocks drop about 0.75 volts, the voltage drop in 10mm2 cable 5m long would be about 0.6 volts over 5m assuming your alternator kicks out only 70 amps. The drop would be even more if your alternator kicks out more. The regulator on the T4 is set at 14.4 volts if its the same as mine, but your only going to see about 13 volts at your leisure battery if your lucky.

To charge a lead acid battery properly you need a minimum of about 13.8 volts, 1 volt over the terminal voltage of a fully charged battery which is around 12.8 volts. Your battery would charge at 13 volts but very slowly.

To improve things your going to have to use thicker cable to reduce the voltage drop or fit and advanced regulator which senses the voltage at the battery terminal and compensates. Even using an advanced regulator sterling recommend 35mm2 cable if your cable run is 1.5 - 4 meters at an output of 45 - 85amps otherwise your just wasting energy heating up the cable.

So I think your going to have to look at least 25mm2 cable as a minimum as this would drop 0.25 volts at 70 amps, 40mm2 would be even better as this would only drop 0.15 volts. At least if you go for 40mm2 cable you would have the required cable if you do decide to fit an advanced regulator in the future.
 

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sorry but i think your overcomplicating this, firstly the voltage drop over 5mt would be 0.5volts, you are going to loose more using the sterling diode 0.75volts than the cable, if you want to overcome this easily then don't use the sterling use a vsr such as a victron cyrix (voltage sensitve relay, see www.victronenergy.com ) where there is virtually no voltage drop at all or use a mossfett based diode again with a lower voltage drop, automotive alternators are rated at their full rpm so are only giving out large amounts of amps if you are redlining it everywhere you go!, i wouldn't advise fitting a regulator as they are quite complicated and involve modifying the alternator but if you do go for something other than the sterling unit as they fry your batteries (merlin, balmar,driftgate)- my advice is keep it simple, if your worried about the cable size then step up to 16sqmm or try to reduce your cable run a little- keep it simple!:)
 

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Sorry davest4, I dont agree with you mate. Firstly just because you fit 6mm on a 90A alt doesnt make that right. I wouldnt give people advice like this because its not technically correct and could in some circumstances lead to fire. Alternators sometimes go into overdrive if the regulator packs up and they can kick out their rated current..........all dangerous situation with undersized cables.

VW use 25mm for the starting charging circuit on my van............so it only makes sense that others follow that. They also dont fuse this cable because its big enough to handle all the alt can throw at it. If you have a worry about volt drop then up the size simple.
 

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sorry but i think your overcomplicating this, firstly the voltage drop over 5mt would be 0.5volts, you are going to loose more using the sterling diode 0.75volts than the cable, if you want to overcome this easily then don't use the sterling use a vsr such as a victron cyrix (voltage sensitve relay, see www.victronenergy.com ) where there is virtually no voltage drop at all or use a mossfett based diode again with a lower voltage drop, automotive alternators are rated at their full rpm so are only giving out large amounts of amps if you are redlining it everywhere you go!, i wouldn't advise fitting a regulator as they are quite complicated and involve modifying the alternator but if you do go for something other than the sterling unit as they fry your batteries (merlin, balmar,driftgate)- my advice is keep it simple, if your worried about the cable size then step up to 16sqmm or try to reduce your cable run a little- keep it simple!:)

I don't think I was overcomplicating it, just backing up what I said.

With regard to the voltage drop over 5 metres of 10mm2 cable. My calculation was:

0.0017 * 5 = Resistance of 5 metres of 10mm2 cable
=0.0085 Ohms

0.0085 Ohms x 70 amps = volts
= 0.595volts

PS. I worked out the resistance of 1 metre of 10mm2 wire based on This Source According to them Copper has a resistivity of about 17 nano-ohms per metre.

You obviously round down when you say its 0.5 volts?
 
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