Voltage drop when split relay connected to 13.3 down from.14.4

[ched999uk]

So it looks like the wire coming out of the relay is on the third pin labelled pin6. This is supposed to be the one that feeds the fridge in a caravan. The one it should be connected to is the one next to the 0V pin! I doubt this will make a difference to be honest but it's quick to try.

Also there should not be any bare wire on show at the relay. The cables should be stripped back so that when inserted and tightened no bare wire is exposed (in case something falls on it, so it cant cause a short).

From the image it looks like your fuses are for your pumps as they are red ones that are 10 amps. There is another fuse but that has a cover on. What worries me a little is there are 2 fairly thick red cables that I guess power your reels but they don't appear to have any fuses in!!!

I know I am a bit paranoid about fuses but they are really critical as a battery can give out so much power to melt insulation and cause fires!! I almost lost a car due to an electrical issue a long time ago. My fault I had 'temporarily' installed some cable as I had 'transplanted' an engine and a wire shorted on exhaust, insulation started smoking and luckily smoke came through dash vents! It too a good few seconds before I realised what it was. Also lucky I had fire extinguisher!!! Part of wiring harness was well alight!!! Fire was put out and disaster averted but it was a wake up call.....  

Anyway back to volt drop. Swap the output to the terminal next to the 0V, trim the 0v wire so no insulation is exposed and see if that helps. 

The single earth wire, I assume from leisure Battery to chassis could be too small. It looks like you have wired your pumps and reels back to the 0V terminal of your battery? If that's the case then the leisure battery earth is OK as it's only passing the same current as relay is charging at. That said taking a power feed from under the dash to potentially supply 30 amps is not a good idea. I am surprised that a fuse hasn't blown, unless it's been tapped in before the fuse box!!! 

Your mate that is an Auto electrician? Sorry but if he doesn't know about relays (voltage sensing or otherwise) I 'm not sure what auto electrics he knows about? He should know that cables have to be correctly sized, fused and routed let alone how to fault find with a multimeter. If he is training then OK but if he is working on peoples cars what does he actually know how to do? Sorry if that's insulting to him but it's just a 12v system, nothing complex. He should be capable of following a 12v cable and measuring at appropriate points to work out where the fault is.

Anyway back to volt drop. Swap the output from relay (one that goes to leisure battery) to the terminal next to the 0V, trim the 0v wire so no insulation is exposed and see if that helps. 

 

[ched999uk]

There's one thing which I haven't done as it felt it was too simple and that was could my battery have a very low resistance and caused this voltage drop at all across the system?

It might sound a bit silly not sure but I might swap this battery with the other battery in the other van and see if I get the same 13.3 mind you the battery is about to be fully charged so I may be able to see.

Please let me know your thoughts on the earthing etc and I think what's spruce says is a good idea to rewire with appropriate size cables and the better relay.

Missed this bit. 

First thing the terminals for the wires in the relay seem way too small for 30 amp cables. All the little wires should be twisted and inserted so every strand goes in the terminal before it's tightened. Any stray strands are not good.

The batteries resistance wont change anything other than a batteries ability to give out current. Lower internal resistance means it can give out higher current. The internal resistance of battery isn't an issue.

Personally I would get someone who knows what they are doing to either supply and install a proper split charge system or buy one like this https://amzn.to/2VFdl4b with appropriate cable length and get someone with experience to install it.

One thing we didn't get to the bottom of is what sort of year the van is and if it's Euro 6 etc. The reason for asking is that some Euro6 vehicles have 'smart' alternators that need a completely different charging system! 

 

[Quickwindowclean]

I think at this stage it probably is a good idea to change the SCR for a Durite. I have two, one in the workvan that was professionally fitted at Hall's Electrical, Swindon (They do a lot of work on emergency vehicles so know their stuff), and one in my campervan that I fitted myself, after. Taking great care and checking and double checking as I went on. I got a 5 metre complete kit online. I worked from the leisure battery back to the starter battery and did a final check before I fitted the fuses and made it live.

Ps, if you go this route, make sure you get a kit that is suitable for your vehicle.

Thanks for the recommendation I'm in London so it's a bit far but I will definitely consider it if I can't get it sorted. I will also make sure I get the appropriate kit for my vehicle and make sure it can handle it.

So it looks like the wire coming out of the relay is on the third pin labelled pin6. This is supposed to be the one that feeds the fridge in a caravan. The one it should be connected to is the one next to the 0V pin! I doubt this will make a difference to be honest but it's quick to try.

Also there should not be any bare wire on show at the relay. The cables should be stripped back so that when inserted and tightened no bare wire is exposed (in case something falls on it, so it cant cause a short).

From the image it looks like your fuses are for your pumps as they are red ones that are 10 amps. There is another fuse but that has a cover on. What worries me a little is there are 2 fairly thick red cables that I guess power your reels but they don't appear to have any fuses in!!!

I know I am a bit paranoid about fuses but they are really critical as a battery can give out so much power to melt insulation and cause fires!! I almost lost a car due to an electrical issue a long time ago. My fault I had 'temporarily' installed some cable as I had 'transplanted' an engine and a wire shorted on exhaust, insulation started smoking and luckily smoke came through dash vents! It too a good few seconds before I realised what it was. Also lucky I had fire extinguisher!!! Part of wiring harness was well alight!!! Fire was put out and disaster averted but it was a wake up call.....  

Anyway back to volt drop. Swap the output to the terminal next to the 0V, trim the 0v wire so no insulation is exposed and see if that helps. 

The single earth wire, I assume from leisure Battery to chassis could be too small. It looks like you have wired your pumps and reels back to the 0V terminal of your battery? If that's the case then the leisure battery earth is OK as it's only passing the same current as relay is charging at. That said taking a power feed from under the dash to potentially supply 30 amps is not a good idea. I am surprised that a fuse hasn't blown, unless it's been tapped in before the fuse box!!! 

Your mate that is an Auto electrician? Sorry but if he doesn't know about relays (voltage sensing or otherwise) I 'm not sure what auto electrics he knows about? He should know that cables have to be correctly sized, fused and routed let alone how to fault find with a multimeter. If he is training then OK but if he is working on peoples cars what does he actually know how to do? Sorry if that's insulting to him but it's just a 12v system, nothing complex. He should be capable of following a 12v cable and measuring at appropriate points to work out where the fault is.

Anyway back to volt drop. Swap the output from relay (one that goes to leisure battery) to the terminal next to the 0V, trim the 0v wire so no insulation is exposed and see if that helps. 

Hi oh so it's wired incorrectly I'm guessing that will make a difference then? I couldn't quite understand which what goes where could you mark one of the pictures the last one I put in in I I took the picture from upside down so you can clearly see. By the way one of the wires the red one in the middle is very thick and it just about pinches a little bit of it so I connect a smaller cable you some masking tape and then put the smaller cable inside? Then I can do my best to make sure everything goes in.

The fuses near the terminals are for the reels I'm sure near the pumps there are additional fuses further from the battery.

So you're saying put the red cable that goes to the leisure battery one spot right after the black cable not where it is right?

Missed this bit. 

First thing the terminals for the wires in the relay seem way too small for 30 amp cables. All the little wires should be twisted and inserted so every strand goes in the terminal before it's tightened. Any stray strands are not good.

The batteries resistance wont change anything other than a batteries ability to give out current. Lower internal resistance means it can give out higher current. The internal resistance of battery isn't an issue.

Personally I would get someone who knows what they are doing to either supply and install a proper split charge system or buy one like this https://amzn.to/2VFdl4b with appropriate cable length and get someone with experience to install it.

One thing we didn't get to the bottom of is what sort of year the van is and if it's Euro 6 etc. The reason for asking is that some Euro6 vehicles have 'smart' alternators that need a completely different charging system! 

No its pre euro 6 I'm aware that it's a completely different system if you have a newer van.

So the red cable needs to go one to the right of the black cable that goes into the leisure battery let me try that and I agree with what you're saying if that doesn't work I will have to to look into getting this done properly

 

[Quickwindowclean]

@ched999uk just to confirm the leisure battery in should actually be be next to the earth the one numbered with 2!? Not the one where it is currently 6 3 from the live in.

It's worth a try to see bear in mind I briefly connected a different relay and I had the same voltage.

So where it is now what has it been doing exactly not charging the leisure battery?

It's worth putting it in properly and testing it over a longer period of time also I've just fully chance to leisure battery I think it charged about 16h perhaps it really was quite low and the split relay generally wasn't able to top it off?

 

[ched999uk]

just to confirm the leisure battery in should actually be be next to the earth the one numbered with 2!?

Yes labelled pin2 next to earth. 

Keep a close eye on battery as it may have lost capacity. 

Running 2 pumps and 2 reels will always be a big ask especially if you don't do many miles. 

Fingers crossed pin 2 works better. 

 

[spruce]

Yes labelled pin2 next to earth. 

Keep a close eye on battery as it may have lost capacity. 

Running 2 pumps and 2 reels will always be a big ask especially if you don't do many miles. 

Fingers crossed pin 2 works better. 

No. The black earth wire should be in OV, the end terminal.

https://puppyandfriend.blogspot.com/2020/06/wiring-diagram-for-self-switching-relay.html

wiring diagram toward the bottom of the page

 

[Quickwindowclean]

No. The black earth wire should be in OV, the end terminal.

https://puppyandfriend.blogspot.com/2020/06/wiring-diagram-for-self-switching-relay.html

wiring diagram toward the bottom of the page

Yes the Earth is currently there as per photograph but what ched is saying is move the Leisure battery cable from (6) to (2) both say switched power are they both the same thing I'll find out later.

 

[spruce]

Yes the Earth is currently there as per photograph but what ched is saying is move the Leisure battery cable from (6) to (2) both say switched power are they both the same thing I'll find out later.

Sorry. I miss understood that.

 

[Quickwindowclean]

I need to swap the battery over and change the cable connection the 12-volt company I called today also recommended this just to iron out the possibility of a damaged battery.

Today the power seemed pretty good after the long charge.

You going to swap the batteries out one of the day this week and I'll update this

 

[Quickwindowclean]

Some time ago I promised to update on this situation.

Well the truth is I became lazy I bought myself a new charger and I started to bench charge the battery every Saturday night

Although most people have said you will need to charge every night or 2nd with the current relay input about 13.3 volts and all the driving around there was enough power to charge every 6 days things were going well so I left this..

However I've just had a fuse go somewhere and the split relay is not charging even the lower 13.3 and it turns out I have to charge it after 2 days so I'm back on the case now to try to finalise this problem.

Looking at the other van it has the very thick battery style 16 mm cables the kind that goes onto your car battery.

Spoke to a shop that specialises in 12 volts and I told them that the other van is 14.2 across the board with the relay and he just basically told me to replicate that so thicker 16m cables from the battery into the relay and another 16m thick cable from the relay into the battery.

I also explained that 14.2 14.4 V from the battery with the thin cable but when the relay is connected as a 1 volt drop across the system. He said it might carry the volt he said but but something about the amperage as well and he's very strongly recommends need to replicate the other than with thicker cables

Common sense is telling me to do the same thing if I can replicate that van with thick cables surely that will resolve the problem however a drill will be required to drill through because there is an engine guard.

So it's a little bit of work how else if anyone can recommend can I do this drilling and what thickness cable do you use going into the relay and onto the auxiliary battery

Also which relay do you use because my relay only works for small cables?

Hope to hear from the usual electric people

Thanks!

 

[spruce]

Some time ago I promised to update on this situation.

Well the truth is I became lazy I bought myself a new charger and I started to bench charge the battery every Saturday night

Although most people have said you will need to charge every night or 2nd with the current relay input about 13.3 volts and all the driving around there was enough power to charge every 6 days things were going well so I left this..

However I've just had a fuse go somewhere and the split relay is not charging even the lower 13.3 and it turns out I have to charge it after 2 days so I'm back on the case now to try to finalise this problem.

Looking at the other van it has the very thick battery style 16 mm cables the kind that goes onto your car battery.

Spoke to a shop that specialises in 12 volts and I told them that the other van is 14.2 across the board with the relay and he just basically told me to replicate that so thicker 16m cables from the battery into the relay and another 16m thick cable from the relay into the battery.

I also explained that 14.2 14.4 V from the battery with the thin cable but when the relay is connected as a 1 volt drop across the system. He said it might carry the volt he said but but something about the amperage as well and he's very strongly recommends need to replicate the other than with thicker cables

Common sense is telling me to do the same thing if I can replicate that van with thick cables surely that will resolve the problem however a drill will be required to drill through because there is an engine guard.

So it's a little bit of work how else if anyone can recommend can I do this drilling and what thickness cable do you use going into the relay and onto the auxiliary battery

Also which relay do you use because my relay only works for small cables?

Hope to hear from the usual electric people

Thanks!

Run the cable from the van battery underneath the van and through a drilled hole in the floor close to where your battery is located. I usually use a cable grommet cut to size and squeezed in the drilled hole, so it seals the hole and tightly secures the cable.

On a couple of vans I've followed the brake pipes and secured the cable to those with cable ties. Despite the advice to the contrary, I have only ever run a positive cable. I have used the van's body as the negative return.

But before you do anything, please make sure a Voltage sensing relay (Durite for example) can be successfully used on your van.

 

[Quickwindowclean]

Run the cable from the van battery underneath the van and through a drilled hole in the floor close to where your battery is located. I usually use a cable grommet cut to size and squeezed in the drilled hole, so it seals the hole and tightly secures the cable.

On a couple of vans I've followed the brake pipes and secured the cable to those with cable ties. Despite the advice to the contrary, I have only ever run a positive cable. I have used the van's body as the negative return.

But before you do anything, please make sure a Voltage sensing relay (Durite for example) can be successfully used on your van.

Hello spruce yes my van is a Ford Connect 2006.

I was going to say which particular split relay I'm going to have to buy a nice one at least £30 and from who?

There is one final thing I'm going to do which I keep talking about doing. Although I'm charging this battery up every time there is a good chance the battery is actually damaged because when it's fully charged and it's starting to draw it shows about 12.7 but the other battery which is always permanently charged because of the cables in the other van when it starts to draw it shows about 13.2 that's no engine running ofcourse.

The thing is the original Van which has the problem has had that battery technically never fully charged for a very long time maybe 2 years.and only noticed the problems when I added electric reel etc so part of me is starting to wonder if that battery is actually not running at full capacity which is making me wonder if that battery could be the reason I doubt it but it's just the last point of call before I spend the extra money and get someone to help me labour wise.

It might be possible that this battery is causing the voltage drop the one which I'm charging once a week. The other van is not parked at my house hence why I keep forgetting. Do you think that could be a possibility as well?

Other than that common sense is putting me towards the thicker cables.

Let me know which relay you recommend for my van I should be able to find the cables and I will will take a screenshot of your instructions regarding how to feed the cable

Cheers.!

 

[ched999uk]

Just a quick simplified lesson. All cable has a resistance to carrying electricity. The thinner the cable the higher the resistance per meter. The higher resistance the larger the voltage drop. The higher current flowing through the cable the higher voltage drop. 

This is Ohms law (V=IxR) so basically if you are pulling large currents over long cables the best way to reduce voltage drop is to have thick cables!

Hope that's not teaching you to suck eggs?

A good relay is this Durite 6m split relay kit This comes with thick enough cables for a 6m run +Ve and -Ve cables and cable protection sleeving (for mounting under van). Can't see a through the floor grommet but that should be easy to source. One good thing about the kit is that it has a fuse at the van battery end, so any short of the cable from van battery to the relay is protected as this is very important for safety. Using the body of the van for -Ve is great as long as you make sure it's a good clean connection. 

One thing that might be worth investing in is a simple multimeter like this Multimeter ac/dc with continuity buzzer it's a cheap one but should enable you to test voltages. Then have a look on youtube for something like multimeter guide or testing caravan/motorhome batteries. That sort of things should help you learn to use a multimeter to see what is happening on your batteries.

Using a multimeter should enable you to see where the voltage drop is. i.e. is it the relay, cable, etc.

Again sorry if you know all the above already but I have no idea your experience.

Hope the above helps?

 

[Quickwindowclean]

Just a quick simplified lesson. All cable has a resistance to carrying electricity. The thinner the cable the higher the resistance per meter. The higher resistance the larger the voltage drop. The higher current flowing through the cable the higher voltage drop. 

This is Ohms law (V=IxR) so basically if you are pulling large currents over long cables the best way to reduce voltage drop is to have thick cables!

Hope that's not teaching you to suck eggs?

A good relay is this Durite 6m split relay kit This comes with thick enough cables for a 6m run +Ve and -Ve cables and cable protection sleeving (for mounting under van). Can't see a through the floor grommet but that should be easy to source. One good thing about the kit is that it has a fuse at the van battery end, so any short of the cable from van battery to the relay is protected as this is very important for safety. Using the body of the van for -Ve is great as long as you make sure it's a good clean connection. 

One thing that might be worth investing in is a simple multimeter like this Multimeter ac/dc with continuity buzzer it's a cheap one but should enable you to test voltages. Then have a look on youtube for something like multimeter guide or testing caravan/motorhome batteries. That sort of things should help you learn to use a multimeter to see what is happening on your batteries.

Using a multimeter should enable you to see where the voltage drop is. i.e. is it the relay, cable, etc.

Again sorry if you know all the above already but I have no idea your experience.

Hope the above helps?

Hi l'm very grateful for every piece of feedback.

Everything is pointing towards the cable.

Just going to check the battery though what did you think about that remember the voltage drop is only when the split relay is connected obviously you know this from the previous posts a few months ago.

Also tried changing the relay same thing it's either the cable or possibly the battery.

Thanks for recommending the relay charger

 

[Quickwindowclean]

Just a quick simplified lesson. All cable has a resistance to carrying electricity. The thinner the cable the higher the resistance per meter. The higher resistance the larger the voltage drop. The higher current flowing through the cable the higher voltage drop. 

This is Ohms law (V=IxR) so basically if you are pulling large currents over long cables the best way to reduce voltage drop is to have thick cables!

Hope that's not teaching you to suck eggs?

A good relay is this Durite 6m split relay kit This comes with thick enough cables for a 6m run +Ve and -Ve cables and cable protection sleeving (for mounting under van). Can't see a through the floor grommet but that should be easy to source. One good thing about the kit is that it has a fuse at the van battery end, so any short of the cable from van battery to the relay is protected as this is very important for safety. Using the body of the van for -Ve is great as long as you make sure it's a good clean connection. 

One thing that might be worth investing in is a simple multimeter like this Multimeter ac/dc with continuity buzzer it's a cheap one but should enable you to test voltages. Then have a look on youtube for something like multimeter guide or testing caravan/motorhome batteries. That sort of things should help you learn to use a multimeter to see what is happening on your batteries.

Using a multimeter should enable you to see where the voltage drop is. i.e. is it the relay, cable, etc.

Again sorry if you know all the above already but I have no idea your experience.

Hope the above helps?

So I contacted the 12-volt shop and they're going to sell me 25 m squared cable which carries about 200 amps for £7 a meter 

But I just found my jump leads which are are cables thicker than that and they carry 700 amps.

I was just wondering I want to test the red thick cable from the positive starter battery to the leisure battery and turn the engine on is it safe to do so? I want to make sure it's putting out all the way through 14.2v.

Also I would like to ask until my relay arrives is it ok to while I'm driving just connect the cable so it charges the battery and then disconnect it when they need to start the van  or park?

I also think cutting a pair of jump leads is a lot cheaper than buying the cable per metre and the quality of the jump cable is very high in amperage and very thick!

 

[spruce]

So I contacted the 12-volt shop and they're going to sell me 25 m squared cable which carries about 200 amps for £7 a meter 

But I just found my jump leads which are are cables thicker than that and they carry 700 amps.

I was just wondering I want to test the red thick cable from the positive starter battery to the leisure battery and turn the engine on is it safe to do so? I want to make sure it's putting out all the way through 14.2v.

Also I would like to ask until my relay arrives is it ok to while I'm driving just connect the cable so it charges the battery and then disconnect it when they need to start the van  or park? ***

I also think cutting a pair of jump leads is a lot cheaper than buying the cable per metre and the quality of the jump cable is very high in amperage and very thick!

A battery that isn't charged sulphates up @Quickwindowclean. Once that happens the battery looses its capacity. This means a 110 amp capacity battery can become a 20 amp for example. Mostly, a battery in this state means it isn't recoverable.

My last leisure battery was over 6 years old. It ran 2 pumps through the day with ease. Once I added a diesel heater that battery failed. I have a voltmeter on the leisure battery. Under load that battery dropped to 10.5v before the heater switched off. The moment the load switched off the battery voltage quickly climbed to 12.5v. Had this happened when I wasn't at the van I would never have seen the rate at which the battery recovered. It didn't mean the battery had regained any charge or was ok again. The battery was flat.

Basically, as your battery has been in this non fully charged mode for some time, I would suggest you have two problems, battery and relay.

*** Also I would like to ask until my relay arrives is it ok to while I'm driving just connect the cable so it charges the battery and then disconnect it when they need to start the van  or park? ***

Using a heavy duty jumper cable is possible  technically but it's not something I would recommend you do. I wouldn't do it. The risk of it going pear shaped is too high. What happens if the positive cable on your leisure battery comes off in transit? What happens if it comes off at the starter battery?

The reason why we don't cut corners with this sort of install is that the results of a failure can have major consequences, a fire being one of them. This is one reason we fit fuses to both sides of the positive charging circuit as close to each battery as possible.

16mm square cable is rated at 110amps. You don't need anything bigger. A Connects alternator is 120/130amp. The fuses don't need to be any more than 70 amp. You need a battery lug clamping tool and a hot air gun if you are going to do the job yourself. The guys @ched999uk linked to also sell made up kits. If you buy a made up set, make sure you have the correct measurements and give yourself a bit extra. Its easy to 'loose' a meter of cable than have it not reach. The main run on a 5 meter length is around 4 meters. And please don't ask me how I know. ?

 

[spruce]

Hello spruce yes my van is a Ford Connect 2006.

I was going to say which particular split relay I'm going to have to buy a nice one at least £30 and from who?

There is one final thing I'm going to do which I keep talking about doing. Although I'm charging this battery up every time there is a good chance the battery is actually damaged because when it's fully charged and it's starting to draw it shows about 12.7 but the other battery which is always permanently charged because of the cables in the other van when it starts to draw it shows about 13.2 that's no engine running ofcourse.

The thing is the original Van which has the problem has had that battery technically never fully charged for a very long time maybe 2 years.and only noticed the problems when I added electric reel etc so part of me is starting to wonder if that battery is actually not running at full capacity which is making me wonder if that battery could be the reason I doubt it but it's just the last point of call before I spend the extra money and get someone to help me labour wise.

It might be possible that this battery is causing the voltage drop the one which I'm charging once a week. The other van is not parked at my house hence why I keep forgetting. Do you think that could be a possibility as well?

Other than that common sense is putting me towards the thicker cables.

Let me know which relay you recommend for my van I should be able to find the cables and I will will take a screenshot of your instructions regarding how to feed the cable

Cheers.!

I'm old school. The only way we knew how to test a starter battery was to fully charge it and then put a battery tester on it. If the needle drops quickly under load the battery is bad (as the Americans say.)

You can't do that with a leisure battery. The only way to do it is to fully charge it and put a known load on it over an extended period of time. A fully charged 110 amp battery should support a load of 10 amps for around 10 to 11 hours. If it fails at 5 hours then the battery has half capacity. Don't let the motor factors guy behind the counter use the starter battery tester on your leisure battery. He will destroy a good leisure battery using that tester. Either way he gets a sale.

We repeat what we have stated many times before. You can only test the true state of charge of a battery after it has rested for around 4 hours. A fully charged battery will read between 12.7v and 13.1v after at least 4 hours rest. That's fully charged. But it could still show this voltage and be running at 1/2 capacity.

 

[Davy G]

A battery that isn't charged sulphates up @Quickwindowclean. Once that happens the battery looses its capacity. This means a 110 amp capacity battery can become a 20 amp for example. Mostly, a battery in this state means it isn't recoverable.

My last leisure battery was over 6 years old. It ran 2 pumps through the day with ease. Once I added a diesel heater that battery failed. I have a voltmeter on the leisure battery. Under load that battery dropped to 10.5v before the heater switched off. The moment the load switched off the battery voltage quickly climbed to 12.5v. Had this happened when I wasn't at the van I would never have seen the rate at which the battery recovered. It didn't mean the battery had regained any charge or was ok again. The battery was flat.

Basically, as your battery has been in this non fully charged mode for some time, I would suggest you have two problems, battery and relay.

*** Also I would like to ask until my relay arrives is it ok to while I'm driving just connect the cable so it charges the battery and then disconnect it when they need to start the van  or park? ***

Using a heavy duty jumper cable is possible  technically but it's not something I would recommend you do. I wouldn't do it. The risk of it going pear shaped is too high. What happens if the positive cable on your leisure battery comes off in transit? What happens if it comes off at the starter battery?

The reason why we don't cut corners with this sort of install is that the results of a failure can have major consequences, a fire being one of them. This is one reason we fit fuses to both sides of the positive charging circuit as close to each battery as possible.

16mm square cable is rated at 110amps. You don't need anything bigger. A Connects alternator is 120/130amp. The fuses don't need to be any more than 70 amp. You need a battery lug clamping tool and a hot air gun if you are going to do the job yourself. The guys @ched999uk linked to also sell made up kits. If you buy a made up set, make sure you have the correct measurements and give yourself a bit extra. Its easy to 'loose' a meter of cable than have it not reach. The main run on a 5 meter length is around 4 meters. And please don't ask me how I know. ?

Agree,some very important points raised and warned about.

My experience
Fuse protection. I wired some extra lights to my Land Rover years ago. Did it in a hurry as I was preparing for a kayaking holiday.

My mistakes : I used wiring that was lighter than I should have used.

I slightly underestimated the length of wire needed so pulled it a bit sharp around metal corners.

I didn't use protective sleeving or rubber grommets

I hadn't got around to fuse protection (I was going to get around to it, of course ) Each on their own a recipe for disaster. Combined, almost certainly a disaster in the making... As it turned out!

Result : the  insulation wore through and the cable started to spark and burn. Luckily there were three of us travelling in it at the time so we were able to spot it and tear out the wires. That's all I have to add as an actual example from personal experience to the sound advice of @spruce and @ched999uk

 

[Quickwindowclean]

I totally accept I think the battery may not be quite at capacity just an example yesterday we probably used 1x electric real 25 x along with mainly one pump working all over 6h and today only managed 3h work reeled in 12x and already the battery is toast..Not sure if that's about right for 110amps but considering the till recently it was lasting a week in putting 13.2 shows you the difference.

I'll definitely be replacing the battery I think that's a good shout I will be getting the split relay but meanwhile I just want to see if a thicker cable is going to input the correct voltage is it safe just to test it it or do I need to connect both the negative and the positives so as if I'm jump starting a vehicle so to speak or is 1 red enough?

 

[Quickwindowclean]

@spruce @ched999uk

I think that's a bad idea scrap that.

For one it will totally ruin the battery as it'll be putting in the full whack of 120amps or so from the alternator and it wont like it.

I think the thin cable in isnt more then 30a so if I dont over do it and put a 16m squared 110a going into relay and the same etc going into Leisure battery I'm sure I'll resolve the voltage drop issue. But now I'm curious with thicker cable going back wont I be putting way to many amps in so could damage the Leisure battery? 

Watched a video here and I'm starting to pick up a few bits. But I'm starting to wonder if I should just pay someone who knows what they're doing it ain't that easy need to drill or find a path from the van battery and fuse etc correct amp fuses too... unsure if I should tackle this or get handy help. Would prefer to pay I'm in the south east happy to drive 1-1.5h for the right person maybe on the forum or place if theres any recommendations .

 

[ched999uk]

To be honest best to pay someone who knows what they are doing. Have a look for motorhome mobile service people and send them an email asking if they can fit a suitable charging system to your van to recharge leisure battery. Also tell them what current you pull of the battery i.e. Pump, hose reel etc. Explain the problem and ask them for a solution. 

Batteries are capable of discharging very large currents that can cause fires so safest to get someone who knows what they are doing to install. 

Sorry can't remember back to beginning plus a few beers but I assume you can't get mains power so you could mains charge each night with ctek or similar?