split charge

Working heavily on this page, soz for the disruption

What does split charge mean exactly I imagine your asking, well basically it's the term given to the way we charge the leisure battery as we drive along, when your at home or on a camp site you'll most likely have a mains charger, more often than not built into the van to charge the battery up, this is fine if you only ever stay on camp sites which have mains electric hook-ups available,

If you are like most people and want to be sure to have the leisure battery charged up like the starter battery is every time you drive the van, and thus be able to stay off electric hook-ups when camping, or stopping the night at the side of the road, or outside a friends house, you'll need to install something that diverts some of the charge going from the van's alternator to the starter battery to the leisure battery as well.

Just to put things really simple for a second, the engine in your van has an alternator, this is a devise that makes electricity when driven by the engine, and this electricity is sent to the battery used to start the engine with, the alternators job is to put back in the power you took out by starting the engine, also everything electrical inside the vehicle (stereo, headlights, brake lights and all that) takes power from the battery, this power needs to be replaced.. much like having a torch with re-chargeable batteries in it, only instead of waiting for the bulb to go dim and then putting the batteries in a charger plugged into the mains, the alternator replaces the power as it's used by the lights, stereo, and all other electrical systems in the van as you drive along.

So as your producing power to re-charge the starter battery, you just need a way to take some of that power and send it to the leisure battery, and as you drive along you will be re-charging the leisure battery as well as the starter battery, doing this is called split charging, your splitting the charge between the starter battery and the leisure battery, the charge isn't split equally between the 2, I'll explain why later.

Your probably thinking, earlier on I said you could connect 2 batteries in parallel to make them act like one big one in the way they are charged and discharged, so why not do that with the starter and leisure battery, that way they'd share the charge when the engine is running.. true, but the whole reason you fit a leisure battery is so you only discharge the leisure battery when your camping, and the starter battery is left fully charged to start the engine, so while they'd share the charge while the engine is running, they'd also share the discharge as you are camping, and you still wont be able to start the engine when the interior lights go dim, so you need a way to connect the leisure battery to the starter battery only when then engine is running, and disconnect it when it's not running.

There are quite a few ways to do this, the absolute simplest way would be to use a set of jump leads, much like jump starting a car, you'd connect the leisure battery to the starter battery, then as you drive the 2 batteries get charged up, but I really really can't ever recommend anyone doing this, unless the 2 batteries are under the bonnet you'll need to have the leads coming out of the bonnet and into the van, but even if both the batteries were in the bonnet, if one of the croc clip on the jump leads ever came off the battery terminal, you'd be in trouble if it touched something it shouldn't. so don't even think of recharging the leisure batter this way, if you do and burn your van down, don't come crying to me, I did warn you it was stupid.

I'll just touch on something you probably already know, electricity flow, for anything to work from the battery's power, it has to take electricity from the positive terminal, run it through the load, then return it to the negative terminal, i've said you should connect the negative terminal of the leisure battery to the van's body or chassis earth in the same was your starter battery is, this is so you only need to run a single positive wire all the way from the battery's positive terminal to the load your running, you connect the negative or earth wire on that load to any metal part of the van, and it'll be connected to the batteries earth terminal through the bodywork, same deal needs to be in place to be able to charge the leisure battery from the vehicles alternator, the electricity being produced by the alternator needs to go to the batteries positive terminal, and needs to return to completer the circuit.. the alternator's earth connection is connected to the metal body/chassis of the van, so you need the battery's negative terminals connected to earth as well to get any charge, so using the dangerous jump lead charging mentioned before, you'd only need to connect one lead between the batteries, the positive one, as the earth connections are already in place taken care of by the connection to the body work.. that still doesn't make the jump lead split charge method safe tho.

So, a jump lead is out, what about a wire connected permanently between the 2 batteries with a switch in the middle??

The manual switch method.

That's is one way, and it's been used in boats for donkeys years, but really it belongs in the age when donkeys ruled the roads, but it is an option, the simplest way to implement it would be to run a length of wire between the 2 batteries positive terminals, you must put a fuse in the wire near each terminal, i.e. you'll have one in-line fuse holder near the starter batteries connection, and one near the leisure battery's connection, these are critical for more reasons that you think, and must be used in any split charge system you install, click here for a diagram and more information, the size of the wire you use is largely upto you, if you use a thin gauge wire it's internal resistance will cause some voltage drop, but that is sometimes deliberately done.. remember that wire has resistance, and if your trying to pull current through it you want as little resistance as possible, well with the split charge your pushing current along the wire, so if you have resistance in the wire, you'll just limit the amount of charge the leisure battery gets.... some people like to limit the amount of charge the leisure battery gets, I personally want to get it charged as quick as possible,

For the actual switch, this can be almost any switch that can handle the current, if your using 20 amp cable, then a 20 amp switch should be fine, it just needs to be a single pole on off switch, I'll assume you know how to wire in a single pole on off switch, if not then you really shouldn't be thinking of attempting to fit a split charger of any kind, but for the 20 amp switch and wire to be safe, you need put no more than 15 amp fuses in the fuse holders near each battery, this will result in kinda slow charging from flat, but this is a similar way that all caravans are wired up to charge the leisure battery.. i.e. using thin cable that limits the voltage and thus current to the battery.

If you want to batteries to charge up properly.. and fairly quickly, then you'll need to put in a bigger cable and switch, it's kind of hard to get a switch that can handle 20 amps cheaply, so even harder to get one to handle say 50 amps or more, however there is a switch called a battery isolator, you will probably have seen them before, usually a red plastic L shaped key, that goes into a black plastic barrel, inters and turn the key to close the switch, turn the other way and remove the key to open the switch (closing a switch means allowing power to flow through it, turning it on, opening a switch means disrupting the power flow, turning it off) those types of switches while thy can be used, are pretty lame for our use, who needs a removable key, so there is a version which the key can't be removed, this one can handle 150 amps through it, more than enough for a standard split charge system, click on the picture of the switch to see a few more types of large current switches.

The manual switch method of connecting the batteries together is a very simple way to do it, for low current charging it could be the cheapest, for high current charging it may be expensive, there is one very major problem with the manual switch method.. the very fact that it's manual, the first time you forget to turn the split charge switch to on, you'll be driving down the road and not charging the leisure batteries, even worse the day you forget to turn the switch to off when you stop the engine, you'll leave the batteries connected together, and if you then spend the night or weekend camped without electricity, you'll be draining the starter battery as well as the leisure battery.

So a better way to do the switching would be to use a relay:

Automatic switch method using a relay.

A much better way to connect and disconnect the 2 battery systems for charging is to use a relay, if you don't know what a relay is, click here for a page describing what a relay is and how it works.

As a relay is commonly used to switch a high current remote source, this makes it ideal for our use, a very primitive system could be to use a small switch on the dash to operate the relay, the small switch will be cheap as it only needs to handle the 150 milliamps the relays coil pulls, the relay gets mounted in the wire between the 2 batteries, so you have a shorter wire run, and the relay handles the higher current the larger wires between the batteries carry, of course still keeping a manual switch on the dash means the system is not automatic, you can still forget to switch the relay in or out of the circuit, just like a large manual switch, however from the relay description page, you'll have noted that the relay needs a voltage to allow it to trigger, and have you noticed that when you turn the ignition key to start your engine, before you actually start it, loads of other things in the cab come on.. like the radio (if it's switched on at is control, the heater fan, lights and wipers will work and so on) the single switch that is the ignition switch has triggered a load of relays in the fuse box of the van, and allowed power to flow to the accessories, so if you were to add one more relay, the split charge relay to the ignition switch, when you turn the ignition on, the batteries will be connected together to be charged when the engine starts, and when you turn the engine off via the ignition key, the split charge relay will turn off also. sorted.. or so you think...

While the method of using an ignition circuit to switch the relay on and off to connect the batteries together for charging works, the problem is that the batteries are connected together as soon as you turn the ignition key, this means that when you start the engine, the starter will be drawing power from both batteries, something you definitely don't want to do, as the leisure battery isn't designed to be used as a starter battery (only in an emergency) also you'll need very very large cables between the 2 batteries to ensure you never blow the fuse when the starter is pulling upto 400 amps, while this may not happen that often, if your split charge relay is already wired up this way, that may explain why sometimes you will find one of the fuses in the split charge wiring blown for no apparent reason.

9 times out of 10 the leisure battery will be at a lower state of charge than the starter battery, so the starter motor will pull it's power from the starter battery as the leisure battery is too low to do anything for it, that means that when the ignition key is turned the leisure battery will be drawing the starter battery down, so if the leisure battery is very low on charge, the starter battery will be trying to put some charge into the leisure battery, if the ignition is left on for too long, you could find the starter battery hasn't got enough power in it to start the engine, Now if the leisure battery is fully charged, and the starter battery is low on charge, then when you try to start the engine the starter will try to pull all or most of it's power through the split charge wiring and relay, which unless it can handle the current, will pop one of the fuses (or if you refuse to fuse, then it'll heat the wires up and burn the relay out)

So a way round this is to switch the split charge relay into the circuit only when the engine has started,  this page here will show you how to wire the relay like this.

Blocking Diodes:

These are used almost exclusively on boats, but some people do use them on motorhomes, basically it's a pair of high current diodes mounted in a large heat sink, a diode is a one way valve for electricity, to fit one of these you need to re-route the alternator output cable through the diode block, the diode block will have 3 terminals, you remove the alternator output from it's original location on the starter motor main terminal (in 99% of vehicles, there are off ones that have the alternator output wire connected directly to the battery) the alternator output is connected to the centre terminal of the diode block, you then run a new wire back from one of the free terminals on the diode block back to where the alternator output wire originally lived.. starter motor main terminal or wherever, and you run a wire from the last terminal of the diode block to the leisure battery,

In use the alternators output goes to the diode blocks centre terminal, from there a diode goes to each of the other terminals, the diode allows the current produced by the alternator to go only in one direction.. out to the other terminal, and then out to the batteries, as the diodes don't allow current to flow backwards through them, the 2 batteries are always separated, no current can flow between the batteries, or back to the alternator, sounds like the ideal solution doesn't it? a solid state box of tricks that keeps the batteries separate but allows them to each get a separate charge,

Well you can't have your cake and eat it with a split charge diode (well you can, but only after modifying you alternator), their biggest downfall is volt drop, the way a diode works as a non return valve for electricity means that is restricts some of the electricity flow through it (like most water non return valves do) you loose from 0.4 to 0.8 volts through the diode, the type that looses 0.4 of a volt is known as a scottkey diode, the 0.8 volt loss is a standard silicone diode type)

Now that fraction of a volt doesn't sound much, but I mentioned on another page that to charge a 12 volt lead acid battery you need to feed it more than 13.8 volts, otherwise it will never charge fully, now the alternator's internal regulator is set to an absolute maximum of 14.4 volts, you don't often see that voltage at the battery terminals even without a diode in the system, 14.2 is more realistic, and on some vans 14 volts is good, can you see where I'm going yet.. if your charging system is absolutely perfect, zero voltage loss in the cables etc, your feeding 14.4 volts to the input terminal of the diode block, at the battery terminals you'll only see 14 volts with a very low loss diode block, and 13.6 volts with a cheaper diode block, now add into this a slightly tired alternator regulator, a little bit of voltage loss in the cables and so on, say you get 14.2 volts from your alternator, now you only get 13.8 volts with a good diode blocker and 13.4 volts with a cheap one, makes you wonder why you bothered don't it :)

If you still want to use a blocking diode, then boating supply shops or marine chandlers are the usual sources for them, there will be a few available, all rated for different currents, you should buy one that's 20 amps bigger than your alternators output (it will say the output on the case of the alternator somewhere), one more bad point with diodes, the high currents they are passing in use means they get hot, that's why they are mounted inside a big heat sink case, they need to be placed somewhere air can flow over them, diodes passing high current actually get worse as they heat up, some can drop upto 1.2 volts in really bad conditions, that means practically no charge going to the battery, (a fully charged battery's terminal voltage is 12.8 volts remember, so if your not putting in more than that voltage, your not putting in any at all, hence the need to put in 1 volt more than it's fully charged voltage to be able to charge it properly)

There is a solution tho, unfortunately it involves spending more money, what you need is a voltage sensed alternator, the alternator on your van is almost certainly a machine sensed alternator.. what's that mean??

well, if you've read the alternator workings page recommended at the beginning of this page, you'll know an alternator produces firstly AC current in 3 phases, at upto 150 volts, this gets fed through the rectifier diodes and converted to DC current, the regulator inside the alternator then controls the field voltage to regulate the output voltage and hence the current, to do this it needs a voltage reference to work to, and most alternators have a very handy place to pick this voltage reference up from, the output terminal.. it's connected to the battery.. eventually, so when the battery voltage is low, the voltage read at the output terminal will be low, and the regulator can adjust the voltage to compensate, this is fine if you don't have too much voltage drop in the cables between the output terminal and the battery or batteries.

But as we've deliberately added some voltage drop in the form of the splitting diode block, the alternator will still be thinking it's producing it's set voltage because that's what it sees at the output terminal, and if we were to measure the voltage at the alternators output terminal it would be 14.4 (hopefully) but the voltage at the batteries terminals will be much lower due to the diode blocks, so we need to measure the voltage reference for the alternators regulator from the battery terminals, and that's what a voltage sensed alternator does, it has an extra wire going to the battery positive terminal, this means that if the diodes are taking 0.8 volts from the charge voltage, the volt sense alternator will know this, and can up the voltage at it's output terminal to compensate.. so you'll see 14.4 volts at the battery terminal, and at the alternator terminal the voltage will be 15.2 volts.

It is possible to have most alternators modified to external voltage sensing, you'll need to find a friendly alternator re-builder to do this for you.. and I mean an alternator re-builder, someone who actually takes alternators apart and fixes them for a living, not a general car mechanic.. ask for someone to convert your machine sensed alternator to volt sensing at halfords, and they'll look at you gone out (mind nowadays you get that look there when you ask for anything other than a furry dice, 20 inch 2 million watt bass box or a neon light for under your saxo :)

What's basically done is the internal link from the regulators voltage sensing connection is disconnected from the output terminal, and brought out of the alternators back plate, it may be possible to connect it to a spare terminal on the alternator if there is one, or put it on a terminal you will never use and re-label it.. like the W terminal if you have a petrol engine, or an iveco engine that uses a sensor on the flywheel to run the rev counter, you then re-fit the alternator (or he does that for you too if he took it off.. costs a lot more then) and you wire in the new wire from the volt sensing terminal to the positive terminal on your battery, and hey presto, you have a voltage sensing alternator, and can use a blocking diode for your split charge system properly.

one warning, unless the regulator is made to protect against this.. if the new voltage sensing wire ever becomes detached from the battery positive terminal, the alternator will see no volts, and think the battery is totally dead, and pump out maximum current and voltage to try and compensate, this will of course boil the battery pretty quickly, and bugger up some of the more voltage sensitive items in your van, check this scenario out with the person who modifies the alternator for you, it may be the case that the regulator is intelligent enough to shut down output if the voltage detected is lower than a certain voltage, but most machine sensed alternators won't have a need for this feature as the internal link between the volt sense input on the regulator and the output terminal is unlikely to ever fail.. but it happens sometimes, i've seen a few burnt out iveco's in scrap yards where the fires started at the alternator area of the van, it was known that the voltage regulators on certain alternators could fail, and when they did maximum voltage and current gets sent up the wires to the battery, this melts the wire and starts a fire.. and usually the driver didn't have a fire extinguisher with him, or if he did it was one of those silly little 1 kilo jobbies that don't last long enough to surprises a high current electrical fire, so the van gets lost for the sake of a few pennies worth of silicone inside the alternator.

No volt drop diode:

This is a relatively new devise, but it's pretty simple in operation, instead of using diodes, they use a few transistors,

 

 

 

this stuff below is for deletion soon.

 

This page has been pulled directly over from my old site, I'm writing a new versions of this page, but with all the hassles I'm having lately, it may take some time, so for now here's the old version of the split charge relay installation page.

A split charge relay is used to connect a starter and leisure battery together for charging only when the engine is running, when the engine is stopped, the 2 batteries become separate units again, so you can flatten the leisure battery, and still be able to start the engine in the morning, when the engine is started, the alternator charges both batteries together, it's a very simple way to do the job, another way involves using a large diode to allow the charge to flow from the starter battery to the leisure battery only, the problem with this system is that diodes drop some voltage through them, upto 0.7 volts, doesn't sound much, but it is a lot when you are charging a battery, as they need over 13.8 volts to charge to any decent level.. the alternator puts out at most 14.4 volts, so you can see that the leisure battery will only get 13.7 volts, not really enough to get a decent charge, a relay doesn't drop any voltage through it, so if the alternator's putting out 14.4 volts, the leisure battery will get 14.4 volts, the diode system is also expensive, and they get hot in use, you can buy commercial kits for adding split charging to your van, but they are aimed at caravan owners, and cost about £25, here's how to do the same job for about 7 quid (the commercial kits are usually 2 relays in one case, the second one is for the fridge power, just use 2 relays to replicate the commercial kits.. they only cost about 4 to 5 quid.

If you are unsure of what a relay is, or just wonder what's inside that makes it work, this page here will explain the workings of a relay.

Above is a wiring diagram of a split charge relay, the diagram alone might be enough to allow you to see how it's wired up, but I will explain how to fit it as well, I'll start off listing the tools and parts you will need to fit this to your van, then go through fitting it in detail, if you're unsure of your skills to fit this kind of thing please get a competent electrical type person to fit it for you, it may cost you a little bit of money, but it will be cheaper than a new alternator, battery or even van if you get something wrong, 
I'm not trying to put you off, this is a very easy thing to fit, and whilst were not dealing with mains voltages here, (touch the wrong wire and it's the last wrong wire you touch), the battery can produce enough current if directly shorted out to cause melted spanners, hands, or if it stays shorted out for long enough it can explode.

Right, if your not a quivering wreck in the corner of the room, the tools you will need....
Spanners, probably just a 13mm spanner for the battery clamp, but it may be a 10mm, (unlikely on a van), you may also need an 8mm spanner for the alternator connection, (more on that later),
Screwdrivers, flat and cross head blades, also an electricians screwdriver may come in handy, (you know the thin flat bladed one),
A terminal crimper, for crimping the lucar type connectors to the wires, if you haven't already got one of these, get one, it's a wise investment, a cheap one should cost you about a fiver, for a bit more you can get one with a selection of terminals, they also have wire cutters, wire strippers, and bolt loppers on them, you'll need the first 2 functions to prepare the wire for the terminals anyway, so this one tool does the job of 3 or 4 separate tools.
A test light, Again, a cheap tool that you will find uses for again and again, a simple screwdriver type one costs about a pound, make sure you get one for use on low voltages, (i.e. 12volts), they look like an electricians screwdriver, but with a point instead of a blade, and a length of wire coming out the top of the handle, with a crocodile clip on the end.
A drill and drill bit's  Electric or battery drill preferably, and a selection of drill bits for drilling holes for the screw to hold the relay, earth points, and holes to pass wires through if needed.
Pliers, Decent sized ones, with a flat end, only really needed to fit the scotch lock.

And the components you will need are as follows,
1x 12 volt, 30 amp, standard automotive relay, cost about £3 to £5, on the bottom of the relay, where the terminals are, there should be some numbers like in the diagram above, if not, don't buy the relay unless you are certain what each terminal does,
6x fully insulated female lucar style spade terminals, blue ones.
2x inline fuse holders, and any terminals needed to fit them, I use inline euro fuse holders (same fuses as in a VW), and they have screw fixings for the wire (make sure they will accept 15 amp wire), others may need crimp on terminals, or be soldered on the wire, ask at the shop what's needed to use them.
2x 10 amp fuses to suit the holders, may be wise to buy a couple of spare fuses while your at it,
3x crimp on ring terminals, 2 of them the yellow banded ones, large, to fit the securing bolts on the battery clamps, and 1 blue banded small hole terminal for the relay's earth terminal,
1x scotch lock wire splicer, or you can use one of the female spade terminals if your alternator has that kind of fixing, best to buy the scotch lock anyway, it's only a few pence.
2x self tapping screws,
Length of 5 amp single core automotive wire, any colour will do, I use blue my self, long enough to go from the alternator to where your going to mount the relay.. routing the wire safely away from any part of the vehicle that can damage the wire, anything from 3 foot, to 15 foot could be needed, 
Length of 15 amp single core automotive wire, Red, long enough to go from both the battery's and the relay, again length depends on the location of your batteries, and relay mounting point, allow at least a foot extra,
Grommets, if needed to line holes to route the wires.
Some small cable ties, to secure the cables in the engine bay. 

Now here's how to use that stuff you just bought, first things first, open the engine bay door/bonnet/cover, or what ever you have, if the starter battery is located somewhere else, gain access to that, also you need access to the leisure battery, usually the first thing you do when working on the vehicles electrical system is disconnect the battery's earth leads, but we'll do that later, you need battery power in a little while, 
(the earth leads are disconnected because it breaks the circuit like disconnecting the positive lead, but if the spanner you're using to undo the negative terminals clamp touches any metal part of the vehicle, it won't do anything, as it's already earthed, whereas if a spanner bridges the positive terminal and any metal part of the van, sparks fly, and the battery could explode, although you usually just bang your head jumping back when you get a spark across the spanner your holding, it's still best to avoid that situation),

Anyway, safety lecture over for now, first find a suitable place to fix the relay, somewhere away from high heat sources, i.e. exhaust manifolds, if both batteries are in the engine bay, fix the relay near the starter battery, it doesn't really matter where you mount it in relation to the batteries, but you ideally want to keep the wiring lengths to a minimum, on my van, the engine is between the front seats, and the starter battery is behind the passenger's seat, I put the leisure battery in the bed box behind the drivers seat, so I mounted the relay in the bed box with the other electrical equipment, and ran the wires from the engine bay, and other battery to that point, once you are certain of where to fix the relay, place it against the item you are going to fit it to, ideally it will be a metal part of the van, but it doesn't matter if it's wood, there is a fixing hole in the tag on the top of the relay, make a mark through that hole onto the material behind it, take the relay away and drill a hole where you made the mark, the hole wants to be slightly smaller than the self tapping screw that you bought.

Now we'll make up the wire from the alternator to the coil terminal on the relay, first we need to find the no charge warning light wire on the back of the alternator, now different alternators have different wiring schemes, if the alternator has an external regulator (a bit like a dynamo's control box, they're rare nowadays, but some type 2 VW's have them), it would be best if you consult your workshop manual, or an auto electrician to determine which wire to tap into, if the control box has separate connectors as opposed to a single multi way plug, you can try to locate the no charge signal wire the same way as for an internal regulator alt... I'll describe how to do that now.

Assuming you have a standard internal regulator alternator, there will be 2 or more wires on the back of it, one of them will be a lot thicker than the rest, that's the main charge wire that goes to the battery, that wire is live all the time, and usually un-fused (if it is fused, the fuses are expensive), so try not to disturb it, it will usually be connected via a 10mm nut, but could be part of a plug, there will be at least one more wire, quite a bit smaller in diameter compared to the other one, if there's only one more wire that will be the no charge indicator light, (unless you have a very new vehicle, with a single wire alternator, if your alternator only has one wire, then you'll probably have to connect the split charge relay wire to an ignition switched source, not ideal, but best in this case)
Usually there will be a couple of thin wires, if you can see the back of the alternator clearly, one of the wires terminals may be marked either IND. or WL, this should be the wire you want, the other wires can be for an RF choke, an earth, or a W terminal, this is used mainly on diesel engines, as the rev counter sensor, or anything else that might need to know the speed of the engine, 

The only way to be sure you have the right wire, is to unplug the one you think is the correct one, turn the ignition on, (but don't start the engine), and if the no charge light doesn't illuminate, you have the right one, if it does illuminate, turn the ignition off, and plug the wire back in where it came from, and try another one, if one of the thinner wires has a nut holding it on, (probably 8mm like mine does), that's more than likely the no charge warning light wire, to be sure you must first disconnect the battery's earth lead, because if you accidentally short that terminal out, and you will blow the regulator, I'm trying to save you money here, once the battery is disconnected,  remove the wire and make sure it can't touch any other terminals, you may have to hold it back to prevent it from slipping back into position, re-connect the battery, and turn the ignition on, no battery light??, good, that's the one you need, now disconnect the battery's earth lead again, and re-connect the wire on the alternator, you can leave the earth lead off the battery now,
On a VW type 2's alternator things are easier, (unless you have one with an external regulator), the diagram above is based roughly on that setup, you will have 2 terminals on the top of the alternator, a thick one, and a thin one, the thick one has B+ next to it, and is the battery connection, the thin one is the no-charge warning light... simple.

Now disconnect the earth leads from both batteries if you haven't already done so, you don't need any power until we come to test the system.

Right, we've found the no charge warning light, now for the wire to the relay, run the length of 5 amp wire from the location of the relay to the alternator, you may have to drill holes to pass the wire through bulkheads, if you do, remember to use a grommet to protect the wire from chaffing on the hole's edges, or you may be able to pass the wire through an existing hole that the van's wiring loom passes, use the scotch lock to tap the new wire into the no charge warning light wire, if you've never used a scotch lock before, here's a rough description, there are 2 cut outs in the body of the scotch lock, one of them passes straight through, that's for the existing wire, the other (usually the inner one.. nearest the tag you fold over), only passes through it half way, that's for the new wire, determine which way the new wire is meant to go in the scotch lock, and position it so it points in the direction you want the new wire to go, 

Now clip the scotch lock over the existing wire, (you just press it over, not too hard, make sure the wire sits in it's groove and not the other one), push the end of the new wire in to it's hole in the scotch lock (the new wire must not be striped, i.e. it must have full insulation to the end), then using your pliers, squeeze the metal tang into the wires, make sure you squeeze it hard, you need to make a good connection, this cuts the insulation of both pieces of wire, and joins them, then flip the plastic tag over and press it down until it clicks in to place, job done, gently pull on the new wire to make sure it is completely in the scotch lock, you may want to wrap the joint in electrical tape if you have some handy. alternatively, if your alternator has female lucar type connectors for the no charge warning lamp, (the ones you bought for the relay), you can cut the existing one off, and add the new wire to the existing one using a new terminal, but it's usually easier to use the scotch lock. 

Next using some of the cable ties, secure the wire in along it's length to prevent it getting damaged, then trim the other end of the wire to length so it reaches the relay position with plenty of slack, fit a female lucar type connector to the end of the wire, (using your crimping tool, bare the end of the wire about half an inch, fold the bared wire over its self halfway along it's length, (so the bared bit is now a quarter of an inch long, and twice the thickness), push it into the end of the terminal until it won't go in any more, and put 2 good crimps on the terminal's round section, make the first one just behind the flat spade part, and the other just behind the first crimp), then fit the new wire to the relay, push the connector onto terminal 86 on the relay.

Now for the wires from the batteries, you should have a length of 15 amp red wire, you will need to cut it lo length for your installation, place one end near the starter battery, and run it up to the relay, (again, drilling any holes you need, or pushing it through existing holes), at the relay end, add about 6 more inches, and cut the wire off, then do the same for the other battery, now, starting with the starter battery, fit the large ring terminal to the end of the wire, (that is providing it will fit on the bolt of the battery's clamp, if not, you will need to purchase the specific terminal to fit, the large ring terminal is the one for about 95% of batteries though), then fit one of the fuse holders, fit it close to the terminal you have just fitted, (about 4 inches away from it is normal), then go to the other end of the wire, up by the relay, and fit a female spade terminal, connect this to terminal 30 on the relay, and back at the battery, connect the ring terminal to the battery's positive clamp,
Fit the terminals and fuse holder to the  leisure battery's wire, if you have fitted quick disconnect clamps to your leisure battery, you just need to strip some insulation from the wire, and fit it under the screw down clamp, this time connect the relays connector to terminal 87 of the relay, using some more cable ties, secure the new cables along they're route to prevent then being damaged.

You're almost done now, next you need to make up the relay's earth lead, if the relay is fitted to a metal part of the van, scrape the paint off from around the hole you drilled to mount the relay, (this is to get a good earth, paint doesn't conduct electricity very well), if the relay is mounted on wood, (this conducts electricity even worse :o), you will need to drill a hole in a metal part of the van near the relay, again clean some of the paint off from around the hole, then cut a length of the 5 amp wire (you should have a little left), if the relay is mounted on metal, make the wire about 3 inches long, if it's on wood, make the wire long enough to go from the relay to he earth point hole you just drilled, on one end of the wire, fit a female spade connector, and on the other end, fit the small ring terminal, connect the spade connector up to terminal 85 on the relay, and if the relay's on wood, screw the ring connectors end of the wire to the earth point you made, then screw the relay to the panel you chose to mount it on, if that panel is metal, you can use the same hole to mount the relay and earth it, push the self tapping screw through the relay's mounting hole, then put the ring terminal over the end of the screw, (so it's behind the relay's mounting tag), then screw them to the panel.

Now check your wiring against the diagram above, if it all checks out, fit he fuses to the fuse holders, (I bet you left them in didn't you, not to worry, I'm only saying that to ensure they do get fitted if you took them out :o), now re-connect the battery's earth leads up, turn the ignition on, and check the no charge warning lamp comes on, if it doesn't, turn off, and go back and re-check your wiring, making sure the connector on the alternator is making good contact with it's terminal, when the light is on as it should be, start the engine, make sure the light goes out this time, if you have to rev the engine, do so, (on one of the van's I fitted one of these relays to, the no charge warning lamp took longer to go out than before I had fitted the circuit, (i.e. the engine needed more rev's to get it to extinguish), the owner wasn't bothered about this, I way, but couldn't find a simple explanation for this, talking to some alternator specialists later, they told me that some alternators are very sensitive to the voltage needed to get them to start exiting, (what the field coils do to produce a charge), the relay added a little more resistance to the circuit, so it needed more voltage to begin charging.. nothing to worry about as long as you don't have to rev the nuts off the engine to get it to charge, 

Turn the engine off, and check the fuses, if they have blown there's something wrong with the wiring, check the connections at the relay, assuming they are all right, remove just the one to the leisure battery and leave the fuse holder open, connect your test light's crocodile clip to the leisure battery's earth terminal, test it by touching the probe on the battery's positive terminal, the bulb should light up, now put the probe on the terminal of the fuse holder nearest the relay, it shouldn't light up, if it does, and the engine is not running, check the wiring at the relay, if it doesn't light up when you touch it on the fuse holders terminal, good, that's what we want it to do, now go and start the engine again, and make the alternator no charge warning light extinguish, now touch the probe on the fuse holders terminal, this time it should light up, if so... that's the job done, you've fitted a split charge relay, replace the leisure battery's fuse, and you're done, if the light doesn't illuminate, check the starter battery's fuse, if it's ok, check the relay's wiring,  including the earth terminal, then make sure the connector on the alternator you made is good, that is most likely where the problem will be.

 

one note to reply to questions I get all the time, this system works, honest, most people are confused because they think the relay will be triggered when the no charge light it on, and go off as the light goes out to indicate the alternator is charging.. it works the opposite way round, and here's why.

When you turn the ignition on, battery voltage is sent up the no charge wire through the bulb in the dashboard, it gets to the alternator and is able to get to earth because the alternator is not turning, so the bulb illuminates, when the alternator starts turning, it produces voltage, this is sent back up the no charge wire, where it meets the voltage from the battery being sent down it from the ignition switch, the voltage has no where to go (as it needs to get to earth to complete a circuit for the bulb to illuminate), hence the bulb can not light, but there is voltage on the wire, (the relay can't trigger from the voltage that's on the wire from the battery before the alternator is turning, because the voltage has gone through the bulb, so there's not enough left to trigger the relay), sounds a bit complicated, but it's really simple, if anything happens to the alternators output, the battery voltage from the ignition switch can get to earth through the bulb and alternator, making the light illuminate.

And one final answer to a question that's cropping up more and more lately, people have read on a  certain web site claiming split charge relays to be dangerous.. this site is a boating site, and they want you to buy their diode type splitter.. at about £200, but in a boating environment apparently relays don't last that long, this is because when you go to sea, the boat gets hit from every side by waves, this send shocks down the whole boat that buggers relays up.. apparently, this kind of punishment doesn't happen in a road going vehicle so we can discount this reason for not using a relay,

The other reason the site says it's dangerous it due to the current capability of the relay, this site gives a scenario where a 70 amp relay is used, and the boat owner had run his leisure battery down by using the inverter all night, he starts the engine, this energises the split charge relay and joins the 2 battery banks together.. fine so far, except he's left his inverter running, and it's got a 1000 watt load on it (only the boating types would do this it seems :) so the little 70 amp relay is suddenly conveying 100 amps to the inverter from the starter battery (as the leisure battery is connected to the starter battery now, and cant provide the power needed), this site then says the relay will melt, wires melt and the boat burn down.. well yes I guess it could happen, luckily us motorhome type people have heard on an invention that can save all this, i've even shown it in my drawings above.. can you guess what it is yet?? yup.. it's a fuse, fuses are there to prevent high current flows over wires that cant take a over a certain current amongst other things, so if the boat owner had spent a quid more and fitted fuses in his split charge relay system, when he started the engine, the relay would have energised, the inverter tried to pull 100 amps through it, and the fuses in the split charge wiring would have popped, no burnt out relay, no melted wiring, no burnt down boat, just a fuse or 2 to replace, and while he's replacing them he may remember to turn the inverter off next time he kills the battery and starts the engine :)