Alternator & Charging System

Have you ever tried to remove the alternator from a Peugeot Boxer 2.5 non turbo? I recommend you get someone else to do it.

The sad thing about removing my alternator to modify it to fit a Sterling advanced regulator is that I had only recently took the alternator off to change the bearings after a trip to Ireland (where I had to have the clutch replaced as the thrust bearing had failed!). Had I known the advanced regulator required special works to the alternator I would have planned the two jobs together, oh well, hey ho.

I don't know if any of the other Peugeot Boxers, Fiat Ducato's, Citroen Jumpers or Citroen Relays are the same, but on mine the alternator is down behind the engine and requires the vehicle up on ramps so you can sit under the vehicle to gain access to the alternator. I think the conduit I fitted on mine hinders the alternator removal as I think there is just enough space to unbolt the alternator and move it towards the centre of the vehicle and out, however no way could I get it out that way. 

It was very difficult to get the following photo as I couldn't get far enough back to get in focus, plus lighting was a problem with it being very bright outside and dark under the vehicle, but hopefully you can just see the various components. The photo is taken from the ground , looking toward the front of the vehicle.

A 2" Cable conduit (from engine bay to electrical dist panel behind driver seat)
B Alternator
C Anti-roll bar
D Power steering rack

The only way I could get the alternator off, was to unbolt it from its bracket, then remove the bracket from the engine block, then its possible to ease the alternator out from its home by passing it in to the offside wing by the crankshaft pulley and halfshaft as shown below.

I do have photos of all the components of the alternator, but I have decide to show only the relevant bits here. 

The advanced regulator requires cables fitted to the commutater brushes in order for it to regulate the alternator output voltage. With most alternators I have stripped down, the brush contacts are fairly easily accessible, but .... this baby has to be different. After much prodding about I eventually found two bits of metal sticking out from a resin block which according to my test meter were connected to the brushes. With the aid of some plumbers flux and electronics solder, I eventually managed to solder a pair of wires on to the 'contacts'.

With wires connected, simply reassemble....

Now the biggest problem with many brush motors or alternators is to hold the brushes back whilst inserting the rotor with its commutator. After close examination I found this manufacturer was 'switched on' enough to think of this problem and kindly left a series of holes which ran through the brush holder  to insert a small pin through (tiny Allen key in my case) thus holding the brushes back in their holder whilst the alternator is being reassembled. After assembly, simply pull out the small pin.

More bits to follow when I have installed the regulator....

Split charge relay

This is where a lot of people panic. Its quite simple to safely keep the batteries isolated from one another when the engine is not running, thus preventing accidental draining of the main starter battery. This is done by using a relay that is activated from the alternator. This simple circuit is commonly known as a 'split charge relay circuit'

I have tried to make the following drawing as simple as possible.

I have coloured the main cable red which is most likely the same as your vehicle, however the other vehicle cables will be a variety of colours. The terminal numbers above are the standard numbers found on automotive relays. Terminals 85 & 86 are the coil, which activates the relay. Terminals 30 & 87 are the switch contact terminals.

Basically, all you need to do is identify the cable which runs from the alternator to the warning light on the dash board. Rather than pull your dash to bits, it may be easier to have a look at the cables on the back of the alternator. You'll find one or two large cables which will be the cables which run back to the battery. You will also find one smaller cable which is the charge indicator cable (no doubt someone will come up with some exceptions)

Now you've identified the charge light cable, its a simple mater of connecting it to the one side of the coil on a 12 volt relay (assuming your vehicle is 12 volts), the other side of the coil is then connected to an earth point (which eventually goes back to the negative terminal on the battery).

I have drawn the above with 30 amp fuses in line with the battery link cable. This size is normally sufficient, however if you have a really dead flat second battery they may blow. Don't increase the fuse size unless your cable and relay are rated for higher currents.

Split charge diode block

There is now another way to split the charging of your batteries. Instead of using relays, its now possible to use a split charge diode block. The first units did   use actual diodes, whilst the units worked, they were not efficient due to the voltage drop of around 0.8 - 1.2volts,this doesn't sound a lot, but in terms of charging batteries it is  quite a drop. To overcome this voltage drop, the modern units as supplied by Sterling use clever circuitry with mosfets, the result is that the voltage drop is now lowered to around 0.04volts

The split charge diode blocks are incredibly easy to install, as shown in the following drawing.

Having now fitted the above split charge block, its a good idea  to fit an advanced regulator to the circuit. This extra (Smart Regulator) will then give the optimum charge rates for your batteries and will also take care of any voltage/power loss in your charging system. Yes its quite technical to strip the alternator (as shown higher up on this page), but the end result is worth the effort.

The combined wiring of the split charge block and advanced regulator is shown below

Alternator to Battery Charger

Obviously not everyone wants to get involved with so much work, well there is an easier route. There is now a unit on the market which combines all the above circuits and devices into one tidy package, and the good thing is, it only requires the installation of four cables (Three main cables, plus an earth). If you were paying someone to install a system for you, go for this combined unit as the extra cost would be set against the time to install the unit. However if your doing the work yourself, the previous systems would work out cheaper.

This combined unit can easily be configured (using switches) to take account of the types of batteries your using. Its capable of charging 5+ times faster and put an extra 50% extra power in to your batteries. Think about this for a moment, why buy extra batteries, which will take a while to recharge, when you can fit this to reap long term benefits!

The easiest way to install the alternator to battery split charger and the split charge block, is to intercept the alternator output cable at the alternator, then you can be absolutely positive you have got the correct cable from the alternator. Then its easy enough to run fresh cables to the batteries without disturbing the original wiring any further. By using this method you should be able to easily remove these units for your next vehicle and return the vehicle wiring back to its original state.

Battery to Battery Charger with Hook-up Charging
Using Sterling's Battery to Battery charger is probably as simple as it gets. There's no need for anything additional, as the B2B unit does it all. The unit detects when there is spare power (when the engine/alternator is running), and uses that spare power to charge the house/second battery at the correct voltage and rate. What could be simpler? 

It's worth pointing out that the B2B unit will not drain the starter battery, as it effectively relies on the surplus power of the alternator to charge the second battery, so you'll always have power to start your engine.

Having installed a B2B unit, then installing one of Sterling's Pro Budget battery chargers to the main starter battery, will give you dual battery charging capability. The mains battery charger will charge the starter batter, the the B2B unit will detect spare charging capacity, and use the spare capacity to charge the house/second battery. This set-up will also allow you to use 12 volt appliances whilst on hook-up.

The B2B is quite and advanced unit and although described in its simplist form above, its quite advanced. For a more in depth description of the B2B unit click here


Having now had experience of Sterling equipment and its suitability to the motorhome environment, I have set up an account with Sterling so I can now offer their equipment at a discount. My store is at

Click here for spilt charge diodes
Click here for advanced charge regulators
Click here for Alternator to Battery chargers
Click here for Battery to Battery chargers


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