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Updated 29/06/2017

            Can I Upgrade My Habitation Battery Bank Without Complications?


Yes you can upgrade the battery bank on many Charger/Power Distribution units, but there are also some which have not been designed to handle the extra load of an upgraded battery bank. 
There has been much said about the limits of a Motorhome Mains/230v Charger when battery banks are uprated, but this page highlights the issues where factors other than the mains charger come into play. 

Motorhome Power Controllers/Chargers where the internal 230v Mains Charger itself is not the limit to the battery bank size.

If you look at the Arsilicii 20amp Charger/Power Unit below you will note that the graphics on it's front show the Starter battery connects in through the Red, bottom left socket and the Habitation Battery through the top left, White socket. 

The box, like most continental built Power Units, has a built in Split Charge relay so that all current from the Alternator/Starter battery flows in through the Starter/Alternator connector, to the split charge relay and then out via the White Connector to the habitation battery. 

Adding extra habitation batteries can result in up to 40amps of Alternator charge power going in through the Red and out of the White connectors. 
The Fridge load, typically 17 amps for a Fridge/Freezer, additionally goes in the Red socket then out to the Fridge via the Green connector.
So the combined current passing in through a single Spade connector on the Red socket can be over 50amps if extra batteries are added.
The sockets on the later units have been uprated to higher power RAST5 versions, but even they will struggle if a second battery is added and allowed to become tired. 

It can be seen in the photo above that both the Starter + and the Habitation battery are both overloaded and burnt, a very common issue where a second battery has been added. 

Below is an early Arilicii Fuseboard with low power connectors :

Something like this Fuseboard above is always too badly burnt to perform a meaningful post mortem, but you won't be surprised to learn that the centre of the fire is the Split charge relay with the Habitation battery sockets one side and the Starter Battery/Alternator feed the other. 
If you upgrade to a Lithium battery, which can have 4 times the power loading of an ordinary battery, without appreciation of the systems and it's capability, then keep a very good Fire Extinguisher handy. 

The burnt Fuseboard above should look similar to this new one below, although this is the latest version Fuseboard with uprated Rast5 connectors to better handle slightly higher current without burning. 
Note the massively upgraded 12v Fridge connector, circled in Red, up from a 19amp rated socket to a 40amp socket, clearly these have also been a past issue? :

Although the connectors are uprated in later versions, they still won't cope with a bigger battery bank. 
Additionally the wiring remains the same which also isn't designed for heavy currents. 
These fuseboards are not expected to pass currents that will even make them warm, let alone hot. As a result they tend to sit in enclosed boxes without ventilation. You can imagine how the the strain of running hot for short periods will place on the electronics leading to other issues, like overheating the of the IC's and not powering on, etc.
If you think they don't get hot, look again at the pictures on this page. 

So even the latest version, although more resistant to burning, will have issues with anything more than a single battery, UNLESS the discharge/recharge load is managed. 

The above examples, and those below, clearly show the complications that can arise if you take a unit outside it's design. You can't just automatically add extra batteries to all Motorhomes without doing your homework. 
Well you can, but there might be Tears. 

This section is specifically aimed at the how the units cope with extra Alternator charge current when battery banks are enlarged. This is not about any limitations of Mains 230v chargers, that is documented on a separate page, HERE. 

While we use a Arsilicii unit above to demstrate the issue, it equally applies to a Benimar's SAPSE unit, Toptron, Calira, CBE, early Schaudt Elektroblocks like the EBL104, etc. 

Any unit where the Alternator charge goes through the Power Unit, needs to be checked to see if it can handle the Alternator current that a big battery bank is going to draw. 

More examples below : 

Some of the Nordelettronica FuseBoard systems also won't be happy about an extended Habitation battery bank.

The above Nordelettronica Fuseboard is an early unit and particularly prone to damage if it has to pass the Alternator current for a second battery. 
Like the Arsilicii unit, all Alternator current goes into this Fuse board before the electronics then send it on to either the habitation battery or Fridge.

These Fuseboards control several functions : Power distribution, Display screen information,  Alternator charging,  Fridge 12v operation, etc.

As can be seen above the wiring isn't terribly chunky on these Fuseboards, but like the Arsilicii it is the connectors that are the weak link. 

The above units can burn out with just a single habitation battery. If the battery is allowed to get too tired the Alternator may be working a lot harder, passing more current and for longer. 

The susceptibility to greater Alternator charge current damage caused by enlarged battery banks was recognised some time ago by Nordelettronica and later Fuse boards have been modified to include heavy duty 'Stud' connectors rated at 50amps for the connection of the Habitation and Starter battery wiring.  
These Stud screw connectors can handle the extra load of a second 90Ah battery. 

One of the new 'screw Studs' can be seen on the new uprated Fuseboard in the picture below, labelled B2, just to the left of the www.nord... on the bottom relay label.
The other studs are to the right of the relay, labelled B1 and B3.

The 'interim' version of these Fuseboards had Stud connectors added, but the manufacturer left the 4 pin sockets in place. Sadly, because it was time consuming to alter the wiring to switch to the Studs, many Technicians didn't bother when they retro fitted a new Fuse board.
On the latest releases of the Fuseboards, the 4 pin sockets are no longer fitted at the factory, to enforce use of the Studs for obvious reasons. 

The photo below of an old (interim version with both 4 pin sockets and studs) and new Nordelettronica NE185TR1 side by side. 


Tribute PVC
If you are replacing one of these Fuseboards mounted in the side of a seat base on a Tribute PVC just to the rear of the Gearlever, can we suggest you insulate the seat frame legs in the area of the Fuseboard, as 5 of these we have replaced had all failed due to the Fuseboard shorting out on the metal seat 'legs' because space is so tight. The cable protecting 'sleeve' you can buy does a good, neat job of this.  
Cable tie the 'sleeve' under the Seat Plastic side cover and it won't show hopefully preventing any further 'shorts'.

The Calira charger units also have the Split charge relay inside the box, so the same limitations apply. While the charger inside the Calira below will take 2 x 80Ah Gel batteries, any prolonged significant current passing through the unit via the far right hand Starter battery and Habitation connector will result in a burn out. 

As can be seen from the blackening of the vents above the plug, the internal fire has caused a lot more damage inside than is visible on the outside. The Plug was melted into the socket which was really badly burnt on the two Starter Battery connectors (Alternator feed) to the PCB. The PCB was destroyed and the entire box scrap.

These MNL connectors are rated at about 20amps max, this website below describes them as having a 19a rating :  

To avoid issues on the Calira, the Battery bank should be less than 200Ah total size (including the Starter battery which the box also charges) and made up of quality, young and perfect batteries. Don't let the batteries get very low, or tired. 
The Calira's are no longer available new, once burnt, you will find yourself between a rock and a hard place. 

Take extra care to look after both the Calira 38/20 and the 30/20. Try and ensure it has only the lightest load with two young, high quality batteries of no more than 80Ah each. Due to their fragility and rarity, maybe only 75Ah ea might be better? 
Whatever you do replace the batteries, before they get tired. A tiring battery can draw a lot more current.

Schaudt Elektroblock EBL 104 - 106.
The Schaudt EBL 104, like other units above, has the Alternator/Starter battery feed going in through Block C (third MNL connector block from the left) and back out to the Habitation batteries through the same Block. 
As per the Calira above the connectors are rated around 20 amps.

So all charge on the Elektroblock (plus 13amp power for the Fridge) goes in through fairly low rated connectors which can get overloaded if a large battery bank is fitted and/or the batteries are allowed to deteriorate. 

Note also that the built in mains charger is very low power, just 10amps. A second indicator that it was designed to support no more than a single 100Ah battery.

Thirdly, the cabling thickness also reflects the fact that, like most Motorhomes of the era, were only expected to have a single battery from the Factory. 

These units are particularly vulnerable to damage from an overlarge battery bank.
This 'weakness' was recognised by Schaudt back in 1998 when the introduced the more modern EBL 99 with much more capable, 50amp +, wiring and connectors which were relocated to the rear of the Units. 

We don't know much about the CBE DS power unit from the PC100 range but it has good quality Stud connectors and generally, quality cable, but the Split charge relay built into the distribution board, doesn't appear to be expected to handle anything but a low Alternator charge rate.
See example photo below from what is labelled on the web as an early PC100 system. Later systems seem to have a bigger relay, separate relay.
The very small Tyco split charge relay is identified in the photo by the tag "relais Parallele batteries". 

Maybe adequate for a single 100Ah battery in good condition, but it will be severely stretched supplying the Alternator current for 2 x 100Ah batteries that are past their best.
Compare it's size to that of the 'Giant' Nordelettronica relay that still caught fire above.


Remember the size of the relay is not just about the current it can pass safely, but the Voltage drop that is generated on a relay with a small contact area. Burning of relay contacts after a short time in use, may lead to some voltage drop and reduced charge rate.

On a later version of the CBE DS 300 this relay has been uprated, and is part of a Boite Securite Ralais but even then there have been reports of overheating and failure.
This picture below shows a failing Solder Joint, possibly due to the board being unable to cope with the high currents involved.


The above examples, from 5 different major Motorhome Electronics manufacturers, shows this isn't just something that affects the odd unit. 
We are seeing more units overloaded by poor advice to add batteries without any proviso on whether the unit is capable of handling that load.

Remember also that any Inverter connected to the Habitation battery may try and draw up to 150 amps from the Alternator if you run the engine while it is operating, assuming it is a high power Alternator. 
For one of the above listed units, that might be 150amps going from the Alternator/Starter battery, in through those connectors, then through the internal Split charge relay, around the circuit board before going to the Inverter connected to the Habitation battery. 

Some British built Motorhomes may have a separate Split Charge relay mounted outside the main Power Controller/charger unit. 
Please be aware that they are not heavy duty items, they will still be subject to overheating/burning if you ask them to look after a bigger battery bank that they were designed to handle, see text below. 

Note also that the cabling to the Habitation batteries is woefully undersized compared to French, German, Italian, etc built Motorhomes. Not just inadequate for heavy Alternator charge currents, but also efficiency. Voltage drop on this cabling can be significant, reducing real World charging by quite a factor. 


Just because you can safely add additional batteries to some vehicles, doesn't mean you can safely do so to all Motorhomes/Caravans. 
If you understand the load you are imposing on the wiring, charger, power distribution unit, Alternator, etc. and then manage it accordingly, then you may be able to work around these limitations.

Things You Might Want to Think About If Increasing The Battery Bank Size, Even Slightly?

Where a Motorhome has separate Split Charge, Fridge, etc Relays (typically older British built Motorhomes) can we suggest you check that the Split Charge relay is of adequate rating if you increase the battery bank size? 
While some are OK as far as the 'current rating' goes in passing the extra power from the Alternator to the bigger Habitation battery bank, it is often a good idea to uprate the 'Split Charge' Relay to a higher amperage. This allows you to take advantage of the lower voltage drop that bigger Relay switch contacts should give, especially after a few months use where burning may degrade a smaller relays contacts. 
Something like this 100A Relay below found on eBay for less than £7?

Like the above relay, the best extra heavy duty relays also often have 'bolt on' connectors overcoming the limitations of the Spade type when currents increase. We sometimes see burnt Spade connectors on 'separate relay' installations when batteries are used beyond their life or the bank is increased. 

One way of installing a heavy duty relay is to use the existing/old Split charge relay to drive the Uprated relay. This prevents the bigger relays coils from overloading the low current Alternator D+ circuit. 
Don't just drive the big heavy Duty relay direct from the D+ circuit unless you are sure the relay coils won't draw more than 0.5 amp max. 

If you get issues with the Ignition Warning light illuminating after fitting a Big relay, then drive it via another low power consumption relay.

Suggest you do not adopt a Voltage sensing 'Intelligent' relay if you didn't have one already, as they can change the way things function introducing undesirable side effects. A good example is the last post in this thread :

Along with decent sized cable, a chunky relay can make quite a difference to the charging rate when Alternator charging on these vehicles, which tend to have less than ideal cable/connector sizing in terms of Voltage drop. Especially relevant when extra charge current is being passed. 

Sometimes the best way of uprating the cable is to run an equal sized parallel cable, rather than ripping out the old and replacing with a single larger cross section cable. Using big fat cable can give issues when it comes to connectors, as many readily available connectors won't take very fat cable, We suggest that DIY solutions are better utilising two thinner cables. 
Bear in mind that just adding a second cable the same size as the original cable will double the carrying capabaility, however we would suggest a slightly thicker second cable would work even better?

It might be worth thinking about running a separate chunky Negative/Earth cable directly from the Starter battery negative Post to the Habitation Negative battery post on a British built Motorhome, even if you don't uprate the Positive cable. 
Even better would be to also run a Negative/Earth lead from the Alternator body to the habitation battery.
Don't trust the Base vehicles Earth to be perfect, especially on a Fiat, Peugeot or Transit Base, as the Engine 'Earths' are known to be a weak point. 

If you suffer Alternator failure, quite common on Motorhomes with enlarged battery banks or Lithium upgrades, then take the opportunity of the Garage working in that area to attach a decent sized (minimum 16mm/110amp?) Earth cable from the Alternator body/Lug to the Starter battery negative.
Also think about asking for new Engine/gearbox earth straps.

On a Fiat based Autotrail, Elddis, etc. uprating the relay and both cables can be nearly as good as installing a B2B if you increase the Habitation battery bank size.       
The aim should be to get the habitation battery voltage to within 0.1v of the voltage at the Starter battery when the Alternator is spinning in order to ensure the enlarged battery bank gets the best possible Alternator charge. 
If the voltage at the Habitation battery is already the exact same 14.4v of the Starter battery when under Alternator charging/Fridge 14.4v load, then you don't need to uprate anything.

Poor cabling, connectors or relays between the Alternator and the habitation battery bank will not only reduce the real world charge to the Habitation batteries, extending charge time, but also place extra strain on the Alternator. 

Remember the Earth Points focused on here are that of the Alternator, not just Engine or Chassis. You might have a fantastic Engine/Gearbox earth point but if the mounting between the Alternator body and the Engine Earth strap isn't good, you will have problems. 
When a modern Motorhome Alternator can pass upto 160amps, it should have it's own dedicated Earth strap to the vehicle body and then onto the Starter Battery.
If you have a Battery 2 Battery charger or a big battery bank, the Alternator Earth may be critical to reliability and usability. While the B2B instructions might say to take connection points from the Starter battery, it is obviously more sensible to go direct to the Alternator for both Positive and Negative, where appropriate, as this is where the mega amps will come from. Same applies to the feed for a big Split charge relay.

All the above is primarily about voltage drop in charging, but it can be an issue with Fridge 12v running as well. If you suffer significant voltage drop to the Fridge, the Fridge will obviously be less effective as well.

Suggestion on how to check the effectiveness of various Earth points. 

This is not an idiots guide, you need to understand the basics.
Turn EHU 'OFF' then get a pen and paper to record the readings we will take.
With the engine running at a fast idle/2,000 rpm, the Fridge on '12v' and a few 'consumers' on to draw some 12v power, record the voltage reading taken between the Starter battery live 'Clamp', which has all the fuses 'built in', and a clean earth on the Alternator body.
Then record the readings at both Starter battery and Habitation battery Posts (the battery posts themselves not the clamps to rule out corroded clamp/battery terminals). 

There should be almost no voltage difference.
If there is any drop something maybe amiss.

Consider repeating the voltage checks using a 'Black/negative Jump Lead' as a temporary Earth strap clamped between 
 the Alternator body to Chassis. 
Always to perfect shiny metal, it is important that the Jump Lead has absolutely perfect connectivity.

Then repeat with the Black Jump Lead running from the Starter battery Negative terminal and the Alternator earthed body or as close to it as you can get on the Engine. 
On a Motorhome with the Starter battery under the Cab floor or Seat where a standard Jump Lead may not be long enough, just Clamp the Black Jump lead between the Starter battery Negative terminal and the Chassis.

Compare voltages and see where the Black jump lead made a difference and fit a strap at that point, if needed.

When are additional batteries a real advantage?

If you rely on the Alternator to charge up the batteries between stays, then having two batteries could half the charging time.
For example if you might normally take 40Ah out of a single 100Ah during a short stay and then rely on your driving to charge that battery up the battery would typically draw around 10amps from the Alternator. 
Therefore a drive of 4 hours might be required. 

Under these conditions, If you then install a second 100Ah battery and this time take the same 40Ah with 20Ah taken out of each battery, then the Alternator will still charge at around 10amps per battery, effectively putting back 20 amps in an hour, so the recharge time will be halved. It isn't quite that simple, but demonstrates the principal.

The overall load on the Alternator isn't any greater because the Alternator is still putting back the same 40Ah, but in a shorter time. 
In reality the reduced stress on the two batteries versus a single battery will mean the dual batteries will be more efficient for longer again aiding shorter recharge times. Obviously batteries that are less stressed will be more efficient, so recharge more efficiently and in a shorter time.
Obviously discharging each battery by more than 40Ah will create a different picture altogether. 

Likewise if you wish to shorten charging times on 230v mains charger, to maybe shorten the running time of a generator for example, then again a second battery can reduce Generator running time (and it's fuel consumption) significantly, so long as the batteries are only shallow discharged and the charger is correctly sized. 
If you also add a second mains charger, then the Generator running time can be cut from about 3 hours to around one hour. That enables you to choose the time slot to charge the batteries to coincide with times when no one is around.

However, adding a another battery and discharging to 80% Depth Of Discharge (so only 20% of power remains in each of the batteries) is obviously going to put a major strain on all the infrastructure with something eventually failing if it isn't all sized to cope.

You can see from the above text, it is more about managing the load on the charging systems, rather than pure numbers. 
One way of doing that can be to switch batteries in and out of circuit, so the charging systems only ever 'see' a single battery at a time. 
But they need to be managed intelligently.

No idea why this fuse board burnt out, but from the seat of the fire, we can guess. 

When adding a second battery don't wire it as below. However, just moving the Earth/Negative connection from Battery A to battery B would be the correct way to wire it, Although it looks only a subtle change, it is actually a significant one.