Thread: Warning on auxiliary batteries

Originally Posted by Wilbur

1. The D4 has a multi-stage charging system (aka smart alternator) that uses a higher voltage until the cranking battery is fully charged then drops back to a float voltage of 13.2 volts.

WRONG, and not even close, what you are referring to is the way a D3 and a 2.7L D4 alternator works.

A D4 3L and RRS TDV8 alternators have a completely different operating system.

Originally Posted by Wilbur

2. AGM batteries will take an impossibly long time to fully charge at 13.2 volts. Even at 13.5 volts, a Fullriver AGM battery takes 60 hours charge to just 55%. Reference, Fullriver batteries, their graph included in details section.

This one is a ripper. Not only can you fully charge any battery, not just Fullriver batteries, with as little as 13.2v, there are plenty of D3 owners on this site who not only have Fullriver batteries, but their batteries are mounted in a caravan or camper trailer who have no problems fully charging their batteries down a long length of cable, while they drive.

Or are you implying they jump in the D3 and drive for 60 hours straight. The reality is that the average drive time to bring two 100 Ah deep cycle batteries ( Fullriver or otherwise ), mounted in a caravan or camper trailer, with a tow vehicle voltage of 13.2v, from around 50% SoC to at least 95% SoC would be less that 6 hours, not 60 hours.

Originally Posted by Wilbur

3. Because the D4 has a multi-stage charging system, extra loads MUST NOT be connected directly to the battery posts. Hopefully when I get my D4 I will be able to find the correct connection points and advise the forum.

With both the D3 and the D4 ( and for that matter the RRS and RR Vogue ) there is a designated earth post clearly indicated in the manual.

Originally Posted by Wilbur

4. Any extra electric loads have the potential to cause problems with the car ECU. With most devices, the risk of trouble is vanishingly small but with dual battery systems there is a slim but real risk of trouble. This presumably is why Land Rover won’t honour warranties if such after-market electronic devices are fitted. To make the ECU impervious to interference by other electronic devices is possible but extremely difficult, especially in an automotive environment. DC-DC converters are less likely to cause problems than solenoid based dual battery systems.

Since when won’t LR honour warranties if a standard dual battery system is fitted. A number of DEALERS have stated they won’t warranty a vehicle with a dual battery system in it, but LR has not made any such statements, furthermore, where customers of those same dealers have gone ahead and fitted a dual battery system, not one, NOT ONE VEHICLE has had a warranty voided when they have fitted one of my dual battery systems, here or anywhere else in the world.

So again, got any evidence to back this claim, especially when you concider that quite a few LR Dealerships fit my gear to NEW LRs



I’m not going to waste my time and everybody else’s time by correcting all you have posted, I will cover one specific section.

You posted about voltage SPIKES but most of the "info" you post about relates to voltage SURGES. Every single electronic device in use everywhere in the world, has SPIKE protection built in, and this includes your ECU. Furthermore, it would take something like someone using an electric welder for an ECU to be damaged by voltage spikes, or you could just have the vehicle struck by lightning.

Whereas voltage SURGES are a way of life in DC systems and are NOT protected against because they cause no problems.

To back the point, do a Google of voltage SURGE protection devices. They are ALL for AC applications.

DC systems, especially those in a motor vehicle will tolerate massive voltage surges with no effects being caused and again a perfect example of the biggest voltage surge that occurs in EVERY VEHICLE, numerous times EVERY DAY is when you start your motor.

Before you turn the ignition key, the cranking battery will have, on average, about 12.5+ volts. You turn the key and the volts cans drop to 8v and then rise to over 15v once the motor fires up. And all this happens over a second or two.

Voltage SPIKES have a duration of millisecond.

Some “FACTS”.

The alternators in D3s and D4s are NOT multi stage chargers.

Multi stage charging is something that battery chargers and DC-DC devices do because of the limitations. They don’t have the grunt needed to “BOOST” charge a battery when it’s in a low state of charge.

Most people think that when you hook up a battery charger or DC-DC devices, the battery is charger 14+ volts. Not so and what actually happens, if the battery is low, the charge will apply a given current ( based on the size of the charger ).

Again, if the battery is low, when this current is first applied, the voltage at the battery will not be 14+ volts, if the battery is very low, the charger voltage could easily be as low as 12v.

As the battery charges, the voltage rises until a point is reached where the charger’s output voltage will be at 14v or higher, BUT this is only when the battery is near fully charged.

The charger will then go though a number of different cycles till the battery is fully charged and the charger then goes into a Float mode.

As for the different voltages for charging different battery types, like 14.4v for AGMs, 14.7v for flooded wet cell batteries, these are NOT the voltages the charger charges at, these are the maximum voltages that the charger can apply to these types of batteries without risking damaging the battery and again, these voltages are only obtainable once the battery is nearly fully charged.

Now once again, the alternators in D3s and D4s are NOT multi stage chargers, they are constant voltage chargers, also known as tapered charging.

What new alternators do is a “BOOST” charge straight after the motor is first started. NOTE, the is a BOOST charge where a MAXIMUM voltage is applied to the cranking battery in an attempt to allow the battery to rise to a fully charged state in the shortest time possible.

Again note, an alternator applies both a high VOLTAGE and a high CURRENT when the battery is in it’s lowest state. This is the exact opposite to how battery chargers and DC-DC devices work. So at the very time when a battery needs the highest charging voltage and current, an alternator can deliver what is needed, but the reverse is the case for battery chargers and DC-DC devices, they can not deliver when they are needed to.

After a given time, with a D3 and 2.7L D4, a time of 10 to 30 minutes, the alternator voltage level drops to the operating voltage, and this can be anything from 13.2v up.

This is not multi stage charging, the vehicle manufacturers don’t give a rats arse if the battery has reached a fully charged state or not, all they are interested in doing is getting a rapid replacement charge into the battery and then lower the operating voltage down as low as they can, as soon as they can so they can reduce the load the alternator is putting on the motor.

A quick electrical lesson. In DC circuits, most devices will reduce their current draw as the voltage applied to them is lowered. So the lower the operating voltage, the lower the current draw, and as the amount of current being draw from an alternator equates to the amount energy the alternator needs to pull from the motor, lowering the operating voltage means less energy required from the motor.

This in turn means less fuel is needed so ultimately and what the vehicle manufacturers are aiming at, there is less exhaust emissions.

This is what lower alternator operating voltages are all about, lower exhaust emissions, and has absolutely nothing to do with “multi stage charging”

D4 alternator voltage operations ( excluding 2.7L d4s ) goes much further but I’ll only go there if others what more info.

[QUOTE=drivesafe;1470281]Some “FACTS”.

A quick electrical lesson. In DC circuits, most devices will reduce their current draw as the voltage applied to them is lowered. So the lower the operating voltage, the lower the current draw,



Umm, not if P=EI still

example 60w= 12v X 5A
60W= 10V X 6A

Or I'm confused but lower voltage and current increases

Cheers Ken

Originally Posted by drivesafe

..... I’ll only go there if others what more info.

ISTR this topic was done to death not so long ago.

Originally Posted by roamer

Umm, not if P=EI still

example 60w= 12v X 5A
60W= 10V X 6A

Or I'm confused but lower voltage and current increases

Cheers Ken

You're assuming the device can increase its current draw to maintain power consumption, yet most devices (eg lights) have no ability to increase their current draw so the result is lower power consumption as the supply voltage lowers. 5A X 10V = 50W

Originally Posted by roamer

Umm, not if P=EI still

example 60w= 12v X 5A
60W= 10V X 6A

Or I'm confused but lower voltage and current increases

Cheers Ken

I'm backing VVV that...

Originally Posted by Graeme

You're assuming the device can increase its current draw to maintain power consumption, yet most devices (eg lights) have no ability to increase their current draw so the result is lower power consumption as the supply voltage lowers. 5A X 10V = 50W

if you lower the voltage and maintain the same power output then yes the current draw must increase....

what generally happens in the real world (automotively speaking) is that as you drop the available voltage in a circuit it uses less power and functions less well. IF the case you are proposing was correct as the power level in the battery deminished (assuming an alternator failure) the headlights would remain at a constant brightness until the current draw became so high that the wiring melted or the fuse blew.

The basic exception to the rule is your startermotor or a dead short... Providing your batteries have the guts to push the volts into a dead short or a stalled motor. While the battery is "healthy" enough to push massive amps into the load there will be a higher current flow even though the voltage reading will be lower than the nominal 12v. As the battery discharges the amps will drop off and we're back into the normal world of deminishing volts=deminishing power.

Got it, thanks that makes sense.

Cheers Ken

Originally Posted by Blknight.aus

I'm backing VVV that...




if you lower the voltage and maintain the same power output then yes the current draw must increase....

what generally happens in the real world (automotively speaking) is that as you drop the available voltage in a circuit it uses less power and functions less well. IF the case you are proposing was correct as the power level in the battery deminished (assuming an alternator failure) the headlights would remain at a constant brightness until the current draw became so high that the wiring melted or the fuse blew.

The basic exception to the rule is your startermotor or a dead short... Providing your batteries have the guts to push the volts into a dead short or a stalled motor. While the battery is "healthy" enough to push massive amps into the load there will be a higher current flow even though the voltage reading will be lower than the nominal 12v. As the battery discharges the amps will drop off and we're back into the normal world of deminishing volts=deminishing power.

A light bulb filament has to be made from a material that has a positive temperature coefficient. (As temperature increases, resistance increases.) Then, as the bulb's temperature rises, its filament's increasing resistance causes less current to be taken than when it was cold. Quite quickly a stable "steady-state" temperature and "running" resistance is reached so that the bulb simply continues to give out a steady amount of light according to the current it is taking from the electricity supply.

Read more: Answers.com - How does a light bulb work

I thought I would just throw this one in !

Cheers Arthur