Motor home battery help

[normspanners]

I decided I’m fitting a second alternator and battery, with a method of temporarily joining to the main battery if needed

That WAS the best way without a doubt and what a lot of boat owners do, it is what I did in the end with my recovery trucks and ended all the constant second battery woes, the more modern ideas now are 12v to 12v chargers then there is no need for a second alternator also you can get 12v to 24v chargers if required.
My mate who is an auto sparks working on cars / trucks had a second 24v alternator in his old van to charge his 24 v battery bank, you can get a split reg that can do 12 or 24 v off the same alternator as a lot of alternators are the same unit it is just the reg that is different, but he has now gone to 12v to 12v and 12v to 24v electronic chargers to charge his auxiliary batteries because the vans as std have massive 120A smart charge alternators, as they cant have second batteries connected to them, but the massive capacity of modern charging allows the 12v system to charge the second battery totally seperately.

 

[normspanners]

What you need is a split charge diode. These are common and cheap, and they enable two (or more) batteries to be charged from the same source, regardless of those batteries' differing capacity.

Sterling make one at around £40 which uses diodes with reduced voltage drop.

Total waste of time it never works I am affraid because of the volt drop through a diode the second battery always lagges by nearly a volt and cant be used on modern alternators.

 

[Kayos]

That was the best way without a doubt and what a lot of boat owners do, it is what I did in the end with my recovery trucks and ended all the constant second battery woes, the more modern ideas now are 12v to 12v chargers then there is no need for a second alternator also you can get 12v to 24v chargers if required.
My mate who is an auto sparks working on cars / trucks had a second 24v alternator in his old van to charge his 24 v battery bank, you can get a split reg that can do 12 or 24 v off the same alternator as a lot of alternators are the same unit it is just the reg that is different, but he has now gone to 12v to 12v and 12v to 24v electronic chargers to charge his auxiliary batteries because the vans as std have massive 120A smart charge alternators, as they cant have second batteries connected to them, but the massive capacity of modern charging allows the 12v system to charge the second battery totally seperately.

It seems obvious in my case, no aircon or ace means I have a spare mount and space to install it

 

[normspanners]

You only have to look at modern ambulances they have gone to great lengths to alleviate the problems they were having keeping up with battery use if it was that simple they wouldnt need to do it.

 

[knighty]

The alternator is shut down by the higher battery voltage, the lagging battery is then not charged enough and will only attain a certain capacity and never go higher it is well known fact this happens. 'Sometimes' you can be lucky and the batteries are matched and receive and equal charge it is a well documented but it very rarely does. the lagging battery then 'pulls down' the good battery when connected together long term.

reply to this and other posts above

the batteries are in parallel... so they've both the same voltage

alternators don't 'shut down' at a set voltage, they deliver a set voltage... once the battery is pulled up (charged) to that voltage no more current will flow (as long as no other loads)

if you pull a lead acid battery up to over 14v it will be fully charged

 

[knighty]

After wasting hours and hours reading up on split charge, joining batteries and the huge amount of different opinions I decided I’m fitting a second alternator and battery, with a method of temporarily joining to the main battery if needed

instead of doing that, you could fit a big relay/contactor between the batteriees

have the relay powered on by the regulator wire from the alternator (the small wire running to the warnight light in the dash)

when the engine is running the alternator will be able to put out more than enough power to charge both batteries (unless you're talking about massive loads)

saves fitting the extra alternator etc.

and you can fit a push button to power the contactor up and join the batteries together.... incase your starter battery runs flat :-)

 

[Kayos]

instead of doing that, you could fit a big relay/contactor between the batteriees

have the relay powered on by the regulator wire from the alternator (the small wire running to the warnight light in the dash)

when the engine is running the alternator will be able to put out more than enough power to charge both batteries (unless you're talking about massive loads)

saves fitting the extra alternator etc.

and you can fit a push button to power the contactor up and join the batteries together.... incase your starter battery runs flat :-)

I'm talking massive loads or I wouldn't be considering the second battery

 

[normspanners]

alternators don't 'shut down' at a set voltage, they deliver a set voltage... once the battery is pulled up (charged) to that voltage no more current will flow (as long as no other loads)

No they do not especially smart charge ecu controlled units.






Auxiliary Battery Charging In Vehicles With 'Smart' Alternators

Vehicle manufacturers are having to comply with increasingly stringent environmental regulations so are continually researching and employing clever technologies to lower fuel consumption and reduce emissions. One of the technologies that has been around for several years, but which is now becoming standard on new vehicles, is the 'smart' or 'intelligent' ECU-controlled alternator.

For those of us wanting to charge a second (auxiliary or leisure) battery whilst driving this presents a problem because traditional split charge systems cannot be used. This article explains why and looks at how Battery-To-Battery chargers overcome these issues and the other benefits they have when compared with split charging.

Note: this issue is not generally applicable to boats as the emissions regulations that apply to vehicles don't apply to leisure craft and so 'smart' alternators on boats are relatively rare.


the current flowing is shut down on a std alternator by the highest voltage battery, the lower voltage battery stays at the lower voltage and even more so with smart charge ecu controlled alternator that varies output voltage, your knowedge is old school I am afraid
Relays cables contacts all produce volts drop so only exasperates the problems the only way to do it properly is as above,
that is why you dont see modern vehicles with twin batteries any more because of the inherent problems, some transits have twin batteries but have a complicated relay setup that isolates batteries from time to time to prevent problems.

Believe what you want, unfortunately the old system is flawed, the facts are well documented, that modern systems do not like twin battery systems and they dont work long term, without damaging batteries long term.

 

[knighty]

the current flowing is shut down on a std alternator by the highest voltage battery, the lower voltage battery stays at the lower voltage and even more so with smart charge ecu controlled alternator that varies output voltage, your knowedge is old school I am afraid
.

As I said before the voltage at both batteries is the same, you can't have 2 batteries on parralel at different voltages


Non of the ecu controlled alternators I've read up on work like that, all the do is very alternator output (and so load on the engine) depending on the load you put on the engine by driving

So when you start up a cold engine they don't put much alternator load on the engine till you're driving or till it's warned up

When you floor it the reduce alternator load so you get more power to the wheels (some shut off aircon too)

Also the transit system is simple, one better is for the starter motor, the other battery dies everything else, there's a big contactor which joins the batteries in parralel when you turn the ignition on. Idea being you can never run both flat if you leave your lights on etc. It's standard on all lwb transits 2007 and after

The important thing here is you can't have 2 batteries in parralel at different voltages.... if you can link me to anything that says different I'll be more than happy to read it

 

[fizzy]

This will dry her hair without dragging the batteries down!

 

[J1nx]

the current flowing is shut down on a std alternator by the highest voltage battery, the lower voltage battery stays at the lower voltage

I’m afraid you have been mis-informed. Two parallel batteries will be at the same voltage.

Charge will be determined by the current flow through each battery. The internal impedance will limit the current so they auto balance. A small battery (of the same type) will have a higher impedance and thus take less charge than a larger one. This keeps them balanced.

Paralleling batteries is common practice in many other applications without issue.

 

[normspanners]

I’m afraid you have been mis-informed. Two parallel batteries will be at the same voltage.

Well I am afraid YOU have been mis-informed if the batteries are at different stages of charge which they will be because of cabling connectors etc etc even the various cells in one battery can be at different stages !

Non of the ecu controlled alternators I've read up on work like that, all the do is very alternator output (and so load on the engine) depending on the load you put on the engine by driving

So the specialists are wrong then ? For one Not all batteries are the same technology and require different voltages and as batteries age they require different voltages

Technical information
Most manufacturers now employ an electronically controlled alternator system by using the engine's ECM, also referred to as the Powertrain Control Module (PCM), but Ford were one of the first to introduce such a system which they refer to as ‘Smart Charging’.

The concept of Smart Charging is actually fairly straightforward. A battery has the capacity to take a slightly higher-voltage charge when cold, so the ECM charges the battery at a slightly higher capacity when cold and balances the charge rate against consumer loads.

The alternator works at maximum capacity only when absolutely necessary and the battery is kept in a constant and healthy state of charge. Battery temperature is estimated from the intake air temperature sensor, which is a good indication of the temperature under the hood.

Battery type warning: Ford specify a silver calcium battery for use with this system. A conventional lead-acid battery is not suitable.

For all of the latest spec vehicles including Mercedes Blue Efficiency Sprinters, VW T5 and T6 Blue motion, Vauxhall Ecoflex and Fords Econetic Transits it is recommended to use a battery to battery charger form range of battery to battery chargers, smart charging alternator kits or Sterling Power products. This is because the alternators on these vehicles will cut alternator power when not needed to save fuel then raise this voltage to very high levels when needed which can damage both relay and leisure battery.

I think these people might have an idea of what they are talking about http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

Batteries have three stages of 1 charge constant current 2 topping charge 3 float charge
and so, if the batteries are at a slightly different state of discharge the minute differences required to charge a battery fully cant be met if the batteries are not EXACTLY equal after all most vehicle batteries are only at 70-80 % charge rate because of the time the vehicle is running because they never achieve the float charge state. unless the vehicle is driven for 20 hrs or more so therefore impossible. also the temperature of a battery makes a huge difference to its state of charging therefore two batteries could be at different temperatures in different areas of a vehicle.

Learn how to optimize charging conditions to extend service life.

The lead acid battery uses the constant current constant voltage (CC/CV) charge method. A regulated current raises the terminal voltage until the upper charge voltage limit is reached, at which point the current drops due to saturation. The charge time is 12–16 hours and up to 36–48 hours for large stationary batteries. With higher charge currents and multi-stage charge methods, the charge time can be reduced to 8–10 hours; however, without full topping charge. Lead acid is sluggish and cannot be charged as quickly as other battery systems. (See BU-202: New Lead Acid Systems.)

Lead acid batteries should be charged in three stages, which are [1] constant-current charge, [2] topping charge and [3] float charge. The constant-current charge applies the bulk of the charge and takes up roughly half of the required charge time; the topping charge continues at a lower charge current and provides saturation, and the float charge compensates for the loss caused by self-discharge.

During the constant-current charge, the battery charges to about 70 percent in 5–8 hours; the remaining 30 percent is filled with the slower topping charge that lasts another 7–10 hours. The topping charge is essential for the well-being of the battery and can be compared to a little rest after a good meal. If continually deprived, the battery will eventually lose the ability to accept a full charge and the performance will decrease due to sulfation. The float charge in the third stage maintains the battery at full charge. Figure 1 illustrates these three stages.

Figure 1: Charge stages of a lead acid battery.
The battery is fully charged when the current drops to a set low level. The float voltage is reduced. Float charge compensates for self-discharge that all batteries exhibit.
Courtesy of Cadex

The switch from Stage 1 to 2 occurs seamlessly and happens when the battery reaches the set voltage limit. The current begins to drop as the battery starts to saturate; full charge is reached when the current decreases to 3–5 percent of the Ah rating. A battery with high leakage may never attain this low saturation current, and a plateau timer takes over to end the charge.


The correct setting of the charge voltage limit is critical and ranges from 2.30V to 2.45V per cell. Setting the voltage threshold is a compromise and battery experts refer to this as “dancing on the head of a needle.” On one hand, the battery wants to be fully charged to get maximum capacity and avoid sulfation on the negative plate; on the other hand, over-saturation by not switching to float charge causes grid corrosion on the positive plate. This also leads to gassing and water-loss.

Temperature changes the voltage and this makes “dancing on the head of a needle” more difficult. A warmer ambient requires a slightly lower voltage threshold and a colder temperature prefers a higher setting. Chargers exposed to temperature fluctuations include temperature sensors to adjust the charge voltage for optimum charge efficiency.

The charge temperature coefficient of a lead acid cell is –3mV/°C. Establishing 25°C (77°F) as the midpoint, the charge voltage should be reduced by 3mV per cell for every degree above 25°C and increased by 3mV per cell for every degree below 25°C. If this is not possible, it is better to choose a lower voltage for safety reasons. Table 2 compares the advantages and limitations of various peak voltage settings.



2.30V to 2.35V/cell

2.40V to 2.45V/cell

Advantages

Maximum service life; battery stays cool; charge temperature can exceed 30°C (86°F).

Higher and more consistent capacity readings; less sulfation.

Limitations

Slow charge time; capacity readings may be inconsistent and declining with each cycle. Sulfation may occur without equalizing charge.

Subject to corrosion and gassing. Needs water refill. Not suitable for charging at high room temperatures, causing severe overcharge.

CONTINUED

 

[GW8IZR]

After a fairly short period of time, two batteries in parallel connected with reasonable sized conductors will equalise to the exact same potential, no matter how much cut and paste to the contrary says.

 

[normspanners]

Table 2: Effects of charge voltage on a small lead acid battery.
Cylindrical lead acid cells have higher voltage settings than VRLA and starter batteries.


Once fully charged through saturation, the battery should not dwell at the topping voltage for more than 48 hours and must be reduced to the float voltage level. This is especially critical for sealed systems because they are less tolerant to overcharge than the flooded type. Charging beyond the specified limits turns redundant energy into heat and the battery begins to gas.

The recommended float voltage of most flooded lead acid batteries is 2.25V to 2.27V/cell. Large stationary batteries at 25°C (77°F) typically float at 2.25V/cell. Manufacturers recommend lowering the float charge when the ambient temperature rises above 29°C (85°F).

Figure 3 illustrate the life of a lead acid battery that is kept at a float voltage of 2.25V to 2.30V/cell and at a temperature of 20°C to 25°C (60°F to 77°F). After 4 years of operation permanent capacity losses become visible, crossing the 80 percent line. This loss is larger if the battery requires periodic deep discharges. Elevated heat also reduces battery life. (See also BU-806a: How Heat and Loading affect Battery Life.)

Figure 3: Capacity loss on standby.
Permanent capacity loss can be minimized with operating at a moderate room temperature and a float voltage of 2.25–2.30V/cell.
Source: Power-Sonic


Not all chargers feature float charge and very few road vehicles have this provision. If your charger stays on topping charge and does not drop below 2.30V/cell, remove the charge after 48 hours of charging. Recharge every 6 months while in storage; AGM every 6–12 months.

These described voltage settings apply to flooded cells and batteries with a pressure relief valve of about 34kPa (5psi). Cylindrical sealed lead acid, such as the Hawker Cyclon cell, requires higher voltage settings and the limits should be set to manufacturer’s specifications. Failing to apply the recommended voltage will cause a gradual decrease in capacity due to sulfation. The Hawker Cyclon cell has a pressure relief setting of 345kPa (50psi). This allows some recombination of the gases generated during charge.

Aging batteries pose a challenge when setting the float charge voltage because each cell has its own unique condition. Connected in a string, all cells receive the same charge current and controlling individual cell voltages as each reaches full capacity is almost impossible. Weak cells may go into overcharge while strong cells remain in a starved state. A float current that is too high for the faded cell might sulfate the strong neighbor due to undercharge. Cell-balancing devices are available compensate for the differences in voltages caused by cell imbalance.

Ripple voltage also causes a problem with large stationary batteries. A voltage peak constitutes an overcharge, causing hydrogen evolution, while the valley induces a brief discharge that creates a starved state resulting in electrolyte depletion. Manufacturers limit the ripple on the charge voltage to 5 percent.

Much has been said about pulse charging of lead acid batteries to reduce sulfation. The results are inconclusive and manufacturers as well as service technicians are divided on the benefit. If sulfation could be measured and the right amount of pulsing applied, then the remedy could be beneficial; however giving a cure without knowing the underlying side effects can be harmful to the battery.

Most stationary batteries are kept on float charge and this works reasonably well. Another method is the hysteresis charge that disconnects the float current when the battery goes to standby mode. The battery is essentially put in storage and is only “borrowed” from time to time to apply a topping-charge to replenish lost energy due to self-discharge, or when a load is applied. This mode works well for installations that do not draw a load when on standby.

Lead acid batteries must always be stored in a charged state. A topping charge should be applied every 6 months to prevent the voltage from dropping below 2.05V/cell and causing the battery to sulfate. With AGM, these requirements can be relaxed.

Measuring the open circuit voltage (OCV) while in storage provides a reliable indication as to the state-of-charge of the battery. A cell voltage of 2.10V at room temperature reveals a charge of about 90 percent. Such a battery is in good condition and needs only a brief full charge prior to use. (See also BU-903: How to Measure State-of-charge.)

Observe the storage temperature when measuring the open circuit voltage. A cool battery lowers the voltage slightly and a warm one increases it. Using OCV to estimate state-of-charge works best when the battery has rested for a few hours, because a charge or discharge agitates the battery and distorts the voltage.

Some buyers do not accept shipments of new batteries if the OCV at incoming inspection is below 2.10V per cell. A low voltage suggests a partial charge due to long storage or a high self-discharge caused by a micro-short. Battery users have found that a pack arriving at a lower than specified voltage has a higher failure rate than those with higher voltages. Although in-house service can often bring such batteries to full performance, the time and equipment required adds to operational costs. (Note that the 2.10V/cell acceptance threshold does not apply to all lead acid types equally.)

Under the right temperature and with sufficient charge current, lead acid provides high charge efficiently. The exception is charging at 40°C (104°F) and low current, as Figure 4 demonstrates. In respect of high efficiency, lead acid shares this fine attribute with Li-ion that is closer to 99%. See BU-409: Charging Lithium-ion and BU-808b: What Causes Li-ion to Die?

Figure 4: Charge efficiency of the lead acid battery.
At the right temperature and with sufficient charge current, lead acid provides high charge efficiency.
Source: Power-Sonic


Watering
Watering is the single most important step in maintaining a flooded lead acid battery; a requirement that is all too often neglected. The frequency of watering depends on usage, charge method and operating temperature. Over-charging also leads to water consumption.

A new battery should be checked every few weeks to estimate the watering requirement. This assures that the top of the plates are never exposed. A naked plate will sustain irreversible damage through oxidation, leading to reduced capacity and lower performance.

If low on electrolyte, immediately fill the battery with distilled or de-ionized water. Tap water may be acceptable in some regions. Do not fill to the correct level before charging as this could cause an overflow during charging. Always top up to the desired level after charging. Never add electrolyte as this would upset the specific gravity and promote corrosion. Watering systems eliminate low electrolyte levels by automatically adding the right amount of water.


Simple Guidelines for Charging Lead Acid Batteries

• Charge in a well-ventilated area. Hydrogen gas generated during charging is explosive. (See BU-703: Health Concerns with Batteries)
• Choose the appropriate charge program for flooded, gel and AGM batteries. Check manufacturer’s specifications on recommended voltage thresholds.
• Recharge lead acid batteries after each use to prevent sulfation. Do not store on low charge.
• The plates of flooded batteries must always be fully submerged in electrolyte. Fill the battery with distilled or de-ionized water to cover the plates if low. Never add electrolyte.
• Fill water level to designated level after charging. Overfilling when the battery is on low charge can cause acid spillage during charging.
• The formation of gas bubbles in a flooded lead acid indicates that the battery is reaching full state-of-charge. (Hydrogen appears on negative plate and oxygen on positive plate).
• • Lower the float charge voltage if the ambient temperature is higher than 29°C (85°F)..
• Do not allow a lead acid to freeze. An empty battery freezes sooner than one that is fully charged. Never charge a frozen battery.
• Avoid charging at temperatures above 49°C (120°F).

 

[normspanners]

After a fairly short period of time, two batteries in parallel connected with reasonable sized conductors will equalise to the exact same potential, no matter how much cut and paste to the contrary says.

yes they will, to a certain degree but cabling and connection conditions vary and it is that differences that cause problems But that is not always good for the seperate batteries or their state of charge.

 

[GW8IZR]

yes they will But that is not always good for the seperate batteries or their state of charge.

I didn't say it was. Saying that a charging system will fail to fully charge a battery because of different capacities and the start voltage shows a lack of understanding of batteries and charging systems.

In any constant potential charging system (even when that constant potential is varied at differing stages of the charge process) provided the current available is sufficient to be greater than the internal leakage of the combined cells, paralleled batteries of the same technology will be fully charged given sufficient time, that is a fact that is indisputable.

Charging banks of batteries in parallel isn't fundamentally wrong.

It becomes complex when the application involves discharging part of the bank in isolation to the rest of the bank, regardless of any hokum pokum about smart charging technology.

 

[normspanners]

I think that all the manufacturers and specialists warning that fitting second batteries to vehicles is not a good idea, have a valid reason for stating these facts.
Why would fors maintain that silver cadmium batteries must be used with smart charge systems

regardless of any hokum pokum about smart charging technology.

It is not hokum pokum saying THAT shows a lack of knowledge, ford would not state that it it requires silver cadmium batteries to match their smart charge systems if it was not required, If other batteries are used problems occur, read some the information available, not all the various specialists can be wrong just because you think you know better.

 

[GW8IZR]

I think that all the manufacturers and specialists warning that fitting second batteries to vehicles is not a good idea, have a valid reason for stating these facts.

indeed they do :-)

 

[knighty]

I think that all the manufacturers and specialists warning that fitting second batteries to vehicles is not a good idea, have a valid reason for stating these facts.

But that's exactly how Ford transits are setup with dual batteries

A big relay which connects them together when the ignition is ok

There's miles and miles of cut and past in this thread but nothing that proves your point

 

[normspanners]

There's miles and miles of cut and past in this thread but nothing that proves your point

try reading it
And try reading the amount of transit battery issues with the old style relays