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Dc-dc charging – how to speed alternator charging
by Collyn Rivers
Dc-Dc Charging
Dc-dc charging charges boat, cabins, camper trailer, caravan and motorhome batteries faster and deeper. Collyn Rivers explains how and why.
Pic: original source unknown.
A rechargeable battery is charged by applying a voltage higher than the battery already has. The higher that voltage difference the quicker such a battery charges. As a battery charges its voltage rises. If that charge voltage is constant, however, the difference between that and the charging battery falls.
Alternators charged at a more or less constant 14.2-14.4 volts until 2000. A few still do. Batteries so-charged rarely exceed 80%. As a result, many in caravans never exceed 65%. Moreover, they take hours for even that.
For some years after, many alternators were temperature controlled. They charged at 14.1-14.2 volts when cold. This reduced to about 13.2 volts once warm. Both types can be made to work well for battery charging via dc-dc alternator charging described below.
Variable voltage alternator charging was introduced around 2013. These are controlled by the engine’s central computer unit. They vary the voltage from 15.4 volts to 12.3 volts. Some drop voltage to zero.
How starter batteries are charged
A vehicle’s starter motor is designed to work with 70%-80% charged batteries. The energy required to start cold engines is tiny. It’s less than 2% of battery capacity. This is typically replaced within two minutes. It’s cheap, rugged and simple. Fine generally for starter battery charging – but not for RV use.
Dc-dc charging
Dc-dc alternator charging overcomes these problems. Working fast, deeply, yet safely, it accepts whatever voltage available. Next, it converts it to that optimally required. It bulk charges at whatever current the battery accepts. Such units thus constantly increase charge voltage as battery voltage rises. This enables charging fully, deeply and rapidly.
Such technology, used for telephone exchange batteries for decades, was later adapted for vehicles. See Battery charging and battery chargers.
Dc-dc charging truly scores with batteries distanced from the alternator. Voltage drop prejudices charging, and fridge operation. Heavy cable is necessary. Locating the dc-dc unit close to the battery ensures adequate voltage. It also extends battery life and can transform three-way fridges.
Voltage sensing relays
These systems require a VSR (voltage sensing relay). The VSR senses starter battery voltage. It directs charge to that battery for two to three minutes after starting. It allows auxiliary battery charging once the starter battery exceeds 13.6 volts. The VSR isolates the starter battery if it drops below 12.6 volts. Some dc-dc chargers have VSR functionality inbuilt.
Regenerative braking
Many hybrid vehicles use regenerative braking. Their starter battery is normally 80% charged. Braking increases alternator voltage. This boosts battery charge to 100%. The battery then provides all electrical energy required. During this, alternator output is zero or too low for charging. This causes the VSR to open. That precludes auxiliary charging for minutes each time.
Regenerative braking necessitates dc-dc charging. It is often known as bc-dc. With this, the charger senses the starter battery voltage. I cover these units in Variable voltage alternator problems with caravans/ The article also shows how to know your alternator’s type.
Bc-dc units are made by companies including Redarc and Sterling Products. Some companies now produce all such products as bc-dc. Moreover, those for use with variable voltage alternators are of Low Voltage form (see above Link).
Installation is generally similar to that below. There is, however, no voltage sensing relay. A signal lead is taken from the ignition switch. Makers give full details.
Installing dc-dc charging
Dc-dc charging ensures a battery is alternator-charged safely, deeply and fast. Ensure this locating the charger close to the main energy load and battery. That load is typically a fridge or fridge freezer.
Dc-dc charging optimises charging but you still need adequate cable. Use 10 mm² (ideally 13.5 mm²) from source to charging unit. Makers explain this – but rarely stress its need.
Most such units ensure starter battery charge priority. Recharging generally takes only two to three minutes. If inbuilt protection is not provided (excepting for bc-dc units) a VSR must be used.
Some dc-dc charging units have an inbuilt solar regulator, and/or mains battery charger. The sketch below shows a typical installation.
Installation may vary from brand to brand and type to type. The unit shown will charge an auxiliary battery from a 12-volt alternator. Furthermore, it does so at up to 40 amps.
How to install a typical dc-dc or bcdc charger. The function safeguarding starter battery voltage is inbuilt. Pic: Redarc.
Programming dc-dc charging
Different battery types require different voltage/current settings. Dc-dc chargers have programs accordingly. No programming is needed for alternator voltage. The systems accept whatever that is.
Lithium (LiFePO4) batteries have different needs. Redarc consequently has units specifically for this purpose. It stresses they be used only with LiFePO4 batteries they recommend.
The specialised Redarc LFP series of dc-dc battery chargers for (specific) LiFePO4 batteries. Pic: courtesy of Redarc.
Issues with dc-dc charging
Basic dc-dc alternator charger does not work well (or at all) with variable voltage alternators. Moreover, doing so may damage the auxiliary battery/s. See above re bc-dc charging.
Initial charging of a deeply discharged battery is generally limited to a basic dc-dc charger’s capacity. Dc-dc chargers under 20 amps may take longer to attain half charge. Thereon, charging is hugely faster. The CTEK Smartpass dc-dc charger overcomes this. Moreover, it allows direct alternator charging until dc-dc charging takes over.
This is of less issue with 30-50 amp units. With these, charging limitations are mostly alternator output, and (for some batteries) the maximum they’ll absorb. This is a lesser issue with gel cells and AGMs. It is not an issue with LiFePO4s.
Pic: CTEK ‘Smartpass’ dc-dc charger. Pic: courtesy of CTEK.
Further information:
If you like this article you’ll truly benefit from my books. All are in down to earth English. Moreover, they are technically accurate. Furthermore, batteries and battery charging is covered in depth in Caravan & Motorhome Electrics.
Solar that Really Works! covers cabins and RVs. Solar for larger homes and properties is covered in Solar Success. The Camper Trailer Book and the Caravan & Motorhome Book cover innumerable issues in depth. Click for my Bio.
See also the many articles on this website. Moreover, click here for Article index.
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Articles by Category
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- Battery charging and battery chargers – how to do it properly
- Blade fuse problems in caravans – they may burn or melt
- Dc-dc charging – how to speed alternator charging
- Electrical converter problems in caravans – problems when used for free camping
- Electrical converters in RVs – they’re unsuitable for free-camping
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- Grid connect solar modules for RVs – here’s how you can use them
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- Inverters for caravans – and motor homes too
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- RV Alternator Charging Problems
- RV Batteries
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- Solar regulators with current shunts – how to fix misleading readings
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Batteries & Battery Charging
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- AGM batteries for caravans – they are still worth using
- Are Lithium-ion Batteries Worth Their Price – homes and properties
- Australian Battery Breakthrough
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- Battery capacity for home and property
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- Battery charging and battery chargers – how to do it properly
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- Blade fuse problems in caravans – they may burn or melt
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- Dc-dc charging – how to speed alternator charging
- Electric and Hybrid Vehicles
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- Generator Battery Charging – Quickly and Deeply
- How long can lead acid batteries last
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- Imported RV electrics
- Interconnecting batteries in parallel or series – here’s how and why
- Lead acid batteries for caravans – they are still a good buy
- LiFePO4 jump starters really do work – they power other things too
- Lighting for caravans – it makes every sense to install LEDs
- Lithium batteries for caravans
- Lithium battery rival
- Lithium battery safety in caravans – are they all the same?
- Lithium-iron batteries in RVs – they are safe to use
- RV Alternator Charging Problems
- RV Batteries
- RV electrical wiring – twin-wire or chassis return – here’s why twin-wire is usually better
- RV Fuel cells – great idea, but cost is too high
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Trailer/Tow Vehicle Behaviour & Suspension
- Caravan and tow vehicle dynamics
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- Caravan wheel placement
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- Loading a Caravan Safely
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Cooling and Heating
- Caravan air conditioning – here’s how
- Caravan fridge problems – how to fix the most common faults
- Carbon Monoxide Poisoning
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- RV Fridge Basics
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General
- Caravan air conditioning – here’s how
- Caravan design need for change
- Caravan facts and opinions – the nonsense so often on caravan forums
- Caravan suspension – it is mostly misunderstood
- 10 Tips for RVing Around Australia
- All solar house – self-building an off-grid all solar house
- Are Lithium-ion Batteries Worth Their Price – homes and properties
- Australian RV Road Rules – Summary
- Baghdad battery myth
- Buy a New RV in 5 Steps
- Buying used caravans – what to check
- Choosing a Caravan Tow Vehicle
- Choosing the right interior fittings for an Australian RV
- Convert to your own all solar home
- Driving across Africa – in 1956/60 the very last time it was possible
- Electric and Hybrid Vehicles
- Electric Vehicle History
- Electric Vehicle Home Charging
- Electric Vehicle Motors
- Electrolysis corrosion in vehicles – how to find and fix it
- Energy and Power
- Ensuring Successful Solar Projects
- Fuel savers do not work – almost all are scams
- Generators for Cabins and RVs
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- Going off the grid
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- How much solar capacity do I need?
- How much solar energy available?
- How much solar input – here’s how to find out
- How to free camp legally in Australia
- How to stop paying for electricity
- Inverters for Homes and Properties
- Is a 4 wheel drive needed for motorhomes
- Is Napisan a Safe Toilet Chemical?
- Lightning risk in RVs – how to reduce that risk
- Living with solar – how make it all work
- Napisan and Look-Alikes safe for Septic Tanks – a professor’s view
- Our Solar Equipped RVs
- Overhung Caravan Hitches
- Problems with stand-alone solar – much applies also to RVs
- Quietening caravan water pumps – easy and cheap to do
- Retarding rust electronically – claims are exaggerated
- RV fault issues – who is responsible?
- RV forum common sense – a rare commodity?
- RV Layout – How to Choose the Best
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- RV Toilets – Which is Best?
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RV Solar
- Australian Battery Breakthrough
- Grid connect solar modules for RVs – here’s how you can use them
- How much solar input – here’s how to find out
- How to tell caravan battery charge – energy monitoring explained
- Lithium batteries for caravans
- Lithium battery safety in caravans – are they all the same?
- Our solar equipped RVs – all proved a major success
- Problems with stand-alone solar – much applies also to RVs
- RV Batteries
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- Solar regulators with current shunts – how to fix misleading readings
Travel
- Caravan design need for change
- Caravan tare weight issues – some declared weights may not be correct
- Caravan wheel placement
- Caravan Length and Stability
- Caravan Tow Ball Weight – how much
- 10 Tips for RVing Around Australia
- Australian Road Rules Confuse
- Australian RV and towing rules and regulations – a general guide
- Australian RV Road Rules – Summary
- Best Way to RV Around Australia
- Buy a New RV in 5 Steps
- Choosing a Caravan Tow Vehicle
- Choosing the right interior fittings for an Australian RV
- Claims for dual-cab ute towing capacity mislead caravan buyers
- Do Not Trust Caravan Declared Mass
- Driving across Africa – in 1956/60 the very last time it was possible
- Electrical converters in RVs – they’re unsuitable for free-camping
- Free camp safely in Australia – this article shows how
- How to free camp legally in Australia
- How to Reverse a Caravan
- Is a 4 wheel drive needed for motorhomes
- Loading a Caravan Safely
- Microwave for RV oven power draw – it’s more than many users think
- Motorhome and trailer tyres
- Need for a WDH – avoid using one if possible
- Overhung Caravan Hitches
- Quietening caravan water pumps – easy and cheap to do
- Reducing caravan sway – here’s how to minimise the causes
- Retarding rust electronically – claims are exaggerated
- RV forum common sense – a rare commodity?
- RV Fridge Basics
- RV Layout – How to Choose the Best
- RV Toilets – Which is Best?
- Safe toilet chemicals – can Napisan be used in septic tanks?
- Sleep apnoea machines for camping – correct choice is vital
- Solar input available for caravans – know what’s available and increase it too
- Top 10 Australian RV Apps
- TV interference from LEDs – here’s what causes it
- Weight Distribution Hitch limits cornering
- What off-road really means
Health & Safety
- Caravan Fuses and Circuit Breakers – how to know which to use
- Caravan nose weight – it’s vital for safe towing
- Caravan weight safe to tow – depends on what tows it
- 10 Tips for Safe Caravan Towing
- Battery ventilation is vital – why take any risk?
- Blade fuse problems in caravans – they may burn or melt
- Carbon Monoxide Poisoning
- Claims for dual-cab ute towing capacity mislead caravan buyers
- Diesel heating in caravans and motorhomes – it’s easy, effective and safe
- Fifth wheelers are safer – here’s why they are
- Free camp safely in Australia – this article shows how
- How to Reverse a Caravan
- Is Napisan a Safe Toilet Chemical?
- Lightning risk in RVs – how to reduce that risk
- LP Gas risk in caravans – deaths & brain damage still occurs
- Making stable caravans – here’s how and why to do it
- Mechanical sway-control has little value at speed
- Napisan and Look-Alikes safe for Septic Tanks – a professor’s view
- Overhung Caravan Hitches
- Overweight RVs – a police point of view
- RV Accident Data (Australia)
- RV Industry Changes Needed
- RV supply cables – choices of current capacity and length
- Safe RV heating – use diesel or LP gas
- Safe toilet chemicals – can Napisan be used in septic tanks?
- Sleep apnoea machines for camping – correct choice is vital
- Towing Without a WDH – Weight Distributing Hitch
- Using correct size cables for RVs is essential
Legal & Compliance
- Caravan and motorhome compliance
- Caravan design need for change
- Caravan tare weight issues – some declared weights may not be correct
- Australian Road Rules Confuse
- Australian RV and towing rules and regulations – a general guide
- Australian RV Road Rules – Summary
- Buying used caravans – what to check
- Gross Combined Mass Upgrades
- Imported RVs – there can be major problems re-registering private imports
- RV Compliance – Here’s how to know
- RV electrical work – Victorian exception
- RV fault issues – who is responsible?
- Tow Vehicle & Caravan Weight Definitions
The Camper Trailer Book
Electric Vehicles
Household Solar
- Ensuring Successful Solar Projects
- Refrigerators for Home and Property Solar
- Solar Regulators for Home and Property Systems
- Battery capacity for home and property
- Best Batteries for Solar Power Storage
- Going off the grid
- Vital things about solar in the USA
- TOP 10 SOLAR SCAMS
- Generators for Home and Property Systems
- Solar Modules for Homes and Properties
- Solar Shadowing – reducing the losses
- Grid connect solar problems – what vendors may not reveal
- Inverters for Homes and Properties
- How to stop paying for electricity
- Have portable solar in your rented home
- Convert to your own all solar home
- Fuel cells for homes and properties
- Upgrading solar system has unexpected traps
- Solar charge your electric car at home
Want to find out more? Our books cover all these topics and a lot more.
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Solar That Really Works! explains every detail of designing and installing solar in boats, camper trailers, caravans and motorhomes.
Caravan & Motorhome Electrics covers every aspect of designing, installing and fault finding of the electrics in fifth wheel and conventional caravans, camper trailers and motorhomes.
The Caravan & Motorhome Book covers every conceivable aspect of camper trailer, caravan and fifth wheel caravan, campervan and motorhome usage.
Caravans and their tow vehicles rarely jack-knife and roll over – but when they do the results are catastrophic. The cause, and how to prevent it, is explained here. Why Caravans Roll Over offers solid advice for keeping yourself safe on the road.
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Solar Success explains how to design and build home and property systems that ensures affordable solar success first and every time.
Between 1959 and 1961 Collyn Rivers and Antony Fleming drove a Bedford QLR off-road truck twice the length and breadth of Africa studying road surface conditions.
A 43 minute film about their adventure, produced and narrated by Antony Fleming, has been viewed on YouTube more than 1.6 million times!
To view the film, and also read Collyn’s telling of the tale, just click the button below.
Whether you’re buying your first RV or updating to a bigger, more comfortable rig, there are a great many things you need to know and consider. This book breaks things down so that you can decide what you want and whether or not what you’ve found is right for you. It’s technically sound and comprehensive so that you can proceed with complete confidence. How to Choose and Buy an RV is the ultimate guide for those times when you want to, well, choose and buy an RV.
Caravans and their tow vehicles rarely jack-knife and roll over – but when they do the results are catastrophic. The cause, and how to prevent it, is explained here. Why Caravans Roll Over offers solid advice for keeping yourself safe on the road.
Caravan & Motorhome Electrics is the totally rewritten successor to the original globally selling Motorhome Electrics. The book’s content now also covers every aspect of designing, installing and fault finding of the electrics in fifth wheel and conventional caravans, camper trailers and motorhomes.
Solar Success explains how to design and build home and property systems that ensures affordable solar success first and every time.
The Caravan & Motorhome Book covers every conceivable aspect of camper trailer, caravan and fifth wheel caravan, campervan and motorhome usage. Like all of Collyn Rivers’ books it is technically sound yet written in plain English.
Solar That Really Works! explains, in clear English, every detail of designing and installing solar in boats, camper trailers, caravans and motorhomes. It is up-to-date, valid globally and technically accurate. It is clear, concise and easy to follow without sacrificing important detail.
This is Collyn Rivers’ newest book. Building on his years of experience and extensive knowledge of engineering and all things caravan and RV, this is the book you need with you when shopping for an RV.
Collyn Rivers has done it again! – if you need to know anything about motorhome electrics, then this book is for you… Collyn must be, without doubt, the foremost authority in Australia on this subject.
Why Caravans Roll Over….and How to Prevent It
Should be compulsory reading for everyone involved with Caravans: Design / Engineering, Marketing, Journalism (print & electronic), Regulations, Inspections, Driver-Training, Caravan Clubs, Towing and Modifications.
Collyn is an accomplished engineer who knows how to design and build successful systems. It is refreshing to see practical advice written in plain language when there is so little solar information around. . . this is an essential text . . . you won’t find a better guide.
Without doubt, this is the best book we have ever read . . . it will be treasured, and read on a regular basis.