Alternator or DC-DC Charging – What is the Difference?

Last Updated: June 26, 2022 . By Annette . Travel Tips, Hints and Tips

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ALTERNATOR OR DC-DC CHARGING

I have been asked a few times about the difference between DC-DC charging and simply charging with the vehicle’s alternator. So I wanted to explain the reason why we have a combination of both to handle All Around Oz’s power requirements in our BT50 and trailer.

This opinion is mine only from quite a few years of playing with 12V systems. We have a 220AH battery bank in the back of the BT50, a 210AH battery bank in the camper trailer and our new van will have a 360AH battery bank.

CHARGING WITH YOUR VEHICLES ALTERNATOR

Charging your auxiliary battery bank with the alternator is a simple, inexpensive and easy way of doing it. The advantage over a DC-DC system is a large charging current to bring low-charge batteries back to service fast. The disadvantage is that today’s Smart Alternators will wind the voltage and current back as the batteries are charged.


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Very few alternators run over 14V, with most having a 13.6 to the 13.8-volt maximum. Late-model popular Gel and AGM batteries need up to 15 volts to get a 100% charge and to keep these expensive batteries in top condition. Alternators can’t do this.

Alternator or DC-DC Charging
The CTEK Smartpass120 is a Current Sensitive Alternator Charging System

CHARGING WITH A DC to DC CHARGER

Charging your auxiliary battery bank with a DC-DC Charger is a more expensive set-up. The big advantage of a DC-DC charger is it will be the best way of looking after the batteries that you rely on. It has different programs for different batteries and most have their own solar regulator built-in. You can feed the 22+ volts from your panels straight into the charger with no voltage drop concerns.

The only real disadvantage of this charging system is that it charges at a much lower rate. Usually around 20 to 30 amps. A big step back from the 120 amps or so from the alternator. If you have a large battery bank as we have then 20 amps can take a long time to charge them to capacity.

Alternator or DC-DC Charging
The CTEK D250SA is a DC-DC Charger

A COMBINATION OF BOTH

We have set up a combination of both in the All Around Oz BT50. The CTEK D250SA is coupled with the CTEK Smartpass120. When the batteries are low from a busy day, as soon as the alternator kicks in and the Smartpass120 is happy with the charge rate, it links all the batteries in the vehicle together. This gives a full alternator charge rate to the auxiliary batteries. At this stage, the D250SA is working as well to bring the charge voltage up to 14.8 volts. A perfect blend for the work we do and the large battery banks we have.

Alternator or DC-DC Charging
The CTEK 250SA AND SMARTPASS 120 are linked together.

I have kept the technical information on these systems very brief. Just the main differences between the 2 systems so hopefully you can see the pros and cons of both. You will find some more info in our YouTube video below.

We hope you found this comparison of alternator or DC to DC charging useful.

FAQ’s DC DC Charging

Does DC fast charge damage batteries?

The main concern with DC fast charging is that it can damage the battery. However, if used properly, DC fast charging should not damage the battery. The key is to make sure that the battery is not charged too quickly. When charging too quickly, the battery can overheat and be damaged. Therefore, it is important to follow the manufacturer’s instructions when using DC fast charging

When considering whether to use the alternator or a dc-dc charger to charge your auxiliary battery bank, there are several factors to consider. The first is the size of your battery bank.

If you have a large battery bank, you may want to consider using a dc-dc charger so that you can charge your batteries at a faster rate.

The second factor to consider is the type of battery that you have. If you have a Gel or AGM battery, you will need to use a dc-dc charger so that you can charge your battery at the proper voltage.

The third factor to consider is the cost of the two systems. An alternator is typically less expensive than a dc-dc charger

In conclusion, there are pros and cons to both charging systems. It is important to consider the size of your battery bank, the type of battery that you have, and the cost of the two systems when deciding which system to use.

Why is a DC current used for charging batteries?

A DC current is used to charge batteries because it can be regulated more easily than an AC current. When an AC current is converted to DC, there is always some loss of energy. Therefore, using a DC current helps to ensure that the full power of the charger is being used to charge the battery

An AC current is also more likely to cause sparks than a DC current. This is because the AC current alternates between positive and negative charges. The positive charges can build up on the battery terminals and eventually cause a spark

DC charging is more efficient than AC charging and is less likely to cause damage to the battery. Therefore, it is the preferred method for charging batteries.

How long does it take to charge a battery with a DC charger?

It depends on the size of the battery and the power of the charger. A small battery may only take a few hours to charge while a large battery may take several hours

The important thing to remember is to not overcharge the battery. Overcharging can damage the battery and shorten its lifespan. Therefore, it is important to follow the manufacturer’s instructions when using a DC charger

If you are unsure of how long to charge your battery, it is best to err on the side of caution and charge it for a shorter period of time. You can always charge it for longer if needed but you cannot undo the damage caused by overcharging.

Can I use my car battery to charge my auxiliary batteries?

Yes, you can use your car battery to charge your auxiliary batteries. However, it is important to not overcharge the auxiliary batteries. Overcharging can damage the battery and shorten its lifespan. Therefore, it is important to follow the manufacturer’s instructions when using your car battery to charge your auxiliary batteries

It is also important to note that not all car batteries are the same. Some car batteries may not be able to provide enough power to charge your auxiliary batteries. Therefore, it is important to check with the manufacturer of your car battery to see if it is compatible with charging your auxiliary batteries.

What is a solar charger?

A solar charger is a device that uses the sun’s energy to charge batteries. Solar chargers come in a variety of sizes and wattages.

It is important to choose a solar charger that is able to properly charge your auxiliary battery. If you are unsure of which solar charger to choose, it is best to consult with the manufacturer of your auxiliary battery.

Can I use a solar charger to charge my auxiliary battery?

Yes, you can use a solar charger to charge your auxiliary battery. Solar chargers are a great way to keep your batteries charged without having to plug them into an outlet. However, it is important to not overcharge the auxiliary batteries.

Overcharging can damage the battery and shorten its lifespan. Therefore, it is important to follow the manufacturer’s instructions when using your solar charger to charge your auxiliary batteries

Solar chargers come in a variety of sizes and wattages. It is important to choose a solar charger that is able to properly charge your auxiliary battery. If you are unsure of which solar charger to choose, it is best to consult with the manufacturer of your auxiliary battery.

How can I extend the life of my battery?

There are a few things that you can do to extend the life of your battery

-Keep your battery clean. Dirt and grime can build up on the battery terminals and eventually cause damage. Therefore, it is important to keep the battery clean and free of debris

-Check your battery regularly. It is important to check your battery regularly for signs of damage. If you see any damage, it is best to replace the battery as soon as possible.

Following these simple tips can help extend the life of your battery and keep it working properly for longer.