- Voltage Regulation: B2B chargers take DC input from a source battery and convert it to a suitable DC output voltage to charge a secondary battery. They ensure that the charging voltage is appropriate for the battery type and state.
- Isolation: These chargers often electrically isolate the two batteries, which is important for preventing issues like battery drain and ensuring that the source and destination batteries operate independently.
- Multi-Stage Charging: Advanced B2B chargers can provide multi-stage charging (bulk, absorption, float), which is essential for proper battery maintenance and longevity.
When do you need a DC to DC Battery charger?
- If you were to wire the starter battery directly to the auxiliary battery without a B2B charger, you might drain the starter battery down until you cannot start the engine anymore. It enables the starter battery to remain fully charged before charging your auxiliary battery.
- A DC-to-DC battery charger is like having a solar charge controller in parallel with the starter’s battery.
- If your car battery is 12V and the other battery is 24V, then you need a B2B charger.
- If you have a lithium (LiFePO4) battery, then you need a B2B charger.
Why Do I need a B2B Charger for a Lithium Battery?
The car alternator is not made to charge a battery with low internal resistance. This will lead to overheating of the alternator.
Victron Energy, a popular solar system manufacturer, did a test where they charged a lithium battery with an alternator.
They found that charging a lithium battery with a car alternator is not always the best solution. At lower RPM’s the alternator was overheating.
- The low internal resistance of a Lithium battery makes the alternator put out a large amount of current.
- A lead-acid battery has a higher internal resistance, thus doesn’t need a B2B charger.
A DC-to-DC battery charger can reduce the charging current without damaging the alternator.
Although there were some flaws with this test setup:
- There was no fan installed on the alternator µ
- The cabling was oversized, decreasing the resistance even further and making the alternator deliver even more current.
- It was a small 70A citroën alternator, which you would find in a small car.
Ultimately, it’s still a manufacturer that wants to sell its product. But it was a good demonstration nonetheless.
DC to DC Charger Wiring Diagram
In this image, you can see the circuit diagram for a DC-to-DC battery charger.
DC to DC Charger with Solar Input
Renogy now has a DC-to-DC charger with two inputs. One is for the auxiliary battery, and one is for solar panels.
It uses their well-known DC-to-DC charger and adds another MPPT.
It comes in a 30 or 50A version. You can only use it with 12V and the max solar panel power is 400W.
Recommended DC to DC battery chargers
There are two main manufacturers who make the Dc battery chargers, they are Renogy and Victron.
Renogy has a 20 Amp, 40 Amp, or 60 Amp version available.
Victron has many versions available for 12, 24, and 48 Volts. The smart edition is able to be connected to your phone through Bluetooth so you can manually program it.
How do I convert 24V to 12V in off-grid solar systems?
Read my article about it here.
What is the difference between isolated and non isolated dc to dc chargers?
Read my article here.