question

remcomeeder avatar image
remcomeeder asked

DC-DC Converter/charger

For our caravan I am looking to upgrade/optimise the 12V system.

At the moment there is a 90Ah 12V lead-acid battery which when we are off-grid runs the lights and 12V outlet to charge phones/tablets.

When plugged in the battery is charged from the mains 230V supply using a Reich C-Go 20A charger. This charger in turn, also acts as an isolator for the 12V coming from the car. So when the caravan is plugged in the car and the engine is running the caravan battery is also charged from the car.

I want to replace the lead-acid battery for a LiFePO4 battery but I need to limit the current to protect the car and wiring between the car battery and the caravan. Ideally I want to limit the current from the car to 10A because of the small gauge wires that re typically used in cars and caravans in Europe.

My first idea was to take a Victron Orion smart DC-DC converter which basically does everything I want except two things. The most important thing is that there is no way to limit the current. The smallest version is 18A DC which is to much for my application. The second disappointment is that it doesn't have VE smart networking. Victron sadly never gives out information on when or even if devices get an update.

The Victron 25A Buck-Boost converter does have the current limiting function that I seek but it is more than twice the price of the Orion. It also lacks VE smart networking and you need to use an ancient Windows application to change the settings.

What would be a good and cost effective solution to my wishes? I don't mind spending money but I don't want to overpay for equipment that is half finished.

I would really like to see that Victron takes one of their smart solar MPPT chargers and create a truly smart DC-DC converter from it. I looked into using a MPPT charger for my application but I quickly learned that it is a bad idea because of how the MPPT system works.


orion dc-dcdc system
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4 Answers
Patrick avatar image
Patrick answered ·

With stock wiring between the tow vehicle and caravan you will be lucky if you get 5 amps coming all the way back if your tow vehicle alternator outputs compatible voltage range 14-14.6v i wouldn't change any wiring just swap the battery in the caravan.

Keep in mind if the caravan is connected and the tow vehicle is not running, the line is connected direct to the battery without a switch or voltage controlled relay the caravan loads will also discharge the tow vehicle battery.

If you want want to charge quickly from the tow vehicle you will need to install new properly sized wiring from the tow to the caravan and then add dc-dc converter inside the caravan like the Orion


-Patrick

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remcomeeder avatar image remcomeeder commented ·
The tow vehicle outputs 14.4V whenever the car is on. It is a Euro 6 vehicle but it is a hybrid so the DC-DC converter is always turned on and it can only supply up to 100A which is low compared to an alternator.


At the moment it does a fairly good job to charge the caravan battery in the current setup. The car actively switches the power to the connector when the car is switched to Ready mode (i.e. started) and it switches the power off when the car is switched off again. But since I am planning to convert to lithium a current limiting DC-DC charger is needed. I don't mind that it will be slow but any charge is better than no charge.

Changing the wiring in the car isn't really going to help since everything has to go through the standard 13 pin Jaeger plug. And the standard wiring is indeed the biggest issue in this case. Inside the caravan the wiring is also small but that can be addressed. I was however quite surprised that the whole wiring setup is capable of delivering 14V to the 12V system in the caravan, even when the fridge is on 12V. I measured the voltage directly at the fridge. I expected it to have dropped significantly because of the small gauge wires.

The best thing would be to have a second dedicated connection to the car for power but that is outside of the possibilities at this moment.

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Patrick avatar image
Patrick answered ·

Personally I would not install a DC-DC converter if you don't intend on upgrading any wiring. When connected to the tow vehicle the new LFP battery would not see 14.4V as the tow vehicle small factory wiring will have considerable voltage drop this voltage drop will limit the charging current.

If you want to be sure your new LFP battery always sees voltage lower then 14.4V consider a smaller Orion like the 12/12-9 you do not need smart or isolated for this application set the fixed output voltage to a "float voltage" like13.5-13.7V

-Patrick

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rvicev avatar image
rvicev answered ·

@remcomeeder

I have found the following 2 low power DC-DC converters / LiFePO4 chargers :

- Powerwerx : https://powerwerx.com/dcdc-charger-lifepo4-8a-adjustable

(can be regulated manually 2-4-6-8 Amps, high efficiency : 95%)

- Dometic : https://www.dometic.com/fr-fr/outdoor/energie-mobile/chargeurs-de-batterie/dometic-perfectpower-dcc-1212-10-152912

(10 Amps by default, but can be regulated in software down to 5 Amps. Mind you, at 85% efficiency this puts a load higher than 10 Amps on your wiring ....)

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jeffrey-nikki avatar image
jeffrey-nikki answered ·

I have tried this platform: https://www.12voltpower.com/

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