I want a simple system that I can move between vehicles. I have looked at the various products and think that I could use a MPPT solar controller but I am not sure.
The requirements are:
Charge the freestanding (but secured!!) leisure battery when driving from the cigarette lighter socket.
Mobile Engel fridge freezer (12v) to be running all the time (running from car when running and leisure when parked)
The current leisure battery is S685L Platinum Leisure Battery 12V 75Ah Wet, but this will change in the future.
Generally the leisure battery will have the capacity to run the fridge when parked, but for long stops I am considering a solar panel to supplement.
Could a solar MPPT work?
Can I change the solar input for a 12V from the cigarette lighter?
You will need a small DC to DC charger. Cigarette lighter is quite low amp draw and the smallest DC to DC is too powerful so you would need to connect this to the starter battery.. See
The manual does not say anything about required input voltage vs battery voltage but Victron write ups of PWM vs MPPT suggests that the panel voltage can be pulled down as low as the battery so it should work (but not having done it myself I can not be categoric). It will not boost the cigarette lighter socket voltage for charging the leisure battery. If it starts as soon as the supply voltage > battery voltage it would let through the vehicles voltage to the battery with some voltage loss so you may get some charging if the vehicle voltage is around 13.8V or higher. However, if the vehicle has a Smart alternator that often reduced voltage to say 12.8V then you will not get much charging.
Thanks both. It is not a simple answer. I currently use 3 different vehicles. I could check the cigarette light voltage when the engine is running. Would that help select the best solution?
I don’t have experience with PWM units. Maybe you can get your hands on a second hand version cheaply so you can test? I would assume that the cigarette lighter voltage needs to be at least the same or higher than the battery to be able to charge the battery.
I have a leisure battery mounted in a portable box with a smart shunt, Orion XS DCDC charger and Smartsolar MPPT 100/20. Two portable 110W folding panels are deployed when camping but even a single 110W panel is enough to keep it running indefinitely when camping in sunny weather. It runs a 40 litre Engel fridge and camping lights. While driving the Orion XS charges the leisure battery. The box can be moved to another vehicle in minutes provided that vehicle has a suitable connection point (more on this below).
My 40 litre Engel consumes 2.5A when running and on average the compressor runs 50% of the time in a warm climate. Larger units might use more current but mine has run on a cigaretter lighter socket for years with no problems and I plug it into either the vehicle or the battery box as required.
The problem with the proposed system is that charging the leisure battery directly from a cigarette lighter socket has issues :
Too much volt drop through the vehicle wiring and fuses to fully charge a second battery some distance away.
Cigarette sockets in vehicles are typically rated 10A and often overheat when operated continuously at anything close to 10A. Your leisure battery will try to draw more than 10A if depleted and there is high risk of melted fittings and blown fuses while driving and charging via the cigarette socket.
Unless you remember to unplug the leisure battery when the engine is not running you have the risk of drawing both batteries down and not being able to start.
Unless the two batteries are same age, type and capacity they will tend to interfere with one another while connected and both are at risk of shortened lifespan. The system needs to have some means of automatic isolation when the engine is not running.
As a minimum you should consider a dedicated fused 16 sq.mm cable from starter battery to a DCDC charger located within about 1m from your leisure battery’s location.
Add a solar regulator (pwm or mppt) configured to charge either the leisure battery only or the start battery (in which case the dc dc charger will power on and also charge the leisure battery when receiving solar power). If your panel/s can produce more than about 19V, MPPT will be more efficient than PWM
Thanks James. That’s really useful. It would be good to better understand how you wire the dcdc charger and mppt. I am looking for a solution that is easy to move between vehicles (I understand that I might need to fit a fused cable fly lead to each car) and doesn’t require connections to be made in a certain order. I had this previously and someone is bound to get it wrong at some point.
I’ll share a few pics and a circuit diagram when I get a chance. I use 50A Andersen plugs for my connections; blue for unregulated DC sources (e.g. solar panels), red for regulated charge sources and grey for consumers. It prevents connection mistakes.
Pic attached below of my system installed in an old Landcruiser. It is built off an old National Luna battery box that used a solenoid based isolator for the start battery. This has fused outlets and a circuit breaker built-in. I stripped out the solenoid and its wiring then added Victron busbars (inside), a Smart Solar MPPT 1000/20 on the left side and the Orion XS facing. The fridge is in the foreground. Blue Andersen connector for the solar and a small portion of the red Andersen connector for the alternator charging supply also visible. An AGM battery and a Smart Shunt are in the box. The default settings for engine shutdown detection on the Orion and the Smart Shunt parameters had to be adjusted a few times to make it work smoothly. It is dialled now. When I upgrade to a LiFePO4 battery I’ll disconnect the LED battery level indicator because it is calibrated for lead acid and draws a much higher parasitic load than the Victron gear.
The Orion XS isolates the vehicle from the system when the engine is not running and the 50A circuit breaker isolates and protects the house battery from overloads. The most current I draw is around 30A when a 12V compressor is attached for pumping tyres.
It looks exactly what I need to build. Very impressive!
So this is totally mobile between vehicles. The only mod needed for each vehicle is the direct feed from the battery to the local anderson connector?
Cheers
Steve
