Hi everyone,
I’m currently making a project for a leisure battery instalation in my car (LR4 if it matters).
I would like to install a LifePo battery and connect it both to solar (using a MPPT controller) and to the car alternator (with a DC-DC charger).
Is the scheme attached correct? Would it be enough for me, or do I need some additional devices (Victron or other)? Any other pitfalls?
12v refrigirators are very hard to satisfy with solar energy, better check before you start spending money.
My 800w installation doesn’t do the job, the fridge (ok, a large Norcold) needs 250w, ~3kwh per day.
So it usually runs on propane with a much better efficiency, ~12 kilos / month.
Thanks everybody for the valuable feedback!
My setup now looks like:
Victron Orion XS 12/12-50A DC-DC Battery Charger
Victron SmartSolar MPPT 100/30 12V 24V
Victron Battery Monitor BMV-712 Smart Black
Victron Battery Smart 200Ah
Two 24V 6A solar panels:
One probably Victron BlueSolar
and the other one (which I already own) Land Rover Discovery LR3 LR4 Lensun 110W Hood Solar Panel – LensunSolar
Does this final setup look correct (assuming the alternator power is 150A)?
I think you’ll need a bms for the battery.
You need a BMS for the battery, please read the manuals.
Thanks for this post I am just getting my head around replacing some of the 12v electrics in my van which caused my leisure battery to die. Could you please point me in the direction of the programme you used to draw your diagram. I feel It may help over on my thread also.
Thanks in advance
Garry
As others have pointed out you need a BMS with those batteries, you might like to consider a battery from a different manufacturer with a built in BMS and Bluetooth to keep the system simpler as it is a small system.
In a system with a single LiFePO4 battery that has a BMS with Bluetooth you can get by without the BMV-712. The BMS isn’t always that accurate at reporting the state of charge but it’s usually close enough. If an upgrade to two batteries is possible then a Battery Monitor is helpful. The SmartShunt may be a better solution if you don’t want to have to mount the display that comes with the BMV-712.
To give an accurate recommendation on the solar charge controller, we need to know the detailed specs of your solar panels. Voc and Isc are what I want to see as well as the watt rating. I suspect that you could get by with the 100/20 solar charge controller.
Are the solar panels going to be permanently mounted on the vehicle or deployed on the ground? If the latter then you’ll want a dual pole breaker between the solar panels and the solar charge controller to allow you to disconnect the panels under load. MC4 connectors (that come with almost every solar panel) are never to be disconnected under load.
Thanks for the feedback, especially on the dual pole breaker, since one of the solar panels may be occasionally dismounted.
My solar panel is 26V, 5.26A and 110W. I guess the other one will be something like it.
Hi Garry
Actually, I just took a scheme from Google Images, and removed the irrelevant parts 
So in case you find the software used to draw such schemes - I’m interested too.
Thanks everybody for the info about BMS. I’ve got 2 subsequent questions:
In case I decide to stick with the Victron battery, would the Smart BMS CL 12/100 be OK for my setup?
Do I need the DC-DC in that case? There is a scheme on the Victron website (attached below), which is similar to my planned setup, has a BMS, and lacks a DC-DC. Is that valid?
Two 110 watt panels will not produce any more than about 18 amps (on the output side of the solar charge controller). So the 100/20 solar charge controller is the right size.
Mismatched panels are not ideal. The general rule of thumb is that your production will be at the lowest common denominator of the panels.
The Victron MPPT Calculator is a great resource for sizing the solar charge controller.
I don’t use Victron batteries so I don’t know much about the BMS that is required with them. I would think that the DC-DC charger is still appropriate. I’m surprised to see a Victron diagram with a LiFePO4 battery, alternator charging and no DC-DC charger.
@inquisistent Also to @HRTKD
With the BMS you have chosen you may or may not need a DC to DC charger. If you have a simple alternator that outputs 14.4 to 14.5V all the time then you do not need a DC to DC. The BMS limits the charge current to a maximum value set by the fuse and output voltage to the 14.2V required by the Victron batteries. Note, the voltage of the alternator HAS to be circa 14.4, ideally 14.5V to compensate for the voltage drop in the BMS.
The BMS does not have any voltage boost circuitry so if you have an alternator that delivers say 14.2V then this BMS is not suitable because with the voltage drop, you will not achieve high charge current. The first port of call here is seeing if you can get a new higher voltage regulator for the alternator. If you can not get a new regulator then a DC to DC is recommended. There are many examples of this and there is a post in the sticky DIY FAQs topic at the top of DIY section.
Finally, if you have a very modern vehicle with a smart alternator that can back right down to float voltage of 13.2V controlled by the ECU then this BMS is definitely not suitable, you must have a DC to DC charger. You can not add a new regulator easily in this case.
We don’t see many of the Victron Smart BMS over at DIYSolarForum.com, so I’m not familiar with it. From the 50,000’ level, it functions like any other BMS. But as I get into the details there appear to be some interesting differences.
Can the Smart BMS actually throttle the charge current? Mainstream BMS do NOT throttle the charge current. It’s either on or off, no throttling.
If the alternator is outputting only 13.8 volts and the Smart BMS knows that the battery needs to be charged in bulk mode, what does it do?
@inquisistent @veitchy
Luka is using draw.io
42' sailboat LFP upgrade - #3 by Lure
I’ve bought two portable (with wheels) 40L 12-24V 55W Chineese compressor refrigerators, not quite energy efficient class. It has dual compartment, can easily go down to -18C (0F) in either of them.
I have used the one in passenger car, powered from its 12V 50Ah batt. Over a hot mediterranean night, with the temp set at -18C and 4C (for each compartment), it does not deplete the battery, so I guess it consumes way less than 0.5kWh per (hot) day/night.
The other I put in a small DC system in a boat. It consists of a Victron 115W-12V panel, MPPT 75/10, Argodiode 80-2SC (for charging also boat engine dual batteries) and a lead acid battery of 12V 75Ah for accessories (not connected to alternator, only juice is from sun). Those are the fridge and several lights, chargers etc - all DC, coming from the “Load out” 10A from MPPT. I had never problem with depleted battery, the fridge holds icing cold throughout the (med) summer, properly for beers (and lights) during nights.
This device is more than a BMS. It has the standard BMS functions such as isolating charge and / or discharge on high / low voltage and temperature. It also has an additional circuit that monitors and limits the alternator current, so if you have an 80A alternator, you fit a 50A fuse and it limits the current to about 40A using the fuse as a shunt, monitoring the V drop preventing the alternator from overheating.
If the alternator is 13.8V, and the battery is depleted and needs bulk, it will charge but as I explained above, it will charge at a very low rate especially as the battery gets to higher SOC.
My vehicle is a 2016 Land Rover, its alternator is managed by its own BMS. The alternator outputs 14.4-14.5V only after starting the engine to charge the starter battery. After that, the voltage drops.
In that case, as far as I understand, the scheme with the Victron BMS isn’t OK for me, and I should stick to the option with DC-DC (and without Victron BMS) included in the original post?
You are correct, you need the DC to DC charger. If you want to remain with the Victron batteries then you could use the small BMS to stop the chargers if there was high voltage or high/low temperature and connect a Battery Protect controlled by the small BMS to shut off loads in the event of a low voltage. Otherwise, consider a drop in battery with inbuilt BMS. The other thing to note about the Victron batteries is they do not output the SOC, you would also need to add a SmartShunt.
