The Springers Solar guide to 12V electrics: PART 9
Your top 5 12-volt questions answered
1, PARTIAL SHADING AND SOLAR PANELS
Where you can help it, don’t shade your solar panel. It seems pretty obvious really but a lot of installations will put harsh shadows on solar panels and markedly reduce the amount of output you are going to get from them. Even the bar of a roof rack will make a big difference. If panels are located on top of your van, consider where the shadow of an antenna will be, as any shadow cast on the solar panels will affect their output.
If hard shadows will be unavoidable with your installation, perhaps consider portable solar panels that you can put out and follow the sun during the day. This way you will be able to park your van in the shade reducing the need to cool it while maintaining a good solar input to your battery system.
2, WHEN DO I NEED TO GET LITHIUM?
Not everyone needs lithium, but some situations will benefit greatly from its use. If weight and space are limited, then lithium may be worth it. If you need to deeply discharge your battery regularly, then lithium will be better. If you are doing the Big Lap of Australia and planning to be off-grid a lot, lithium is going to provide more benefits. The biggest downside of the lithium battery is the upfront cost. If you mainly stay in powered caravan parks or only use your RV a couple of times a year then an AGM battery may be the best choice. The is no right or wrong answer to the lithium question. All things being equal, you will replace AGMs more regularly and they will take up more room and be heavier. Your own expectations and needs from a battery will determine which one is best for you.
3, CAN YOU RUN LITHIUM BATTERIES IN PARRALLEL
First off, why would you want to run batteries in parallel? As your 12V requirements increase, you may need to increase the battery capacity of your RV. With AGM, it’s easy, and you just add another battery to your existing batteries. Some lithium batteries can be run in parallel and some can’t. If the lithium battery has an inbuilt BMS (battery management system) it will normally stop you running them in parallel.
Having said that, there are some lithium batteries coming to market with inbuilt BMS that will allow you to run a limited number of similar batteries in parallel. If you have a lithium battery without a BMS, you may be able to run multiple of these in parallel. If you are not sure of your future needs, make sure you ask this question of your lithium battery supplier.
4, DOES CABLE SIZE REALLY MATTER?
In a word, yes. The bottom line is don’t skimp on cable because if you do, your system will not run as efficiently as it could. Two things affect the cable size, the first is the current-carrying-capacity of the cable.
This is particularly important for cables carrying charge to the battery and for high load applications such as fridges, compressors or winches. The second consideration is voltage drop, which is the amount of energy lost as the length of cable increases.
Voltage drop will occur no matter the length of the cable. As the length of the cable increases, the size or thickness of the cable must increase to keep voltage drop to a minimum. Non-critical items such as fans or LED lights could have a 10 percent drop in voltage without too much of an issue.
Critical appliances like fridges should not experience a voltage drop of more than three percent. An example of this is if your fridge needs 10 amps and the distance from the battery to the fridge is 2-3m then a 1.63mm diameter cable will suffice. That same distance from a 50-amp DC2DC charger to the battery will require a 4.11mm diameter cable. Should the charger distance to the battery be 4.5-6m then a 5.19mm diameter cable will be required.
And don’t forget to insert a fuse or circuit breaker to any electrical circuit that is added. Fire in a van is not your friend.
5, WHY DO I NEED TO LEAVE MY ELECTRIC TOASTER AND KETTLE AT HOME?
Some electrical items are best left at home. Hairdryers will flatten a 100-amp battery in around an hour or less so are not practical for smaller systems. If used for short amount of time it may be okay, but best left at home unless you have a big battery system. Non-critical items such as fans or LED lights could have a 10 percent drop in voltage without too much of an issue.
Kettles will draw about 2400W, these and toasters will turn your battery to toast (flatten it) pretty quickly, but the good news is that gas is a great way to make breakfast and heat or cook generally. Coffee makers are around 600W so a couple of coffees a day won’t be too bad on the batteries.