Why do I need a Battery Management System?
If you wake up one morning out in the solitary dessert and find your milk is off because your fridge stopped working at night, it's not the worst thing in the world. Realising the chap from Wolf Creek is on the horizon but your engine won't start because your battery is flat...well, that's considerably worse. Trying to placate him with some UHT enriched cornflakes probably won't make the situation any better. It's time you thought about a battery management system! If you live, of course. Just putting that out there.
What is a Battery Management System?
There are numerous types, but essentially it's a system that will enable your battery or more likely both of your batteries to stay up to full capacity as much as possible, ideally with the starting battery left unscathed whilst your secondary/auxiliary battery (or batteries) do the hard work of running your lights, laptop, mobile phones etc
A battery management system can be as simple as a switch between the two batteries that you manually turn on every time you park up for the night, or an isolator (will get to that) that sits between the two batteries so that whilst the secondary/auxiliary battery drains, the starting motor does not. Or it can be a $2000 system that actively monitors your batteries, solar and any devices plugged into it, providing real-time displays of drain rate and telling you next week's lottery numbers.
Erm...yes, moving on. Firstly, let's get the caveat out of the way: I am not an expert in Battery Management Systems, or indeed an expert in anything. The information listed here is from what I've read in various forums, articles and from my previous experiences of seeing my battery run flat a lot.
To answer the first question in this blog post: having a single battery run your car as well as a fridge and charge you mobile phone won't leave you with enough power in the battery to start your engine in the morning (unless you leave your engine running all night). Having two or more batteries is the key, and any way to manage those batteries is better than none. Having the right battery type for the job also helps, and that's where our story begins.
Yeah there is always a boring bit. Ideally it seems you need two or more different types of batteries: the first or main battery which runs your engine needs to be a cranking engine, and they use the term CCA for Cold-Cranking Amperes. Why cold? Because when you start your car in the morning, it has to function in a cold environment e.g. zero degrees centigrade. Why Cranking? Because you 'crank' your engine to start. I thought Amperes were....nannies? Get out.
Basically starting batteries are designed to release a high burst of current, measured in amps, and then be quickly recharged. They're not designed to be run flat and if you do run them flat, they generally reduce their lifespan of the battery. Your secondary or auxiliary batteries need to be the opposite of that, pumping out current/amps for longer intervals and not impartial to being charged down to around 30% of its life. These are commonly called deep cycle batteries.
4x4 Australia has a good but slightly boring article here and Optima can tell you all about CCA here.
These batteries can be made of different materials (lead-acid, gels, lithium) but the most common are AGM, or absorbed glass mat. For me, I'll be going a solid standard lead-acid battery for my cranking (CCA of 700+ with 66 Amps per hour), and the best AGM battery I can get for about $250 to $300 dollars which should be in the region of 120-130Amp hours i.e. delivering more amps per hour.
What is an amp hour?
Great question! The number of amps hours is the number of amps provided continuously per hour (don't hate me). Put it this way, every device you have such as a fridge or mobile phone or laptop, will consume energy to power itself - so you can measure the power drain through amps or power*. This can be measured in amps needed per hour. A good fridge for example could draw 3.5 to 4 Amps per hour/AH on 12V which your car batteries provide unlike the 240V in your home. A mobile phone battery is typically about 2 AH.
So if you're battery has a 100AH, it means it can supply 1 amps for 100 hours or more likely, supply 5 amps for 20 hours. Good enough for a night's rest.
(Trying not to make things complicated, you can work this out by an equation from your school days if you wanted: Power = Voltage * Current. So if you have something like an induction cooker that draws 2000 Watts and you're plugging in at home i.e. a 240V mains plug, it draws a current of 8Amps. However, in your little vehicle, these batteries work at 12V, so really that induction cooker will need 166Amps per hour).
My Charging Requirements
My Planned Battery System
Providing the vehicle I buy doesn't already have one installed, I'll be going for a CTEK Battery Management System which includes an isolator to protect your main battery and negates the requirement of a solar regulator. So it will consist of three things:
All of that above should cost less than $600 if I'm hunting around on ebay and various discount or second hand sites. Additional things to consider:
So about those lottery numbers...
Let it go....there is something even better though. This fantastic chap at campertrailer.org put together spreadsheet to calculate your energy drain when running fridges, TV, lights etc and even includes solar. The best bit is it's free! You can find the link right here, and if Richard ever reads this, thank you Richard!
http://search.supercheapauto.com.au/search?w=cable has red and black 25Amp cabling
The blog will be a record of everything - from idea conception to old age in making this adventure happen
You can find the excellent 2006 Antipodean Adventure blog by Dwyer Rooney here