Solar System - Battery Charging.
As we mentioned on the last page, unfortunately solar systems need some management. We need to make sure it is running efficiently and not ruining out equipment. Lets look through some of these (Note: the first two are the most important ones).
Batteries can be overcharged. This can be dangerous at worst and at least will damage your batteries. When you have bought some batteries you will realise how expensive they are and when you have had a system for a while you will realise that you system is only as good as it's batteries so you really want to protect these. You can do it manually or automatically, manually is cheap but a really big pain and visa versa.
Basically, your batteries will have a voltage at which they will be full and this is the point at which you want to switch off charging. Manually, you can check a voltmeter and when it reaches the max, flip a switch that disconnects a battery. This is of course fairly labor intensive, as you have to be there. Automatic systems use a circuit that detects the voltage of the battery and disconnects the battery if it hits the maximum and reconnects when it dips below the maximum. You can built your own, there are a few circuits out there on the web, or you can buy them without too much trouble. If you are looking about these are normally called charging regulators. I picked mine up of ebay pretty cheaply, and they had a few cool functions built in.
In our example we had a 12 volt battery and we learnt at 12 volts it's pretty much empty and at 12.7 it is just about full. You can check you battery's state but looking at this voltage.
Note: These are resting voltages (not power being drawn from the battery, none at all!)
If you leave you batteries connected to the panels when the are not producing any power, they will drain a bit of power from your batterys. To prevent this it is a good idea to introduce a diode (diodes only let current flow in one direction) into your system. That way current easily flows from the panel to battery but can not flow from the battery to the panel, thanks to our little one-way device.
Most of your equipment will operate perfectly within ranges of Volts/Watts/Amps. But just incase there are spike in power it is best to lose a $1 fuse than a $100 charge regulator or panel. So between your equipment install some fuse that match your needs. You may never need them if you planned correctly but if anything goes wrong you'll love them. And they are very cheap insurance.
Temperature has an effect on charging, some more complicated systems take this into account and charge differently depending on the temperature. A hot battery will overcharge before the voltages tell you it's full, so if you have your battery with your panel it might get exposed to the sun and become hot and your charging regulator needs to keep this in mind. And if you are in an area that drops below 0 degrees Celsius, battery capacity can drop to about 1/4 of normal. batteries tend to like 18 to 25 degrees Celsius(68 to 77 degrees Fahrenheit). So if they are out in the sun keep the shaded and ventilated, or if they are in the cold keep them insulated and perhaps used a bit of your battery power to keep them warm.
Because batteries are so expensive people often try to get the most of them and make them last as long as possible. Batteries often last alot longer if you only every deplete them to at most 50%. Some people even only ever try 20% leaving 80% in the battery at all time. To do this you need to monitor under charge (as well as overcharge) and cut off usage. The same methods and circuits for overcharge can be used. Manually, if you are using some of you power keep an eye on a voltmeter, or get out a calculator and work out how long you can keep devices on for. Or you can build or buy automatic circuits to do this for you.
Every 6 months or so you should check you batteries clean the off, especially if dust builds up between the poles. And if corrosion builds up on your contacts whip out the baking soda and give them a clean too (Don't get any in the cells though).
Cables and connections
It's safer to use larger cables and good connections that can make good contacts and support whatever current loads you need. If a large current tries to go through a small wire it might burnt it out (and burn other things along the way) bringing your system to a hold and maybe even destroying it.
Now for inverters to make AC power onto the next page.