The regulator/charge controller needs to be of sufficient size to cope with the amount of power coming to it from the panels, on small systems of only one or two panels the regulator does not have to be very powerful or complex to efficiently charge most batteries likely to be connected to it. Simple solar regulators are commonly available with maximum charge ratings of between 5 amps and 40 amps depending on the model, with fixed equal in/out voltage.
Generally the smaller the regulator the less "features" it offers the user, as the amps get higher, it is more likely that a specialist battery type is being used and so more and more features are offered. It may have a basic display to inform the user of critical information and it might also have facility for data logging to computer, it would charge the batteries in a “Three stage” charge process. The three stages are called…BULK, ABSORB and FLOAT. When charging batteries, to charge them correctly (to prolong life for example) the “charger” has to change the voltage slightly as the battery’s capacity (state of charge) changes.
All batteries have specific charging requirements, so you need to make sure the charge controller is compatible with the particular battery you intend to use.
The example above is the way it has been in the solar regulator world for many years but the latest charge controllers are far more advanced units, not only performing all the previous tasks but doing much more as well. In particular, at the moment, the outstanding piece of equipment in this area is the OUTBACK MX 60 regulator/maximiser (for full spec. see website).
Briefly some of the main features are; It can accept higher voltage on input to output, 60 Amp charger, programmable battery voltage12—60V,auto maximum power point tracking of solar array voltage up to 140Vdc open circuit (Allowing higher array voltage to minimise cable size/cost and permit longer distance between the array and controller). 4 line 80 character display, rs232 for p.c. connection/data logger.Battery.30 day history, Temperature compensation (especially valuable when ambient temp. can change dramatically as it can here in Spain) The product comes with default settings for battery types and voltages but can be re programmed to specific battery needs .As well as these features it also constantly monitors the batteries and when necessary “maximises” it’s input to output. This helps to reduce battery “cycling”
For example; If your batteries are full and receiving just a small float charge to keep them tip top and a large load is applied to them, the MX will sense this and instead of continuing to float the batteries, will apply as much current as it can to supply the load directly from the solar, thereby reducing or eliminating the load on the batteries. A less sophisticated unit would wait until the large load dropped the battery voltage enough to lower it into a different charge stage. Most battery manufacturers give information on expected life/cycling as a guide to durability for customers and as such is something that system designers should try to minimise.
The MX60 is the first of a new generation of charge controllers and is a great asset to any system large or small although it’s price does reflect it’s abilities and as such is usually only used on multiple panel systems where the price is less of a percentage of the overall system cost. The ability to charge at 60 amps is also generous and usually means that one unit is sufficient for the whole solar array, preferable to buying two lesser units to achieve the same current rating…..
My recommendation to anyone interested in a “large” system to check this piece of equipment out before deciding to buy any other charge controller, it really is that good!!!
