Charge Controllers

A charge controller, or charge regulator is basically a voltage and/or current regulator to keep batteries from overcharging. It regulates the voltage and current coming from the solar panels going to the battery. Most “12 volt” panels put out about 16 to 20 volts, so if there is no regulation the batteries will be damaged from overcharging. Most batteries need around 14 to 14.5 volts to get fully charged.

 Do I always need a charge controller?

YES – however in exceptional cases if the panel size is very small then we can usually get away without one.  Generally, there is no need for a charge controller with the small maintenance, or trickle charge panels, such as the 1 to 5 watt panels. A rough rule is that if the panel puts out about 5 watts or less for a 100AH battery, then you don’t need one.

 Why 12 Volt Panels are 17 Volts

The obvious question then comes up – “why aren’t panels just made to put out 12 volts”. The reason is that if you do that, the panels will provide power only when cool, under perfect conditions, and full sun. This is not something you can count on in most places. The panels need to provide some extra voltage so that when the sun is low in the sky, or you have heavy haze, cloud cover, or high temperatures, you still get some output from the panel. A fully charged “12 volt” battery is around 12.7 volts at rest (around 13.6 to 14.4 under charge), so the panel has to put out at least that much under worst case conditions.  The charge controller regulates this 16 to 20 volts output of the panel down to what the battery needs at the time. This voltage will vary from about 10.5 to 14.6, depending on the state of charge of the battery, the type of battery, in what mode the controller is in, and temperature

 Contrary to popular belief, solar panels work best at cooler temperatures. Roughly, a panel rated at 100 watts at room temperature (25C) will be an 83 watt panel at 40C. Conversely at freezing or below a 100W panel can produce over 120W

 Charge controls come in 3 general types (with some overlap):

Simple 1 or 2 stage controls which rely on relays or shunt transistors to control the voltage in one or two steps. These essentially just short or disconnect the solar panel when a certain voltage is reached. For all practical purposes these are dinosaurs, but you still see a few on old systems – and some of the super cheap ones for sale on the internet. They can be ignored for our purposes as generally the trend on new controllers is to go for MPPT. Their only real claim to fame is their reliability – they have so few components, there is not much to break.

3-stage PWM such Morningstar, Xantrex, Blue Sky, Steca, and many others. These were pretty much the industry standard until quite recently, and you will still see these types around, such as in the very cheap systems offered by discounters and mass marketers.

Maximum power point tracking (MPPT), such as those made by Xantrex, Outback Power, Morningstar and others. These are the ultimate in controllers and rapidly becoming the new standard, with prices to match – but with efficiencies in the 94% to 98% range, they can provide considerable increases in amp output on larger systems since they provide 10 to 30% more power to the battery. For more information, see our article on MPPT.

Most controllers come with some kind of indicator, either a simple LED, a series of LED’s, or digital meters. Many newer ones, such as the Outback Power,, Morningstar MPPT, and others now have built in computer interfaces for monitoring, control and fine tune the settings.  The software provided will allow the production of colour graphs of the daily/weekly/annual performance and output. The simplest usually have only a couple of small LED lamps, which show that you have power and that you are getting some kind of charge. Most of those with meters will show both voltage and the current coming from the panels and the battery voltage. Some even show the total amps provided over the period.

All of the PWM type charge controllers are 3 stage, and the MPPT units are 4 stage. (in reality, “4-stage” is somewhat advertising hype – it used to be called equalize, but someone decided that 4 stage was better than 3). And now we even see one that is advertised as “5-stage”….

What is Equalization?

Equalization does somewhat what the name implies – it attempts to equalize – or make all cells in the battery or battery bank of exactly equal charge. Essentially it is a period of overcharge, usually in the 15 to 15.5 volt range. If you have some cells in the string lower than others, it will bring them all up to full capacity. In flooded batteries, it also serves the important function of stirring up the liquid in the batteries by causing gas bubbles. Of course, in an camper van, this does not usually do much for you unless you have been parked for months, as normal movement will accomplish the same thing. Also, in systems with small panels or oversized battery systems you may not get enough current to really do much bubbling.

What is PWM?

Quite a few charge controls have a “PWM” mode. PWM stands for Pulse Width Modulation. PWM is often used as one method of float charging. Instead of a steady output from the controller, it sends out a series of short charging pulses to the battery – a very rapid “on-off” switch. The controller constantly checks the state of the battery to determine how fast to send pulses, and how long (wide) the pulses will be. In a fully charged battery with no load, it may just “tick” every few seconds and send a short pulse to the battery. In a discharged battery, the pulses would be very long and almost continuous, or the controller may go into “full on” mode. The controller checks the state of charge on the battery between pulses and adjusts itself each time.

The downside to PWM is that it can also create interference in radios and TV’s due to the sharp pulses that it generates. If you are having noise problems from your controller then the simplest thing to try is to shield the controller using something like Bacofoil.

 What is a Load, or “Low Voltage Disconnect” output?

Some controllers also have a “LOAD”, or LVD output terminals, which is intended to be used for smaller loads, such as small appliances and lights. In reality camper vans don’t need this feature and these terminals should be left unused. For completeness the advantage is that the load terminals have a low voltage disconnect, so it will turn off whatever is connected to the load terminals and keep from running the battery down too far. The LOAD output is often used for small non-critical loads, such as lights if you use solar power for lighting farmyards or use in remote areas, hardly a problem in camper vans as the prime use is to recharge the batteries not use them to power awning lights at night until the battery voltage drops. Do not use the LOAD output to run even very small appliances or inverters. Inverters can have very high surge currents and may blow the controller.

This is a long winded article to say yes you do need a charge controller but the type you use depends on your set-up, battery bank(s), winter use etc. And of course how deep your pockets are.


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