DC Isolators in Solar Arrays and Circuit Breakers

The Electrical standards for ultra-low voltage state that both the positive and negative conductors (wires) of a solar array need to have a disconnection function. (this means the ability to be turned off) When the panels are producing energy disconnecting under "load" will cause an arc as the contacts are opened. Automatically reconnecting circuit breakers can become welded in place while connecting or disconnecting under load which is why DC Isolating Switches are used, being manually operated you will know it's still working correctly as you turn the rotary on and off. However, these DC Isolators are expensive, more expensive than using a manually operated circuit breaker which you can manually trip and reconnect. This is why we supply double pole (pos and neg) circuit breakers in housing as its a 2 birds with one stone approach. Protection and Isolation.

Solar panels themselves can't short circuit even if you connect the two outputs of the panel together as the internal wiring is rated higher than the panels output. If, however, you have 3 panels in series and one fails. The power output of the other 2 panels will be more current than what a standard 16A circuit breaker would be capable of handling. For this reason, circuit protection may not be required, but isolation is. On 1 or 2 panels a single 16A 500VAC circuit breaker is adequate. But with 3 panels, you should isolate each panel with a circuit breaker to ensure safety and isolation can be achieved.

At this point, 3 circuit breakers cost more than 3 fuses and 1 x DC Isolator so the choice is yours to make. Isolate and protect yourself.

Smart Alternators what are they?

A typical alternator that most people might have a basic understanding of generates power that is used to recharge a vehicle's battery. Why that's correct in principle the reality is that when the voltages are only 13.3-13.8 volts as typically found after the first 5 minutes of starting a vehicle. This is why an alternator is only used to replace the energy used to start the vehicle in the first place. Many people may make short journeys to and from work and have already found how quickly their battery needs a replacement this is due to it not getting adequate charge.

Also if you revise charging voltages why are they important in our FAQ you see this isn't enough voltage to fast charge (or bulk charge) a vehicles battery. This problem is compounded if a secondary battery is attached.

Now for the Smart Alternator, it goes one step further and is controlled by the engine management system which controls when the turning of the alternator by the motor is applied. This additional load that is placed on the engine also consumes fuel, therefore, increasing emissions and that costs the manufacturer Carbon Credits so they now actively limit the time the alternator is on. Which means more flat batteries which is why we see the rise of EFB or AGM batteries as start batteries to try to counter the problem.

The engine management system knows how much power is drawn by every factory fitted item in the vehicle and therefore if you turn on lights, wipers and are using electric fans to cool the motor the vehicle knows to provide just the right amount of current the vehicle needs to operate with little wasted energy. Unfortunately, that previously wasted energy was actually absorbed by secondary battery banks needing a charge. These days this doesn't occur as much, in fact, with recent tests we have found a factory Iveco van only outputs a maximum of 22A above the engine management system requirements. That's typically the same amount of current required to run a DC powered fridge while driving. So your batteries aren't really getting any charge while driving from the alternator. Many vehicles now have smart alternators like Mercedes, VW, Fiat, Renault, Ford & more.

To try and combat this problem DC chargers draw their power from the start battery and by design try to flatten the start battery while the engine is running by feeding the secondary battery bank the correct voltage up to the max current of the charger. This in-turn causes the start battery to flatten which in-turn forces the alternator to come on and recharge the start battery While this is a very crude overview of the process the result is the alternator running for longer charging the secondary battery bank with the added benefit of being charged at the correct voltages for the secondary batteries which may be more than the output of the alternator. All in all that can lead to batteries being charged 30% quicker than the old alternator systems and est. 80% quicker than the new smart alternator setups.

Charging Voltages why are they important?

A 12v battery is made of six 2 volt cells. When we discuss charging we have to consider the application in which they are used and how long you want them to last. This ties in with Depth of Discharge (D.O.D.). Many variables exist but the gist is the faster you discharge and the higher the voltage on recharge or higher the current is on recharge the quicker the active material deteriorates which causes end of battery life.

Batteries typically have voltage ranges to charge for bulk / cyclic applications and float life applications. There is also a stipulation on the max initial charge current, the larger the battery the higher the current. If comparing brands an initial inrush current that is higher than another brand may be an indication of a better quality product with a lower internal resistance if made with better raw material which will also be reflected in its cost. Alternatively, it will indicate a thicker plate which is ideal if you require a deep cycle battery.

AGM batteries should bulk charging voltage between 2.4 and 2.45 volts per cell, and float voltage charge between 2.25 volt and 2.31 volts per cell. That is 14.4-14.7 volts bulk and 13.5-13.9 volts float. These figures are not temperature compensated and this needs to be factored in.

See temp. compensation charging FAQ but in short, allow for the addition of 0.03v per degree C below 250C and the reduction of 0.03v per degree C for every degree above 250C. Temperature compensation can not be calculated if you do not have a temperature sensor which is typically an optional extra on many chargers. It does come standard on all CTEK chargers above the 7A rating.