spec of charge controller

rama

Hi all - if a charge controller does not specify in its specs on what the MAX PV ARRAY INPUT is, is there a way to determine so I'll know how big of an array it can support?

Take this guy for example - its max charging current is 60A and can charge up to 60V of battery.

Does it mean that for a 48V battery system, the max pv array it can support is 48V*60V = 2880W?

Another method I know of is that some say for 48V battery you need 68V from array to charge so the controller can handle 68V*60A = 4080W.

Very confused.... would appreciate it if someone can point me in the right direction. thanks....

BB.

Re: spec of charge controller

rama wrote: »

Hi all - if a charge controller does not specify in its specs on what the MAX PV ARRAY INPUT is, is there a way to determine so I'll know how big of an array it can support?

In the manual, they will have a lot more configuration information. Unfortunately, the possible ways of setting up the controller is pretty complex and there are different ways to setup a controller for successful operation.

Take this guy for example - its max charging current is 60A and can charge up to 60V of battery.

Does it mean that for a 48V battery system, the max pv array it can support is 48V*60V = 2880W?

Actually, a bit more for several reasons.

First, the nominal charging voltage for a battery bank is ~58 volts or so. The actual energy into the battery bank is:

• 58 volts * 60 amps = 3,480 watts

Next, typically, the maximum energy from a solar panel + charge controller (dirty panels, less than 100% clear sky, solar panels are hotter than STC/Lab tests assume, charge controller and wiring losses, etc.) give us a reasonable maximum output of 0.77 of the STC/Marketing rated solar panel output:

• 3,480 watts / 0.77 = 4,519 Watts Maximum "Optimal" Solar Array

Now, if you live in very cold climates (very clear sky, windy/cold day, cold panels--more energy, sun reflecting off of snow, etc.) you could get more energy... But the amount of extra energy happens for relatively few hours per year and it does not usually make much sense to "over size" the charge controller to 100% (or more) of panel/array STC rating if you are trying to get the most power per $$$.

Another method I know of is that some say for 48V battery you need 68V from array to charge so the controller can handle 68V*60A = 4080W.

So, there is the above reasoning why I would not have an issue with using up to ~4,520 watts of array without any concerns about wasting money.

And, in reality, Xantrex, MorningStar, Outback, Rogue, and others can actually connect to even larger solar arrays and operate just fine... However, if the Isc (short circuit current) exceeds the controller's maximum input current--you will need a protective fuse/breaker to prevent a controller failure from causing a fire. For example, if the controller has a maximum of 60 amp input:

• 60 amps * 1.25 NEC safety factor = 75 amp circuit

Or, rounding up to an 80 amp capable wire and rated fuse/breaker.

Note, the above is in disagreement with NEC--I have some issues with what the NEC specifies for solar charging equipment ratings (and deratings). In the case of MPPT type charge controllers, the above is perfectly safe and complies with how the rest of the NEC (US National Electric Code) is written (fuses/breaker protect wiring, not connected devices--And all connected devices shall be able to accept the maximum current required to trip the fuse / breaker).

Remember, there are other issues... For example the Vmp of the array should be >~70 Volts to allow for voltage drops and hot panels.

And Vmp of the array (for typical large MPPT controllers) should be around 100 VDC maximum... Above that voltage, you are close to the Voc (Voltage open circuit) of the charge controllers (very cold days, no load on panels) which can damage charge controllers. For the Xantrex MPPT:

Maximum PV array voltage (operating)       140 Vdc
Maximum PV array open circuit voltage      150 Vdc

Note that the Xantrex (now Schneider Electric) controller has an Array Sizing tool which can help you configure the series/parallel array and Vmp voltage. Note that Schneider has chosen to make their website one of the most confusing/difficult and unreliable sites I have seen at a professional website to link into:

Xantrex / Schneider GT sizing tool is missing

The "real link" to the sizing tool is not working for me right now (with Firefox), but this "hacked" link is working:

Schneider XW sizing tool direct link

Clear as mud?

-Bill

rama

Re: spec of charge controller

Thanks BB - but would it make sense to use the MAX INPUT current value of the controller to estimate max array size instead of the MAX CHARGING current? I just thought since we're talking about the array (input) maybe we should use the input value instead.

If the controller has a MAX INPUT of 50A, then max array size (for a 48V battery bank) would be 50A*58V/0.77 = 3766W...?

Does this seem right?

BB.

Re: spec of charge controller

Rama,

It depends on the controller type... A PWM controller is really nothing more than a fancy "light switch" that turns on and off between the solar array and the battery bank... So, for a PWM (pulse width modulation--just a term for on XX% of the time and off for YY% of the time) controller's input current equals the output current.

For a MPPT controller--it is really more like an AC variable transformer... In the case of a MPPT (maximum power point tracking) charge controller, it takes high voltage/low current and "steps it down" (or converts) to low voltage/high current for the battery bank.

So, ignoring any losses for this example... You could have 6 solar panels with Vmp of 20 volts and 5 amps each (100 watt panels)...

One configuration would be three panels in series (3*20v=60volts) and 5 amps... Two of these string in parallel (6 panels) will have an output of Vmp/Imp of 60 volts and 10 amps. The total power from the array:

• 60 volts * 10 amps = 600 watts

The other configuration would be to place all 6 panels in series... That would be Vmp of 120 volts and Imp of 5 amps. Again the total power of the array would be:

• 120 volts * 5 amps = 600 watts

Now, a MPPT charge controller can take in 60 volts @ 10 amps or 120 volts @ 5 amps--it just looks for the maximum power (Vmp*Imp=Pmp) of the attached solar array....

Now, for the battery bank, it looks at what the present voltage of the bank is and outputs that voltage with the available power...

For your case, you have a 48 volt battery bank which will be around 42 volts "Dead" (don't go there) or ~59 volts at maximum "Absorb" voltage... The MPPT controller will output two different values of current:

• Idead-batt = 600 watts / 42 volts = 14.3 amps
• Inear-full-batt = 600 watts / 59 volts =10.2 amps

So, within reason, what we care about is the Array's Wattage--not its specific voltage and current... The controller will take the power and down convert it to what the battery bank needs.

Now--In reality, it is a bit more complex... We do care about the input voltage and input current from the Array... Too high or too low and things may get damaged or the controller will not charge.

-Bill