Controller recommendation

cptdondo

I have room for 2 of these panels:

https://www.solar-electric.com/rec-rec320np-black-solar-panel.html

They are spec’d as follows:

• Vmp: 34.2 Volts
• Voc: 40.3 Volts
• Imp: 9.37 Amps
• Isc: 10.22 Amps

I am looking for a controller recommendation.  I guess my question is if I need to charge 12V batteries, am I looking for a 20A controller or a 60A controller?  (Assuming that the max charge into 12V batteries would be 60A).

I don’t need the biggest and best; just a simple one (or two).

Would this be a good fit?

https://www.solar-electric.com/lib/wind-sun/TSdatasheet.pdf

I don’t mind it being PWM.

If not, a brand and model would be awesome!

mike95490

640W @ 13V is a 49A controller, 60A is a common value in controllers.

With those panels, and a MPPT controller, you get 49A, with a PWM controller you get 18A, into a 12V battery. 

Why are you not looking at a 24V system, what are your loads you need to power ?

cptdondo

The existing system is 12V, so I am limited.  I am trying to replace an existing undersized 150W panel and controller.

So would this be a better choice?

https://www.solar-electric.com/outback-power-flexmax-fm60-150-mppt-charge-controller.html

Photowhit

cptdondo said:

The existing system is 12V, so I am limited.  I am trying to replace an existing undersized 150W panel and controller.
So would this be a better choice?
https://www.solar-electric.com/outback-power-flexmax-fm60-150-mppt-charge-controller.html

I think that's the best bang for the buck, in a quality controller.

Solarguy1

mike95490 said:

640W @ 13V is a 49A controller, 60A is a common value in controllers.

With those panels, and a MPPT controller, you get 49A, with a PWM controller you get 18A, into a 12V battery. 

Mike, I'm confused about this. Could you educate me on this, please? I'm trying to learn...

Wouldn't his 2 panels put out only 9 amps if connected in series, or approximately 18 amps if wired in parallel?

Where does the 49 amps come from?

Thanks!

BB.

This is the issue of "matching" your source power (solar panels) with the thing you are trying to charge/supply power too--In this case a 12 volt battery bank.

Everyone is pretty understanding of how a battery performs... More or less, a 12 volt battery holds 12 volts whether charging or discharging (a first approximation, normal operation for a lead acid battery is 10.5 volts "dead" to 14.8 volts being charged--And around 12.0 to 12.7 volts fully charged).

A solar panel is a "current source"... More or less, your 34.2 volt panel will output 9.37 amps--No matter if the load is a "dead short" or a 12 or 24 volt battery. Above ~34.2 volts, the output current ramps down, eventually to zero amps at 40.3 volts (Voltage open circuit Voc). (of course, there are other 2nd order effects, temperature, internal resistance, and the amount of sun light hitting the panel all affect output current and voltage).

So, how does that "affect your design choices"... A PWM controller (Pulse Width Modulation) is really just an On/Off switch (controlled by a computer). If you have full noon-time sun, and the output current is 9.37 amps, the power into the battery bank is:

• Power = Voltage * Current
• Power Dead Short = 0 volts * 9.37 amps = 0 Watts
• Power into 12 volt battery = 12 volts * 9.37 amps = 112 Watts
• Power into 24 volt battery = 24 volts * 9.37 amps = 225 Watts
• Power into "34.2 volt battery" = 34.2 volts * 9.37 amps = 320 Watts (Vmp = Voltage maximum power)
• Power into "40.3 volt battery" = 40.2 volts * 0 amps = 0 Watts

That is the "issue" of needing to match the proper solar panel Vmp voltage to the battery bank voltage. The typical 12 volt battery on a PWM controller should be around Vmp=17.5 to 18.x volts for "optimum" operation.

An MPPT charge controller is sort of like the automatic transmission on a car (or the DC equivalent of a variable transformer)--It matches the IV (current voltage) curve of the solar array to that of the battery bank.

Power = Voltage * Current
34.2 volts * 9.37 amps from solar panel = 320 Watts = 14.75 volts battery charging * 21.7 Amps into battery bank

-Bill

BB.

I should add the "=" sign is the "MPPT controller" Power in = Power out (through the magic of a digital switching power supply, the guts of the MPPT controller).

-Bill

mike95490

PWM controllers : Amps in = Amps out     18A in, 18A out
MPPT controllers :  Watts in = Watts out    Watts are Volts x Amps    12v x 2A = 24Watts