Matching my panel with a charge controller

kevinhenrycalgarykevinhenrycalgary Solar Expert Posts: 33
I am getting ready to do another install on a small trailer. I did one a few years back and received a lot of valuable advice from those of you on this forum. That system has been working flawlessly.

Unfortunately, solar terminology is not second nature to me so I find I am having to re-educate myself.

I have a Suntech STP175S-24/Ab-1 panel
Pmax 175W
Imp 4.95A
Vmp 35.2V
Isc 5.2A
Voc 44.2V

Am I correct to say this is a 24volt panel?

In order to keep costs down I want to use a PWM controller and was thinking of the Morningstar ProStar PS-15

I will be charging a 12 volt battery.

My confusion involves the designation of the Prostar 15. It states the system voltage can be 12/24V.

Does this mean the controller will charge a 12 volt battery with a 24 volt panel or does it mean it will charge a 12 volt battery with a 12 volt panel as well as charge a 24 volt battery with a 24 volt panel?

My last install involved using the Morningstar Sunsaver MPPT controller with two 12 volt panels, in series, to charge a 12 volt battery. Do I need to go to something like the Sunsaver MPPT to handle the charging of the 12 volt system with the 24 volt panel?

Any feedback is greatly appreciated.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: Matching my panel with a charge controller

    The 12/24 volts refers to the charge controller being set to charge EITHER a 12 volt or 24 volt battery bank.

    For a PWM controller, the ideal Vmp (Voltage maximum power) is either Vmp~17.5 volts for a 12 volt bank OR Vmp~35 volts for a 24 volt battery bank.

    You could use your Vmp~35 volt solar panels to charge a 12 volt battery bank with a PWM controller--however, you will loose ~50%, or a bit more, of your solar array's usable output power.

    If you have a Vmp~35 volt solar array, you should install a MPPT type charge controller (like the MorningStar 15 amp MPPT controller or Rogue 30 amp controller--both will work with either a 12 or 24 volt battery bank).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Matching my panel with a charge controller

    You are correct: that is a "24 Volt" panel.
    But you can't use it with a PWM controller to charge a 12 Volt battery. Most of the power will be lost to heat if you do. When a PWM controller is listed as "12V/24V" it means 12V in = 12V out, 24V in - 24V out: they do not have the ability to down-convert extra array Voltage to additional charge current the way a MPPT controller can.

    With just one of these panels to a 12 Volt system you could use the Morningstar 15 Amp MPPT controller: http://www.solar-electric.com/mosumpsochco.html
  • kevinhenrycalgarykevinhenrycalgary Solar Expert Posts: 33
    Re: Matching my panel with a charge controller

    Thanks guys. I was suspecting this was the case. It is all coming back to me now. I believe it was you Bill who gave me all the useful advice for my last install.

    I got such a good deal on the panel that it is probably worth it to spend the extra on the MPPT instead of switching panels. Just have to look for a good price on an MPPT. Problem up here in Canada is the shipping costs to come across the border. I have family travelling to Washington next week, perhaps I will get them to take a look.

    Thanks for setting me straight.
  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: Matching my panel with a charge controller

    And thank you too Kevin.

    I have been posting links to your thread and videos for people asking about small RV installs.

    How has it been working out?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • kevinhenrycalgarykevinhenrycalgary Solar Expert Posts: 33
    Re: Matching my panel with a charge controller

    It works great. Not a single glitch. If memory serves me correct I think I had it pumping in 11+ amps to the battery in optimum test conditions. In practical use I have a hard time drawing the battery bank down below 90% and it only needs to be putting in a couple of amps. Seems I can park in the shade for a week and it still charges.
  • soleilsoleil Solar Expert Posts: 45
    Re: Matching my panel with a charge controller

    Several months ago I installed in my RV the Rogue MPPT controller Bill mentioned. It's been working very well and I would also recommend it. (My install thread: http://forum.solar-electric.com/showthread.php?t=9915 )
  • simmtronsimmtron Solar Expert Posts: 87 ✭✭✭
    Re: Matching my panel with a charge controller
    Thanks guys. I was suspecting this was the case. It is all coming back to me now. I believe it was you Bill who gave me all the useful advice for my last install.

    I got such a good deal on the panel that it is probably worth it to spend the extra on the MPPT instead of switching panels. Just have to look for a good price on an MPPT. Problem up here in Canada is the shipping costs to come across the border. I have family travelling to Washington next week, perhaps I will get them to take a look.

    Thanks for setting me straight.

    Get it shipped by POST, it is cheap and the is no broker fees to pay. I shipped lots of stereo equip by post from USto Canada and find it safer than UPS or Fedex
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