Matching my panel with a charge controller

kevinhenrycalgary · August 2011

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.

BB. · August 2011

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

Cariboocoot · August 2011

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

kevinhenrycalgary · August 2011

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. · August 2011

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

kevinhenrycalgary · August 2011

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.

soleil · August 2011

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 )

simmtron · September 2011

Re: Matching my panel with a charge controller

kevinhenrycalgary wrote: »

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

JamesF · September 2023

I think I'm in a similar situation as Kevin. I purchased a teardrop trailer with a Lightleaf D150 solar panel and a Bluetti EB70S. I'm unable to charge my battery because (from Bluetti support) the voltage of the panel is too high for the battery. Photos of both devices are inserted. I know absolutely nothing about this subject and would love to boondock soon. What's the best way to go about getting this system to work? Any help would be greatly appreciated!

Matching my panel with a charge controller

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