175W 24V Solar Panel to charge 12V Battery

Agreed. There are traps for the unwary by considering only the open circuit voltage capability of the regulator.


"You are looking for a MPPT ( maximum power point tracking) regulator that specificaly specifies it will charge 12 volt batteries from a 24 volt source.

They do exist and will do the job well...but not all MPPT regs will cope with the 24 volt pannels"


To make that perfectly clear (no disrespect, Bantam) perhaps that second sentence could read


"They do exist and will do the job well...but not all MPPT regs CONNECTED TO A 12V SYSTEM will cope with the 24 volt pannels".


This regulator will accept panels up to 65V open circuit. In our caravan owners club there was some discussion about whether or not you could series up or use any panels to a max of 65V on that reg to charge a 12V system. A member asked Jaycar, who consulted the manufacturer and the answer was NO. You cannot mix and match. It is strictly 12V panels for a 12V system and 24V panels for a 24V system. I don't understand why, but that was the answer.


Subsequent investigations revealed it is a common restriction.


If you're looking for one of the exceptions, I have had excellent results with the Aussie-made GSL MPPT 30-2. It will take almost any panels in any series, parallel or series-parallel arrangement up to 95V and charge 12, 24 or 48 volt systems. See page 5 of this document.


(No connection, etc. Just a very satisfied user.)


Cheers

Sorry about all the white space. In preview there wasn't any so I added line feeds. Submit seems to have doubled them :-(

Racey,

MPPT controllers do in fact act a bit like dc-dc chargers. They allow the panel to operate at its optimum voltage (about 36V for a 24V panel) and convert it to that required by the battery. Effectively, the excess voltage is traded for extra current.

Not all MPPT controllers can handle the big voltage jump from a 24V panel to a 12V battery, but many can, and it`s a good efficient way to go if you can.


Cheers

John

What we need to understand is that modern MPPT regulators are not regulators at all.

They are dc to dc switchmode converters and charge controllers.

They take what ever comes from the panells...supplies the optimum load to the panel for what it is doing at the time...( tracks the maximum power point)
then by magic and hokus pokus makes " fresh new electricity" from it, of the best voltage and current that it can to charge the batteries.

cheers

I understand the basic principles of the regulator. However I can't see how a 175 watt 24 volt panel with a max current of 5 amps can deliver a nominal 175 watts into a 12 volt battery. The maximum current would still be 5 amps. Unlike a dc-dc charger which has available supply an current of in excess of 100 amps. That's my logic.

Cheers
Racey

Racey,

The current coming out of the panels is not the limiting factor of the current going into the battery. But the watts are.

If the panel specs say max current of 5 amp that will occur at its Vmp, the max power voltage, in this case 175/5 = 35V.

Most MPPT regulators are also multi stage smart chargers. The regulator takes that 175 watts and with its magic holds the panel at its Vmp (35 volts) and steps that down to what the battery needs. Say that is 12 volts. If the regulator was 100% efficient, it would deliver 175 watts to the battery. At 12 volts the current will be 175/12, = 14.6 amps.

Cheers

Racey mate sorry but you obvioulsy dont understand......the good DC to DC MPPT regulators......take the maximum output of the pannel regardless of current and voltage...stick it into a magic box.....and makes new elctricity of what ever voltage is needed by the battery and what ever current results.

The only thing that remains the same is the amount of energy.

Appart from a small amount of losses....wattage is preserved..input and output voltage are irrelivent to each other and more current can come out than goes in...as long as there is less voltage.

A bit like a transformer,...actially there is one in there.

cheers

Racey - not sure where you got the information that "!2 volt panels seam to have a max rating of around 130watts" - I have 2 x 200W panels from Marsol.

On a good bright day 23+ amps will be shown on the regulator!

Hi Polaris, I was not aware of 12 volt panel with such high output. As I mentioned previously panels which I had seen over 130 watts had operating voltages into the 30's meaning they were more suitable for 24 volt operation (in my opinion :-D).
Thanks to the commentators for their input.

Cheers
Racey

The pannel is a 24 volt panel...that is the whole point of the thread.

and there are charge controllers that will convert 24 volt pannel supply to 12 battery output with little or no loss.

cheers