175W 24V Solar Panel to charge 12V Battery

Submitted: Sunday, Jan 13, 2013 at 20:51
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Hi Guys

I have a Suntech 175W 24V solar panel at home in the shed that I am looking at installing on my Nissan patrol to charge a 120 amp AGM battery and would like to know what sort of regulator setup I should be looking at. Any help would be apprecitated. Suntech 175W Solar Panel

Cheers
dicko1980
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Reply By: garrycol - Sunday, Jan 13, 2013 at 21:38

Sunday, Jan 13, 2013 at 21:38
I would looking to use a 24v to 12v battery charger (not a battery converter) to charge the battery.

Garry
AnswerID: 502482

Reply By: Polaris - Sunday, Jan 13, 2013 at 21:58

Sunday, Jan 13, 2013 at 21:58
This controller will charge either a 12v or 24v battery. The specification regarding input is as long as it is <50V. Typically a 24v panel will have an open circuit voltage of 40v to 44v.
It auto switches 12V or 24V - depending on the battery it is connected to.

Have a look .... 12V / 24V solar controller on eBay.

AnswerID: 502485

Reply By: Peter_n_Margaret - Sunday, Jan 13, 2013 at 23:04

Sunday, Jan 13, 2013 at 23:04
Most MPPT regulators can charge 12V batteries from 24V panels.

Cheers,
Peter
OKA196 Motorhome
AnswerID: 502494

Reply By: The Bantam - Monday, Jan 14, 2013 at 01:06

Monday, Jan 14, 2013 at 01:06
just condensing what has been said and adding

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

A mate of mine sold a few into big ass christmass trees this season..because large 24 volt pannels come cheaper and the lightng systems run 12 volts.

They worked very well

cheers
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Follow Up By: Member - Frank P (NSW) - Monday, Jan 14, 2013 at 10:53

Monday, Jan 14, 2013 at 10:53
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



FrankP

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Follow Up By: Member - Frank P (NSW) - Monday, Jan 14, 2013 at 10:55

Monday, Jan 14, 2013 at 10:55
Sorry about all the white space. In preview there wasn't any so I added line feeds. Submit seems to have doubled them :-(
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Reply By: Racey - Monday, Jan 14, 2013 at 09:24

Monday, Jan 14, 2013 at 09:24
I suspect that you would get full capacity from the panel operating on 12 volts. The maximum current from the panel is approx 5 amps and with the regulator hold the voltage down to to suit the 12 volt battery the overall result would be equivalent to a panel of around 80watts. Whilst I realise some controller are suitable for 12 and 24 volt systems, I don't believe they act like dc to dc chargers. !2 volt panels seam to have a max rating of around 130watts.

I would be interest in any feed back.

Cheers
Racey
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Follow Up By: Member - John and Val - Monday, Jan 14, 2013 at 09:43

Monday, Jan 14, 2013 at 09:43
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
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Follow Up By: The Bantam - Monday, Jan 14, 2013 at 11:47

Monday, Jan 14, 2013 at 11:47
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
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Follow Up By: Racey - Monday, Jan 14, 2013 at 12:49

Monday, Jan 14, 2013 at 12:49
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

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Follow Up By: Member - Frank P (NSW) - Monday, Jan 14, 2013 at 13:49

Monday, Jan 14, 2013 at 13:49
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.

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Follow Up By: The Bantam - Monday, Jan 14, 2013 at 16:21

Monday, Jan 14, 2013 at 16:21
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
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Follow Up By: Polaris - Monday, Jan 14, 2013 at 22:44

Monday, Jan 14, 2013 at 22:44
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!
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Follow Up By: Racey - Tuesday, Jan 15, 2013 at 08:27

Tuesday, Jan 15, 2013 at 08:27
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
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Follow Up By: The Bantam - Tuesday, Jan 15, 2013 at 11:33

Tuesday, Jan 15, 2013 at 11:33
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
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