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Benz
31st August 2012, 04:06 PM
Hey Guys just after a little help on my 12 volt solar system for my 130 defender.

I have an existing system which isn't quite giving me enough power and I plan on changing it.

I have a Dingo 20/20 (http://www.plasmatronics.com.au/common/DINGO.html) regulator which can handle 20A of solar input.

The current solar panel, which is roof mounted, is a 240W 24v panel which I got on clearance and suited my needs perfectly when we only ran one fridge.
we have since added a freezer to the set up so we need MORE POWER!

Plan is to turf the 24v panel and replace it with a 12v and then add a portable fold up panel to the system which we can pull out if we stop for a long period of time (longer then about 3-4 days)

I would like to run both the roof mounted and fold up/portable panel off the same regulator as it would save on cost and eliminate the problem you get when regulators cancel each other out if they try to charge at the same time.

This is where I need help.

If the panels are wired in parallel,
Do they have to be similar wattage panels?
Or do they have to be Identical?
Or you can mix and match different wattage panels as long as the Voltage output is similar?

Or is trying to add the fold up panel to the existing regulator not worth the effort and adding it direct to the batteries via a different regulator the right thing to do?

Thanks in advance for any help you can provide :D

Ben

bee utey
31st August 2012, 05:18 PM
You are running a 24V panel on a 12V system? You may only be putting out its short circuit current, i.e. around 8 amps. Check if it has two sections wired in parallel which is much better.

You can run as many panels in parallel as you like so long as they have the same nominal output voltage. Their peak open circuit voltage/total short circuit current should not exceed the regulator rating. I have around six random sized panels that are all linked together at my house, they all end up producing current at whatever voltage they hit at the regulator.

If you want to get more out of your existing panels get a MPPT regulator (maximum power point tracking) as they let the panels operate at their maximum power output voltage. This is then transformed to battery charging voltage at a higher current than the panel itself is producing (basically like a transformer does but by switch mode control).

Benz
31st August 2012, 05:26 PM
You are running a 24V panel on a 12V system? You may only be putting out its short circuit current, i.e. around 8 amps. Check if it has two sections wired in parallel which is much better.

You can run as many panels in parallel as you like so long as they have the same nominal output voltage. Their peak open circuit voltage/total short circuit current should not exceed the regulator rating. I have around six random sized panels that are all linked together at my house, they all end up producing current at whatever voltage they hit at the regulator.

If you want to get more out of your existing panels get a MPPT regulator (maximum power point tracking) as they let the panels operate at their maximum power output voltage. This is then transformed to battery charging voltage at a higher current than the panel itself is producing (basically like a transformer does but by switch mode control).

yeah I know the 24V panel is not ideal.
the regulator will handle up to 100v though so no problems there.
only bought it because it was cheap and provided enough power to suit our needs.

haha it's ended up costing me more now hasn't it :(
should of done it right the first time

Benz
31st August 2012, 05:33 PM
So they all just need to have the same 'Maximum Power current'

for example 18v?

bee utey
31st August 2012, 06:37 PM
So they all just need to have the same 'Maximum Power current'

for example 18v?

(You mean voltage at maximum power output, not current.) More or less, otherwise you are wasting weight and panel size if they are too far off ideal. Solar cell's actual output voltage varies so much with load, temperature and sun intensity that so long as the panels are all approximately the same MP rated voltage they will be fine. Most "12V" panels will be 36 cells in series, approx 17-18V MP and will produce about 70% of their rated output power into a battery at 13V in cool conditions.

https://www.aulro.com/afvb/images/imported/2012/08/1.jpg

Typical output curve, this one maxxes out at 40W at 17V or delivers 32W at 13V

Blknight.aus
31st August 2012, 06:48 PM
Maximum no load voltage is the important one for what you're doing.

DeanoH
31st August 2012, 07:12 PM
What '24 volt' panel are you running ? Is it a panel designed for a domestic installation ? or is it a '2 X 12 volt' panel designed for various applications ? Without knowing the manafacturer and part number it's a bit difficult to determine if it's running to its maximum efficiency.

Please supply this info. for specific as opposed to 'generic' advice. :)

Deano. :)

Benz
31st August 2012, 10:51 PM
What '24 volt' panel are you running ? Is it a panel designed for a domestic installation ? or is it a '2 X 12 volt' panel designed for various applications ? Without knowing the manafacturer and part number it's a bit difficult to determine if it's running to its maximum efficiency.

Please supply this info. for specific as opposed to 'generic' advice. :)

Deano. :)

when I think about it it's probably a domestic one as it puts out 36v...

I'm getting rid of it anyway? why does it matter?

I'm buying both a new panel for the roof of the car and a new portable panel (one which I can get out on long stays and if camped under a tree)

Benz
31st August 2012, 10:55 PM
(You mean voltage at maximum power output, not current.) More or less, otherwise you are wasting weight and panel size if they are too far off ideal. Solar cell's actual output voltage varies so much with load, temperature and sun intensity that so long as the panels are all approximately the same MP rated voltage they will be fine. Most "12V" panels will be 36 cells in series, approx 17-18V MP and will produce about 70% of their rated output power into a battery at 13V in cool conditions.

https://www.aulro.com/afvb/images/imported/2012/08/1.jpg

Typical output curve, this one maxxes out at 40W at 17V or delivers 32W at 13V

haha oops yeah I mean that

DeanoH
1st September 2012, 11:55 AM
........................................I'm getting rid of it anyway? why does it matter? .................................


Some '24 volt' panels are manafactured as two '12 volt' sub panels and wired in series to give 24 volts. It can be possible to re-configure these panels by connecting the sub panels in parallel to make a '12 volt' panel of the same power output.
If your panel was of this type you could save yourself the cost of a new panel and still have the desired result. :)

Deano :)

Benz
1st September 2012, 12:09 PM
oh I see

I'll have to unbolt it from the roof and have a look

thanks
deano

Benz
1st September 2012, 04:46 PM
Okay so I have pulled the panel off the roof.

no brand names as such on the back but the info label reads:

Model: PMW250PW
Watt: 250W
Voltage: (VMP36.0V) 24.0V
Current: 6.95A

I also pulled the cover off the back and took a photo.

It looks to me that the panel has 2 sections wired in series with what looks like diodes

can this be rewired to give me 12V?

sorry about the crappy photo. the other half has our nice dslr.a

bee utey
1st September 2012, 05:20 PM
Park it in the sun, measure the voltage across each diode. You may have a 3 section panel with a nominal 8 volts per section (around 11V open circuit). If you get 16V, 0V and 16V you have a 2 section panel. Remove the centre diode and connect the two sections in parallel, terminal 1 to 3 and terminal 2 to 4.

The diodes are blocking diodes for when the panel is part of a string of panels on the roof of a house, any section being shaded goes down to zero voltage and the diodes allow the current to flow through the rest of the panel string.

Benz
1st September 2012, 06:11 PM
thanks bee utey.

just before reading your post I pulled the centre diode and wired terminal 1 to 3 and terminal 2 to 4.

tested the panel on the regulator and was getting around 13 to 13.5V in the late afternoon (5 pm) sun but only about 1 amp of output.

will try it again tomorrow when the sun is a bit higher.

fingers crossed I get some good results.

DeanoH
2nd September 2012, 09:37 AM
Park it in the sun, measure the voltage across each diode. You may have a 3 section panel with a nominal 8 volts per section (around 11V open circuit). If you get 16V, 0V and 16V you have a 2 section panel. Remove the centre diode and connect the two sections in parallel, terminal 1 to 3 and terminal 2 to 4.

The diodes are blocking diodes for when the panel is part of a string of panels on the roof of a house, any section being shaded goes down to zero voltage and the diodes allow the current to flow through the rest of the panel string.

This (highlighted bit) is the important bit here. 0 volts across the centre diode. Though the open circuit voltage on a '12 volt' panel in good sun can be around the 20 volt DC mark.

If you read (in good sun) an open circuit voltage of around 10-14 volts across all three diodes then you have a 3 X '8 volt' panel as bee utey described.

Still not too bad, If this is the case (in theory) I'd 'drop off ' one '8 volt' panel and run the other two into a suitable reg and end up with a good 160+ watt supply. :)

Deano :)

Benz
2nd September 2012, 04:56 PM
This (highlighted bit) is the important bit here. 0 volts across the centre diode. Though the open circuit voltage on a '12 volt' panel in good sun can be around the 20 volt DC mark.

If you read (in good sun) an open circuit voltage of around 10-14 volts across all three diodes then you have a 3 X '8 volt' panel as bee utey described.

Still not too bad, If this is the case (in theory) I'd 'drop off ' one '8 volt' panel and run the other two into a suitable reg and end up with a good 160+ watt supply. :)

Deano :)

yeah just confirmed the panel is a 3 x 8v one.

this will mean I cant use it in conjunction with a separate folding panel on the same regulator right?

Blknight.aus
2nd September 2012, 05:11 PM
depends on the voltage of the other panel and the style of regulator, without seeing all of it Id advise not doing so.

if its reading 14v open circuit you might be able to just parallel the 3 internal panels on that one and use that to drive the regulator but it'll cost you effeciency.

bee utey
2nd September 2012, 05:22 PM
I suggest you either sell the panel to a 24V vehicle owner or purchase a suitable MPPT regulator, such as this one:

Powertech MPPT Solar Regulator Charge Controller 30A 12/24V | eBay (http://www.ebay.com.au/itm/Powertech-MPPT-Solar-Regulator-Charge-Controller-30A-12-24V-/320963205276?pt=AU_Solar&hash=item4abae5d89c)


NOTE: This unit WILL charge a 12V battery from 24V solar panels, but not vice versa.

Specifications
Max PV array : 360W(12V) or 720W(24V)
Battery system voltage : 12VDC or 24VDC
Max PV open circuit voltage : 65V
Max input current : 30A
Rated load current : 30A
Ambient temp range : -20ºC - 50ºC
Efficiency : 97%
Dimensions : 205(L) x 145(W) x 55(H)mm
Run any other panels with their own regulator.

Blknight.aus
2nd September 2012, 05:38 PM
I suggest you either sell the panel to a 24V vehicle owner or purchase a suitable MPPT regulator, such as this one:

Powertech MPPT Solar Regulator Charge Controller 30A 12/24V | eBay (http://www.ebay.com.au/itm/Powertech-MPPT-Solar-Regulator-Charge-Controller-30A-12-24V-/320963205276?pt=AU_Solar&hash=item4abae5d89c)

GSL MPPT12-1 12/24V 12A Solar Charge Controller Regulator. Aust made, 2yr wnty | eBay (http://www.ebay.com.au/itm/GSL-MPPT12-1-12-24V-12A-Solar-Charge-Controller-Regulator-Aust-made-2yr-wnty-/140694802257?pt=AU_Solar&hash=item20c2104f51)

Run any other panels with their own regulator.


same tech as whats in the jaycar sold MPPT unit if your not willing to risk an ebay purchase

DeanoH
2nd September 2012, 09:16 PM
...................................this will mean I cant use it in conjunction with a separate folding panel on the same regulator right?

Correct.

bee uteys solution is the best technically, but at $188 for an MPPT reg that will do 3 panels of the size you've got I'd be looking for a smaller (hopefully cheaper) version if they exist.

Don't know if I'd parallel the three '8 volt' panels together. Too little room to move in less than full sunlight and correctly aligned.

As a cheap (not technically best) solution you could use 2 '8 volt' segments in series into a standard '12 volt' reg. If the voltage was too high for the regs input I would put a string of diodes in series with the output of the panels to reduce the panel voltage to get it in spec with the regs input. A silicon diode drops about 0.6 volt across itself REGARDLESS of the current flowing through it, so to lose 4 volts use 7 diodes. and 10 Amp power diodes are cheap.

10pcs 10A10 10 Amp 1000V 10A 1KV Axial Rectifier Diode | eBay (http://www.ebay.com.au/itm/10pcs-10A10-10-Amp-1000V-10A-1KV-Axial-Rectifier-Diode-/300553693802?pt=AU_B_I_Electrical_Test_Equipment&hash=item45fa656a6a)

Sort of messy and not technically 'elegant' but doable to get a cheap result.

Deano :)