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Help interpreting Solar info please

Submitted: Sunday, Jan 01, 2006 at 20:23

Lunar

Howdy all, I am looking at buying a Uni-Solar 128w Flexible Laminate Solar Panel with the following electrical characteristics

Rated Power: 128 W
Nominal Voltage: 24 V
Peak Power: 128 W
Peak Voltage: 33 V
Peak Current: 3.88 A
Open Circuit Voltage: 47.6 V
Short Circuit Current: 4.8 A

it is from the States hence the 24V. I have been buying bits and pieces as I go along to spread costs, I have already bought a PowerTech 20A Solar Charge Controller (http://www.jaycar.com.au/productView.asp?ID=MP3129) with the following characteristics,

Specifications
*Battery Voltage: 12V
*Maximum PV panel open circuit voltage: 26V
*Continuous load/charge current: 20A
*Maximum charge/load current (5 mins): 25A

My question is that the open circuit voltage on the panel is greater than that of the charge controller, so my charge controller won't work with it? But i am confused as I got a 20 Amp charge controller that can easily handle a 128 12 volt panel? I just don't understand why my charge controller is to small for a 128 Volt panel. I guess it's because the regulator is a 24 Volt regulator, so if it was a 12 Volt regulator my charge Controller would be fine? If so is there any way I can modify the panel to work with my charge controller? Thanks alot.
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ThreadID: 29297 Replies: 5
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AnswerID: 146241   Submitted: Sunday, Jan 01, 2006 at 20:41

Michael B replied:

Hey Lunar,

And I thought that I had problems.......If u get yours sorted, give me a answer to my question........

Michael B (SA)
Reply 1 of 5
AnswerID: 146274   Submitted: Monday, Jan 02, 2006 at 05:47

hl replied:

That's a big mother of a panel!
And your regulator is not suitable as the no load voltage will be far too high.
You need a regualtor designed for a 24V panel, unless that panel can be wired to provide 12V output.
Cheers
Reply 2 of 5
AnswerID: 146287   Submitted: Monday, Jan 02, 2006 at 07:36

Footloose replied:

What are you trying to power with the solar power ? If it's a 12v battery then get a panel that supplies 12v.
Reply 3 of 5
FollowupID: 399848   Submitted: Monday, Jan 02, 2006 at 14:52

Lunar posted:

yeah that's the original intent but this one is REAL cheap and u can role it up so ideal for camping, was hoping to be able to modify it for use over here, even if I had to spend another 100 or so to modify it it would still be a very good deal.
FollowUp 1 of 1
AnswerID: 146348   Submitted: Monday, Jan 02, 2006 at 20:20

Mike DiD replied:

Solar Panels are essentially constant current sources - whether you connect it to a 24 volt battery or a 12 volt battery, you will get about 3.5 amps from it when in direct sunlight. (Into a 1 (one) volt battery you will get abt 4.5 amp)

However if you connect a 24 volt panel to a 12 volt battery you are only getting half the power of it - so it's only going to be as effective as a 12 volt 60 watt panel.

Mike
Reply 4 of 5
FollowupID: 399895   Submitted: Monday, Jan 02, 2006 at 22:01

Lunar posted:

Thanks Mike, sounds like I'm back to the drawing board :(.
FollowUp 1 of 1
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AnswerID: 146827   Submitted: Friday, Jan 06, 2006 at 15:44

Pajman Pete (SA) replied:

What about one of these:

24 Volt Solar Regulator

Charge two batteries in series at 24V and draw your power from them in parralel at 12V. You will need some diodes in the wiring but any sparky should be able to sort that out for you.

Pete

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Reply 5 of 5
FollowupID: 400291   Submitted: Friday, Jan 06, 2006 at 15:54

Pajman Pete (SA) posted:

That didn't work,

try this one:

Regulator

Ebay item 5850561750 if I still haven't got it right!

Cheers

Pete

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Any mug can be uncomfortable out bush.
VKS737 Mobile 3580
FollowUp 1 of 2
FollowupID: 400298   Submitted: Friday, Jan 06, 2006 at 16:43

Lunar posted:

Thanks mate, starting to get a bit complicated and I like kiss, I already have a PV I am happy with, I spent more on it so I could get accurate readings, but cheers for the info and good thinking.
FollowUp 2 of 2