Reply With QuoteI should add, I based my reply on the suitability of the 120 watt panel from the original post where he says
"Where we go away, " etc etc
so this is a weekender or occasionally used setup I am assuming..
cheers from the bush
the hawkers are AGM, and have done little work. I have several banks of them doing various jobs around the place. very good batteries if you come across them second hand. the panel is only a few years old
quote
"120W@12v does mean 10amps this is basic electrical maths , but a 120W solar panel in it's raw form will not give you this. CORRECT!!!
"If the panel is producing it's full 120W and is wired to a 12v regulator ( not accounting for loses ) will deliver 10amps" NO IT WONT if its connected to a battery via a on-off style of regulator.
"it could even give you 6volts at 20amps." NO, this is not correct UNLESS you are using a switch-mode MPPT regulator, which (when ignoring losses) can increase current as it acts as a dc-dc converter.
120/12 = 10, but that doesnt happen with panels as you have correctly noted
here is a picture showing what the amperage is when the 30 watt panel is connected across a 6 volt battery
it is 1.87 amps. which is still below the short circuit current. the absolute maximum current you can get out of a solar panel is its short-circuit current. full stop
Last edited by Bluedog; 05-02-12 at 03:16 PM. Reason: image too big for hotlinking - click link
member. Austech dog squad: if it can be fixed the dogs will sniff it out
I should add, I based my reply on the suitability of the 120 watt panel from the original post where he says
"Where we go away, " etc etc
so this is a weekender or occasionally used setup I am assuming..
cheers from the bush
member. Austech dog squad: if it can be fixed the dogs will sniff it out
ageno2gen1 (06-02-12)
The controversy comes about because 12V solar panels are not 12V. They're rated at 18V. Same as 24V panels are not 24V. They're 36V. When 18V is used, ohms law and real world figures start looking similar eg 120 / 18 = 6.6 roughly.
I guess they call the 18V panels "12V" to make sense when used on a 12V "system" or with 12V batteries. Although 12V batteries when fully charged are not exactly 12V either lol. Confusing ain't it?!
The reason you need a higher voltage is that to charge a 12 V battery you need to raise its voltage above its Open Circuit Voltage (OCV).Originally Posted by Learjet
The OCV is the battery voltage with no input or output & is measured around half an hour after charge & load is disconnected.
For most 12 V cells OCV is 12.6 V Fully charged.
Some deep cycle & gel cell batteries have a higher OCV in fully charged state.
Also to equalise lead acid cells you need to raise the voltage of a12 V set to between 14.5 & 14.7 V depending on OEM spec. Some may specify higher.
Anyway back to OP, can we all agree that he cannot draw 300W continuous for 4 hours or even 1 hr from his "90-100amp deep cycle batteries" (unless he has a few of them) whether or not he has a 120W panel in full sun charging them.
If he does they will surely die.
Batteries really don't die, they are murdered, sometimes slowly but in this case it will be fast.
Cheers, Tiny
"You can lead a person to knowledge, but you can't make them think? If you're not part of the solution, you're part of the problem.
The information is out there; you just have to let it in."
300 watts = 25 amps... That would give the 100ah battery a 4 hour rate so it's capacity would be effectively about 75ah. I don't see a problem with 1 hour of use, 2 hours would be pushing it but could be done as long as fewer charge cycles are taken into account from a heavy discharge.
that 300 watt figure might be just what the OP's inverter is rated at.
if we think about running what he wants : mobile phone charger, laptop, compact fluorescent lamp in the main room and one intermittently (maybe the dunny light.)
phone charger about 5 watts (~1 amp at 5 volts) for an hour
laptop 4 amps or so at 18 volts max about 80 watts for 2 hours, then a lot less when charged and running
compact fluorescent lamp 15 watts
so, load is now 100 watts or less after 2 hours.
lets add a 19 inch lcd tv set at 45 watts
hopefully being a weekender he will be using either ice in a esky or a 3way fridge running on gas. (they are inefficient on 12v)
hows the calculations look now?
posted for the purpose of a great debate on this subject, cheers fellas
member. Austech dog squad: if it can be fixed the dogs will sniff it out
Making a lot of assumptions here.
OP is the one that said "300watts for up to 4hrs as a long run if possible."
Cheers, Tiny
"You can lead a person to knowledge, but you can't make them think? If you're not part of the solution, you're part of the problem.
The information is out there; you just have to let it in."
info about solar panel required?
hi can anyone tell me that how much charging in amperes does a solar panle do in one hour of rating 100 watts??and watts the mathematical method to calculate this for higher ratings as well??
if 100 amp hr battery is attached with solar panel and it is installed in an area where sunlight is minimum 10 hours present...
kindly do needful i shall be very thankfull
with best regards
To many variable's, but if you read the whole thread you would have found the answer.
Watts/volts will give you max amount of amps a panel can produce. Multiply this by hrs to give you amp hrs. e.g
100/18 = 5.5
5.5 * 10 hrs = 55 amp hrs.
But as i said, to many variables and you will never really get that amount.
Stop being so stupid.. it’s my turn!!
This thread is too long and full of confusing info.
Why not go by a simple tried and tested basic rule of thumb.
Do not worry about all the variables and details of the moment, like sun hours a day, surface temperature and mppt, season, cloud, etc.
panel power x 4 is roughly the daily output in watt hours.
Example: 100W panel gives you about 400 watt hours a day!
...and 75% of that will end up in your 12V battery which equates to 25A/h per day (which might be improved with a high quality mppt regulator).
This is what you can expect as an average over the whole year in most of the populated parts of Australia with the panel in northerly aspect mounted at a 30° angle and no partial shade.
The only variable here to consider is the quality of the panel.
A 100W panel does not always deliver 100W ! ...it rarely does, but with Ebay it is the luck of the game.
Last edited by Uncle Fester; 06-07-12 at 12:18 PM.
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ageno2gen1 (06-07-12)
Hi mate, some controllers have a 5v usb outlet that may be suitable for your needs.most phones and camers,s have a usb charger now.you could also go a larger 24v panel and use a controller that will charge at 12v .NOT ALL CONTROLLERS WILL DO THIS>this will give more amps.
dreamax 600,strong 4663
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