I have a 120Ahr battery fed by two 80watt PV panels through a 30amp controller. Given how I camp, this is quite adequate for my needs.
On sunny days, even in Victoria's winter, the battery is back to float (13.4V) by late-morning/early arvo.
Even on overcast days I am able to get at least three days out of the battery with the miserly trickle I get from the solar panels. The next sunny day gets it all back to 'normal'.
In the five years I have had this set-up I have only had to use the genny to top-up the battery once ... after four days of steady rain.
I have been thinking (something I usually try to avoid because it is somewhat painful ) that I might add an extra panel to the roof to boost/reduce the re-charge time.
My question is ... if I add a 120watt panel to the existing two 80watt panels (giving 280watt of panels) will the 30amp controller be able to 'cope' with that?
With my limited knowledge, 280watt would produce 24amps and therefore my question is superfluous ?
Cheers - John
-- Edited by rockylizard on Wednesday 24th of August 2016 08:28:24 AM
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2006 Discovery 3 TDV6 SE Auto - 2008 23ft Golden Eagle Hunter Some people feel the rain - the others just get wet - Bob Dylan
Compared to your 5 years, my 2 with current set up is limited but from what I have learnt about 12v and Solar use your addition will cope, with room to spare.
I hope it's not too cold down there mate, if you are were I think you are.
Keep Safe on the roads and out there.
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DOUGChief One Feather (Losing feathers with age)
TUG.......2014 Holden LT Colorado Twin Cab Ute with Canopy
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SHHHHHHHHH ... Rocky is north of the QLD border at the moment
... thanks for the reply ... my brain - somewhat limited by the passage of time and the application of logic too often - feels the 30amp controller should work .. but I jest hadda arsk.
Cheers - John
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2006 Discovery 3 TDV6 SE Auto - 2008 23ft Golden Eagle Hunter Some people feel the rain - the others just get wet - Bob Dylan
You should have heaps of leeway, Rocky. My 200W panels generate between 17 and 20 volts on a good day, so using 19 volts as a guide you should be getting about 14-15 amps on a bright sunny day - minus any efficiency losses.
Cheers
Joe
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Hino Rainbow motorhome conversion towing a Daihatsu Terios
Some weird figures being posted due to not really understanding
The only formula is based on peak power point of the panels!!!
The max current you can get from a solar panel is the WATTS divided by the PPP [peak power point] voltage , with most 36 Cell panels as used for 12V battery charging that voltage is around 17V
So 280 W of panels with a peak power point at 17V will at the most generate around 16A [IF you are lucky & get the rated light input[isolation] & the panels are operating "around 25C]
Even under short circuit they are current limited & the current would only be around 18<20A , All panels should have the specs giving :
[a]OPEN circuit voltage ,for 12vBattery charging panels around 21 <22V[of little interest unless connecting panels in series]
PPP voltage[ the best operating point for the panel, that gives max output ] [c] PPP Current[ the current that the panel will put out if operating with the degree of light intensity & design temp,around 25C [d] short circuit current.[ as per [c] but with terminals shorted] & of no real interest
Under extremes of isolation input [extremely bright sunlight ]often slight cloudy days with sunlight reflecting off the clouds ,the output can be higher, the panels actually generate more watts.
-- Edited by oldtrack123 on Thursday 25th of August 2016 11:43:37 AM
Alan, the output current from a solar panel can be calculated by dividing the panel maximum power by its Vmpp (voltage st maximum peak power.) The Vmpp for the panels commonly used for 12 V batteries is approx 17 V. Divide 280 by 17 and you get 16.5 A.
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PeterD Nissan Navara D23 diesel auto, Spaceland pop-top Retired radio and electronics technician. NSW Central Coast.
You got better replies in the other forum, didn't you?
I reckon so
Gday...
Thanks for the replies which confirm that my question was indeed superfluous.
I am not sure whether I got better replies on "the other forum" or not ... but at least now I know I can connect another 120watt panel without worrying.
Thankfully I didn't get very many of the following type of responses ... that's a helluva lotta words for a 'yes' or 'no' answer. and I am still not sure whether it is saying 'yes' or 'no'.
Some weird figures being posted due to not really understanding
The only formula is based on peak power point of the panels!!!
The max current you can get from a solar panel is the WATTS divided by the PPP [peak power point] voltage , with most 36 Cell panels as used for 12V battery charging that voltage is around 17V
So 280 W of panels with a peak power point at 17V will at the most generate around 16A [IF you are lucky & get the rated light input[isolation] & the panels are operating "around 25C]
Even under short circuit they are current limited & the current would only be around 18<20A , All panels should have the specs giving :
[a]OPEN circuit voltage ,for 12vBattery charging panels around 21 <22V[of little interest unless connecting panels in series]
PPP voltage[ the best operating point for the panel, that gives max output ] [c] PPP Current[ the current that the panel will put out if operating with the degree of light intensity & design temp,around 25C [d] short circuit current.[ as per [c] but with terminals shorted] & of no real interest
Under extremes of isolation input [extremely bright sunlight ]often slight cloudy days with sunlight reflecting off the clouds ,the output can be higher, the panels actually generate more watts.
Cheers - John
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2006 Discovery 3 TDV6 SE Auto - 2008 23ft Golden Eagle Hunter Some people feel the rain - the others just get wet - Bob Dylan
I've got 530 Watts over 3 Panels (160 + 170 + 200) flat mounted on the roof and use a 30 Amp controller. My controller records total Amp's in over 3 days and total amps coming in every minute of so. The most I've ever seen coming in at anyone time was 22 Amps. Where going by "oldtrack's" calculations my system is capable of just over 31 Amps. That said, that would be for absolute ideal conditions for panel position and angle which when panels are flat mounted would probably never happen.
If I was to add another panel (on the cards) then I'd upgrade to a 50 Amp controller.
Regards Steve.
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Steve, Di & Ziggy We named our Motorhome "Roadworx" because on the road works "On The Road Again" Ford Transit with 302 Windsor V8 conversion, C4 Auto, 9 Inch Ford Diff All Lighting L.E.D., 260 Amp/h AGM, 530 Watt Solar + Kipor Backup Gen.
Hi John
Sorry ,but I thought you would see the answer for any sized panels with.
"The only formula is based on peak power point of the panels!!!
The max current you can get from a solar panel is the WATTS divided by the PPP [peak power point] voltage , with most 36 Cell panels as used for 12V battery charging that voltage is around 17V
So 280 W of panels with a peak power point at 17V will at the most generate around 16A [IF you are lucky & get the rated light input[isolation] & the panels are operating "around 25C]"
Next time you ask a question, I will not go into any details that could help you understand or may help you see which is the correct answer!!!
However, I have only the very basic knowledge of anything electrical and have no 'method' to, or knowledge of how to, measure the PPP or anything else that them goddarn panels may churn out.
To be painfully honest, even your "clarification" in your last post, is way over my head and provides me with absolutely nothing I could use - particularly when the question was simply "how many 'watts' will a 30amp controller cope with?" ... elaborated a bit within the post with the further information - " ...if I add a 120watt panel to the existing two 80watt panels (giving 280watt of panels) will the 30amp controller be able to 'cope' with that?"
Simplisticly (because that is what I am - simple) a yes or no would have alleviated my ignorance. I doubt I will ever need to sit a test to determine/prove I can attach a 120watt panel to my existing 80watt ones.
Cheers - and thanks again for your time, expertise, in-depth information, (albeit wasted on a simpleton like me) and tolerance - John
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2006 Discovery 3 TDV6 SE Auto - 2008 23ft Golden Eagle Hunter Some people feel the rain - the others just get wet - Bob Dylan
It does depend on the voltage. As noted in earlier posts, for our 34' 5th wheel, we have a maximum of 1400 W at 90 V going to controller which gives us 15.5 amps to controller. We use a 45 amp controller. The battery suite is 48 V so this is 29 amps to the battery from controller. It is dependent on the voltages utilized.
Reed and Elaine
12v. 30a Smart Regulator.
2 x 85w panels. 1 x 80w panel 1 x 50w panel
(Mixture of ex yacht, and size of, avail when bought)
Plus I coupled up 2 x 40w panels sitting on carport roof when home.
it ran them fine.
Same one now sits on this van with 1 x 200a panel.
I swapped it out for another one when that van went.($350-$80 changeover)
And a 6a in Ute, for the 80w panel for rear battery.
Both do same job. He got a new one.
You can combine any size panel to any size regulator.(Up to it's max)
It only sees the max Amp's coming through the single wire coming in.
Not the separation of, at other ends.
I was told by a Solar installer that if you fitted 1 x 120 watt panel and 1x80 watt panel the 120 watt panel would only match the output of the 80 watt panel, is this correct?
I purchased 2x80 watt thinking its watt it had . I wired them in in parelell . No issues . Two 120 watt two 80 watt . Works fine just used junction box before regulator to fit all 4 the wires .
I was told by a Solar installer that if you fitted 1 x 120 watt panel and 1x80 watt panel the 120 watt panel would only match the output of the 80 watt panel, is this correct?
Just shows some solar installers do not know much
You can parallel connect as many different rated panels as you like provided the specs show the same MPP[Max power point]
For 36 cell panels ,the usual sized panels for charging 12V batteries ,that is usually around 17V
if you divide the rated Watts by the MPP you will obtain the rated current output
The current available to the regulator will be the sum of all the panels
If panels are series connected,, which is no doubt what the solar installer was referring to,since that is how most grid feed panels are connected, they must be the same current rating ,but they can be different voltages
In that situation the current is the rated output current of a panel, but the voltage is the sum of all panels.
Do not think you can use a controller for panels of widely differing voltages. Our Roadtrek has a 315 W (about 40 V) and a 100 W (12 V) panel. This required two different controllers. The battery suite is set at 12 V nominal. The reason for the widely differining wattages and voltages is that is what son could fit on the "interesting" and limited roof of a Roadtrek.
Reed and Elaine
Hi Reed
It is a bit complicated depending on how the panels are connected
They can be:
[a
]Parallel connected
Similar MPP rated voltage, but differents watts, just add up the watts .& ensure that is within the regulators rating.
Parallel connected,
Different MPP voltage ,same or different watts rating
NOT a good idea
[c]
series connected
different mpp voltage but same CURRENT rating@MPP
the voltage will be the sum of each panel & the current will be that of one panel
The regulator must be able to handle the total voltage & wattage output
[d]
series connected
Same wattage but different current@PPP
Not good as some panels could be subject to excess current
Roadtrek
Our 315 W panel is approximately 40 V so it goes through one MPPT controller where it is changed to 12 V
100 W panel is approximately 12 V and it goes through another MPPT controller where it is also changed to 12 V. Controllers have to handle 26 amp in one case and 10 amps in the other
We have two LFP batteries. Each is four CALB (Chinese Aviation Lithium Batteries) cells in series.
5th wheel
This can be compared with system on our 5th wheel. Two series of three 235 W panels in series (90 V) which are then in parallel at 90 V nominal to 45 amp controller which converts to 48 V nominal. 1400 W is then only at 15.5 amps to controller and then 29.1 amps to battery. Run from rear panel to controller is about 14 m so higher voltage is fairly important.
Son has been in solar business since 1991 with research in field at New Mexico State University Alternative Energy Labs for 5 years before that. His firm did the low voltage work at a 2 megawatt farm two years ago.
Question my question is ... if I add a 120watt panel to the existing two 80watt panels (giving 280watt of panels) will the 30amp controller be able to 'cope' with that?
Answer Layman answer is YES it will cope if all panels are wired in parallel. (All positive wires together, and all negative wires together)
How do I know I have a 300 watt solar panel on my roof, going through a 20 amp controller
I was told by a Solar installer that if you fitted 1 x 120 watt panel and 1x80 watt panel the 120 watt panel would only match the output of the 80 watt panel, is this correct?
Where has your solar installer worked, on grid connector caravans? If your friend has had all his experience on grid connect he will be thinking of panels in series, in that case he is correct. The ones telling you he is wrong are thinking of panels connected in parallel and they are also correct in their thinking.
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PeterD Nissan Navara D23 diesel auto, Spaceland pop-top Retired radio and electronics technician. NSW Central Coast.
) that I might add an extra panel to the roof to boost/reduce the re-charge time.
