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Solar controller

So solar controllers are rated at max volts in/ max amps out say 150/80. But reading further they list max PV watts.Question is how does the controller know how many watts, as long as voltage and amps are not exceeded? My panels (2) 420 watt come down at 73 volts or so and 10 amps +or-, I have never seen more than 36 amps charging. Wanting to add another 420 watts, all wired in parallel.

What say the folks that know way more than I do?
Bruce, Linda, and Macy
Zoey RIP 1/20/19
1999 U295 40' build #5400
2017 silver Jeep Wrangler, 1260 watts of solar on top
Moving around the country

Re: Solar controller

Reply #1 –
I run each panel thru its own controller,
350 Watt panel with 40 Amp controller, Then a 50 amp Circuit breaker, then to battery,
Cheers, Brian,
1989 Foretravel Grand Villa, 36 foot ORED, 300 HP Catapillar and Four Speed Allison Auto,
Right Hand drive, two Mid doors, Makes a good flow thru ventilation in hot weather,
Located in Melbourne, Australia,  The Land Down Under,
Honda Blackbird, 1100XX.    2002 Gemini 105 MC Catamaran,

Re: Solar controller

Reply #2 –
So, you have 36 volt panels in series now to bring 72 volts down to the controller rated for 150v and 80 amps. You now want to put all three into parallel wiring so you bring 36 volts down to the controller. If your controller is rated at 80 amps, you will now have the potential of bringing just over 100 amps down to the controller. Too many. You can just add another controller and send the two to a common bus or battery. The controllers will put out 12V+ each and will work together to give you a 1260 watt potential. This total is very unlikely as you won't ever have the sun perpendicular to the panels so the total will be quite a bit less.

Make sure the wires are sized for 420 watts/11.67 amps at 36 volts as they will need to be larger than for 72 volts. Check an online chart for the wattage/amp at 36 volts for the distance to the controller. Loss should be less than 3%

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Solar controller

Reply #3 –
Here is the calculator and the total amps produced by three 420 watt panels with the controller feeding 12V to the batteries. Note that some will use 14.4v in calculations compared to 12V.

Convert Amps, Volts, and Watts (A, V and W)

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Solar controller

Reply #4 –
My 2 Panels are wired in parallel so 72 volts # 6 wire. Thanks for the calculator.
Bruce, Linda, and Macy
Zoey RIP 1/20/19
1999 U295 40' build #5400
2017 silver Jeep Wrangler, 1260 watts of solar on top
Moving around the country

Re: Solar controller

Reply #5 –
My experience with multiple chargers running at same time is they may conflict and confuse. Multiple chargers can be solar and 120v powered chargers where each charger learns how 'full' the common battery is by measuring voltage, expecting the voltage to be from the battery. Confusion comes when voltage is coming from the other battery charger, fooling the charger to think the battery is 'full'.

With our solar charger set to a higher voltage than our inverter/charger, when we ran generator for an hour, temporarily turning off solar controller allowed our Prosine-2000 to get max amps into battery.

Without turning off solar charging, have seen zero 12v amps flowing from Prosine when battery is at 50%.

Exact matching all solar profiles could help, but wonder how others handle this situation.

Re: Solar controller

Reply #6 –
Quote from: bbeane –
My 2 Panels are wired in parallel so 72 volts # 6 wire. Thanks for the calculator.
You don't need to use such heavy wire. Based on your stated amperage and allowing for a margin of error, you could easily use #10 or #12 wire, or quite possibly smaller.
Dave and Kathy Bennett
2004 U270
Build #6253
1600W Solar
700 AH Battle Born Lithium
2015 Jeep Wrangler

No matter what happens, remember you always get the trip out of it.

Re: Solar controller

Reply #7 –
Quote from: bbeane –
My 2 Panels are wired in parallel so 72 volts # 6 wire. Thanks for the calculator.
I think you mean series unless you actually have  72 volt pa
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: Solar controller

Reply #8 –
Quote from: craneman –
I think you mean series unless you actually have  72 volt pa
72 volt panels.
wire is already there 2 panels 840 watts. My controller says max of 1000 watts, additional panel would bring things to 1260watts by 14.4 volts is 87.5 amps in theory.  Now my panels are at least 6 years old no telling. On a good day I've never seen over 40 amps. I guess another question is what percentage of their rated power do panels actually put out in our rv world.
Bruce, Linda, and Macy
Zoey RIP 1/20/19
1999 U295 40' build #5400
2017 silver Jeep Wrangler, 1260 watts of solar on top
Moving around the country

Re: Solar controller

Reply #9 –
Quote from: bbeane –
My 2 Panels are wired in parallel so 72 volts # 6 wire. Thanks for the calculator.
Yes, as Craneman says, your panels must be wired in series to have 72 volts. There are no 72 volt panels for RV use (but lots of 72 cell solar panels)  but 36 volt panels are probably the most available now. The back of the panel will have the voltage on the data sticker. If you have two 36 volt panels wired in parallel, the voltage stays the same but if wired in series, the voltage doubles. Here is a YouTube video that makes it clear:

https://www.youtube.com/watch?v=0Bx7_qNcCd8

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Solar controller

Reply #10 –
72.3 volt 144 cell 51x81 inch panels old sun power panels. Wired in parallel. Thinking about adding one more 435 watt panel as you can't find to 420s at that voltage any longer.
Bruce, Linda, and Macy
Zoey RIP 1/20/19
1999 U295 40' build #5400
2017 silver Jeep Wrangler, 1260 watts of solar on top
Moving around the country

Re: Solar controller

Reply #11 –
Learn something new here all the time
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: Solar controller

Reply #12 –
Quote from: craneman –
Learn something new here all the time
Kind of wish I didn't go with such large panels, hard to find one to match them. I got a deal on this whole system 840 watts 1200 installed with an Outback 150/80 controller.
Bruce, Linda, and Macy
Zoey RIP 1/20/19
1999 U295 40' build #5400
2017 silver Jeep Wrangler, 1260 watts of solar on top
Moving around the country

Re: Solar controller

Reply #13 –
Quote from: bbeane –
72.3 volt 144 cell 51x81 inch panels old sun power panels. Wired in parallel. Thinking about adding one more 435 watt panel as you can't find to 420s at that voltage any longer.
Time for me to eat some of my crow cake. Yes, learn something everyday. That is a monster large panel.

How about adding any voltage solar panel with another controller? Mix and match works. One panel and an extra controller are cheap.

In the event the advertised voltage or amperage specs of a controller are exceeded, it may damage it or reduce the output. Freezing mornings with bright sun may see higher than placarded voltage and amperage. I just went conservative in sizing our controller and have had zero issues with it.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Solar controller

Reply #14 –
Right now we are sitting under cover at our place in Yuma. Fixing to head out in a week or so. I'm going to pay close attention to the system to see what it is actually producing. With a few exceptions I don't think these used panels produce anywhere near the specs, that's the reason they are so cheap.
Bruce, Linda, and Macy
Zoey RIP 1/20/19
1999 U295 40' build #5400
2017 silver Jeep Wrangler, 1260 watts of solar on top
Moving around the country

Re: Solar controller

Reply #15 –
Here is a good wire size calculator.  Interactive Wire Size Calculator

For a 300 watt panel at 36 volts and 8 amps and a round trip length of 50 ft and a voltage loss less than 1% use #8 wire.

And this is for wire in an open space. Wire size needs to  increase when it is run in a conduit.  4 wires in a conduit reduces amp capacity by a multiplier of 0.6. In the example above you would use 13 amps in the calculator and it would sugget 6 ga wire.

I wired each of my panels in parallel for improved performance. Cables run down behind the refrigerator to a fuse block which acts like a combiner and then to the solar charge controller only a foot and a half away.  The fuses are accessible in a bay from the ground. 
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Solar controller

Reply #16 –
Quote from: bbeane –
Right now we are sitting under cover at our place in Yuma. Fixing to head out in a week or so. I'm going to pay close attention to the system to see what it is actually producing. With a few exceptions I don't think these used panels produce anywhere near the specs, that's the reason they are so cheap.
After 10 years, solar panels only lose 5% efficiency on average. Dirt on the panels is the usual suspect when the they seem to lose some steam. Naturally, it depends on how dirty but it can approach 50% for filthy panels.

If you get a chance, put a voltmeter on a panel that is on the ground and watch the voltage increase  as you move the panel until the sun is perpendicular. If a panel array could track the sun. the efficiency would be a lot more.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)
 

Re: Solar controller

Reply #17 –
Part of what I was referring to about the efficiency in an RV application, panels are usually flat, somewhat dirty ( most of us are not going to clean panels weekly when traveling), not optimally oriented to the sun. IIRC my Outback keeps historical performance data. When we get out from under the rv port I'll see what's happening.
As far as an additional controller that can happen along with wire, and breakers. Just trying to KIS
Bruce, Linda, and Macy
Zoey RIP 1/20/19
1999 U295 40' build #5400
2017 silver Jeep Wrangler, 1260 watts of solar on top
Moving around the country