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Djmacks · 01-20-2022, 04:56 PM

I have 320 watt of solar panels putting out approximately 10 amps at 13.5 volts. By my calculations I should be getting approximately 23 amps output. I'm taking the amperage readings right at the Y connector on top of the motorhome. Does the low amps sound right. The reading was taken on a sunny day.

twinboat · 01-20-2022, 05:06 PM

You need to be on the equator on a cyristal clear day.

DavidEM · 01-20-2022, 05:48 PM

Dividing 320 watts by 13.5 will give you approximate maximum amp output, less for a PWM controller than a MPPT one. So yours should put out 23 amps but only while pointed directly perpendicular to the full sun.

One thing that will drastically reduce your amperage, about as much as you note, is if you are using a PWM controller with a 24V nominal panel. Your 320 watt panel is almost certainly a 24 V nominal panel. That will waste about half of the expected amps. Another thing that can waste some amps, but only 5-10% is small wire size.

David

Djmacks · 01-20-2022, 10:53 PM

The way you explain it makes since to me now.Thanks

Persistent · 01-21-2022, 06:57 AM

We need make and model of solar panel.
Make and model of solar controller.
Assuming wiring is adequate.

Peak output while point directly at the sun on a cloudless day may be close to 320 watts.
Measure both the voltage and the current.
Multiply the voltage by the current to get actual watts. This is the wattage flowing from the panels. It is unlikely it will be close to 320 watts. The load on the system will probably limit output.

Next measure voltage and current out of the solar controller.
Multiply the voltage by the current to get actual watts. This is the wattage flowing from the system. Again it is unlikely it will be close to 320 watts. It will likely be less that the wattage calculated from the panel. It depends on the efficiency of the solar charger and the load.

As posted above, some designs are very inefficient.

As posted above

DavidEM · 01-21-2022, 08:12 AM

One point I forgot to make above. It may be that 10 amps is all your batteries can take. If they are close to full they won't take as much current as if closer to empty.

So, if interested, draw down your batteries by turning off shore power and the solar panels and turning on some fixtures that draw DC. Let this run until the battery voltage is about 12.0. Then check the voltage and current again at the maximum sun angle which may be an hour or more on either side of noon.

David

UTTransplant · 01-21-2022, 02:41 PM

I have 900 watts of solar panels flat mounted on my motorhome roof. About the best we ever get is 600 raw, maybe 40 amps into the batteries. We now have lithium batteries which can take a lot more power in at once though. I am actually running the generator right now too since I needed the dryer, and we are putting 120 amps in. Couldn’t do that with lead acid.

ByeTheWay · 01-21-2022, 03:07 PM

RE: Solar Panel Output
Lot of good information in posts above. In the winter 10 amps from 320 watts may be all you'll see in Bulk. If you tilt your panels you could see more. And as mentioned 10amps is what's going into your batteries. Which also takes into account what is being used at the time by your rv. As you get into Absorb and Float charging the number will be less. I am attaching some solar links to help with your solar knowledge:

RV Electrical General Info
RV Solar Electric Scottsdale supplier
solarseller.com alternative energy by John Drake Services, Inc. Parts and advice
https://www.solar-electric.com/ Flagstaff supplier
https://unboundsolar.com/brands/bogart-engineering Monitors
https://handybobsolar.wordpress.com/ General Info
http://solarpanelsvenue.com/mixing-solar-panels/ Solar panel info

I first started solar in 2000 with 150 watts, and thought I had it made. Over the years I added panels as I could afford them. I now have just over 1100 watts.

Good Luck on your solar journey.

sibe · 01-22-2022, 04:51 AM

i have 4 100 panels.. 5.09 A each rated.. best ever loaded was 16.2 amps 11-13 avg is what i see in my area .. eastern PA NY NJ. just added 2 more. 22-26 A on good day parked good.. cheap pwn 30a

Bobertgoes · 04-06-2022, 09:17 AM

Yes, you rarely will see your max output.

Question... when I built my system I did in series into MPPT. Am I losing amps somehow? I now have lithium batteries. Is it better to run two panels parallel or series?
I liked series as I only needed two wires to enter and not 4 and the wires could be smaller gauge, but the new lithium battery doubled my amp hours and also can take a lot more amps from the solar.

John Hilley · 04-06-2022, 10:56 AM

Quote:

Originally Posted by Bobertgoes

Yes, you rarely will see your max output.

Question... when I built my system I did in series into MPPT. Am I losing amps somehow? I now have lithium batteries. Is it better to run two panels parallel or series?
I liked series as I only needed two wires to enter and not 4 and the wires could be smaller gauge, but the new lithium battery doubled my amp hours and also can take a lot more amps from the solar.

The Series Connection is probably the most efficient for your system with the MPPT Controller. The current will be that of the smallest panel, but the voltage will be the sum of all the panels.

greeneville1 · 04-06-2022, 03:27 PM

We have a 2021 Tiffin Allegro Bus 45OPP that came from the factory with (6) 170 watt PV panels (1020 watts) and (2) 30amp charge controllers feeding (6) Lifeline AGM house batteries. On a sunny clear day with sun directly overhead, we have regularly witnessed 26-28 amps input per each of our (2) controllers. It has greatly reduced the amount of time that our inverter/charger runs. As electrical contractors installing pv systems, we are happy with a system that actually produces 70% of panel total ratings due to system losses. Stay safe.

vsheetz · 04-06-2022, 03:32 PM

PV watts/current also vary with the SoC (state of charge) of the battery bank. It can be high noon on a sunny day - but if the battery bank is full the current flow to the battery will be little if any.
Put another way, you can't put more charge into a fully charged battery.

rffowler55 · 04-06-2022, 03:42 PM

Quote:

Originally Posted by greeneville1

We have a 2021 Tiffin Allegro Bus 45OPP that came from the factory with (6) 170 watt PV panels (1020 watts) and (2) 30amp charge controllers feeding (6) Lifeline AGM house batteries. On a sunny clear day with sun directly overhead, we have regularly witnessed 26-28 amps input per each of our (2) controllers. It has greatly reduced the amount of time that our inverter/charger runs. As electrical contractors installing pv systems, we are happy with a system that actually produces 70% of panel total ratings due to system losses. Stay safe.

We have a large off-grid solar power system at our home and 70% is a very good estimate of what you might expect. In our area over a 5 year period I tracked the cloud cover and it averaged just over 50% since we are in an area that averages over 80 inches of rain per year. Even a small amount of cloud cover, shading on the panels of your solar array or the panels not pointing in an optimal direction will reduce the .7 even further. The panel wattage advertised is always stated based on optimum conditions so use the .7 when trying to determine how many panels you need to meet your solar power objectives.