Watts to amps question

[JCANCO]

On the roof of my RV I have 6 panels @ 490 watts total hooked to a 30 amp controller and 2 recently installed new panels @ 200 watts total hooked to another 30 amp controller. The panels are all 18 volt. The controllers are both hooked to the RV's 120v to 12v converter's battery lug.

#1 QUESTION - Do you figure the amps for the controllers at 18v or 12v?

And since all my panels lay flat I'm know I'm losing some efficiency (wattage). Depending who you talk to they say from 10-40% of wattage. But due to traveling this is an accepted loss. This will be the first summer in the SW desert with my completed system. I have noticed more amps going to the 4 Batteries now that the sun is higher in the sky.

My automotive style amp gauge shows no discharge until the inverter (2500 watt with 15" 2/0 wires) load is over about 300 watts (which I rarely get to).

As I added panels I upgraded from #12 wire a dual #10. The #12 got quite warm, but the dual 10's are cool. The new panels are on a single #10.

#2 QUESTION - The system is working well but there's always room for improvement. This is my first system and I'm a novice at this. So any suggestions would be appreciated.
Thanks

[Mike90250]

On the roof of my RV I have 6 panels @ 490 watts total hooked to a 30 amp controller and 2 recently installed new panels @ 200 watts total hooked to another 30 amp controller. The panels are all 18 volt. The controllers are both hooked to the RV's 120v to 12v converter's battery lug.

#1 QUESTION - Do you figure the amps for the controllers at 18v or 12v?

And since all my panels lay flat I'm know I'm losing some efficiency (wattage). Depending who you talk to they say from 10-40% of wattage. But due to traveling this is an accepted loss. This will be the first summer in the SW desert with my completed system. I have noticed more amps going to the 4 Batteries now that the sun is higher in the sky.

My automotive style amp gauge shows no discharge until the inverter (2500 watt with 15" 2/0 wires) load is over about 300 watts (which I rarely get to).

As I added panels I upgraded from #12 wire a dual #10. The #12 got quite warm, but the dual 10's are cool. The new panels are on a single #10.

#2 QUESTION - The system is working well but there's always room for improvement. This is my first system and I'm a novice at this. So any suggestions would be appreciated.
Thanks

1) take out the parallel 10's and use a single #8. Just as with batteries, parallel wires don't share loads till they are both glowing equally bright. Then it's too late.

2) watts:amps I'll assume you are using a simple (<$200 PWM controller)

Say the batteries are at 12.5V while charging. So you figure watts / 12.5 or
(490+400) / 12.5 = 71.2A at full power Lucky you.

[paulcheung]

Change the charge controller to a MPPT charge controller and put it near the battery then you will get more power and lighter wires from the panels when you wire them in series.

[inetdog]

A 200W 18V panel will produce 11.1A at full power. If you use a PWM controller and so are running the panel and the CC closer to 13V, you still only get 11.1A. That is because the panel output is current limited.

[Sunking]

Let's Get You Straight &amp; Mad As He!!

On the roof of my RV I have 6 panels @ 490 watts total hooked to a 30 amp controller and 2 recently installed new panels @ 200 watts total hooked to another 30 amp controller. The panels are all 18 volt.

Are you sure the 200 watt panels are 18 Volts @ Max Power? Largest 36 Cell Panels I know of is 160 watts. 200 watt panels are likely 54 cell operating @ 27 Volts, and if you are using PWM controllers is robbing you blind which you will shortly understand. OK time to make you mad as he!! with some education.

OK let's start with PWM Controllers. They are rated at some amperage as in your case 30 amps. The key thing to know about PWM controllers is CURRENT INPUT = CURRENT OUTPUT. Take note that has nothing to do with VOLTAGE. OK you have 6 panels totaling 490 watts. So I assume you have then all wired in parallel as it is the only option you have operating on a 12 volt battery system using 12 volt battery panels right? I also assume each panel is rated: Pmax = 80 watts, Vmp = 18 volts, and Imp = 4.55 amps. So with 6 of them installed in parallel you have 18 volts @ 27.3 amps ( 18 x 27.3 = 490 watts) input to the charge controller. OK we know with a PWM CC Input Current = Output Current, so on the output of the Controller we must have 27.3 amps period. This is what is going to piss you off and I like it. With 27.3 amps charging into a 12 volt battery you have 12 volts x 27.3 amps = 325 watts. You just turned your 490 watt panels into 325 watts out of ignorance. Are you Happy Happy Happy?

If you knew about MPPT Controllers, you could have saved yourself a lot of money and wasted power. With a MPPT Controller Output Current = Panel Wattage / Battery Voltage . So take your 490 watt panels and you get a charge current of 490 watts / 12 volts = 41 amps of charge current to your batteries. Sadly with PWM you are stuck with 27 amps. Oh well.

Back to those 200 watt panels and your PWM Controller. If I am correct and those are really 54 cell Grid Tied panels here is what you get with PWM. A 200 watt 54 cell panel produces 7.4 amps. Two in parallel is 14.8 amps into th ePWM Controller. That means you have 14.8 amps output to the 12 volt battery which means only 12 volts x 14.8 amps = 177 watts out of 400 watt input. Use a MPPT Controller and you get 33.3 amps.

Are you mad yet? You should be.

[JCANCO]

Thanks for all the comebacks! And Sunking......not mad....just more educated. Next thing I must ask is if I go to MPPT should I replace the two PWM controller with one MPPT? My total watts of all 8 panels on the roof is 690 watts. The voltage I listed was based on the manufacturer's info and my voltmeter (18 to 20 volts).

[paulcheung]

Please post the panels specs, so we can see if you can use one controller.

[JCANCO]

I've got a hodge podge of panels.
2ea 30watt
2ea 80 watt
1ea 170 watt
3ea 100 watt
I won't be of much help on specs. Never saved the paperwork.
My rear 30 amp charge controller has on it : 2- 30 watt panels, 2- 80 watt panels, 1-170 watt panel and 1- 100 watt panel.
My front 30amp charge controller has 2- 100 watt panels on it.
These panels were bought separately over a 2 1/2 year period from CA to NM. I bought em all new on sale, at a solar flea market or online as my budget permitted.
As I type this I am on inverter power. The inverter shows a 220 watt (average) AC load. Voltage from the panels show 13.6 volts and the amp meter is pulsating between 0 and +15. The charge controllers show the batteries are fully charged. For a non tech person this seems OK.
I know I'll never get full efficiency out of my panels cause they lay flat. If that assumption is correct... could a 40amp MPPT handle all the panels?
I have pulled a set of #8's to replace the dual 10's.

[paulcheung]

If you can't provide the information of the panels like VOC VMP IMP etc. we can't tell you if you can group them to one controller. according what you posted, I don't think one controller will work for all different panels.

[JCANCO]

Sorry, I didn't save the info. Being a newbie I figured they just would work. Lesson learned.
But I do thank you all for the info you provided.

[russ]

There should be data plates on the backside of each panel