Seeking your MPPT CC Advice - Off Grid

[TriggerGolf]

Hi Friends,

I am about to acquire (2) Jinko 305w 36v panels. Plan is to get familiar with small off grid setup, used for garage to charge batteries & take on occasional camping trips. Possibly these panels and CC might get mounted on a van one day.

Considering the camping & van use, what MPPT charge controller vendors/models would you recommend? An LCD screen with in/out/charge state would be a nice to have. I have a Watts Up meter that I could wire in as an alternative.

Jinko 305w/36v potentially output 8 amp, with 2 panels is a 20amp CC the way to go, or should I spend a few more dollars on a larger capacity CC in case of future growth?

Is there a trusted/reliable solar panel sale websites you recommend ?

I found Rogue recommended in other posts, however this unit is out of stock

http://www.roguepowertech.com/products/chargecontrollers/mppt/mpt3048.htm

Thanks,
tG

[solar pete]

Hi TriggerGolf and welcome to solar panel talk.

Small off grid/back up systems are not my gig. However there are far more knowledgeable people around who might chime in and help you out.

Just a reminder that posting links is not really cool for newbie's but as its relevant to the post it's ok, cheers

[Mike90250]

......Jinko 305w/36v potentially output 8 amp, with 2 panels is a 20amp CC the way to go, or should I spend a few more dollars on a larger capacity CC in case of future growth?....

That's 600W of panels. What's your battery bank voltage, that will determine the Controller amperage requirement. Most MPPT controllers are robust enough to take a bit of over panel, and will just throttle back to stay within limits. Check the fine print first.

600w:
12/15V = 40A
24/30V = 20A
48/60V = 10A

Only you can decide about future growth.
I have been very happy with Mornngstar products, but not all have built-in meters or web servers. Midnight KID might be an option for you.

[TriggerGolf]

That's 600W of panels. What's your battery bank voltage, that will determine the Controller amperage requirement. Most MPPT controllers are robust enough to take a bit of over panel, and will just throttle back to stay within limits. Check the fine print first.

600w:
12/15V = 40A
24/30V = 20A
48/60V = 10A

Only you can decide about future growth.
I have been very happy with Mornngstar products, but not all have built-in meters or web servers. Midnight KID might be an option for you.

I currently have (1) 12v wet cell marine battery, 120aH. To get started with no additional batteries I will need a 40A CC. Built in web server or RESTful endpoint would be handy for monitoring/threshold alerting via client on home network (For future).

Thank you for the advice.

tG

[Wy_White_Wolf]

I currently have (1) 12v wet cell marine battery, 120aH. To get started with no additional batteries I will need a 40A CC. Built in web server or RESTful endpoint would be handy for monitoring/threshold alerting via client on home network (For future).

Thank you for the advice.

tG

40A into a 120Ah lead acid battery is too high of a charge rate and will destroy it. That is a rate of C/3 (120/40). You need to try and keep that rate between C/8 and C/12 (15A to 10A) with C/10 usually being about ideal.

WWW

[Amy@altE]

Can you confirm the panels you are getting? What is the Voc and Isc? I'm seeing a 72 cell one with 45.6Voc and 9.05A Isc. For a 12V battery and 1 panel, 9.09A x 2 (24V nominal in, 12V nominal out) x 1.25 NEC requirement = 22.72A charge controller output per panel. If you take WWW's advise (and I suggest you do) and don't use 2 panels with one battery, a Midnite Kid would be perfect for you for 1 panel. Then if and when you do add a second battery, you can add a second panel and charge controller. Or if you do get a second battery right away (you shouldn't add a new battery to an old battery anyways), you could get 2 Kids or a Morningstar TS-MPPT-45 with either a local or remote meter.

[TriggerGolf]

40A into a 120Ah lead acid battery is too high of a charge rate and will destroy it. That is a rate of C/3 (120/40). You need to try and keep that rate between C/8 and C/12 (15A to 10A) with C/10 usually being about ideal.

WWW

WWW - thanks for saving my battery. Is a 40A CC is only a 40A CC and can not be configured to charge at 20A or 10A?

I will take your suggestion & run a single panel (305w) to charge a single 12v battery at 20A.

Can you confirm the panels you are getting? What is the Voc and Isc? I'm seeing a 72 cell one with 45.6Voc and 9.05A Isc. For a 12V battery and 1 panel, 9.09A x 2 (24V nominal in, 12V nominal out) x 1.25 NEC requirement = 22.72A charge controller output per panel. If you take WWW's advise (and I suggest you do) and don't use 2 panels with one battery, a Midnite Kid would be perfect for you for 1 panel. Then if and when you do add a second battery, you can add a second panel and charge controller. Or if you do get a second battery right away (you shouldn't add a new battery to an old battery anyways), you could get 2 Kids or a Morningstar TS-MPPT-45 with either a local or remote meter.

Amy - JinKO JKM305P-72
Pmax 305W
Power Tolerance 0-+3%
Max Power Volt (Vmp) 37.4V
Max Power Current (Imp) 8.16A
Open Circuit Volt (Voc) 45.6V
Short Circuit Current (Isc) 9.05A

I will check out the mentioned controllers. Thank you.

tG

[Sunking]

WWW - thanks for saving my battery. Is a 40A CC is only a 40A CC and can not be configured to charge at 20A or 10A?

Charge current is determined and controlled by panel wattage. There is a couple of controllers out there that will allow you to limit current to some point but completely defeats the purpose. If you want to limit the current you select the right panel wattage, and that is real easy to determine Charge Current x Nominal Battery voltage Panel Wattage. So 10 amps x 12 volts = 120 watts. 5th grade math.

But that has nothing to do with what you want to do. At this point you have no clue what is needed because you failed to take the first most important step. You did not determine your daily Watt Hour requirement Until you do that you are just wishing and throwing money away. Once you know what the requirement is, then you design a system to meet the requirements. Fail to do that and 1 of 3 things happen.

1. You grossly under size the system. Once that mistake is made to correct usually involves replacing everything you bought and that happens in about 95% of the time.
2. Over size the system which works but waste a lot of money. That happens about 4.9% of th etime
3. You guessed right and everything is matched up and works. .1% of the.

Right now you are at result #1

[Amy@altE]

Depending on where you get your panel, you may also want to consider getting 2 smaller panels, like a Kyocera 140 and wiring them in parallel. This can accomplish 2 things. 1. Kyo140s can ship by UPS, anything bigger has to go by truck and will cost at least $200 to ship. 2. you can use a PWM charge controller that would be much less expensive than a MPPT. if you are buying locally and don't have to worry about shipping, then the issue is moot.

[TriggerGolf]

Hi Solar Gurus,

I was time crunched on the 305 panels. The seller happened to be in the area this Saturday.

Instead of 305 watt, I can get (2) BP SX3200b panels for much less and use the savings towards second battery. Can you please comment on the following.

STC Power Rating 200W
PTC Power Rating 175W 1
STC Power per unit of area 13.2W/ft2 (142.1W/m2)
Peak Efficiency 14.21%
Power Tolerances -9%/+9%
Number of Cells 50
Nominal Voltage not applicable
Imp 8.16A
Vmp 24.5V
Isc 8.7A
Voc 30.8V
NOCT data not available
Temp. Coefficient of Power -0.5%/K
Temp. Coefficient of Voltage -0.11V/K
Series Fuse Rating 15A
Maximum System Voltage 600V

400W, 24v/30v=13.3A

With two batteries (12v 120aH) that will have charge rate of C9.

Which PWM controller would you recommend?

Thanks for the knowledge and help.


tG

[Amy@altE]

Wow, you got me on that one, I had never heard of a 50 cell module. I used to sell 54 cell modules, but never 50. I did confirm the specs, it is right. BP made very nice panels, but those are probably very old.

Anything bigger than a 36 cell module with a PWM charge controller is throwing power (and money) away. So you'll still need an MPPT with them. I'd still go with the Kid, but you could probably use 1 for the 2 panels, double check with their sizing tool, http://www.midnitesolar.com/sizingTool_kid/index.php.

[Sunking]

Hi Solar Gurus,

I was time crunched on the 305 panels. The seller happened to be in the area this Saturday.

Instead of 305 watt, I can get (2) BP SX3200b panels for much less and use the savings towards second battery. Can you please comment on the following.

STC Power Rating 200W
PTC Power Rating 175W 1
STC Power per unit of area 13.2W/ft2 (142.1W/m2)
Peak Efficiency 14.21%
Power Tolerances -9%/+9%
Number of Cells 50
Nominal Voltage not applicable
Imp 8.16A
Vmp 24.5V
Isc 8.7A
Voc 30.8V
NOCT data not available
Temp. Coefficient of Power -0.5%/K
Temp. Coefficient of Voltage -0.11V/K
Series Fuse Rating 15A
Maximum System Voltage 600V

400W, 24v/30v=13.3A

With two batteries (12v 120aH) that will have charge rate of C9.

Which PWM controller would you recommend?

Thanks for the knowledge and help.


tG

Simple no one would recommend a PWM Controller period. That would turn you 200 watt panels into 100 watt panels.

Here is a good reason why. To use PWM controllers you have to use expensive 12 volt battery panels. So let's say you have 2-150 watt battery panels (300 watt total) and a 20 amp PWM controller. Panel cost are roughly $2/watt for battery panels so that cost you $600 in panels. A 20 amp PWM controller cost you $40 to $50 for a total cost of $650.

To get the exact same amount of power with MPPT you now buy one single 200 watt cheap grid tied panel that cost roughly $1/watt or $200, plus a $200 MPPT 20 amp controller for a total cost of $400 or $250 less than PWM.

Which system do you choose to use? The $400 dollar or your way at $650

Simple answer huh?

[TriggerGolf]

What do you think about these BP panels? They are $100 each. With a 20amp MPPT controller and (2) 120aH batteries (12v)

Am I at #2 with the above?

[Amy@altE]

You need at least a 30A MPPT. They are rated at the output, not the input current. When it drops the volts it raises the amps at the output. I don't have time right now, but put the numbers into the Kid calculator I linked to. Check to see if that will work. It is by far the best priced product in that range and quality level.

[jony101]

You mention you wanted to get a controller with a display, most controllers (that have any type of display) have the hard to see LCD screens, I instead use a 90 volt 30 amp combo meter and connect that between the charge controller and the battery. It has large LEDs that I can read from 5 feet away. They work on pwm or mppt. With these types of meters you dont have to worry too much if the controller your going to get has a display or not.

It makes your life much easier to have some sort of LED display instead of relying on the watts up or multimeters, I also have 2 of those LCD dc wattmeters connected but only as a backup. With the combo meter I can see how much voltage and amps are going into my battery in real time. At night time I leave connected and it tells me the battery voltage so I know how my battery is doing.

Below you can see the box I made it also has a 99 volt LED meter to display the solar panel voltage. The mppt controller is to the right with very small LCD screen. My recommendation is get a LED display.