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StirCrazy

Kamloops, BC, Canada

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Joined: 07/16/2003

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Posted: 07/04/21 03:10pm Link  |  Quote  |  Print  |  Notify Moderator

I would run them in series on a MPPT controler if you can. the beausty of the MPPT is the conversion to a lower "charging voltage and that nothing is lost except for the efficency. also running in series means higher voltage lower amprage which lets you run a smaller wire with less line loss than you would get with a lower voltage, but higher amprage, on the same wire size. of course like PT and others have mentioned you have to be aware of the effects of shading so you have to place your panels a little smarter. another side benifit of running in series is the morning and evening charging will start sooner and finish laiter and you will get a higher amprage during that time than you would in parralel as you have a higher voltage hiting the controler.

the panels you referenced you could easy run two in series on that, but if it was for myself I would go with at least a 40 amp MPPT controler.

Steve


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cliffy49

Blue Grass

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Posted: 07/04/21 04:01pm Link  |  Quote  |  Print  |  Notify Moderator

StirCrazy wrote:

I would run them in series on a MPPT controler if you can. the beausty of the MPPT is the conversion to a lower "charging voltage and that nothing is lost except for the efficency. also running in series means higher voltage lower amprage which lets you run a smaller wire with less line loss than you would get with a lower voltage, but higher amprage, on the same wire size. of course like PT and others have mentioned you have to be aware of the effects of shading so you have to place your panels a little smarter. another side benifit of running in series is the morning and evening charging will start sooner and finish laiter and you will get a higher amprage during that time than you would in parralel as you have a higher voltage hiting the controler.

the panels you referenced you could easy run two in series on that, but if it was for myself I would go with at least a 40 amp MPPT
controler.

Steve



You are at least the second person to say that I should use a 40 MPPT controller. To be honest, I can not understand why a 40 and not a 20. At the bery best, this panel is only going to be putting out a little over 8 amps if wired in series and 17 if wired in parallel.

Can you please explaiin to me what I am missing in all of this. I apologize for the questions but my solar knowledge is zero and I am trying to learn.


cliffy49
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pianotuna

Regina, SK, Canada

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Posted: 07/04/21 04:25pm Link  |  Quote  |  Print  |  Notify Moderator

cliffy49,

Never apologize for asking questions!

Here are some reasons to go with a larger capacity controller.

It is quite likely you may wish to expand the system in the future by adding panels. If the controller is maxed out--then there is a extra (large) expense for doing so.


In addition, electrical equipment that is "pushed" to the edge of its capacity may be stressed a LOT more and fail prematurely. There is a cloud lensing effect that may cause the panels to output 25% more than usual. That may damage a controller that is teetering on the edge of being too small.

In at least one type of controller there are three modules that work together. First one cuts in, then as solar production increases another cuts it, and so on.

I've already given my reasons to wire in parallel.

I hope you will be happy with the system! It is the best money I spent on my RV.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, soon to have SiO2 batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

BFL13

Victoria, BC

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Posted: 07/04/21 05:32pm Link  |  Quote  |  Print  |  Notify Moderator

Your panel specs for amps are for the input to the controller. The amps "size" of the controller is for its output. That is what you are missing. Read this again.

A 20 amper will just run what one of those 285s can do, so at least a 40 amper would be needed. I would choose a 40 instead of going to a 60 because the panels will get hot in the sun and be about 10% down in watts from that heating, so that keeps you under what a 40 can do. Also if mounted flat they will not get full sun, so that keeps the watts down too.

Tracer makes a decent 40 amp MPPT that would do at a good price. Lots of other choices with various features and prices.

MPPT uses output watts / battery voltage for amps out (which go to loads first and any left over go to the battery)

2 x 285 = 570w less 10% for heat = 513w minus say 2% wiring loss panels to controller, so now 503w input to the controller. controller efficiency maybe 96% so output watts = 483w so picking three battery voltages:

483/12 = 40.25 amps
483/13 = 37 amps
483/14= 34.5 amps


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Almot

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Posted: 07/04/21 11:28pm Link  |  Quote  |  Print  |  Notify Moderator

You could use #6 and trim the last 1/4" slightly, to fit the controller terminal.

The thing I see on the photo, with (looks like) 1" long bare metal that will protrude outside the controller casing - doesn't look safe.

Huntindog

Phoenix AZ

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Posted: 07/05/21 02:59am Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

Your panel specs for amps are for the input to the controller. The amps "size" of the controller is for its output. That is what you are missing. Read this again.

A 20 amper will just run what one of those 285s can do, so at least a 40 amper would be needed. I would choose a 40 instead of going to a 60 because the panels will get hot in the sun and be about 10% down in watts from that heating, so that keeps you under what a 40 can do. Also if mounted flat they will not get full sun, so that keeps the watts down too.

Tracer makes a decent 40 amp MPPT that would do at a good price. Lots of other choices with various features and prices.

MPPT uses output watts / battery voltage for amps out (which go to loads first and any left over go to the battery)

2 x 285 = 570w less 10% for heat = 513w minus say 2% wiring loss panels to controller, so now 503w input to the controller. controller efficiency maybe 96% so output watts = 483w so picking three battery voltages:

483/12 = 40.25 amps
483/13 = 37 amps
483/14= 34.5 amps


I am not so sure of your figures. I just finished an upgrade. In my initial testing I was getting 714 watts from an array that had a max of 720 watts.

Using your method, I should only be able to get 590 watts.



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BFL13

Victoria, BC

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Posted: 07/05/21 06:54am Link  |  Quote  |  Print  |  Notify Moderator

"I am not so sure of your figures. I just finished an upgrade. In my initial testing I was getting 714 watts from an array that had a max of 720 watts.

Using your method, I should only be able to get 590 watts."

To sort this out, need your volt and amp measurements at the input and output terminals of the solar controller while it is in Bulk (which is when it is in MPPT)

My example also assumes the panel is aimed at a high sun with clear sky. Be even fewer amps output with panel flat on roof, eg.

It is hard to get the input amps to the controller, so if no clamp ammeter just see what the input voltage is. It should be whatever the controller decides is Vmp at the time.

Huntindog

Phoenix AZ

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Posted: 07/06/21 04:07am Link  |  Quote  |  Print  |  Notify Moderator

Almot wrote:

You could use #6 and trim the last 1/4" slightly, to fit the controller terminal.

The thing I see on the photo, with (looks like) 1" long bare metal that will protrude outside the controller casing - doesn't look safe.
Some shrink tubing would fix that up.

Huntindog

Phoenix AZ

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Posted: 07/06/21 05:38pm Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

"I am not so sure of your figures. I just finished an upgrade. In my initial testing I was getting 714 watts from an array that had a max of 720 watts.

Using your method, I should only be able to get 590 watts."

To sort this out, need your volt and amp measurements at the input and output terminals of the solar controller while it is in Bulk (which is when it is in MPPT)

My example also assumes the panel is aimed at a high sun with clear sky. Be even fewer amps output with panel flat on roof, eg.

It is hard to get the input amps to the controller, so if no clamp ammeter just see what the input voltage is. It should be whatever the controller decides is Vmp at the time.
I took a pic of my Victron screen during the intial test:
Pmax-714W
Vmax-60.14
battery max-13.69
min- 12.76

I have not had time to mess with a volt/ohm meter yet.


BFL13

Victoria, BC

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Posted: 07/06/21 06:58pm Link  |  Quote  |  Print  |  Notify Moderator

Those Victron terms don't mean anything to me, such as Pmax. Please use volts and amps and where you measured those.

The easiest measurement is output watts, where the controller will have a reading of battery voltage and the solar amps output (not to be confused with amps to the battery!!!) Multiply those to get your output watts.

Pick a number for your controller's efficiency--say 97% --then now you have your approx input watts. Compare that with your panel watts rating.

If you do that with the panel aimed at high sun your input watts should be less than panel rating by about 10% for panel heating and another 2% or whatever for wiring loss.

If panels flat, then you can get a rough idea of the loss there from your latitude and the day of the year.

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