Need help choosing a solar controller

[StewB]

I have 6, 53 watt Siemens panels I am going to use to keep 4 100amp batteries charged up at my cabin.

I am looking for some help picking a 30 amp controller suitable for the job. I looked on ebay and see many different suppliers with an amazing range of price.

Any one have some advice on one to pick?

Thanks very much.

[BFL13]

You can "stack" any controllers. I have "stacked" (placed in parallel on the same bank) a PWM Solar30 and a 20a MPPT Eco-Worthy and they added their amps just fine. (You do have to set their adjustable voltage to the about same voltage for best results, but that is a given)

I have also "stacked" two same size, same brand PWM 20a controllers and they added their amps too.

Point being, you don't have to spend kabillions to get "special" controllers that claim they can be "stacked" as though any "others" could not be "stacked".

It is just a normal case of using more than one charger on the same battery bank. Easy-peasy.

[TechWriter]

Check out the new Kid (30A MPPT controller) on the block. If your power requirements increase, you can "stack" two Kids to get a 60A controller.

Use the Kid's Sizing Tool to check you PV array requirements.

[BFL13]

pianotuna wrote:
53 watt panel

PT, those guys are as bad at math as your are! 🙂 The USA NEC says you need a 20% margin but these guys say you should multiply by 1.25 for controller size in amps. That is a 25% margin.

Hint for the "math disadvantaged"--

- 25 expected amps. 20% is 5 amps so you need a 30 amp controller.

1.25 x 25 = 31.25 (6.25 more not the NEC required 5 more.)

[pianotuna]

53 watt panel

[MrWizard]

if those are the ones i think they are
they 16.5 working volts
yes you will wire them parallel plus on plus..neg on neg

use a 25~30 amp PWM controller with two set points and LCD display to tell you whats going on

us 8ga or larger wire from panels to controller
and 4ga wire from controller to batteries

this should work OK with a minimum of FUSS

how much time you spent at AND away from the cabin, will determine your set points

13.2v float if your only there on week ends or less

if you live there and can tend to the batteries you can raise that a little

[grizzzman]

StewB wrote:
Not knowing much of anything about how to wire this up, I assumed -
Each pos and neg off of each panel to a post on the back of the mounting frame with 10 gauge wire.

Then an 8 gauge pos and neg run about 15 ft to the controller mounted inside the cabin.

Then an 8 gauge 16 ft run to the batteries.

4 100 amp 12V Batteries wired in parallel with 4awg cable to posts (neg off last battery pos of first)

Hi SteveB If you go with PWM your wire size is to small assuming 15 and 16 foot numbers were one way. Well the run from the panels are under 3% but the run to the battery will loose about .40 of a volt. While that sounds small it isn't. FLA batteries need to gas a bit. A stationary battery will stratify. Heavy amounts of the asid down low causing grid corrosion and light levels of asid up high causing freezing issues and sulfation. The number one cause of battery failure in stationary solar charged batteries is sulfation. About 80% in fact.

I would suggest a solar controller that has adjustable bulk and float settings and set them to your battery manufacturer specs.

I would move the controller close to the batteries (within a few feet) And use at least #4 cable the 30 feet to the panels (remember the round trip is 60 feet) good luck!

[time2roll]

I agree if the wire run is long... go series with an MPPT.
I tend to recommend Morningstar controllers as I prefer top quality.

Otherwise low price on china/ebay is fine.

[pianotuna]

Hi,

Looks like voc is 21.6 volts. Use any PWM controller that allows for variable set points. A temperature probe on the battery bank is a nice item to have.

[Golden_HVAC]

If they are 12 volt nominal panels rated around 3 amps each, then you could look for a MPPT controller that can take in up to about 150 volts and put out up to about 25 or 30 amps at 12 VDC (that can be 13.5 volts normally).

In this way, you only have about 3 amps going through the wire, and practically no voltage loss across the wire due to amperage. Using #10 wire will lessen any voltage loss even further. The 6 panels would be in series, so that you connect the negative wire to the first - terminal on panel #1, and continue with only 1 wire from +12 of panel #1 to -2 then +2 to panel # 3, 4, 5, and 6. + output of #6 panel then returns to the controller. On a cold sunny day, it might see as many as 130 volts, perhaps as much as 150 volts. Under charge load, it will probably see about 100 volts X the amperage rating of your panels (say 2.5 volts) and at the controller this 100 volts input is changed to 13.2 - 13.5 volts to charge the battery bank.

I would recommend #10 UV rated direct burial wire from Home Depot. For mounts, I would suggest aluminum angle from Home Depot. On the roof of my motorhome, I cut 6" long and drilled three holes for #10 screws into the roof, and 5/16" hole for the bolt into the panel frame.

If I where to wire it up with a lower cost PWM controller, then I would run two wires from the panels to the controller, with 3 panels on each line. This would put about 9 amps on each run of #10 wire, you can go as high as 15 or 16 amps, but to put the whole 18 or 19 amps on #10 wire, you might see 5% or 8% loss due to high amperage on the wire.

If you find that you want to expand the system, this place sells panels for about $1 per rated watt. SunELec.com

Good luck,

Fred.

[StewB]

Not knowing much of anything about how to wire this up, I assumed -
Each pos and neg off of each panel to a post on the back of the mounting frame with 10 gauge wire.

Then an 8 gauge pos and neg run about 15 ft to the controller mounted inside the cabin.

Then an 8 gauge 16 ft run to the batteries.

4 100 amp 12V Batteries wired in parallel with 4awg cable to posts (neg off last battery pos of first)

[JiminDenver]

No one controller is the end all for everyone. You need to narrow the field with what features are important to you and how you plan on wiring the panels.

[BFL13]

You will want the controller to recharge your usage while at the cabin, then you will want it to "maintain" the batteries while you are not there (Float them)

You can get a controller with a single adjustable voltage. Pick that high, like 14.8 for while there and then re-set it at say 13.4 for floating before going home.

Or you can get a controller with two adjustable voltages, so after it gets to 14.8 or whatever, it drops to 13.4 or whatever by itself whichever voltages you choose.

Your expected amps is maybe 20a with that total wattage. You need a controller that will not overheat at 20amps. You must have margin above 20 so 25 or 30 is good for that. Or with some controllers, they clip the amps to their rating size and will not overheat at that max rating, so you could pick a 20a one of those and be ok.

I have a 20a MPPT Eco-Worthy that is about $102 US that has two adjustable voltages. I also have a Solar30 PWM with one adjustable voltage that is about $35. Either would do the job.

I suggest getting one like these with a read-out display for your settings and not go cheaper with a $20 job that has no display and no adjustable voltage. ( it would work, sort of, but for a few dollars more you get so much more)

A factor in all this is wiring gauges. Some set-ups need fatter wire to use PWM at 12v than 24v MPPT would need. The difference in wiring cost might narrow the gap between PWM and MPPT controllers.

The MPPT will give a few more amps than the PWM but for your cabin application, who cares? Pretend they will do the same thing and look at the other factors like the wiring or whatever.