Need help choosing a solar controller

KD4UPL wrote:
BFL13, what is the NEC reference about a "20% margin". That's pretty vague.

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OK I may have been wrong on that. I will try to find where I picked up that 20% margin for NEC idea.

This says that the actual NEC rule is for a 25% margin, by multiplying by 1.25.

It says NEC does not apply to autos, trains, etc. Not clear about RVs.

From:

http://www.senecass.com/NEC2000.pdf

"The ampacity of conductors in PV source circuits shall be at least 125% of the rated module or
parallel-connected modules short-circuit current [690-8]. The ampacity of the PV-output circuit
conductors shall be at least 125% of the short-circuit output current [690-8a]. The ampacity of
conductors to and from an inverter or power conditioning system shall be 125% of the rated
operating current for that device [690-8a]. In a similar manner, other conductors in the system
should have an ampacity of 125% of the rated operating current to allow for long duration
operation at full power [215-2]. These NEC requirements are to ensure that the connected
overcurrent devices or panelboards operate at no more than 80% of their ampacity. Operation
when snow or cloud enhancement increases the PV output above normal may require additional
ampacity. Daily expected values of solar irradiance will exceed the standard test condition of
1000W/m2 at many locations."

pianotuna wrote:
53 watt panel

They are the M55 model

Thanks for the link

BFL13, what is the NEC reference about a "20% margin". That's pretty vague.

OP, There are a lot of charge controllers available for sure. The PWM controllers are less expensive but leave some of the array's potential output "behind". To get the most out of the array an MPPT charge controller is necessary. If the input voltage of the controller will allow wiring your panels in series will simplify the wiring and reduce voltage drop.
Morningstar and Blue Sky would be my 2 choices for a small charge controller. Both offer PWM and MPPT versions. Most with options for remote temp. sensors, meters, etc. You need to decide what features you want.
A proper charge controller won't need you to reprogram it depending on if your using the cabin or not. You would simply program it to the manufacturers recommended charging specifications for the batteries and leave it alone.

I'm proof that you can "stack" three Eco-Worthy's.

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.

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.

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.)

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

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!