oversize arrays for low light conditions

jtdiesel65 · January 2021

Has anybody figured out a way to utilize an oversized array without exceeding max charging amps on the battery? Perhaps there is some controller technology out there for this? You can current limit a cc but that defeats the purpose. I've heard of adding east or west facing arrays but that's not optimal. You can use an aux relay to turn on a diversion load but that's not really what I'm after. Thx

wellbuilt · January 2021

Sure thing , most Quality controllers can be set for max current 10 13% of the amp hours of your battery bank .

For instance my battery has 430ahs so my charger is set for 53 amps I use a out back flex max 80 that is good for 80 amps 4000watts of solar panel .

I have 4500 watts so I’m a little over paneled .

I have a second flex max 80 and 15 more panel to go in for winter , it’s like some one turned off the sun around here , there is snow in the forecast for the next 5 days so no sun power for me ☹️

Photowhit · January 2021

Sounds like you are arguing with yourself!

jtdiesel65 said:

Has anybody figured out a way to utilize an oversized array without exceeding max charging amps on the battery?
Perhaps there is some controller technology out there for this?

Well yes!

jtdiesel65 said:

You can current limit a cc but that defeats the purpose.

How?
Sounds like exactly what you want to do?

jtdiesel65 said:

I've heard of adding east or west facing arrays but that's not optimal.

Actually quite optimal in many situations. In Florida 'sea breeze' situations where it's not uncommon to cloud up mid-day for instance.

jtdiesel65 said:

You can use an aux relay to turn on a diversion load but that's not really what I'm after.

Also not what you are asking.
Solar charging can just be turned off, and in most systems is many days of the week.

jtdiesel65 said:

Has anybody figured out a way to utilize an oversized array without exceeding max charging amps on the battery?

With lead acid battery banks, the electro-chemical action of charging the battery, will limit the current flowing to the battery. The charge controller basically operates to regulate the voltage and the battery bank will limit the current.

Dave Angelini · January 2021

The battery I am charging below is a LFP and it needs the current limited or it will be ruined. Easy to do!

Image: https://us.v-cdn.net/6024911/uploads/editor/uf/lhnow1412zzr.png

Vic · January 2021

Hi jt..,

Your present CCs, the MidNite Classics, will limit the charge current going into the batteries. This uses the current measuring accessory, the WbJr. This does limit the battery charge current, and NOT limit the current output of the Classic CCs. So heavy loads can still be satisfied, and still limit the battery charge current.

The WbJr is very inexpensive -- about $50. It mounts onto a standard 50 mV 500 A Shunt, which is often present in DC Conduit boxes, e-panels, etc.

This is a pretty slick option, when needed. FWIW, Vic

mike95490 · January 2021

Just be careful when you overpanel your Charge controller. They can regulate charging amps by shifting the MPPT point around to less efficient conditions, but there are limits to how much it can shift efficiency. Some can revert to PWM regulation, but the instantaneous peak surges of highly overpaneled controller would still cook the controller if the PV array native amps, exceeds the output rating of the controller

jtdiesel65 · January 2021

Vic said:

Hi jt..,

Your present CCs, the MidNite Classics, will limit the charge current going into the batteries. This uses the current measuring accessory, the WbJr. This does limit the battery charge current, and NOT limit the current output of the Classic CCs. So heavy loads can still be satisfied, and still limit the battery charge current.

The WbJr is very inexpensive -- about $50. It mounts onto a standard 50 mV 500 A Shunt, which is often present in DC Conduit boxes, e-panels, etc.

This is a pretty slick option, when needed. FWIW, Vic

That is what I'm looking for.I want to over panel the battery and be able to use all available wattage at any time without exceeding max charge rate. afaik plain charge limiting doesn't allow that. Do you need a wiz bang junior on each charge controller?Is there a setting that needs to be changed to enable this?Also what if there is a Non classic charging source? I would assume that function would still operate.

Vic · January 2021

Hi jt..,

At this point, each Classic that needs battery charge current Limiting, needs its own Shunt and WbJr. The decision on how many Classics that need to be Limited is based upon weather having the unbridled current (without any Limiting), would cause battery charge current to exceed the max limit desired for battery charge current (as you would guess).

Here is how to do this neat trick:
http://www.midniteftp.com/support/kb/faq.php?id=37

It your power needs will be satisfied with two Classics, then you should need no additional hardware.

YES, you are correct simple current Limiting -- setting the CC's output current cannot do this task well, unless the demands for power are always the same, or one wants to avoid using all possible power from the PV arrays.

Thanks, Vic

jtdiesel65 · January 2021

I would assume the shunts are wired in series. Are there any wiring changes other than that? Do you still wire all charging sources at the head of the chain of shunts like:

bus bar with all charging sources plus inverter -> shunt#1 -> shunt#2 -> shunt #n -> battery ? Or do you have to move each lead off the classic to the shunt with it's whizbang jr. Maybe I'm overthinking this and you just need a shunt per whizbang because you can't physically put two whizbags on one shunt.

Sounds like I should have this setup even without new panels in case the generator comes on and is in bulk and then the sun pops out.

thanks!

BB. · January 2021

I am no expert--But I would guess that it is "one shunt" and 1 or multiple WBjrs connected to the shunt voltage tap (the small screws).

The WBjrs are just very accurate volt meters that can measure from (typically) 0.000 to 0.200 volts or so... The shunt will not be affected by the "loading" of multiple WBjr boards (the shunt voltage will not change with 2 or more WBJr cards attached).

https://www.solar-electric.com/midnite-solar-whiz-bang-jr-current-sense-module.html
https://www.solar-electric.com/lib/wind-sun/Midnite-whiz-bang-install.pdf

Those two screws on the "side" of the shut (facing us) are the voltage sense contacts.

You might try contacting our host NAWS or Midnite and see if they have something (like threaded male/female standoffs) to attach (stack) several WBjrs to one shunt.

You could put several shunts in series (between negative battery bus and "ground" bus)--But that would be more expensive (shunts are not cheap), and you would get another 0.050 to 0.100 volts drop in your wiring per shunt.

-Bill

Vic · January 2021

jt.., & BB Bill,

i may be wrong on the need for a separate Shunt for each Classic that needs to have its charge current Limited.

That Knowledge Base description does not specifically state the case for more than two total Classics.

jt, please ask the question on the MN Forum, regarding the wiring/Shunt details for three or more Classics.

Obviously, if your system only needs two Classics then you only need one Wb and one Shunt. Sorry for my imprecision, have never used this function.

FWIW, Vic

jakobw · January 2021

jtdiesel65 said:

Has anybody figured out a way to utilize an oversized array without exceeding max charging amps on the battery? Perhaps there is some controller technology out there for this? You can current limit a cc but that defeats the purpose. I've heard of adding east or west facing arrays but that's not optimal. You can use an aux relay to turn on a diversion load but that's not really what I'm after. Thx

If you're AC-Coupled off-grid, this is very easy to do. Most PV inverters allow for a certain percentage of overprovisioning and we typically plan to over-provision on commercial systems. The battery inverter limits the charging current and all PV power is directly available for loads at any time.

https://www.sma-sunny.com/en/7-reasons-why-you-should-oversize-your-pv-array-2/

DC-Coupling is more tricky (per all the explanation above). I could be wrong but I believe that only Midnite and possibly Victron have the ability to limit charging current in DC-Coupled systems. Midnite with the WB

JR and Victron via thier battery monitor kit and DVCC (Distributed Voltage Current Control).

If it helps, MN states the following regarding more than two Classics:

Image: https://us.v-cdn.net/6024911/uploads/editor/5w/eej5vx8bv6c1.png

And here is their note on overprovisioning:

Image: https://us.v-cdn.net/6024911/uploads/editor/zc/kfvot3ux97cz.png

mike95490 · January 2021

Morningstar Solar controllers have user adjustable output current limits too, but have no way to compensate for loads diverting charge away from batteries ( Midnight Solar Classic controllers with Whiz-BangJr module can limit battery charge regardless of loads)

But generally, with lead acid batteries, this is a non issue unless you are excessively overpaneled. The normal charging of LA batteries, when they are quite low, can usually accept high charge current, until they are 80% full. At that point, cell internal resistance and a lower voltage differential automatically reduces charging currents to a normal rate, unless the Absorb voltage is set abnormally high

MStar1 · February 2021

Morningstar MPPT controllers can be way oversized and will not exceeding the max rating of the controller if that is all you need. Only our ProStar MPPT controllers (25A/40A; 12V/24V) have a max battery current limit setting based on net battery current to take into account the load current from the built-in load control circuit.
https://www.morningstarcorp.com/whitepapers/morningstars-trakstar-mppt-technology-maximum-input-power/

Dave Angelini · February 2021

Any MPPT can be oversized! It is how they deal with the extra heat in a hot environment. Some will derate output based on heatsink temperature. There is a limit to how much you want to do this in hot environments. It is typically about 20% more than rated, Max!

Much better to just disable a string in summer and not generate the heat in the first place.

Marc Kurth · February 2021

It seems to me that this application needs a battery bank that can handle the maximum current charge rate.

Dave Angelini · February 2021

Well of course but the mppt's can limit on Soc to battery, but the OP wants max power in bad weather. We get up to 600 watts in the rain alot and that covers our house loads during the day! It makes the battery seem bigger also and go longer for more days!

Below is from the cell tower I consult on. It was a good day but deteriorating fast...Won't cause any issues with Happy Hour at the X

littleharbor2 · February 2021

Beautiful picture but the wires are really distracting.

Dave Angelini · February 2021

Something has to hold the fire camera on the tower.

They had 100 knots up there a week ago. They call them the Mono winds and they are very rare and only in winter during a storm. Anything weird on the border to Baja?

Some friends are heading down to Loreto next week?

oversize arrays for low light conditions

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