Sharing Panels with Grundfos Pump and Solar Chargers

Re: Sharing water pump PV with house PV

I usually recommend a new thread to keep configuration questions separate between posters.

We can leave it here for now and see what happens.

And welcome to the forum.

-Bill

Re: Sharing Panels with Grundfos Pump and Solar Chargers

Tulumtam,

I went ahead and moved the thread... And I have a bit of time to try and help a little bit...

The system currently has 8 Grundfos 80w panels (Vmp 33.3v, Imp 2.4A, Voc 41.5v, Isc 2.6A). 2 of these panels are connected in series to the SQFlex pump through the pump controller. As the well is only 9 feet deep, this provides sufficient power for the pump. The other 6 panels are currently wired in parallel into a 24v 220 a/h battery bank through a BlueSky Boost 50 charge controller. We want to add another 110 a/h to the battery bank, but the array of 6 panels is a bit small for the additional battery capacity.

Can I parallel another small MPPT charge controller (either the SunSaver MPPT - Max. PV Voc: 75v; or the Steca Solarix MPPT 2010 - input voltage range 34-100v) with the BlueSky and put in a switch so that the 2 panels used for pumping can contribute to battery charging when the pump is not in use?

It is possible to share one array with two charge controllers... But they must be PWM type charge controllers (the simple on/off type).

MPPT controllers actually adjust current ("sweep") to figure out the optimum Vmp*Imp=Pmp throughout the day. If there are other loads on the panels, the sweeping will result in confusion for the controller.

Also, some MPPT controllers are true "4 wire boxes"... Meaning that they measure current through the solar panel ground return turn leg (PWM generally do not) and if the systems have a common battery ground, the current measurement capability of the MPPT controller can be bypassed.

Both the Blue Sky and (as I understand) the Grundfos pumps are MPPT (Maximum Power Point Tracking) controller (internal to pump).

If you wish to switch the Pump Array to another Charge Controller--As long as you switch both legs (+ and -) of the solar array to a dedicated MPPT controller (or even PWM) you should be OK. You would need a Double Pole / Double Throw Switch or two pole relay with NC/NO/COM contacts (COM connection to array, Pos#1 to Pump, Pos#2 to Battery Charger).

You could connect the relay to your float switch (if you have one) and have the array toggle between the pump and the charge controller. (could this confuse the charge controller--it may, some controllers only "sweep" every 5-15 minutes and if your pump cycles often, the controller may not optimize for your setup--I don't know, just guessing).

If you choose to Add Array1 plus Array2 to one solar charge controller, the Vmp of Array1 and Array2 must be the same (within ~10% difference maximum).

Otherwise, if you have a second MPPT controller attached to the battery bank, the rules for connecting the second controller are as normal (Voc-cold, Vmp-hot, power/fusing requirements) and a separate lead from Controller #2 to the battery bank so that they controllers do not confuse each other.

If you have lightning in the area or other issues (backup AC/DC generator or battery bank for the pump, etc.)--It could make the installation a big more complex (just a warning--I don't know what your system looks like).

-Bill

Re: Sharing Panels with Grundfos Pump and Solar Chargers

There are two common ways to run circuits...

First is to daisy chain... Basically run one wire 10' and drop a connection to each load along the way.

The second is to run a wire from the source to each load. Basically, think of a star with the battery at the center (also sometimes called a "home run" as each connection runs back to "home").

What happens is the battery is a huge source of energy and also a fairly good capacitor... It is (hopefully) a source of clean DC power.

Charge controllers as they run through their different charging modes frequently get very choppy current on their output to the battery as they charge it.

If you share one cable from the battery and daisy change the controllers off of the shared cable--you can get electrical noise cross-talking into the other controller. Even if the cable is, in theory, heavy enough to carry the current for both controllers--the electrical noise has been known to confuse controllers and cause them to either think the battery is closer to 100% charge, or sometimes mess up the MPPT tracking algorithm that is supposed to find Pmax from the array--causing the controllers to substantially produce less power than they would with a clean circuit.

So, by "home running" the wires back to the battery bank (with a proper fuse in each + lead near the battery bank before the wire is taken to the controller(s))--Helps ensure the each controller is measuring the bank voltage properly without interference (noise, increase voltage rise in cable, etc.) caused by a second charge controller.

Several controller brands have been seen here to be sensitive to electrical noise on the cables/batteries--And I believe that the Blue Sky has also been seen to be sensitive to the 120 Hz ripple of inverter input current.

By the way, if you have parallel batteries, review the SmartGauge webpage for suggestions on how best to wire a battery bank so that parallel strings properly share current.

By the way, I am not saying you will or won't have issues with a single run--Just the chances of problems are usually less.

-Bill