?How do I run 28 volt panel to run 12 volt pond pump on the cheap?

monkfarm

I already have 3 extra 28 volt used 200 watt panels I bought on a 7  solar panel deal , and would like to use a commercial 12 volt sprayer pump (one is a 8 amp 12 volt, the other I'm looking at is a 12 amp/ 12 volt)  to feed a 30 foot pond that really helps the frogs and toads here in west central Wisconsin.  I understand parallel / series hookups for my panels.  I am afraid  28+Volts would fry my pump.
     I have a 12 volt panel hooked up to a cheap bilge pump already, but would like to try something else, as these $22 bilge pumps are trash after a few months. I would like to hook up another setup to have 2 pumps going. 
     None of the other posts really addressed this other than buying a $245.00 charge controller. 
     I could buy a couple of 100 watt 12 volt panels for about $200, but would like to use what I have.  I am retired and am trying to do this on the cheap.   

littleharbor2

A 28 volt 200 watt panel sounds like a 54 cell panel. I may be wrong. 12 volt panels are usually 36 cells.You need a MPPT controller to charge a 12 volt battery bank properly. You can find a proper MPPT controller for less than $245.00 though. Look at the EPever/EPsolar line. A 20 amp version is all you would need. You can still use it with a cheap PWM controller but will get a fraction of the 200 watt potential. If you are trying to do PV direct to the pump I would think you would be risking burning up the pump due to high voltage.

BB.

Are you doing this with a battery bank for 24 hour per day operation, or only want to run the pump when the sun is shining?

-Bill

Tecnodave

One approach to pond aeration  is to pump only when there is sun, there are pump drivers rated to do that (current boosters)  but the diy way is use a DC-DC buck converter to regulate the varying solar input to a voltage that the pump works with. These can be found on Amazon or eBay for less than $20 or so, get one rated at twice the power as these are very overrated.  I use a 800 watt one to charge my 90 watt notebook computer directly from my solar system batteries...24-32 volts in 20 volts regulated out ...12.99 at Amazon......it's rated to 46 volts in.

billybob9

I think some vehicle manufacturers solved this problem with their 24vdc systems by hooking up the light ( two ) in series to make 12x2=24. So this would mean buy another pump. 

NANOcontrol

I use these 72V max buck converters down to 12V on my 60V. They only cost $6 each and you could use two in parallel and wouldn't need a battery.  I modify them to operate at power point for high efficiency, but you could use them as purchased if the panels are oversized for the application.  Buck converters tend to pull panel voltage into a death spiral if unmodified. You would likely get acceptable performance regardless.

monkfarm

Sorry so late getting back to you all!   Wow!!  Thank you so much for all the replies!!  
Billybob 9, you have an interesting solution, I may just run another 2 pumps.  But, I think I will explore all your excursions!
      Bill or BB,  No, I don't want to run a battery, and am satisfied with just running my pumps whenever there is enough sun to run my pumps.
  I used my old backhoe last summer to deepen and widen the pond so it will take a lot of water.  
    Tecnodave, I am considering adding aeration to the pond using solar, but this is just adding water from a large spring fed creek.  We have some creatures that burry tunnels in the bottom of the pond, and we need to replenish the water.  It originally was a spring fed pond, but the spring went away, coinciding with a fracking operation a few miles away, interestingly enough.
   Little harbor 2, this is what this post is all about, avoiding burning up my pumps with too much voltage.  Yes,  I think a 28 volt panel that puts out 30 something volts would burn out a 12 volt pump. (not trying to be a smart ass, I'm not that technical in my knowledge)  I don't know how many cells it has, but I am amazed at how much voltage it puts out even on a cloudy, dark day.
   Nonocontrol,  those max buck converters sound interesting, probably have to put them in a dry box, tho, right?  Great price, I wonder if they hold up.  No, I don't want to use a battery.  Interesting that you modify them. 

BB.

There are some buck converters that are in aluminum cases... But you do need to ensure that everything is protected from rain and small bugs/animals.

Here is an example of a medium size (12 amp) DC to DC buck converter... Not that cheap (around $40), but gives you an idea of what they can do and a link that will stay around for awhile (vs EBay links which "disappear" pretty quickly):

https://www.amazon.com/Converter-DROK-Voltage-Regulator-10V-75V/dp/B071LGTTRN

Regarding the air pumps... Are they brushed motors (universal motors like simple electric drills/DC motors)?

If brushed, they will need the brushes checked and replaced. Brushed motor brushes do not last that long. Roughly 1,000 to 8,000 hours is typical. Here is an interesting article with the details:

https://www.plantservices.com/articles/1997/001/

If they are electrically commutated (like DC computer fans), the motors will last much longer.

-Bill

bill von novak

BB. said:

There are some buck converters that are in aluminum cases... But you do need to ensure that everything is protected from rain and small bugs/animals.

Here is an example of a medium size (12 amp) DC to DC buck converter... Not that cheap (around $40), but gives you an idea of what they can do and a link that will stay around for awhile (vs EBay links which "disappear" pretty quickly):

https://www.amazon.com/Converter-DROK-Voltage-Regulator-10V-75V/dp/B071LGTTRN

That might work.  But beware - some DC/DC converters will happily collapse the input to the lowest voltage they can operate at (2.5 volts for example) and keep it there, resulting in almost no power.  To get them to work well they need a low voltage disconnect that disconnects them completely when the input is below normal panel voltage (say, 12 volts.)  That way the operating point will never drift down into the weeds.