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Let me start off by saying I am in no way an engineer or electronics pro; merely an amateur/DIY-er and High School Physics & Biology teacher. I enjoy building things in my off time to both bring better scientific inquiry into my classroom and build my overall background knowledge of various subjects.

Currently, I am trying to scale down a hydroponic system to an all-in-one, single plant hydroponic growing system that runs on a AAA NiMH 1.2v*850mAh and is trickle charged by a solar cell. I hope to keep this set-up as SIMPLE as possible for my Freshmen & Sophomores to build w/o much knowledge on electricity/circuits.

BELOW is the current/iteration set-up w/o battery and PV cell

The Set-Up (sans Battery & PV cell)

My first iteration of this prototype came from the plans found here and after asking a question on this board about running the PV cell directly to the pump was met with some frustration by both myself and the user who was trying to help (to which, if you are reading this; I apologize for not having the information you needed at the time but after much work, I think I have the required info!).

The voltage put out by the PV cells is fine, but due to the current needed to kick over the pump, I would have needed several PV cells in parallel just to get it started which then would run the pump at an unnecessary current (nominal voltage) and would have issues running on cloudy/low light days. So I ditched possibility of adding a few (3-7) thousand microFarad capacitors in-line; I would try something else...

The current iteration is to have a single, rechargeable AAA (open to ideas) run the 4.8VDC vacuum pump (open to ideas) while being trickle charged by a PV cell (one of the following below):

  • 60mm x 80mm: SUN - 1.5V @ 0.246A ~ Indoor - 0.9V @ 0.0015A
  • 136mm x 110mm: SUN - 6.8V @ 0.21A ~ Indoor - 4.8V @ 0.0012A
  • 130mm x 150mm: SUN - 5.5V @ 0.375A ~ Indoor - 4.1V @ 0.0025A

I have soldered a 1N914 blocking diode inline with each positive wire from the PV cells above and all work properly. The circuit diagram I was trying to follow can be found here and the schematic is below:

Recharging circuit diagram

Ultimately I am replacing the 1300mAh battery with a smaller one to keep the project simple enough and keep the pump running at a slower, steady rate. The pump I am using can be found here.

Vacuum Pump specs

So I soldered two additional leads to a AAA battery clip and put in the rechargeable NiMH AAA 1.2V @ 850mAh (See Below)

Soldered battery clip leads AAA Rechargeable battery

This battery runs the pump at right around the speed I want it to, but I have no way of knowing if the solar cell is trickle charging the battery, let alone which of the aforementioned solar cells would be the best to hook up to the extra leads to the battery terminal.

At this point, I am at a stalemate with my electronics & engineering knowledge. I will take suggestions, constructive criticisms, ideas, etc. on how to get this project up and running efficiently. Keep in mind I am hoping for the simplest setup for students with very little electronics knowledge, but I am more than happy and willing to go the extra mile for them in doing any pre-PCB building/soldering if necessary. Your help and guidance is greatly appreciated!

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  • \$\begingroup\$ you can refill with a passive siphon, like a cat waterer that uses a soda bottle; no moving parts or gizmos required. passive hydroponics is the way to go, especially if you only have one plant to feed. \$\endgroup\$ – dandavis Mar 25 at 18:38
  • \$\begingroup\$ your battery won't charge until the pv puts out 0.6v more than the battery pack. you need to know the amount of work to be done to calculate the system, which depends on the pump head; how high is the water lifted? pumping 1l of water 1m uses 2.7wh. for batteries, wh=mah*v. \$\endgroup\$ – dandavis Mar 25 at 18:47
  • \$\begingroup\$ @dandavis - regarding your first comment: this is a good idea/option admittedly I had not even looked into passive hydroponic systems. The passive syphon is also GENIUS! Although it may be a bit too large for a single plant operation. \$\endgroup\$ – DTK421 Mar 26 at 16:20
  • \$\begingroup\$ @dandavis - regarding your second comment: the water is lifted from the low end of a large reservoir about 15.6 cm to the watering ring. You can see it in the first picture posted in the original question above. I really would love to get this solar pumping option going at least as a demo; perhaps if I mixed the two ideas together. Riddle me this... solar panel to charge battery to run an air pump (w/ aquarium air stone inside reservoir) and the basket sits in the water as a passive system. Whaddaya think? \$\endgroup\$ – DTK421 Mar 26 at 16:23
  • \$\begingroup\$ I don't see what the air pump is for. Sterilize the food first and use UV LEDs to keep up. You will have to change out the water completely every month or two. If you have passive refill, you can use your pump on a timer to flush and drain for times when a month won't cut it. \$\endgroup\$ – dandavis Mar 26 at 19:27

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