solar water fountain question

System · July 2010

I recently set up a small solar panel to run a water fountain in my yard. The panel is rated at 7 volts, 140ma output, while the pump is rated at 6 volt, 120 ma consumption. It works great, except that every time the sun is obscured by light clouds, the pump stops. I’d like to put a battery into the circuit so the panel could charge the battery, and then the battery would run the pump when there isn’t enough direct solar power. Do I need any special electronics to do this …or can I just wire a battery (series or parallel?) into the circuit?

BB. · July 2010

Re: solar water fountain question

If you add a battery and charge controller--you will probably need 2x the amount of solar panel to account for the additional losses (charge controller and batteries).

And, you will probably not find any off-the-shelf 6 volt solar charge controllers.

Unless you want to make a hobby out of designing your own solar system--the simplest would probably to purchase 1-2 more solar panels and parallel them with the original panel.

It won't run the fountain in the dark, but it will at least still move some water with partial cloud cover.

The "big problem" is usually the batteries. If they are not properly charged and prevented from over discharging, batteries will not usually last very long.

Choosing the correct battery chemistry, matching cells, some sort of circuit to prevent cell reversal, overcharging, turning off at night(?), etc... all tend to make the problem of adding batteries fairly complex and not always satisfying.

Not that it cannot be done--it is really how much effort do you want to put into the project and what you are looking for (ride through 15 minutes of clouds vs 6 hours on a cloudy day, vs running past dusk in winter, etc.).

-Bill

niel · July 2010

Re: solar water fountain question

in addition to more compatible pv you might smooth it out with some capacitors, but it will still stop without the sun and no battery. with a battery you solve the intermittent operation of it along with gaining more complexity and costs as bb pointed out.

System2 · July 2010

Re: solar water fountain question

Thanks for the response. I'm willing to tinker with this a bit, but (as you can guess from my original question) my electrical / electronics skills and knowledge are limited. So ...here's a few more questions. I have a couple of 3.7 volt lithium Palm Pilot batteries (7.4 volts total). What happens if I connect the positive side of the batteries to the positive side of the panel ...negative side to negative side, so that the panel is charging the batteries at the same time the batteries are running the pump? Do I need the "controller" you mentioned in order to prevent the voltage from the batteries from harming the panel??

mike95490 · July 2010

Re: solar water fountain question

digger89 wrote: »

..... I have a couple of 3.7 volt lithium Palm Pilot batteries (7.4 volts total). What happens if I connect the positive side of the batteries to the positive side of the panel ...negative side to negative side, so that the panel is charging the batteries at the same time the batteries are running the pump?

Smoke, and then you can add the lithium to the water, and see more smoke !!

System2 · July 2010

Re: solar water fountain question

So, apparently the answer is "no, that can't be done"? ...well, I guess that makes sense to the electrically knowledgeable. Now I know. My apologies: I thought I was posting to the Solar Beginners Corner ....

BB. · July 2010

Re: solar water fountain question

Mike was trying to be funny. Humor on the Internet is sometimes difficult to pull off (electronics joke is devices fail when the magic smoke is let out--etc.).

Lithium batteries are notoriously difficult to charge and discharge... Depending on specific cell chemistry... You can actually explode lithium cells from over charging and from over discharging. Charging without a speciallized lithium designed charge controller (and discharge controller) can actually be quite dangerous.

I don't have the time right now--I will be back later with better answers.

-Bill

mike95490 · July 2010

Re: solar water fountain question

digger89 wrote: »

So, apparently the answer is "no, that can't be done"? ...well, I guess that makes sense to the electrically knowledgeable. Now I know. My apologies: I thought I was posting to the Solar Beginners Corner ....

Didn't mean to startle you with shouting SMOKE, but smoke is a very likely result.

Just using a simple PV and pump is about the best you can get, adding another PV will help with clouds, but adding lithium batteries without charge controller circuits.....
Even sony has had fires in their lithium batteries.

solar water fountain question

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