Sizing solar power needs for a DC fountain pump motor?

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webgiant
Posts: 252
Joined: Mon Aug 17, 2009 5:36 pm UTC

Sizing solar power needs for a DC fountain pump motor?

So I saw a nifty little device in a Harbor Freight store the other day: \$13 for a solar-powered "pool/pond" fountain. The floating device is wide enough for two 6"x6" amorphous solar cells, and sports a small pump which shoots water up about 19" through the center of the device, while the sun is shining. I've taken the thing apart (more on "why" later). The pump runs off about 7V and 186mA. The combined generation of the cells is 10.86V, 186 mA, in full sun.

My question is how to figure out the panel needs for an induction motor based on using this solar panel or a different solar panel, with a battery backup. I'd like to rewire the parts into a solar-powered outdoor birdbath with a battery backup so that it will continue to recirculate the water after the sun has gone down. I'm new to low-voltage and I an unsure about the reasons why the solar panel puts out 10.86V but somehow this does not burn out the pump motor at 7V. I have some basic circuit designs for solar power devices which charge a battery while powering a DC device, but they are based on an LED, which is effectively more of a straight resistive load than an induction load. The pumping parts I've already worked out, its just the power needs that need calculating.

stianhat
Posts: 175
Joined: Mon Jun 13, 2011 6:31 pm UTC

Re: Sizing solar power needs for a DC fountain pump motor?

Well, solar panels have three (well, 4) important characteristics - unsure as to what you are listing so it is hard to answer.

Voc = Voltage at open circuit ( Ioc = 0 by definition )
Isoc = Current at short circuit ( Vsoc = 0 by definition )
Imp and Vmp = Current and voltage at maximum power

As a general and slightly unhelpful "by the way" I can remember that it is usually common in cheap appliances to include some kind of zener diode to dump the power that is at a higher voltage than the appliance can handle. I am fairly certain that the pump can handle the voltage since the voltage is dependent on current drawn (so the pump will just pump more water). Solar powered things are usually pretty tolerant since they can end up anywhere between Anchorage and Panama City. The listings on the pump is in that case the voltage and current it requires to achieve the volumetric flow spec - the actual voltage and current limit can be higher

EfrainG
Posts: 1
Joined: Mon Aug 05, 2013 5:42 am UTC
Location: 41 Rosemount Viaduct, Aberdeen , AB25 1NQ

Re: Sizing solar power needs for a DC fountain pump motor?

I thinks it will near about 12 volts with 3 to 6 watts water panels. I am using it and my DC fountain pump motor 12V DC input. It can be use with 3 - 5WATT solar panel or 12 volt deep cycle battery.

Cronos51101
Posts: 24
Joined: Fri Feb 03, 2012 7:12 am UTC
Location: PA, USA

Re: Sizing solar power needs for a DC fountain pump motor?

I'm not too big into solar panel capacities, but what I do know is that you should consider that your panel needs to collect at least enough energy during the day to run all night too. Also, a cloudy day will result in less power to charge. Finally, a deep cycle battery is more tolerant to deep discharges, but lead acid batteries are still sensitive to being fully discharged. Consider that the system should disconnect the battery if the system voltage drops below 11 - 10.5 volts or so (for a 12v battery). You could probably set it up so that the circuit will reset and turn the pump back on when the solar panel voltage reaches an appropriate level. Just some thoughts...
"It's hot... like REALLY hot..."

webgiant
Posts: 252
Joined: Mon Aug 17, 2009 5:36 pm UTC

Re: Sizing solar power needs for a DC fountain pump motor?

The battery will most likely be a NiMH battery pack rather than a lead-acid pack. Actually, I can't decide if I'd prefer the lack of battery memory in a NiMH pack or the fact that NiCds trickle charge much better than NiMH batteries.