Solar Panel Help
 

Hello,

im helping a friend with making a water pump and making it solar powered. The pump is like to make a waterfall type thing so the solar water pump kits online dont work. I have the solar panel(20vDC 2amps or something similar) and the motor needs 12vAC 1.8amp. Will i be able to power it if i just connect leads? or will i have to get a DC to AC inverter/converter? Anyone have any good ideas?

thankss

Re: Solar Panel Help
 

You are correct, in that you need an inverter circuit. I doubt the pump will operate on DC. I'm not aware of any off the shelf devices for 12VDC to 12VAC but I'm sure they must exist somewhere. Some are better than others, in the quality of the waveform produced. Not knowing how your pump works, you may get away with a square wave, you may not.

Might take a look at building something like this:
http://www.aaroncake.net/circuits/inverter.asp
or like this:
http://www3.telus.net/chemelec/Proje...t-Inverter.htm

You might also consider using a 555 timer, and a band-pass filter to create a pseud0-sine wave.

Perhaps one of the EE's on this forum can chime in.

Re: Solar Panel Help
 

Can you post a link to the motor/pump in use. 12 volt AC motors are not common devices unless they are designed to work with lawn lighting transformers. A 12 volt 2 amp solar panel is a pretty big device as well. Can you link that part too?

Re: Solar Panel Help
 

I am currently running a 12VAC fountain pump from a lawn lighting transformer and it works well. Al, do those put out a sine or square wave? I'm not sure if the pump is motor driven, or solenoid driven.

But yes, I too am interested in seeing some model specs on both the pump and the panel.

Re: Solar Panel Help
 

Sandrag,
The transformer is simply that in most cases. It steps down the voltage and isolates the wiring from the house wiring. Sine wave is the waveform and 12 volts is an RMS measurement. Peak voltage is much higher. In most of the country, this is classified as low voltage wiring and therefore does not need to be in conduit.

Re: Solar Panel Help
 

Solar panels are expensive, so it's probably worth making an effort to find the most efficient motor you can to run the pump.

Why spend $500-1000 for a solar panel to power a $5 pump?

Re: Solar Panel Help
 

Although still more expensive than most other power sources, solar panels themselves have come down dramatically in price.

I'm currently qualifying a design for a 3kW residential/cottage solar + battery + grid-interactive system (can give or take from the grid as needed).

High-output solar panels can be had for about $3-4 a Watt, and those are for panels that put out 200+ Watts.

You can eBay clusters of cells, and broken panels for far less if you're just doing a small-scale hobby job like this.

Now for the original post:

You could build your own inverter, but if this something you expect to have around permanently, and you're concerned about your own workmanship and durability - I might suggest sourcing/trading for another pump or finding a transformer that allows it to run off 120V mains, and purchasing an automotive inverter.

Generally, inverters are expensive, but with good reason - for the solar power system above, I will expect to drop about $2000 on a high-quality true sine wave 3000W inverter. (You will probably need a very clean waveform for your motor application, so square wave, or modified sine won't cut it)

But a commercially available 75W true sine-wave automotive inverter can be had for as low as $19 - which probably a lot less than the time and effort to source and build your own comparable inverter, and hopefully offsets the cost of a 10:1 transformer, or even a different motor.

Re: Solar Panel Help
 

Another alternative is to buy a marine bilge pump, you can get a 500 GPH 12v DC pump at Walmart for under $20.

Re: Solar Panel Help
 

Without a detailed design it's very hard to give ideas or solutions, but some things to think about:

1) Use the panel to charge a battery. Use the battery to power the pump.
2) Use an inverter to drop the voltage correctly.
3) Look at some electronics from flashlights- they have quite a few ways of doing 'constant current' drives which can sometimes be used to do 'constant voltage'. That may very well drive your pump.
4) Rewire your panel to hit your target voltage.

Remember that your panel only puts out that juice under full sunlight- so you really want to be certain how everything is sized.

You don't talk about the height of your waterfall- sizing a pump for the proper head isn't very difficult but if you miss... nothing will work.

Good luck!

(I'd probably go the battery route with a good inverter... but I don't know what you're building- spending 500$ for gear to save 5$ worth of electricity a year isn't worth it).

Re: Solar Panel Help
 

Indeed, the exact specs of pump and panel will allow for intelligent answers.

Often, solar panels are rated in a funny kind of way: The peak voltage is measured open-circuit, and the peak current is measured short-circult. That means that a panel rated this way for 20 V DC and 2 A will produce neither under normal conditions.

A 20 V panel is usually used for a nominal 12 volt system (13.8 volts, as in automotive). It is probable that you will be unable to get 1.8 Amps out of it in full sunlight while maintaining 13.8 volts.

My recommendation would be to find a different motor that runs on 12 V DC at about 1.2 Amps. Then, connect a battery* in parallel to account for clouds and other short-term shadows. That will give reasonable results.

*NiCd batteries, like a bank of "D" cells, will provide the best results, long-term.

If you must use the 12 V AC motor, the idea is to use an electronic circult like a 555 timer to switch a transistor on and off at the desired frequency (likely 60 Hz), which will turn the DC into AC. Some low-pass filters you make will help shape the ugly triangle or square wave into a reasonable sine wave and you'll be good to go. None of this is difficult or expensive for the voltages and currents involved here.

Re: Solar Panel Help
 

Hey guys sorry i didn't get back sooner

http://www.goldmine-elec-products.co...?number=G16393
this is the solar panel i'm using
unfortunately i could not find any information on the pump
all i know is that it is a 12vAC ~1amp water pump
sorry, that's all the information i have

i'm guessing i will have to make an inverter? or will something like this work?
http://www.dcacpowerinverters.com/it...sp?ic=PW200-12

Re: Solar Panel Help
 

Except that inverter gives out 120 V AC, about 10 times what you want/need. I suppose a transformer could be found easily enough to bring the voltage back down again. but you do lose a lot in those conversions, and given your limited power budget to start with, you may find it does not work.

Re: Solar Panel Help
 

That's a 0.2A solar panel, not 2.0A. It'd make a great trickle-charger, but that's about it.

Re: Solar Panel Help
 

Agreed,
Actual usable current for this size solar panel is actually much less than the 0.2 amps. It cannot supply enough power to run a pump directly but could be used to recharge a small battery during daylight hours. The biggest problem is the 12 volts AC for the pump. I would bet that the pump is likely a 12 volt DC pump with some diodes internal to allow it to be connected to a 12 volt AC lighting system. Of course the only way to tell for sure would be to open the pump and I am not recommending that. Warranties get voided that way. If the pump was a DC pump, then bypassing the diodes would get you a simple solution to part of the problem.

Re: Solar Panel Help
 

If the pump were indeed a DC pump with a set of diodes to rectify the AC the pump could be hooked directly to a 12volt battery with no further circuitry needed.

-Mike AA