Need some resistance help

[No_idea]

Hey guys, ran into this site trying find an answer to my question, hope I can explain it well enough without knowing the proper terms... I currently have a 15 watt 12v solar panel plugged into a solar charge controller. The controller is plugged int a 12v 720 cca dual purpose battery. This is all working properly.

I am trying to run a small solar fountain pump for my wife. It works great in the day on its own but would like to run off my 12 v battery at night along with some l.e.d lights. I plan to use a photocell to have the battery supply power once its dark.

Now I know I can't hook up the pump straight to the battery, but my main question is what could I use or what size resistor should I get that would lower wattage or voltage to run pump safely. The pump apparently is 7 volt and the small solar panel generates about 1.6 watts.

Again I hope I supplied the useful enough information. And thanks you guys for your time.

 

[(*steve*)]

You need a switchmode regulator to convert the 10 to 14 volts from your battery to the 7V required by the pump.

Some things to consider:

1) ensure you have sufficient capacity so that the battery doesn't go flat at night in winter after a cloudy day.
2) maybe run the pump at a slightly lower voltage to reduce power requirements.
3) consider some form of low-voltage cut-out
4) look here. Not necessarily the best price, but an idea of what I'm talking about.

 

[No_idea]

Thanks for the reply. I will look into the switch regulator, I never heard of them before to be honest. Also the solar charge controller has a built in low voltage disconnect, so that won't be an issue.

Will the switch regulator drop the wattage to around 1.6 watts? Or will I need a resistor at all once I find a regulator?

 

[(*steve*)]

Will the switch regulator drop the wattage to around 1.6 watts? Or will I need a resistor at all once I find a regulator?

That will just happen. At the correct voltage the pump will only draw the power it needs, not what is available (unless there's a serious fault).

 

[Wabajig]

How much current does this solar fountain draw? Or wattage?

 

[Lenp]

No switchmode!
It's overkill. Just use an LM317 regulator. Check on line for the specs. $1-2 COST!
LEN

 

[(*steve*)]

No switchmode!
It's overkill. Just use an LM317 regulator. Check on line for the specs. $1-2 COST!
LEN

Perhaps you failed to notice that this is a solar powered arrangement.

Using a switching regulator will allow the pump to operate for almost twice as long.

A switching regulator might cost $5 or thereabouts. Or even less!

 

[Wabajig]

Maybe use a series pass circuit from solar panel to only charge the battery to 7V. This will reduce your capacity of the battery, but may be more cost effective and efficient. You will need to discharge the battery safely to +7V before hooking up solar pump and circuit. Also use a diode out of the battery to your pump to eliminate counter EMF from your motor in the configuration of the cathode to your +7V supply and anode to ground (6A100). Good Luck.

 

[BobK]

Do not listen to the above advice, you do not charge a 12V battery to 7V. You don't even discharge a 12V battery to 7V normally.

Bob

 

[davenn]

No switchmode!
It's overkill. Just use an LM317 regulator. Check on line for the specs. $1-2 COST!
LEN

switching regulators are substantially more efficient and hence less power is wasted as heat by the regulator
This makes them ideal for battery type power supplies

Dave

 

[Wabajig]

This isn't a alkaline battery, they are lead acid. You can charge them to anything you want. 12V or 13.8V is the maximum, no minimum, just less capacity. Good luck.

 

[jackorocko]

This isn't a alkaline battery, they are lead acid. You can charge them to anything you want. 12V or 13.8V is the maximum, no minimum, just less capacity. Good luck.

No this is horrible advice to charge a 12V battery to 7V, especially a lead acid battery. You will severely reduce the life of the battery. Lead acid are known for sulfation, do you happen to know how sulfation occurs? Let me help you out.

http://batteryuniversity.com/learn/article/sulfation_and_how_to_prevent_it

 

[Wabajig]

Sulfation was the fate of the battery anyway. It is trickled charged by solar, and then drained by large current source. But thinking back, I think the better idea is to charge a 6V battery with a series pass regulator from the solar. Since most 6V batteries can be charged close to 7V, this would make a direct source for his pump.