Connecting a solar panel and battery together?

[Fordulike]

I'm in a bit of a tinkering mood and fancy doing the following:

I've got one of those garden features, which cascades water over a globe using a very low wattage pump.
The pump is tiny and can't see it being more than 5w, but does a nice job of pumping enough water at 12v.

The mission is to connect the pump to a solar panel and also a battery, so that during sunny days, the panel should power the pump and have a little extra to charge the battery.
Then when the sun disappears, the battery should keep the pump going.
I've got my eye on a 12v 20w panel and plan to use a small 12v lead acid battery.

Firstly, is this feasible? And secondly, would I need to incorporate some form of charging circuit, or just hook up directly to the battery?

 

[Scimitar]

It will work fine, but if you discharge a lead acid battery too flat too many times, it will die. You would need to either incorporate a timer, or state of charge monitor.

 

[Deleted member 4366]

You need a charge regulator to stop over-charging the battery. If you had a big enough battery, it probably wouldn't be a problem. Sometimes the panels come with a regulator, or you can buy one in Maplin for not a lot.

You've then got a problem of over-discharge. If you let the battery go down too far, you'll kill it.
Battery Protection - Low Voltage Disconnects - www.solar-wind.co.uk
or make one:
Low Battery Cut-off and Overload Protection Circuit. |Homemade Circuit Designs Just for You

 

[Fordulike]

Thanks Scimitar. The battery will be used just to run the pump during the odd evening when the missus is entertaining friends. I've spotted one on eBay that says that it'll recover from deep discharge with no problem. I'll incorporate a switch to turn it off after she's done with it.
It's gonna be experimental anyway and I could always boost the battery back up with my car battery charger.

Thanks d8veh for your info. I can't see the battery discharging to empty, but I'll keep the protection circuit in mind in case it doesn't go to plan.

 

[flecc]

This is a good application for a car battery that's at the end of it's useful car starting life. You could get many years out of one used for this purpose. As Dave has mentioned, being larger means no overcharging protection would be needed, and since such a battery would probably be a freebee, it wouldn't matter when it packed up.

 

[Fordulike]

Would this one suffer from overcharging?

ULTRAMAX AGM 12v 7Ah (as 6Ah 7.2Ah & 7.5Ah) - FLYMO CT250X STRIMMER BATTERY | eBay

 

[Fordulike]

The solar panel I'm buying provides 0.29A @12v. It has a blocking diode built in.
Can anyone advise me if connecting this directly to the battery, shown in above post link, will cause an overcharge?
I obviously don't want to create a battery overheat situation and a potential fire risk!

Maybe I'm out of my depth with this project and should just stick to running 1500w MAC motors lol

 

[Deleted member 4366]

The blocking diode is normal. It stops the battery from draining into the panel when the sun goes down. With a small gel battery like that, you need a charge regulator. Without a regulator, the panel might go as high as 18v. A wet battery wouldn't need one as long as you kept an eye on the acid level, but I think the charge regulator would be cheaper.
CMP Solar Panel Charge Controller Regulator 10A 12V 24V | eBay

 

[Fordulike]

Thanks d8veh, £5.79 seems a small price to pay for charging safety.

A total mind melch, wibble wibble idea, would a large capacitor work?
The pump only needs to run on for about an hour after sunset, so could a capacitor be used instead?
Do they need a charging regulator?
Don't think they suffer from total discharge problems either.
It's only a mad thought and I'm sure I'm about to be shot down in flames lol

 

[Deleted member 4366]

In theory, you could use super capacitors, but I've only seen low voltage ones.You mustn't charge them over their nominal voltage. You can put five in series for 12v applications, but you'd need some extra circuitry to ensure that the charge is evenly distributed to prevent over-charging one in the string, and you'd still need a charge regulator. So, it could be done, but probably more expensive and more complicated. A normal capacitor wouldn't hold enough charge.