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Connect timer w Rechargeable 9v to Solar panel? Answered

I am using a rechargeable 9v battery in my irrigation timers.  I would think it would be easy to hook up a small solar panel to charge the batteries during the day and then I don't have to worry about them failing and me not noticing until my garden goes brown.  Two wires join in a pastic coated cap that hooks to the 9volts.  Can't I just take the cap apart and connect the leads from the little solar panel?

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solartimer (author)2013-06-10

https://www.instructables.com/files/deriv/FR9/IA91/HHS9E27R/FR9IA91HHS9E27R.THUMB.jpg

Hopefully I uploaded this right and you can see it. Rough, but the best I can do. On which side do I put the diode/resistor?

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solartimer (author)solartimer2013-06-12

Got it. Must have at least 9v to charge the battery. That's easy to get.

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iceng (author)solartimer2013-06-10

The solar array needs to exceed the 9v battery  and the 14¢ diode in order to charge the battery.

At night the battery cannot discharge through the solar cells because of the one way diode.

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steveastrouk (author)2013-06-10

How long does a battery last anyway? That let'syoujudge the panel youneed. I'll guessthat a solar nightlight will be enough.

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solartimer (author)steveastrouk2013-06-10

The battery usually lasts close to a year. I'm looking for suggestions on how to wire it, rather than panel size. If anyone has an idea on that, it would be great. Thanks.

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steveastrouk (author)solartimer2013-06-10

Enough of the tiny cells from solar lights to get a very small current into your battery, add cells until it works. Add a blocking diode, so it doesn't go flat at night

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solartimer (author)steveastrouk2013-06-10

I have a 5v solar panel I planned to use. I'll gladly add a diode if someone can tell me how to wire it up. Thanks.

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steveastrouk (author)solartimer2013-06-10

5V can't charge a 9V battery ! You need enough to drive a current of around 2mA into the battery, via a resistor

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solartimer (author)steveastrouk2013-06-10

Even as a trickle charger? The battery only is used to open the timer valve every couple of days.

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steveastrouk (author)solartimer2013-06-12

Can't make the current flow INTO the battery unless the voltage of the panel is higher than the battery !

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iceng (author)2013-06-10

At night that solar cell becomes a resistor and drains the battery.

That is why you must place a one way schottky ( low forward drop ) diode
in series as the pic shows.

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solartimer (author)iceng2013-06-10

Thank you! Ok, so I just add the timer wires to the nodes for it to be an inline trickle charger?

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iceng (author)solartimer2013-06-10

Use your rechargeable 9V battery as you normally would.
The solar array and 14¢ diode will as the sun dictates add energy to your system.

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iceng (author)iceng2013-06-10

BTW this outperforms the  schottky diode.

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mpilchfamily (author)2013-06-09

Depends on what kind of rechargeable battery you have.

The solar panel will only trickle charge the battery during the day. Chances are the solar panel won't be able to keep up with the power the timer is using throughout the day. But at the very least it will extend how long the battery is usable before it has to be replaced.

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solartimer (author)mpilchfamily2013-06-09

It's your standard 9v rechargeable battery. The timer is for the irrigation system. It only needs to turn the valve on and then off once each every couple/three days, so power use is minimal.

Any idea how to wire it? I can take the cap apart with the 2 wires apart and wrap the solar panel wires around the battery nodes, or I can wrap all the wires together, red to red, black to black.

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Josehf Murchison (author)2013-06-09

9 volts how many watt hours is the battery and how many watts is the solar cell.

Example 9 volt battery 5 watt hours will need a 1 watt solar cell to charge for ten hours to fully charge.

If it is using the battery while charging 1.5 watt solar cell.

A charger circuit is best to ensure the battery wont overcharge.

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