solar powering a quartz clock

[nic_marsa11]

hello all, you helped me before, which i'm very grateful for. I'm completely new to electronics so i need help again.

Attached is what i think I'm meant to make in order to power a clock motor from a solar cell. If anyone can point out mistakes I'd be very grateful.

Also, I'm finding it surprisingly difficult to find parts. Farnell only accept £20 minimum order and don't stock BAT45's. Maplins stock similar items, but since I'm new and skint i hesitate to deviate from specs. Anyone got suggestions on where to shop?

cheers
nic

 

[ericgibbs]

hi,
In the UK, try here: Rapid | Distributors of electronic components, electrical products and educational supplies

Your clock will only run when and while the capacitor is charged,sunshine of course,, how much current does the clock require to run.?

**broken link removed**

 

[MikeMl]

Depending on the answer to Eric's question, you will likely need to use a "SuperCapacitor" (1Farad @ 2.5V) to keep the clock running at night.
Some solar panels do not require the external diode (the diode is intrinsic).

 

[nic_marsa11]

Your clock will only run when and while the capacitor is charged,sunshine of course,, how much current does the clock require to run.?

**broken link removed**

thanks for the link, i'll check it out.

In the attachment I've written that the clock needs 150uA to run. I need the clock to run over night. I was told the cap is a super capacitor that would be charged enough to keep the clock running until the next day. Do you think I've got the right spec and set up for this to happen?

cheers

 

[nic_marsa11]

Depending on the answer to Eric's question, you will likely need to use a "SuperCapacitor" (1Farad @ 2.5V) to keep the clock running at night.
Some solar panels do not require the external diode (the diode is intrinsic).

The solar panels are separate components and the capacitor I've written in the attachment is a super capacitor 22f at 2.3 V. will my set up and spec work? (apologies if i'm repeating my qs.)

cheers

 

[MikeMl]

C*ΔV = Q = I*T

Solving for: ΔV = I*T/C = (150e-6A * 86400s) /22F = 0.59V

Which means that if you initially charge the capacitor to ~2.1V, 24 hours later with no sun, the capacitor will still be at 2.1-0.59 = 1.5V, so it should work.

You will have to determine if your watch will stand 2.1V, or if you will have to regulate the voltage?

The best system would charge the capacitor to the highest voltage it can stand, and then regulate the voltage to the watch...

 

[nic_marsa11]

thanks for the help mike, the equation helped too, I'll try to use that in future. I'll be powering a quartz clock motor. Not that I have much experience, but I'll imagine the motor can withstand a bit. But we'll see!

I'll go for that capacitor then. However I'm still confused on my schottky diode. I've been recommended the BAT45, which has the values of 30mA and 15V attached to it. However, and forgive my ignorance, can these values vary? For instance there's a schottky diode component called a 'VISHAY SEMICONDUCTOR' product no. 'SD101C/D7', and it has 30mA and 40V attached. Will the difference of 25V change much?

Thanks a lot

 

[MikeMl]

The 15 or 40V refers to the diode's reverse breakdown voltage. In your circuit, with the battery charged to its peak voltage of ~2.5V, you will have only 2.5V reverse voltage across the diode even if the solar panel were a dead short, which it wont be.

What is the open circuit output voltage of your panel in bright sun?

 

[nic_marsa11]

Ah, so the higher the voltage the better, thanks. The Solar cells says 2 volts on it and that's all the info I've been given. In my opening statement I've an attachment which is a circuit diagram of what I've got/ planning to get. I'm wondering if i've got it connected all correctly, obviously i want the solar cell to power the capacitor, not the clock directly. Could you tell me if it's right? I'd be very grateful,

Cheers
Nic

 

[Damo666]

Ah, so the higher the voltage the better, thanks. The Solar cells says 2 volts on it and that's all the info I've been given. In my opening statement I've an attachment which is a circuit diagram of what I've got/ planning to get. I'm wondering if i've got it connected all correctly, obviously i want the solar cell to power the capacitor, not the clock directly. Could you tell me if it's right? I'd be very grateful,

Cheers
Nic

Hi Nic. In my opinion, the solar cell would charge the cap and run the clock simultaneously during daylight hours. In the evening, when there's no light - the capacitor would run the clock. This circuit is self sustaining and would work perfectly i'd say. By the way, forget Maplins. One decent place to source hard to get components in our neck of the woods is Cricklewood electronics. They sell some quite hard to source transistors, etc, etc. All the best. Damian.

 

[nic_marsa11]

cheers for the vote of confidence Damo, thats what i want to hear! I've found a shop called rs components near me. They've the capacitor but not the BAt45 diode. They've got a few at 200mA and there's a schottky barrier diode at 30mA and 4V but its not a 2 pin affair. Its a box with 3 legs, does this matter?
I'm trying to get the maths my end but its slow. Like a limping tortoise.