Hi everyone,

I would like help building an electronic circuit. The circuit consists of a charging unit (4.2v max output). A rechargeable Lith-ion battery and a light source.

The light source is a white LED (single) with the idea that the LED will be connected to a PCB that supplies power to the LED from the attached battery. The charging unit is to be detachable, rather like a mobile phone charger except in my case its a series of solar panels connected in series/parallel i.e. two pairs connected in series and then joined in parallel to give approx 4.2v output.

I am happy with the charger itself but struggling to understand what is required on the PCB in order to connect the charging unit so that it can start to charge a lith-ion battery and then what is required between the battery and the light source. I presume a resistor? a capacitor? etc. Any suggestions where I can obtain the necessary components would also be very useful.

Thank you

 

Maybe you have already read these:
http://www.batteryuniversity.com/print-partone-12.htm
http://www.powerstream.com/li.htm
Assuming battery of 4V _ 2.6V,LED,=1.4V/ .02mA= 70Ω or close =68Ω @ 1/4 W. Do not discharge below 3V. It would be helpfull to know battery capacity, solar cell open circuit V, & short circuit current.

 

Thanks Bernard for your reply; i do have some more information if you or anyone would like to offer further help.

My LED is 'super bright white' with the following spec:

Peak forward current: 100mA
Continuous forward current: 30mA
Forward Voltage (Vf): 3.2 (typical), Max 3.6V

My battery spec:

NiMH PCB mounted
Voltage: 3.6V
Capacity: 70mAh

My solar panels in direct sunlight give a respectable 4.2V output; not sure what you mean Bernard when you ask for 'Solar Cell open circuit voltage and how I would measure this? Additionally, I'm not sure what you are asking for when you mention 'short circuit current'. Could you explain/expand and once again suggest how I would measure this?

As you can probably gather. I am not very knowledgeable about this type of thing but willing to learn. I aim to arrange the components on as small a PCB as possible and include an interface for my solar powered charging unit. My question essentially remains the same, 'How do I connect these components together so that I can charge my battery which in turn provides power to my LED when I operate a switch connected to the PCB?

A diagram would be great if anyone can afford the time and produce one, once again thanks to anyone that offers any help.

 

put 2kohm or 3 kohm resistor

 

Solar cell open circuit V is measured with nothing but volt meter connected to cell, for short circuit measurment , set meter on a current range higher than expected cell output, like one amp, & connectl directly across output. Measure ahead of blocking diode if possible. Charging V will be around 70% of OC V.
A little confusion on battery type: first stated Li, now Ni ?? Sure it isn't 700mA?? One or 3 cells??
With battery & LED V so close, it would be best to measure LED V drop @ 20 mA. A LED current limiting resistor will be around 30Ω.

 

Hi,

Sorry Bernard for the battery confusion I have had to change it to the one stated i.e. a PCB Mounted NiMH rechargeable battery. The capacity is stated as 70mAh, is this going to be problem? Please click on the following link for a description off the sellers website.

http://www.maplin.co.uk/Module.aspx?ModuleNo=30958

What would I need between the charger (solar) and the battery? I am presuming that I will require some control over how the power supply is regulated, to prevent possible overcharging of the battery, would I be right in my assumption?

Unfortunately, at the moment I am away from home so cannot get the V/I measurements that Bernard suggests I take. I'll update when I'm next at home.

LED spec can be found by following this link:

http://www.maplin.co.uk/Module.aspx?ModuleNo=45923



Thanks guys for your help

 

Sorry guys, just to add to my previous post, the battery can be found as stated at the following address

http://www.maplin.co.uk/Module.aspx?ModuleNo=30958

When you arrive at the web address, go to the bottom of the page and you will find the spec for the 'BN22Y' battery. You can view the battery by ensuring that the right battery code is selected in the project range window towards the top of the page.