Solar Li-ion battery charger

[camerart]

Hi,

I am building a portable amateur radio kit, into a redundant hand drill case, approx 1Ft square X 4inches.

I have solar cell 6" x 6" 0.5V 8W. These can be cut/divided to give o.5v but less watts, then joined to give the correct voltage range.

I have buck converters for upping the voltage.

I have protected? Li-ion cells 18650. I want to make a 12v pack with a set while a second pack is charging.

My main concern is charging Li-ion cell safely, and would like to know how to charge these cells safely, please. I think the buck converters are able to keep the variable solar voltage at a set level, but I am yet to test this.

Cheers, Camerart.

 

[BradtheRad]

Li-on cells require more care when charging, as compared to nicads or Nimh type.

You should see if you can find a way to string sufficient solar cells together so they will charge the battery pack directly at a safe current.
I get the idea your solar cell calculates to produce .5 A at 16 V (if you cut it into 32 pieces).
That may be capable of charging a 12V pack, however you must not exceed the safe figure for the size Lion cells you are using.

Whatever you end up doing, it will depend on how these factors interrelate:
* how much current your radio draws
* what voltage it operates at
* how many hours per day you will operate it
* how much current is safe to charge your batteries
* how fast your solar panel can charge them
* how long is your charging session

There's a chance you can get by on less than 12V. That is, if your radio needs higher current and less voltage, rather than the opposite.

 

[amayilsamy]

Kindly sent Solar cell voltage , current and battery current capacity. Then only we can choose the topology like Linear, Buck , Boost,etc..

 

[camerart]

Li-on cells require more care when charging, as compared to nicads or Nimh type.

You should see if you can find a way to string sufficient solar cells together so they will charge the battery pack directly at a safe current.
I get the idea your solar cell calculates to produce .5 A at 16 V (if you cut it into 32 pieces).
That may be capable of charging a 12V pack, however you must not exceed the safe figure for the size Lion cells you are using.



Whatever you end up doing, it will depend on how these factors interrelate:
* how much current your radio draws
* what voltage it operates at
* how many hours per day you will operate it
* how much current is safe to charge your batteries
* how fast your solar panel can charge them
* how long is your charging session

There's a chance you can get by on less than 12V. That is, if your radio needs higher current and less voltage, rather than the opposite.

I know how to string the cells together, but I'm looking for advice on the materials to use, UV front, and rear panel, so they are stiff enough not to break the cells.

I have buck converters to change the voltage.

Regarding charging Li-ion battery, this must be done expertly, with upper and lower voltage limits.

Cheers, Camerart.

- - - Updated - - -

Kindly sent Solar cell voltage , current and battery current capacity. Then only we can choose the topology like Linear, Buck , Boost,etc..

Forgive me for correcting you, but I think you mean: "Kindly send solar cell voltage and current, also battery current capacity."

If I'm correct, then the answer is: I can make the solar panel how I want to, but I imagine the output will be 5V and 4Watts, then through a buck converter?. The battery cells are 18650 joined together into what ever suits. The radio uses 12V and up to 2.5 Amps, this will be used when possible.

Regards, Camerart.

 

[Externet]

Dividing a single 6" x 6" solar cell will give you big problems. They are very fragile and you will end with unuseable shattered pieces of different sizes not worth wiring them in series, even if you are an expert in attaching wires to them. Do not do it.
Find a panel with 30 or more cells providing about 20 V and use a "whatever volts in ---> 14 volts out" dc to dc converter and use a lead acid battery instead.

If you still want to use Li-ion cells, the solar panel should be around 8 volts and the dc to dc converter should be a "whatever volts in to 4.1 volts out". The li-ion cells have to be removed from its battery holder and recharged in parallel. When fully charged, can be put back in series into use as a 12 volt battery.

 

[BradtheRad]

I know how to string the cells together, but I'm looking for advice on the materials to use, UV front, and rear panel, so they are stiff enough not to break the cells.

The bare crystalline solar cells I have worked with are more fragile than glass. They should have a backing that is unbendable (example, 3/16 inch plywood).

The cells should not be attached directly to the backing. Instead they should be in contact with something soft, which is stuck to the backing. (Example, paper towel.)

The adhesive should consist of a spot of glue, which will allow you to pull off the cell later if necessary.

The resulting assembly should be lightweight. Its edges should have cushions of some kind. This will minimize impacts to the solar cells.

It will be a major challenge to cut up a solar cell exactly on long straight lines. Unless you have a laser, or high-speed water jet, etc. Next best tool is a tiny grinding wheel. Tedious.

I found it nearly impossible to solder wires to my solar cells. It worked to use conductive liquid silver. The wires should be thin and flexible, maybe 30 gauge. You want the wire to bend, because the solar cell does not.

First I attached wires to either side of the cell, with a dab of water-base glue 1/2 inch from the stripped end. When dry, I flowed the liquid silver onto the bare end of the wire, to bond it to the solar cell. Any stress should pull on the glue bond, not the electrical bond.

Add a second wire to handle the current if it is too much for one wire. 30 gauge wire can carry 1/4 A, according to the chart:

http://amasci.com/tesla/wire1.html

 

[camerart]

Sorry for this late reply, thanks for your reply.

 

[pmadithya]

Hello,

Could anyone provide me a schematic or charging ic to charge a Li ion battery 11.1V,5.2Ah using 10W solar panel. Panel Specs - Maximum Power Voltage- 17.5 ,Maximum Power Current (A) - 0.57.