# charging laptop battery using solar energy

Discussion in 'The Projects Forum' started by ayane, Sep 4, 2009.

1. ### ayane Thread Starter Active Member

May 3, 2009
39
0
I had came across many solar charger products whereby they use a battery pack to store the solar energy and charge it to their laptops.

I had in mind thay i want to use the solar energy going to through regulator to charge my laptop battery.

I am using a 20w solar panel which generates a short circuit voltage of 12 to 13v and the short circuit current will generate a max of 1.6A depending on the sun intensity.

The solar panel is connected to the Dc-Dc converter and to the laptop.

I am using two sets of 4 solar cells in series connected in parallel therefore my panel consist of 8 solar cells.

The dc converts any input voltage between 12-13.8 volts to a range of 16v to 24v.

Since my compact laptop requires 18.5V , i set it to 19V, because the converter only have specific range like 18, 19 ,20etc..

The question is I was wondering why the laptop battery does charge not as the charging indicator does not light even with an solar current output of 1.10 A ?...

By the way the converter has an efficiency of about 0.85%.

Does it mean there is insufficient current to charge the laptop battery?..

I had this concept whereby any amount of current will charge the battery depending how much it takes to charge eg: trickle charge, float charge..

Correct me if i am wrong ..thx for reading...

Will adding another 4 cells in parallel solve the problem?

2. ### ayane Thread Starter Active Member

May 3, 2009
39
0
bty my laptop battery has a capacity of 4400mah

3. ### jj_alukkas Distinguished Member

Jan 8, 2009
751
5
How did you calculate that? I think it is simply 0.85 or 85% or am I wrong?

A Laptop has a digital charge monitoring circuit inside it. If the supply ain't good or doesn't have the correct current, it wont charge. They are used mainly to prevent the customer from using duplicate chargers and cause Li-ion battery explosions and also to only use their own company accessories. You can try connecting an external DC adapter of the same voltage and current rating other than your laptop's charger and see if it is charging. If it isn't, you would have to drop the plan as then, the only way to charge it would be to remove the battery and charge it, which is not safe.

4. ### ayane Thread Starter Active Member

May 3, 2009
39
0
i was told the manufacturer when i buy the efficiency of the converter is 85. The dc converter is specially designed for laptop notebooks as mentioned on the cover..

Today as i was testing, the solar cells are generating a range of current from 0.64A to 1.10A. Most of the time its generating 1.10A.

The light of the converter activates for the whole time as there is sufficient voltage..

I am curious there are some products such as solar rolls are able to trickle charge a laptop directly from the sun.

i have attached a link below:
http://www.treehugger.com/files/2008/10/7-portable-solar-laptop-chargers-worth-considering.php

5. ### t06afre AAC Fanatic!

May 11, 2009
5,939
1,222
The efficiency means that in your case 85% of the input energy is converted to energy you can use on the output. The rest is converted to non useful energy in form of heat,radiation etc.

Last edited: Sep 4, 2009
6. ### steveb Senior Member

Jul 3, 2008
2,433
469

Since battery charging is a little tricky and the engineers have already worked out the details for your particular computer and battery type, you could implement a solar powered voltage supply directly, without worrying about the battery. Allow your circuit to detect when there is enough sunlight to fully power the computer as a proper DC source, and only allow this output power to be active when full current capability is possible in direct sunlight. You would need to figure out how many cells are needed for your power requirements, including efficiency/conversion losses.

With this approach, you can use the computer, or charge the batteries, and the solar source will automatically turn on when it can perform as the equivalent to an AC/DC adapter plugged into the wall.

Although this may not accomplish all of your goals, it is the safest way to go in terms of not degrading the batteries and not injuring someone.

7. ### ayane Thread Starter Active Member

May 3, 2009
39
0
thanks for those advices. I had initially thought of powering up the laptop without the use of the battery but we need a very huge panel typically about a total of 16- 20 cells. Cost will be a factor.

Actually i am doing a research for my university's project. My main objective of the project to come out with a solar charger without an external battery pack to extend the time usage of the laptop battery.

Nevertheless, i will continue my testing tommorow to see whether i can find some solutions to the problem and update if possible..

8. ### ayane Thread Starter Active Member

May 3, 2009
39
0
Today i found certain stuffs to determine the cause.

1. Initially the Dc-Dc converter out was 18v which was insufficient, i adjust it to 19v.

2. The solar panel was able to barely charge in which the charge indicator on for about 4 seconds and off . The proccess was repeated many times. By than the current generated by the panel was about 1.2A and when its goes in the converter about 15% was lost.

3. Adding a 4 new cells in series only did increase the current to about 1.8A which also generate in the same result.

4. I did try a fully charge 7Ah lead acid battery and it was able to charge the laptop like the adaptor. I can say the current was insufficien to generate the charge.

5. I did measure the charging current from adaptor to the battery. It takes spike of about 1.7 plus Ampre to power up the laptop. After, it takes a constant of 1.072A to maintain the on status. This is without the battery.

6. When i attached the battery and measure the current flowing from the adaptor to the laptop is about 1.88A tp 2.4A whereby the laptop battery will charge. so the charging current is determine by the current measured minus 1.072A. This could varied depending of the amount of percentage the battery will charge.

Correct me if i am wrong for my observation...thx

My new plan is to use a solar controller to charge my 4Ah lead acid battery . The lead acid battery is connected to the dc-dc converter and to the laptop. Any suggestions thanks..

9. ### loosewire AAC Fanatic!

Apr 25, 2008
1,584
435
Overall the sun light wiill not be good for your computer,the sun will take your computer If you Insist on testing it abilitly regardless of spec,s the sun wins.

10. ### jj_alukkas Distinguished Member

Jan 8, 2009
751
5
If you are able to charge it using the battery, then the only way to use a solar charger is through a battery. Your panels are insufficient to provide the current which the laptop thinks is Ok to charge. So You will need to charge another battery first and then transfer it or use a bigger panel with higher current. Your last plan might work.

One other way without all this is to charge the laptop battery directly after removing it from the laptop but it is not safe at all.

11. ### ayane Thread Starter Active Member

May 3, 2009
39
0
I had tried out the second plan, it was working. I just had to take note of some pointers.

1. prevent the lead acid battery from being overcharge and discharge.

2. had to fully-charged the battery frequently ( at least one or twice monthly) to prevent it from getting permantly damage.

12. ### ayane Thread Starter Active Member

May 3, 2009
39
0
i was wondering if whether i should charge my lead acid battery till 13.8V . It seems in theory that 12.7V indicates a 100 percent charge.

When i measured the voltage without connecting any load it is 12.7V. Measurements are taken after 12 hours of charging. I supposed this is the nominal voltage.

When i connected to laptop( laptop battery 100% charge), it lasted about 5 mins before my controller cuts it off at 11.6V. The lead acid battery is acting as an ac supply as the laptop battery is fully charged

Does it mean that my lead acid battery is not fully charged?

Does it mean that my laptop draws too much current? From theory, my laptop drains about 1 plus A with just surfing and using wireless..
In that case, it should last about 1 hour plus...

Should i changed the battery to 7.5Ah supposingly the battery capacity is insufficient?..