Lithium Ion Batteries... - Electronic Circuits Projects Diagrams Free

uksnowman · 26th January 2008, 03:50 PM

Hi Everybody

My knowledge of electronics is quite limited and was wondering if anybody can help me out.

I want to build a Solar Torch, however have been banging my head against the wall with respect to the electronics deisgn.

The solar cells will charge a Lithium Ion battery and the battery will power my LED array (5 LED's).

Very simple idea but have had complications with the charging circuits for Lithium Ion batteries.

I need a 6V supply for my LED array which draws 240mA and therfore the obvious choice would be a 7.2V Li Ion battery, however, I appreciate I need a protection PCB to prevent over charging and discharging.

The batteries I have looked at which have protection PCB's/IC's have overdischarge limits set in the region of 4V which leaves me 2V short of my required supply voltage.

Am I correct in thinking that I need to utilise a 11.1V Lithium Ion battery which has a protection PCB which limits over discharge voltage to 9V and then regulate this there after to my 6V?

Can anybody recomend an electronics outlet where I can by small solar cells and Lithium Ion Batteries with integrated protection circuits? I have spent alot of time on Battery Space but is quite expensive with respect to shipping.

Any help with the above would be very much appreciated.

Kind regards

Matt

Roff · 27th January 2008, 12:32 AM

Overdischarge limit means they will not be allowed to discharge below that voltage (e.g., 4V). When they are charged, they will be at 7.2V. I don't see why this would present a problem for you.
The problem I have had when contemplating charging Lithium Ion batteries is the complicated charging circuit required, and the catastrophic failures (flames) that have been encountered by some laptop manufacturers. Maybe some of the other guys here have experience that will be helpful.

justDIY · 27th January 2008, 04:12 AM

lithium is an expensive and tempermental battery to waste on a solar application.

go with good 'ol poisonous NiCad batteries. they'll take a lot of abuse and are dirt cheap. three in series for 3.6v and then use a constant current boost converter to drive your led string.

Oznog · 27th January 2008, 04:27 AM

Li-ion, he's right- overcharging is complicated to avoid with solar and will damage the cell way too early in its life and it can potentially catch fire.

What white LED array needs 6v @ 240mA for 5 LEDs? That's not consistent with any technology I know. Whites have a forward voltage of like 3.5v-4v usually.

New plan: one BIG LED and a single-cell NiMH and a kick-up driver. Those thing work great! Single NiMH cell won't be damaged even if you run it all the way down (with two cells one will reverse and be damaged). And like 2 or 3 series solar cells can charge that. In fact you can rip up some solar garden lights to get that.

Oznog · 27th January 2008, 04:52 AM

Actually you could use a "protected" li-ion like these:
http://www.dealextreme.com/details.dx/sku.6979

I did some asking around, I was curious what all "protected" means. I know each cell will protect against overdischarge by shutting off, but also they'll shunt voltage over 4.2V or whatever past the cell to protect against overcharge, which also may address balancing issues to boot. Really a charger should shut off completely when it reaches 4.2V and let the cell voltage drop back down but if the cell's going to shunt the extra current to limit cell voltage to 4.2V then the overcharge rate is pretty trivial- esp since you're talking about a solar panel which isn't going to put out hundreds of mA. In fact, for this type of cell, it's gonna be able to run a flashlight @250mA for like 10 hrs when charged. It'd take a week of full sun to charge it with a small panel too! You'd think in the first 10 hrs of use you'd find a wall socket at some point to top them off again.

dknguyen · 27th January 2008, 09:26 AM

Why not just use a lead-acid? They're durable and very hardy to mischarging and dead cheap. Your application isn't exactly mobile either so why bother with an expensive, high maintenance lithium battery?

uksnowman · 28th January 2008, 10:48 AM

Hi everyone

Many thanks for replies and suggestions, they are very much appreciated.

To answer a few of your questions as I feel I may have been a little vaigue in the opening question:

This is my final year university project 'The Solar' torch and I am trying to design something as 'Eco-Friendly' as possible...eco materials etc and hense I want to use a Lithium Ion batteries...

The LED array characteristics (6V 240mAh) I have obtained from testing a standard LED Torch as this is the light output I am after. The test incorporating hooking the torch up to a 6V Power Supply and measuring the load with a multi meter.

The 'over discharge' information is very interesting and appears I have mis-interpretted its meaning, if this is correct, then it should be a simple case of connecting my two 4V 100mAh Solar Cells (in series) to my Lithium Ion 7.2V 750mAh battery..

The batteries I have been looking at are as follows which come pre-wired with a protection circuit:

http://www.batteryspace.com/index.as...OD&ProdID=1340

In response to charging times..it appears approx. 10 Hours in bright sunlight will charge these batteries with monocrystalline solar cells and provide approx 3 hours burntime with the previously stated 6V 240mAh load.

My next challenge is the LED Circuit, I need a Constant, Flashing and Off functions..I have done some brief readings about 'multi-vibrator circuits' and the 555 DIL timer chips, is this my only option?

I only have a foundation in electronics and am 'learning as I go', so if anything I a have said dosen't make sense please say!!

justDIY · 28th January 2008, 03:05 PM

Nickel metal hydride batteries are far more "eco friendly" than lithium ion. The main ingredient of NiMH, nickel is easily recovered and recycled, compared to toxic cadmium or volatile lithium.

you might want to consider the new phosphate iron based lithium batteries, they are tolerant of trickle charging which is the only method you'll get from a small solar cell.

audioguru · 28th January 2008, 04:57 PM

It will take more than 10 days to get 10 hours of "bright sunlight".
But if you are in the Sahara Desert then it might take only a few days.

uksnowman · 29th January 2008, 03:56 PM

OK, so now I am lost.

Have I completley missed the point with respect to my Solar Cells?

This is what I have at present in my Solar Torch Design:

2 off 4V 100mA Solar Cells connected in Series, charging a 750mAh Battery (Say a 7.2V Lithium Ion..for arguments sake).

Say there are NO system losses and it is a bright sunny day without any shadowing obstructions. Therefore, am I correct in assuming that the solar cells will output 100mA per Hour and therefore it will take 7.5h to charge my battery.

uksnowman · 29th January 2008, 04:08 PM

Hi Everyone

I am working on an Electronics Design for a Solar Torch for a University Project.

However, my knowledge of electonics is quite weak and I don't quite know if what I have designed is actually practical....

Could you have a look at the attached Circuit Diagram and give me your opinion? I have also attached a flow chart which gives a rough idea of what I am trying to achieve.

Any critisism or alternative suggestions will be very much appreciated!!!

Kind Regards

Matt

uksnowman · 29th January 2008, 04:14 PM

Hello again

I have just posted another thread with respect to my design so far, but will put it up here for your information....

Attached is a Flow Diagram of what I am trying to achieve and the circuit schematic so far.

Any critisism or alternative suggestions will be very much appreciated as to be honest I have no idea if it can practically work!!

PLEASE BE GENTLE!!

Kind Regards

Matt

**Nigel Goodwin** · 29th January 2008, 04:17 PM

How do you expect to charge a 7.2V battery off of a 5V USB input?.

audioguru · 29th January 2008, 04:28 PM

Solar panels are rated at noon in the Sahara Desert. The sun is directly overhead in the Sahara destert and then the current will be 80mA if the solar panel points directly at the sun.
Elsewhere on earth and at different times the current is less.

Two lithium-ion cells need a total voltage of 8.4V to reach full charge. Your 8V solar cells have three series diodes reducing their max voltage to only 5.9V.

The 5V from the USB input has one diode that reduces its voltage to only 4.3V which is much too low to charge two lithium cells in series.

ronsimpson · 29th January 2008, 04:30 PM

You are wasting too much energy in R3. It is OK but a real torch would not do that.

Will a 555 drive 5x30mA=150mA?

USB in/out: 5 volts will not charge 7.2 volts and 7.2 should not go to USB out.

It is not a good idea to parallel LEDs. For a school project…OK but in production you will find that the LEDs will not share the current equally. For example my red LEDs have a voltage drop of 1.7 min. 2.0 typically and 2.2 max. If a 1.7 and a 2.2 are parallel then one gets very hot and the other is very dim. In production we sort the LEDs so all the 2.0 are together and all the 2.1 are together.

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26th January 2008, 03:50 PM	(permalink)
uksnowman	Lithium Ion Batteries... Hi Everybody My knowledge of electronics is quite limited and was wondering if anybody can help me out. I want to build a Solar Torch, however have been banging my head against the wall with respect to the electronics deisgn. The solar cells will charge a Lithium Ion battery and the battery will power my LED array (5 LED's). Very simple idea but have had complications with the charging circuits for Lithium Ion batteries. I need a 6V supply for my LED array which draws 240mA and therfore the obvious choice would be a 7.2V Li Ion battery, however, I appreciate I need a protection PCB to prevent over charging and discharging. The batteries I have looked at which have protection PCB's/IC's have overdischarge limits set in the region of 4V which leaves me 2V short of my required supply voltage. Am I correct in thinking that I need to utilise a 11.1V Lithium Ion battery which has a protection PCB which limits over discharge voltage to 9V and then regulate this there after to my 6V? Can anybody recomend an electronics outlet where I can by small solar cells and Lithium Ion Batteries with integrated protection circuits? I have spent alot of time on Battery Space but is quite expensive with respect to shipping. Any help with the above would be very much appreciated. Kind regards Matt

27th January 2008, 12:32 AM	(permalink)
Roff	Overdischarge limit means they will not be allowed to discharge below that voltage (e.g., 4V). When they are charged, they will be at 7.2V. I don't see why this would present a problem for you. The problem I have had when contemplating charging Lithium Ion batteries is the complicated charging circuit required, and the catastrophic failures (flames) that have been encountered by some laptop manufacturers. Maybe some of the other guys here have experience that will be helpful. __________________ Ron

27th January 2008, 04:12 AM	(permalink)
justDIY	lithium is an expensive and tempermental battery to waste on a solar application. go with good 'ol poisonous NiCad batteries. they'll take a lot of abuse and are dirt cheap. three in series for 3.6v and then use a constant current boost converter to drive your led string. __________________ If you don't have a planet, what good are gold bars? want to contact me directly? gmail gordonthree check out my project website: http://projects.dimension-x.net Favorite numbers: 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

27th January 2008, 04:27 AM	(permalink)
Oznog	Li-ion, he's right- overcharging is complicated to avoid with solar and will damage the cell way too early in its life and it can potentially catch fire. What white LED array needs 6v @ 240mA for 5 LEDs? That's not consistent with any technology I know. Whites have a forward voltage of like 3.5v-4v usually. New plan: one BIG LED and a single-cell NiMH and a kick-up driver. Those thing work great! Single NiMH cell won't be damaged even if you run it all the way down (with two cells one will reverse and be damaged). And like 2 or 3 series solar cells can charge that. In fact you can rip up some solar garden lights to get that. __________________ I thought what I'd do was I'd pretend I was one of those deaf-mutes.

27th January 2008, 04:52 AM	(permalink)
Oznog	Actually you could use a "protected" li-ion like these: http://www.dealextreme.com/details.dx/sku.6979 I did some asking around, I was curious what all "protected" means. I know each cell will protect against overdischarge by shutting off, but also they'll shunt voltage over 4.2V or whatever past the cell to protect against overcharge, which also may address balancing issues to boot. Really a charger should shut off completely when it reaches 4.2V and let the cell voltage drop back down but if the cell's going to shunt the extra current to limit cell voltage to 4.2V then the overcharge rate is pretty trivial- esp since you're talking about a solar panel which isn't going to put out hundreds of mA. In fact, for this type of cell, it's gonna be able to run a flashlight @250mA for like 10 hrs when charged. It'd take a week of full sun to charge it with a small panel too! You'd think in the first 10 hrs of use you'd find a wall socket at some point to top them off again. __________________ I thought what I'd do was I'd pretend I was one of those deaf-mutes.

27th January 2008, 09:26 AM	(permalink)
dknguyen	Why not just use a lead-acid? They're durable and very hardy to mischarging and dead cheap. Your application isn't exactly mobile either so why bother with an expensive, high maintenance lithium battery? Last edited by dknguyen; 29th January 2008 at 04:29 PM.

28th January 2008, 10:48 AM	(permalink)
uksnowman	Thankyou Everyone!!! Hi everyone Many thanks for replies and suggestions, they are very much appreciated. To answer a few of your questions as I feel I may have been a little vaigue in the opening question: This is my final year university project 'The Solar' torch and I am trying to design something as 'Eco-Friendly' as possible...eco materials etc and hense I want to use a Lithium Ion batteries... The LED array characteristics (6V 240mAh) I have obtained from testing a standard LED Torch as this is the light output I am after. The test incorporating hooking the torch up to a 6V Power Supply and measuring the load with a multi meter. The 'over discharge' information is very interesting and appears I have mis-interpretted its meaning, if this is correct, then it should be a simple case of connecting my two 4V 100mAh Solar Cells (in series) to my Lithium Ion 7.2V 750mAh battery.. The batteries I have been looking at are as follows which come pre-wired with a protection circuit: http://www.batteryspace.com/index.as...OD&ProdID=1340 In response to charging times..it appears approx. 10 Hours in bright sunlight will charge these batteries with monocrystalline solar cells and provide approx 3 hours burntime with the previously stated 6V 240mAh load. My next challenge is the LED Circuit, I need a Constant, Flashing and Off functions..I have done some brief readings about 'multi-vibrator circuits' and the 555 DIL timer chips, is this my only option? I only have a foundation in electronics and am 'learning as I go', so if anything I a have said dosen't make sense please say!!

28th January 2008, 03:05 PM	(permalink)
justDIY	Nickel metal hydride batteries are far more "eco friendly" than lithium ion. The main ingredient of NiMH, nickel is easily recovered and recycled, compared to toxic cadmium or volatile lithium. you might want to consider the new phosphate iron based lithium batteries, they are tolerant of trickle charging which is the only method you'll get from a small solar cell. __________________ If you don't have a planet, what good are gold bars? want to contact me directly? gmail gordonthree check out my project website: http://projects.dimension-x.net Favorite numbers: 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

28th January 2008, 04:57 PM	(permalink)
audioguru	It will take more than 10 days to get 10 hours of "bright sunlight". But if you are in the Sahara Desert then it might take only a few days. __________________ Uncle $crooge

29th January 2008, 03:56 PM	(permalink)
uksnowman	OK, so now I am lost. Have I completley missed the point with respect to my Solar Cells? This is what I have at present in my Solar Torch Design: 2 off 4V 100mA Solar Cells connected in Series, charging a 750mAh Battery (Say a 7.2V Lithium Ion..for arguments sake). Say there are NO system losses and it is a bright sunny day without any shadowing obstructions. Therefore, am I correct in assuming that the solar cells will output 100mA per Hour and therefore it will take 7.5h to charge my battery.

29th January 2008, 04:17 PM	(permalink)
Nigel Goodwin	How do you expect to charge a 7.2V battery off of a 5V USB input?. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

29th January 2008, 04:28 PM	(permalink)
audioguru	Solar panels are rated at noon in the Sahara Desert. The sun is directly overhead in the Sahara destert and then the current will be 80mA if the solar panel points directly at the sun. Elsewhere on earth and at different times the current is less. Two lithium-ion cells need a total voltage of 8.4V to reach full charge. Your 8V solar cells have three series diodes reducing their max voltage to only 5.9V. The 5V from the USB input has one diode that reduces its voltage to only 4.3V which is much too low to charge two lithium cells in series. __________________ Uncle $crooge

29th January 2008, 04:30 PM	(permalink)
ronsimpson	You are wasting too much energy in R3. It is OK but a real torch would not do that. Will a 555 drive 5x30mA=150mA? USB in/out: 5 volts will not charge 7.2 volts and 7.2 should not go to USB out. It is not a good idea to parallel LEDs. For a school project…OK but in production you will find that the LEDs will not share the current equally. For example my red LEDs have a voltage drop of 1.7 min. 2.0 typically and 2.2 max. If a 1.7 and a 2.2 are parallel then one gets very hot and the other is very dim. In production we sort the LEDs so all the 2.0 are together and all the 2.1 are together.