Charge a three cell LiPo

[bestcallumuk]

Hi, I want to buy this: SparkFun Electronics - Polymer Lithium Ion Batteries - 6Ah three cell LiPo 6Ah battery. It has three cells. If you look at the bottom of the page where it says "Similar Products" it shows the "LiPoly Charger - Single Cell 3.7-7V Input" and "LiPoly Fast Charger - 5-12V Input" but in the description they say charges one cell. How do you charge it? Thanks in advance.

 

[bestcallumuk]

Hi, I want to buy this: SparkFun Electronics - Polymer Lithium Ion Batteries - 6Ah three cell LiPo 6Ah battery. It has three cells. If you look at the bottom of the page where it says "Similar Products" it shows the "LiPoly Charger - Single Cell 3.7-7V Input" and "LiPoly Fast Charger - 5-12V Input" but in the description they say charges one cell. How do you charge it? Thanks in advance.

Also, something to stop the LiPo catching alight when discharged too low. Thanks again.

 

[bestcallumuk]

Hi, I want to buy this: SparkFun Electronics - Polymer Lithium Ion Batteries - 6Ah three cell LiPo 6Ah battery. It has three cells. If you look at the bottom of the page where it says "Similar Products" it shows the "LiPoly Charger - Single Cell 3.7-7V Input" and "LiPoly Fast Charger - 5-12V Input" but in the description they say charges one cell. How do you charge it? Thanks in advance.

Missed something, I would like to charge it via USB.

 

[bestcallumuk]

Could I use a zener diode to stop the battery catching alight? How can I do this?

 

[bestcallumuk]

Another thing, a battery voltage monitor on a LCD. Actually on second thought no LCD, what about a red LED?

 

[Hero999]

The simplest way is to use a voltage regulator with an output voltage of 4.2V per cell and a current limit of <0.5C

The charge current should be reduced if the cell voltage is under 3V per cell the current should be reduced to 0.1C so you need to add a resistor if the charger doesn't do this automatically.

Fire can be prevented by using a battery protection system and the safest way is to buy a professionally designed charger.

 

[bestcallumuk]

The simplest way is to use a voltage regulator with an output voltage of 4.2V per cell and a current limit of <0.5C

The charge current should be reduced if the cell voltage is under 3V per cell the current should be reduced to 0.1C so you need to add a resistor if the charger doesn't do this automatically.

Fire can be prevented by using a battery protection system and the safest way is to buy a professionally designed charger.

Sorry, I forgot to say, I'm a complete beginner! How would I do this?

 

[Hero999]

Sorry, it's not a project for a complete beginner.

EDIT:

If you don't know what you're doing then buy a Li-ion charger. Li-ion batteries can explode and catch fire if charged incorrectly so making a charger for your first real project, is not a good idea.

 

[Chippie]

Lithium poly batteries are completely different in chemistry to Nimh or Nicd...

The charging regime is Constant Current Constant Voltage....anything else will result in the batteries being damaged and a risk of personal injury from the ensuing fire. There are designs on the web for making simple chargers but what you describe is something far more ambitious, beyond the ability of a complete novice.

Chargers are specifically designed to cease charging when the pack reaches its terminal voltage, 12.6v in the case of a 3 cell pack. ...the cells need to be balanced to one another too...the difference between cells should not be more than 20mV. Ideally use a balance charger or a charger with an external cell balancing unit
They should not be allowed to fall below 3v per cell when being discharged

I use lipo packs in my model aircraft so I know what I am talking about...

 

[Hero999]

Here's a link to a charger for the batteries you've linked to.
Smart Charger (3.0 A) for 12.8V (4 cells) LiFePO4 Battery Pack, 110-240VAC with Trail-Tech Male plug

 

[bestcallumuk]

...There are designs on the web for making simple chargers but what you describe is something far more ambitious, beyond the ability of a complete novice...

What about just a simple charger for 3 cells and (possibly, not strictly needed but would be nice) a red LED for low power. I NEED something to stop it catching fire, for some reason I don't think catching fire is a good idea.

 

[bestcallumuk]

Here's a link to a charger for the batteries you've linked to.
Smart Charger (3.0 A) for 12.8V (4 cells) LiFePO4 Battery Pack, 110-240VAC with Trail-Tech Male plug

I may try that, thanks! So there is no way to USB charge even if it's very slow? If not is there a cheaper way? I live in the UK so a UK plug would be nice but any other would be fine, I'll find one of them converter-me-bobs.

 

[audioguru]

Nobody read the ad. The battery has 3 cells in parallel!
It charges like a single cell and is 4.2V when fully charged.
Many Lithium-Ion cell phone and laptop batteries I took apart also have cells in parallel. I re-wired them in series and they power my electric RC model airplane.

You need a charger for a 6Ah Lithium-Polymer single cell battery. It will automatically turn off when the battery is fully charged. You also need a protection circuit that prevents a fire if the battery has a current too high (maybe if it is shorted) and disconnects it when its voltage drops too low.

Lithium burns with a very hot white flame like magnesium in flares. Water on it makes the fire burn hotter.

 

[Hero999]

No, a USB port isn't powerful enough.

Hang on a second, I read the cells in the link you posted and they're in parallel not series and the charger I linked you to is for four cells in series.

Here's a charger for the battery you linked to.
Smart Charger (6.0A) for 3.2V (1cells) LiFePO4 Battery Pack, 100-240VAC, CE listed

I don't know of a UK supplier, I got that site form a US member.

EDIT:
I hate the way this site doesn't warn you when someone else posts while you're editing.

It looks like audioguru noticed and clicked the reply button before me.

 

[audioguru]

Do not use a charger designed to charge a LiFePo battery for the Li-Po battery because it has a much lower output voltage and the Li-Po battery will be no where near fully charged.

 

[Hero999]

Do not use a charger designed to charge a LiFePo battery for the Li-Po battery because it has a much lower output voltage and the Li-Po battery will be no where near fully charged.

Yes, you're right, I got the battery chemistries confused.