How to charge Li-ion cells

[H2SO4]

I have from one and a half laptop batteries eleven 3.8 volt Li-Ion Cells. the battery had a 8 pin power conencter and without a shcematic i had only one choice, rip the protection circuitry out. Now i know that was stupid, on account their Li-Ions. So now i have 11 great cells which i need to charge. But how, and how safely.

[H2SO4]

heres the cells

[5614]

Do you know what voltage the charger gave?

 

I'd suggest take one and try charing it with a 9V battery for starters. The charger for a laptop I've got has an output of ~18V.

 

You got 11 of them... wire one up and see what happens.

 

Remember they'll probably be pole sensitive ie. make sure you connect the positive/negative the right way round!

[H2SO4]

I charged one up to 4 volts with my 280mah 1-13 volt charger. But now i have another problem. Im planning to take all these and wire them in parallel and series to goet a 12 volt battey. Then put it in a box with a small 95 watt dc-ac 120 volt inverter, so i cvan have a "silent" low power generator. But how would i charge it? Basicaly to this psu it would be liek a short circuit.

[alt_f13]

1-13 volt charger? Wouldn't it work the same way if they were connected the way you want them to be?

[5614]

I don't get what your prob is now.

 

Connect the cells up to form your battery and it will look something like this:

where the black are the cells, the red is to a circuit (whatever you are powering) and then you the blue leads would be to the charger.

 

You shouldn't have the red and the blue connected at the same time, but this is the same with many rechargable batteries, you have to turn the item off before charging its battery.

 

ps. admire the Paint skillz

[Bettina]

What I learned in school is that each cell is rated at 3.7v....

 

The caution here is that they should ONLY be charged with a LIPO charger.....no other kind will do because they could explode.

 

Also, if any cell drops below 3v, it is ruined and won't charge again....

 

Just FYI..... and be careful

 

Bettina

[H2SO4]

Im sorry when i said 1-13 volt charger i meant power supply. Ive successfuly charged a few, but Im not sure if their actualy charged correctly, like if they will still give me their full amperage. I usualy do this out in the backyard on concrete so if it blows its not gonna do anything. I left one out on accident and it overcharge and it was totaly ruined, but no leaking or anything. 5614 that is exactly how i was thinking to wire them. The paint skills are incredible. I dont have a current meter, so what should i connect to a cell to see if it will give me its full 1500 mah? Lets say i conect a motor which drains 1500 mah, will the battery run it for 1 hour if it is charged?

[5614]

no other kind will do because they could explode

Ah! I've just found what to do with the batteries of an old laptop I have lying around

 

Relating that more seriously: if you (H2SO4) had 11 cells originally, have destroyed one but only need 9 for your battery then you still have 1 more to destroy... may it die in style! Unless you like connected it to 240V AC I doubt it would actually blow up, you're only charging it with a max of 13V.

 

Lets say i conect a motor which drains 1500 mah, will the battery run it for 1 hour if it is charged?

That certainly works in theory. May as well try it. Before I got a multimeter I used to attach an LED just to see if there was a decent voltage (I could tell approx. according to the brightness) but I got a multimeter now so gone are the old days! I never had to measure the current. Is there one at school you could use or borrow?

 

Also say it took 1hr to charge one battery, I'm not sure how long it would take to charge an array of 3x3.

[H2SO4]

Im guessing id need a high amperage charger to charge more than one in a parralell and series circuit, liek the one you described. But no, i do not have an current meter. And im on summer vacation so i do not have access to one. Im guessing it would take just alot longer to charge an array of 3x3, but my charger only delivers 300 mah, so surely after awhile i would blow the power transistor.

 

 

Ok so heres another question concerning my power supply. If i took a voltage regulator such as the lm317 and swapped it out with the low power power transistor, would the psu most liekly work and deliver much more current? Im wondering if instead of buuilding a new one, i might just swap the power transistor. The one that is in their is relatively low power

[herme3]

Li-ion cells can be quite dangerous. I've heard that if they explode, you should never clean it up with water. If you use a wet paper towl or cloth, I've heard that it will burn you very badly because the contents react with water.

 

There was something else I was reading that explained why you should never use a Li-ion cell without the protective circuitry. I can't remember what it said. Does anyone else know?

[Externet]

Each cell must be charged independently by itself. If they are all healthy, can be charged in parallel.

To charge, connect a regulated supply of exactly 4.1000 Volts at any current that cells will not get warm with.

Miguel

[5614]

What happens if you charge them in series with 4.1001V across each one?

 

I don't see an issue charging in series as long as you have the correct voltage across each cell (and therefore a bigger battery voltage). I also don't think that degree of accuracy is required for the voltage. ~4V should be fine.

[Externet]

If 4.1001 V are applied to charge that Li-ion cell, it would be a violation of the manufacturer specifications to charge such cell.

 

There is other chemistries of Li-ion, 4.2000 V is the voltage for those. As the question does not specify which, am answering on the safe side.

 

--->..." I don't see an issue charging in series as long as you have the correct voltage across each cell "...

 

And how will you ensure that on a series connection ?

 

Miguel

[Pangloss]

I figured out how to recharge my worn-out Li-ion battery-powered cell phone today: I went to the Sprint store and asked them for a new phone, got one for free, had them transfer my phone number and contacts to the new phone, and walked out the door. ;-)

[5614]

If 4.1001 V are applied to charge that Li-ion cell' date=' it would be a violation of the manufacturer specifications to charge such cell.

 

There is other chemistries of Li-ion, 4.2000 V is the voltage for those. As the question does not specify which, am answering on the safe side.[/quote']We're talking about making our own charger here. If we make a home made charger which supplies 4.1001V then surely the batteries would charge fine? And lets talk about Li-ion batties that are meant to have a 4.1001V to charge them with.

 

What I'm saying is that you said he should charge them with 4.1000V and I'm saying I don't think it matters whether it is 4V or 4.2V and that he certainly does not need to be accurate to 4 decimal places when creating his home made charger.

 

And how will you ensure that on a series connection?

I would assume they all have equal resistances and so if I wanted 4V across 2 cells in series I would attach an 8V voltage across them. Whilst in reality they will have fractionally different resistance, but as far as I can see this is insignificant.

[Externet]

Hello 5614

 

..."We're talking about making our own charger here"... -->Yes, apply 4.100v to each cell.

If you want to make it 'not-home-style'; pick the chip of choice:

 

http://search.national.com/iphrase/query?query=liion+charger&render=1&categories=Product+Folders

 

 

..."I don't think it matters whether it is 4V or 4.2V"... --> Yes, it matters.

The voltage has to be the one matching the cell chemistry; If too high; degradation takes place; if too low, will not reach full charge.

That is why circuitry inside battery packs are so precise, microcontrolled.

 

..."I would assume they all have equal resistances"... -->Wrong assumption.

 

Miguel

[5614]

..."I would assume they all have equal resistances"... -->Wrong assumption

 

It was a simplification I made because I, apparently incorrectly, assumed that when charging you did not need to be as precise as 3 decimal places.

 

If you do need to be that accurate then the assumption is wrong at that detailed level. I assume this is what you mean.

 

Whereas if you only needed about 4V (and something like 4.2V was alright too) then the differences in resistances of a few "identical" lithium ion cells is small and could be assumed as neglibible.