Charging my $8 Lithium Transmitter Battery

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Re: Charging my $8 Lithium Transmitter Battery

Postby prong » Fri Aug 05, 2011 1:41 pm

Thanks for the info - I'm learning heaps but there's still a lot to learn.

Excuse my ignorance but how do you charge the cells individually when they are hard wired into a 2 cell pack? Do I need to seperate the cells again?

I've been setting up and programming my radio and have had it switched on for quite a while. I'm not sure if I managed to get my pack fully charged last time - it did seem to take a while, but when I put it in my radio it showed 7.9V. After 3 or 4 hours it had dropped to 7.4V. I've just put it on the charger again and it's currently charging at 0.8A and one cell is showing 4.20V and the other 4.05V. How close to the same should they be when they are balanced?
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Re: Charging my $8 Lithium Transmitter Battery

Postby bmsweb » Fri Aug 05, 2011 9:18 pm

prong wrote:Excuse my ignorance but how do you charge the cells individually when they are hard wired into a 2 cell pack? Do I need to seperate the cells again?


If you're using a Charger like the Turnigy Accucell 6 from HK then all you do is use the leads that have the Alligators on the end and connect them to either end of each cell ignoring the other cell. So positive to positive and negative to the negative of the cell. Once I did that I just set the charger to 1S and charged them at 1amp. Just don't short anything out ;)

Hope this helps.
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Re: Charging my $8 Lithium Transmitter Battery

Postby kaptain_zero » Fri Aug 05, 2011 10:56 pm

If the Alligator clips have nothing much to clip on to, I just use a couple of those small rare earth magnets. They will normally stick to most 18650 cell ends and the alligator clips will stick to the magnets. As bmsweb said, make sure you don't short anything out... NEVER a good idea when playing with Lithium cells.

Regards

Christian

As for cell balance, I like to see both cells at the same voltage.... so 4.20 and 4.20, but it's not a perfect world and so I can imagine something like 4.18 and 4.16 being reasonable. 4.15 and 4.05 is not terrible but it's not something I would be happy with.

The discharge curves on Lithium Ion cells is not linear..... by the time a cell goes from 4.2v fully charged to it's nominal 3.6v there is maybe 10% left of the charge and you should not continue to use it without charging first.... well.... unless you're model is still in the air.... if it is, land it asap and then charge that battery back up. :mrgreen:

The big danger with unbalanced cells is that if it gets far enough out of whack.... and the protection circuit does not kick in..... that lithium cell could turn into a terrorist cell..... [poof].
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Re: Charging my $8 Lithium Transmitter Battery

Postby prong » Sat Aug 06, 2011 1:01 pm

Thanks Paul and Christian. My $8 Lithium battery seems to be fully charged and reasonably balanced now. I'll check them next time I'm charging and see how they look. If they are unbalanceds I'll follow your advice and try charging them individually.

Christian, these cellas are nominally rated at 3.7V so wouldn't the pair still have a reasonably amount of juice left at 7.4V? I've set my low voltage warning on my transmitter at 6.6V. I seem to remember Bruce mentioning this voltage in the guide. Are you saying that is too low?

I didn't do the resistor mod on my Turnigy 9X, just upgraded the firmware to er9x which allows me to set the warning voltage to anything I like.

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Re: Charging my $8 Lithium Transmitter Battery

Postby kaptain_zero » Sat Aug 06, 2011 7:53 pm

The nominal voltage listed is 3.7v, but at 3.6v there is only about 10% of the charge left. Remember, when you charge Lithium Ion cells in 2 hours, the first hour the voltage will slowly increase to the maximum permissible of 4.2v, after that it's usually about another hour of constant 4.2v charging but with steadily decreasing amperage. Thus the discharge of such a cell is not linearly followed by the voltage. In use, the voltage drops slowly to begin with... when the cell is almost exhausted, the voltage suddenly begins to fall at a rapidly increasing rate...

As for the alarm setting using er9x, I have read there is a hardware issue inside the 9x radio that if you set the warning too low.... and I'm going by fuzzy memory here, anywhere below about 7.2v or something like that, the radio will not give you a warning because that particular circuit does not detect any drops past the 7.2v. Again, we're talking my useless memory here.... you would be much better off searching the 9x/er9x threads over on RCgroups as I am pretty sure that's where I read about the problem and possible hardware fix (I just never bookmarked it....<sigh>). Personally, I have set my radio to warn me when it hits 7.4V. This leaves plenty of juice to land my aircraft with a nice safety margin. Charging my pack after that is only kinder to the cells and will help them last much much longer than draining them down to the bitter end.

Just use your balance charge setting with a balance harness every so many charges.... the individual cell charge is just to get them both to the same level if they are waaaay out when you build the pack... it should not be necessary to do that again, once done.... If it does become necessary again... I'd suspect a faulty cell.

Regards

Christian
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-- Pablo Picasso
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Re: Charging my $8 Lithium Transmitter Battery

Postby kaptain_zero » Mon Aug 08, 2011 4:11 am

So I found the thread I was referring to when it comes to the 2s lipo voltage issue. Take the time to read, not just the first post, but the following ones as well, you will find the description of the problem and how to deal with it. For those who can't be bothered to read it, but want to know what's going on... it's all about the voltage regulators inside the 9x. As I understand it, the stock regulators need 2V more than the required 5V out to function. This means that you need a minimum of 7V out of your pack. As some have noted, a 2S pack is not empty at 7.0V, but for me personally... it's close enough. While I've had my warning set to 7.4v, I think I'll drop it to 7.2v and test it to make sure that it warns me before it's too late. One may need to calibrate the voltage reading in er9x and that calibration setting is in er9x, but you need known good volt meter to calibrate against.

http://www.rcgroups.com/forums/showthread.php?t=1413832


Regards

Christian
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Re: Charging my $8 Lithium Transmitter Battery

Postby Sid Sideslip » Thu Sep 08, 2011 2:41 am

OK, my pack got the Connection Break Error before it finished charging (I think it was around 59%, maybe a bit less).

Anyway, I've just measure the two cells and one is at 4.02 volts and the other is significantly lower at 3.84 volts. The pack gives a total of 7.84 volts.

I've posted up photos of my balance lead connector, which is I think is wired up correctly. Let me know if I'm wrong there.

Should I maybe charge the cells separately for starters, given how far out they are atm?

Edit: Having read through the thread again I decided to individually charge the cells. I got the Connection Break error on the first cell at 90 mins charging @ .5amp, 92% charge completed and 4.12 volts. I'll charge the second cell and see how that goes.

Image

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Re: Charging my $8 Lithium Transmitter Battery

Postby Sid Sideslip » Thu Sep 08, 2011 7:28 am

OK, I've charged both cells individually now and (apart from the dog interrupting proceedings by jumping up and pulling an alligator clip off during the second charge) they have both finished.

Both cells interrupted charging with a disconnect error under the nominal 4.2v cut-off at 4.09v for one cell and 4.1v for the other. Both registered "93% charged" on my particular charger.

Tx powers up nicely and reads 7.8volts, so all good for now.

Er, except I'm still picking bits of hot glue out of my jumper. :roll:
What goes up...better bloody stay up (until I say otherwise).
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Re: Charging my $8 Lithium Transmitter Battery

Postby bmsweb » Thu Sep 08, 2011 7:36 am

Mine took a while to charge individually, but once I got both to 4.20, eventually the charger stopped with the message Full! Once I got both of the cell fully charged it all works perfectly. Mine charge to full simply using the balance lead now.
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Re: Charging my $8 Lithium Transmitter Battery

Postby kaptain_zero » Thu Sep 08, 2011 9:05 pm

Just a quick thought, Sid. Do you have a multimeter kicking around? I'd be curious to see the actual charge voltage coming out of that charger, particularly just before the disconnect error message. To me it sounds like the protection circuit on the cell is kicking in due to excessive voltage. Then again, these cheap batteries/protection circuits don't have the best reputation for quality control, though I have not run across too many bad ones. I've had 2 bad circuits and one bad cell (this was a premium one no less) so it can happen and this is over about 30 - 40 odd lithium cells of varying sizes. I use 10440, 14500, 17670, 18650 and RCR123a... to name a few.

A separate Digital Multi Meter aka DMM should show what's going on. I know the charger measures voltage, but we need a "second opinion" from another meter as things are behaving strangely. If the DMM reads markedly different, something is up and a third, known to be accurate, DMM, should be called in to settle the issue of "Is it the Charger or the Cells or.....?"

Looking at your picture, the balance plug is wired correctly, but I cannot vouch for your soldering as I can't really see it that well.

Regards

Christian
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