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Old 22nd August 2013, 12:56 PM   #1
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Default Problems with 12V Li-ion battery from Ebay

Hi,

I have bought one of those cheap 12v batteries you can get on Ebay, and a TA2020 amp from indeedhifi (yes, I know its cheap junk!!). My problem is the charge circuit attached to the battery, which causes the terminal voltage to drop as soon as I turn on the amplifier. I Think the charge circuit simply wont allow High currents in order to protect the battery, but as the amp has a large power supply cap, a High inrush current occurs everytime I turn on the amplifier.

I have tried to remove the circuit, which do solve solve the turn on problem, but then there is no battery protection. (I have no external battery charger, but use the power supply the came with the battery).

Has anyone used the cheap batteries and found a Way to fix this problem?
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Old 22nd August 2013, 01:33 PM   #2
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Can you give some details about the battery.

LiION batteries by nature are capable of high currents. Look at how many of them are used in battery powered tools for example.
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Old 23rd August 2013, 06:26 AM   #3
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You can try adding a soft start circuit so that the battery protection does not kick in.

Gajanan Phadte
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Old 23rd August 2013, 12:54 PM   #4
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I dont know much about the battery, except its chinese and it should be Li-ion battery:


The charge circuit looks like this:
Click the image to open in full size.
I really dont know how it works, but it somehow limits the output currrent by. I have tried to remove the charge circuit and use a 500mA power supply to make a "direct charging", but as a result some gas were produced inside the vacuum sealing, as can be seen in this picture:
Click the image to open in full size.

I thought the 500 mA was a fairly safe to chage the battery at, am I totally wrong?
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Old 23rd August 2013, 01:12 PM   #5
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LI Batteries should be charged, like lead acid, at 1/10th of the rated value but the voltage must be capped at the fully charged battery rate, to avoid damage.
Discharge rates don't really count.
So a 5Ah battery at 12volts should charge at 500mA and be capped at 14volts..
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Old 23rd August 2013, 06:19 PM   #6
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The battery is rated to 6800mAh so I should be allright with 500mA, but its chinese so I dont know what to make of that. Further, it is rated to nominal voltage 10.8 V. I just figured, that the battery would be "capped" when the terminal voltage reached the power supply voltage of 12.6 V?
Notning has explodded yet, but it seems risky to keep charging the battery when it swells up like that, or what do you think?
The battery consistant of three cells of each 3.6 V nominal coupled in series, and was completely discharged before at started charging. (I know you're not suppose to do that, but I accidently left the amplifier turned on) The weird thing is, that two of them did swell up and reached at terminal voltage of 4.2V, whereas the third remained uncharged and still vacuum sealed. Any reason why they do not charge uniformly?
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Old 23rd August 2013, 06:20 PM   #7
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Sorry for the large pictures btw....
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Old 26th August 2013, 04:14 AM   #8
dangus is offline dangus  Canada
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Maybe starting the amp with a small resistor in series would fool the protection board. Or, maybe you can get a different protection module with a higher current limit.

I'd be tempted to start over with some 18650 cells salvaged from laptop or tool battery packs, and stick them in a 3S1P protected battery holder, or with a 3S1P PCM. Here's one with a 4A limit, less than $4 with free shipping. http://www.fasttech.com/products/103...d-for-3-cell-r There's also an 8A PCM, presumably for 3S2P batteries.

Or, use a 12V 7AH sealed lead-acid battery, which may not cost much more than the holder alone. And is easier and safer to charge.

Or, use 10 NiMH cells salvaged from a tool battery.

If you're going to charge unprotected lithium cells, invest in a smart hobby charger. The iMax B6 can be bought on eBay for around $20. They'll charge and cycle lead-acid, nicad, and NiMH as well.

Last edited by dangus; 26th August 2013 at 04:35 AM.
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Old 26th August 2013, 06:32 AM   #9
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I suggest you properly dispose of that swollen cell,quickly. DO NOT puncture it.
Fire=Bad.
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Old 4th October 2013, 05:33 PM   #10
haggis is offline haggis  United Kingdom
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The pcb shown in your picture is for cell protection. It's supposed to protect against overcharge( usually 4.2V max per cell) and excess discharge(2.75V per cell. Some do over temperature and short circuit protection.

Cells in a battery pack are not identical. The lowest capacity cell charges first and will go into overcharge/swell/burst into flames. This can happen at lower voltages than 3x4.2V eg 12.6.

In this case there would not appear to be any charge circuit or capacity balancing required for a Li-on series cell battery pack.

This pack and the way it's used is fundamentally unsafe and a significant fire hazard. Don't use it.
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