Idea on how to test if battery has protection circuitry

[Rick Law]

I have an old Nokia 2G locked phone that I had no use for.  The battery is BL-5C (little retangular box kind).  I want to make use of it, but how I use it will depend on if the battery has protection circuit.

The one way I can think of checking is to discharge it to below 2.4V and see if it cuts off.  I need to discharge that to perhaps as low as 2.3V.  A protection circuit I removed from a StarTac battery cuts out at about 2.35-2.36V.

But, as I understand, discharging it to 2.4V is not really healthy for a battery.  So, I am in search of a better way to check if it has protection circuitry.

Ideas, anyone?

[SeanB]

It does have it, all cellphone batteries that are removeable ( at least the lithium ones) have the protection circuit in there. Only ones that do not are the dodgy mystery ones that you buy in a shady shop, which come in a plain pack with the phone model scribbled on it, and where you might be able to fit it in the actual phone with only a little work, but even most of those have the protection on the cell.

Simple test, are the contacts gold plated PCB material, then they are part of the protection board in the end. Otherwise simply charge it with a 5V supply and a series 1R resistor, and check the voltage is 4V3 for the most part, then rises to 5V and the current drops to zero at the same time.

[RoGeorge]

Nokia BL-5C certainly does have a protection circuit embedded in the battery.

To test this, you can discharge it while watching for the protection circuit cutoff. It should have protection for under-voltage, over-voltage, over-current and over-temperature. I tested myself for the first 2 and they worked just fine, even for a badly damaged battery. Even the Chinese clones (without the Nokia hologram stamp) I tested had them. Never tested thought for over-current (like a short circuit) or over-temperature, so I'm not sure about how well they work.

[KD0CAC John]

Ok so you guys say he doesn't need in this application .
What about answering the question in the title of the thread ?

[pyroesp]

What about answering the question in the title of the thread ?

To test this, you can discharge it while watching for the protection circuit cutoff. It should have protection for under-voltage, over-voltage, over-current and over-temperature.

[joseph nicholas]

While dumpster diving I found a cheap li-po battery someone threw away.  I tore it open, and found the circut potection board malfunctioned but the battery was in working condition. 

[Rick Law]

Since there appears to be no better way, I decided to just discharge to test.

Yeah, there is protection.  The BL-5C cuts off at 2.0V.  On my UT61E log, the reading was 2.072V before it drops to 0V.  Curious why it is so low.  At 2.0V, the battery is already over-discharged, but I suppose at least it limits the damage.

[RoGeorge]

Yeah, there is protection.  The BL-5C cuts off at 2.0V.  On my UT61E log, the reading was 2.072V before it drops to 0V.  Curious why it is so low.  At 2.0V, the battery is already over-discharged, but I suppose at least it limits the damage.

All battery protections are just for faulty or critical situations. The daily use must not trigger any protection. As an example, a mobile phone will shutdown itself somewhere between 3.2V ... 3.5V, long before the 2.0V under-voltage protection will trigger.

[Rick Law]

Yeah, there is protection.  The BL-5C cuts off at 2.0V.  On my UT61E log, the reading was 2.072V before it drops to 0V.  Curious why it is so low.  At 2.0V, the battery is already over-discharged, but I suppose at least it limits the damage.

All battery protections are just for faulty or critical situations. The daily use must not trigger any protection. As an example, a mobile phone will shutdown itself somewhere between 3.2V ... 3.5V, long before the 2.0V under-voltage protection will trigger.

Under normal operation, you are right, the phone will shut down.  But he whole point of the protection circuit is in case there is a problem.  In case there is a problem, this protection will discharge till 2.0V which is not really healthy for the battery.  If they are throwing in the money to make a protection circuit, why make an almost useless one?  I imagine 2.0V cutoff vs 2.4V cutoff should not represent a great cost delta.

My theory now is, there may be something wrong with this battery's protection circuit.  May be it was made with sub-par parts, or may be it is just age.

Back when phone was new, I brought an extra battery - carried around during trips in case I am out of juice and far from AC plug.  May be I will discharge that one to see if that one is also 2.0V cut off.  Kind of not want to knife the other battery in the heart since that is tested to have almost full nominal capacity, but I am curious.

[RoGeorge]

Indeed, 2.0V is very low. The battery from the charts posted before has triggered at 2.27V (pointed by the blue cross). Other batteries I have shutoff at about the same voltage, the lowest one being 2.15V. The lowest allowed voltage also depends with temperature. I saw in datasheets that some protection chips have slightly (digitally) adjustable trigger values around the expected minimum and maximum voltage.

[rs20]

Why is everyone ignoring this suggestion?:

...Otherwise simply charge it with a 5V supply and a series 1R resistor, and check the voltage is 4V3 for the most part, then rises to 5V and the current drops to zero at the same time.

[Rick Law]

Why is everyone ignoring this suggestion?:

...Otherwise simply charge it with a 5V supply and a series 1R resistor, and check the voltage is 4V3 for the most part, then rises to 5V and the current drops to zero at the same time.

I did not ignore it.  This was not applicable for me - I was looking at the more basic over-discharge function.  I should have thank him tho...  That I did forgot.

I have in my drawer protection boards that do over discharge only, and protection boards that do both over-volt charge and over discharge.  This method is testing over volt charge only -  some of the protection board I have would fail this test (they are discharge protection only).  (Been there, done that.  Tried over-volt with my over-discharge protection only boards.  It wont react.)

[vealmike]

Why is everyone ignoring this suggestion?:

...Otherwise simply charge it with a 5V supply and a series 1R resistor, and check the voltage is 4V3 for the most part, then rises to 5V and the current drops to zero at the same time.

What happens if you try to overcharge a Li-ion without a protection circuit to stop you?

[vealmike]

Yup.
It's a method of ascertaining that your now useless battery did not have a protection circuit, with the added bonuses that it may also demonstrate the uselessness of fire extinguishers on Li-ion AND provide totally new household furnishings courtesy of your home contents insurer.

But other than that, it should work.

[SeanB]

Yup.
It's a method of ascertaining that your now useless battery did not have a protection circuit, with the added bonuses that it may also demonstrate the uselessness of fire extinguishers on Li-ion AND provide totally new household furnishings courtesy of your home contents insurer.

But other than that, it should work.

I think the original post meant to monitor intensively when charging the battery under test. Once it gets very hot, or its voltage goes beyond 4.3V, cut off power immediately.
It will be plain stupidity to do this in a non-monitored fashion.

Yes, monitor like you would a pot of boiling oil on a gas stove. How many houses have burnt down because somebody went out leaving a pot on the stove. This is the same, just generally a pouch phone battery just will go pop if not constrained. So watch it, monitor voltage and current and you will see the sudden drop as the controller turns off the charge switch. When you disconnect the charge the cell voltage will be readable as the controller will still have the discharge switch turned on, and as soon as the cell voltage drops below full it will turn on the charge switch as well.

Shorting a cell to see if it has protection is not a good idea, you never want to rely on the controller switch being able to break a high current, and often the traces on the board will blow open as well before it trips. That is there as final protection, nothingf else, the pack is not warrantied to work after it is used, just not to burn.

[vealmike]

Sorry but it's not a good suggestion on many levels. Suggesting it on a beginners forum where the advisee (is that a word) is unlikely to know better is just plain dangerous.
 
You're not adhering to the constant current followed by constant voltage charge method. The cell manufacturer is expecting charge current to taper off when the terminal voltage equals the charge termination voltage. At the point where the cell designer was expecting a 10mA charge current, the suggested method is bunging in 700mA. That's a difference between 0.043W and 3W and that's assuming a 4.3V charge termination voltage, which neither of us knows is correct.

At this point, the cell isn't charging any more. It's depositing Lithium on the anode, it's heating, internal pressure is rising. The internal CID means you should get away with this (CID trips, cell is useless but safe), but that doesn't make it a sensible thing to do.

I tried explaining gently with (I hope) a little humour so as not to cause "loss of face". Hopefully this time there's enough here to put anyone off trying this.

[Rick Law]

Why is everyone ignoring this suggestion?:

...Otherwise simply charge it with a 5V supply and a series 1R resistor, and check the voltage is 4V3 for the most part, then rises to 5V and the current drops to zero at the same time.

What happens if you try to overcharge a Li-ion without a protection circuit to stop you?

Best case: getting hot.
Average: vent.
Worst case: explode and fire.

Valuable reminder.

I have mostly use over-discharge protection circuit only - because at the time when I got my stock, they don't have that dual (over discharge + over volt charge) protection at the amperage I wanted.  At first I was concerned but after a couple of years, I got comfortable.  I had a very bad case of "Familiarity Breeds Contempt" now cured by this chain of replies.  Thanks guys.

[amyk]

One overdischarge (and 2V is not much as far as overdischarging goes) won't kill it, as long as you charge it immediately afterwards. In fact this article shows that storing them completely empty(!) leads to the longest life:

http://jes.ecsdl.org/content/163/9/A1872.full
http://jes.ecsdl.org/content/163/9/A1872/F2.large.jpg

https://www.eevblog.com/forum/projects/diagnosing-lithium-cells/ is also worth a read, and there are various stories of sub-2V cells (which have been in that condition for an unknown length of time) being OK after charging. AFAIK brief excursions down there are fine, it's letting the cells sit in that state which causes damage.

Charging batteries, especially if you're doing testing, should not be done near anything combustible anyway, and preferably in a flameproof container.

[vealmike]

It depends on the chemistry. In a Li-ion cobalt cell I'm using. The CID seems to go somewhere below 2.2V.

The cells gas on over discharge as well as over charge. Gassing means a loss of electrolyte, which means a permanent loss of capacity. So you are partly right, the longer you leave it, the worse it gets.

If you have a series pack (without balancing) over discharging REALLY screws with cell balance and will lead to early life failure due to cycling (that was a fun 6 months of my life.)

[jazer]

What's the general opinion of ganging multiple protected cell phone cells in parallel for greater capacity?

Can the protection circuitry be expected to handle capacity differences between the cells (identical cells, but with normal variability), or is this just a Bad Idea (tm)?

[amyk]

Lions are usually paralleled without protection, and the protection applies to the pack as a whole. Nevertheless, ensure the voltages are very closely matched before connecting them together, and they will stay matched and behave as one cell.