mccpi
Posts: 34
Joined: Sat Jun 16, 2018 5:16 am

Confused by LiPo CutOff voltage and the DW01 protection IC

Fri Aug 17, 2018 6:04 pm

Hi,

I am a little confused.
The WeMOS battery shield provides a efficient boost converter and and a charger circuit but with no overdischarge protection.

My 1000mAh LiPo cell (such a silvery pouche-thingy) has a DW01 based protection board.
According to the datasheet of the DW01, it disconnects the LiPo from the load, if the voltage
drops below 2.5 V -- which in most cases is under load.

But: While the voltage of a LiPo should not fall below 3.0V according to a couple of sources of the internet.
The wikipedia even mentioned 3.3V as the cut off voltage ("Entladeschlussspannung" <german>).

The DW01 is THE protection chip used in those silvery cells. Otherwise I would tend to believe the internet sources
or the wikipedia.
But because the differences are nearly 1V between both maxima I think, that I did something wrong.

But: WHAT is correct? Is it sufficient and LiPo-life-preserving to totally trust the DW01 protection circuitry
of the cell?

Thank you very much for any help on this...

Cheers!
mcc

Brandon92
Posts: 501
Joined: Wed Jul 25, 2018 9:29 pm
Location: Netherlands

Re: Confused by LiPo CutOff voltage and the DW01 protection IC

Fri Aug 17, 2018 6:27 pm

Could it be possible if you attach the datasheet and what for kind of product you are using (link). Also, if possible, the datasheet of you current battery?

Because when i searches for "WeMOS battery shield" if find others with a other chip on it.

mccpi
Posts: 34
Joined: Sat Jun 16, 2018 5:16 am

Re: Confused by LiPo CutOff voltage and the DW01 protection IC

Fri Aug 17, 2018 6:52 pm

Hi,

I am unsure of copyright issues this may have or not...so I will put links
to the informations instead:

The WeMOS battery shield:
https://wiki.wemos.cc/products:d1_mini_ ... ery_shield
(This has no protection circuitry at all.)
A video about this shield (review/testing/data)
https://www.youtube.com/watch?v=aND0j2Y2IkM
(GreatScott ist testing version 1.1 of that shield. My shield and that one linked above are of version 1.2!)

The DW01 protection IC (this IC is on the tiny PCB in top of the LiPo cell behind the orange Capton tape part...not on the WeMOS shield!)
https://cdn.sparkfun.com/assets/learn_t ... et_V10.pdf

The LiPo battery I bought (data is in Chinese, sorry. But scroll down - there is a hint about the usage of the DW01)
https://www.aliexpress.com/item/3-7V-10 ... 10372.html

The Wikipedia-Article talking about 3.3V cut of voltage:
https://de.wikipedia.org/wiki/Entladeschlussspannung
(The englisch version of that page does not have the same information. "Entladeschlsusspannng" ist german for "Cuttoff voltage")

Cheers!
mcc

Brandon92
Posts: 501
Joined: Wed Jul 25, 2018 9:29 pm
Location: Netherlands

Re: Confused by LiPo CutOff voltage and the DW01 protection IC

Fri Aug 17, 2018 7:21 pm

Thanks for the information.
If I use google translate that picture, the ("Entladeschlussspannung" <german>) is 2.75V for this battery. So I expat that at that value, you cant get energie out of the battery.
mccpi wrote:
Fri Aug 17, 2018 6:04 pm
drops below 2.5 V -- which in most cases is under load.
What for kind of load are you using.

mccpi
Posts: 34
Joined: Sat Jun 16, 2018 5:16 am

Re: Confused by LiPo CutOff voltage and the DW01 protection IC

Sat Aug 18, 2018 3:40 am

Hi,

currently I use a Raspberry Pi Zero W (connected via Wifi, so Wifi is on) as load.
What confuses me is, that there are so many different values are given for the cut off voltage of LiPo
cells, which all works with the same kind of chemistry.

A company selling LiPo cells is interested in producing cells with a high capacity for lower production costs.
Specifying a lower cut off voltage (as may be advisable) will give more useable capacity (may be for the cost
of a shorter lifetime of the LiPo cell...but that happens the cell is already sold).

I am trying to figure out, what cut off voltage is advisable based on physical reasons -- not based on marketing reasons.
But takeing the highest mentioned cut off voltage (say 3.3V, wikipedia) blindly is as wrong as taking the lowest value blindly
-- on the other end of the scale.

Please dont get me wrong here: I don't accuse any company for giving wrong technical data here. The premissions are simply
different: I dont want fires :) and a long living LiPo cell and the company want to sell as many cells as possible for as less production
costs as possible. This is called capitalism :)
(And: NO, I am no communist, despite the fact, that I used the word "capitalism" :) :) :)

Without harming the lifetime of my LiPo cell and without the risk of a fire: Can I solely rely on the cut off mechanism of the
DW01-PCB in the cell ... or is it kind of "last resort if anything else fails" ?

Cheers
mcc

Brandon92
Posts: 501
Joined: Wed Jul 25, 2018 9:29 pm
Location: Netherlands

Re: Confused by LiPo CutOff voltage and the DW01 protection IC

Sat Aug 18, 2018 11:43 am

Okey, you load is not to much.
mccpi wrote:
Sat Aug 18, 2018 3:40 am
A company selling LiPo cells is interested in producing cells with a high capacity for lower production costs.
Specifying a lower cut off voltage (as may be advisable) will give more useable capacity (may be for the cost
of a shorter lifetime of the LiPo cell...but that happens the cell is already sold).

I am trying to figure out, what cut off voltage is advisable based on physical reasons -- not based on marketing reasons.
But takeing the highest mentioned cut off voltage (say 3.3V, wikipedia) blindly is as wrong as taking the lowest value blindly
-- on the other end of the scale.
The correct voltage should always be precedent in the datasheet of the product. And I think, I guess, that between different methode / form factor have different voltage. When I take a look at this battery (Li-polymer), datasheet. It has the same voltage as you battery.

When I take a look this battery (Li-ion), datasheet its a bit different.
mccpi wrote:
Sat Aug 18, 2018 3:40 am
Without harming the lifetime of my LiPo cell and without the risk of a fire: Can I solely rely on the cut off mechanism of the
DW01-PCB in the cell ... or is it kind of "last resort if anything else fails" ?
If safety is a imported to you, why are you buying a battery that doesn't provide you all the information. And (possible) from on unknown brand.
Unfortunately, I can't answer that question. Because I'm not a expert on this.

mccpi
Posts: 34
Joined: Sat Jun 16, 2018 5:16 am

Re: Confused by LiPo CutOff voltage and the DW01 protection IC

Sat Aug 18, 2018 1:33 pm

If safety is a imported to you, why are you buying a battery that doesn't provide you all the information. And (possible) from on unknown brand.
Unfortunately, I can't answer that question. Because I'm not a expert on this.
...because it is my very first LiPo I bought...

Brandon92
Posts: 501
Joined: Wed Jul 25, 2018 9:29 pm
Location: Netherlands

Re: Confused by LiPo CutOff voltage and the DW01 protection IC

Sat Aug 18, 2018 2:11 pm

Okay.

To give you some idea's that you could do.
I think it's smart to monitor, by you pi or a dedicated ic, the voltage of you battery. And if you want to make it even better, also the current. So you can calculate how much energie there is still in you battery.
But if you only measure the voltage, you can set at a certain level. I don't want to take more energy from the battery. So, you pi decide that it's is better to shutdown itself. And "spare" the battery the (possible) over-discharge.

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Imperf3kt
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Location: Australia

Re: Confused by LiPo CutOff voltage and the DW01 protection IC

Sun Aug 19, 2018 11:58 pm

You can 'safely' discharge a LiPo down to 0v if you wish, but don't expect to be able to recharge it.

The reason you see different cut-off values, is because of slight chemical differences between batteries. The exact figure, should be provided by your supplier, if it isn't, I'd suggest anywhere from 2.9v to 3.2v
If you want maximum longevity, go with 3.2v
If you want maximum run time, go with 2.9v.
Don't go below 2.65v, after this point it becomes dangerous to recharge the battery.
Stop plugging your fan directly into the GPIO 5v
https://www.electronics-tutorials.ws/power/transient-suppression.html

hippy
Posts: 3919
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: Confused by LiPo CutOff voltage and the DW01 protection IC

Mon Aug 20, 2018 5:53 pm

mccpi wrote:
Sat Aug 18, 2018 3:40 am
Without harming the lifetime of my LiPo cell and without the risk of a fire: Can I solely rely on the cut off mechanism of the DW01-PCB in the cell
"No" would be my one word answer.
mccpi wrote:
Sat Aug 18, 2018 3:40 am
... or is it kind of "last resort if anything else fails" ?
My understanding is that this is "last resort", a failsafe. Once the LiPo drops to 2.4V the DW01 will disconnect the battery, not allow it to be used or charged.

You probably will be safe allowing the LiPio to discharge to the level the DW01 renders that battery unusable for safety reasons but it is not a sensible thing to do. Your battery lifetime will be limited to how long you run it before it drops to 2.4V. After that it's 'game over' for that battery.

Even if you don't reach that level, dropping towards it will increase the risk of fire when you try to recharge it.

I am surprised the battery shield you have has no low-voltage protection. I would suggest finding one which does or looking at adding some other mechanism to prevent under-voltage.

As to what cut-off to use: I too would suggest 3.2V. You can go higher if you want to be safer but that will reduce its run-time. You can go lower if your battery allows it. I would tend towards adopting the "better safe than sorry" principle.

hippy
Posts: 3919
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: Confused by LiPo CutOff voltage and the DW01 protection IC

Mon Aug 20, 2018 6:42 pm

A further note on cut-off voltage: If you look at a typical LiPo discharge curve you will find it decreases slowly then 'falls off a cliff edge' as illustrated here -

https://www.dronaaviation.com/wp-conten ... 00x225.png

That fall is common to most LiPo batteries and is so rapid that it doesn't really matter much where you set the cut-off. If the cut-off is set high you will likely only lose a small percentage of run-time, and the higher you set it the safer you will be.

For most cases a slightly reduced run-time will be more preferable to the greatly increased risk of damage or fire by setting the cut-out lower.

If you are a battery expert with the tools and experience to perfectly set the optimal cut-out it may be different, but most people will not have that expertise and will gain little apart from increasing the risk of fire.

mccpi
Posts: 34
Joined: Sat Jun 16, 2018 5:16 am

Re: Confused by LiPo CutOff voltage and the DW01 protection IC

Tue Aug 21, 2018 3:34 am

Hi,

the curve is of a Nokia BL5C, which is a Li-Ion accumulator...not a LiPolymere.

Cheers
mcc

hippy
Posts: 3919
Joined: Fri Sep 09, 2011 10:34 pm
Location: UK

Re: Confused by LiPo CutOff voltage and the DW01 protection IC

Tue Aug 21, 2018 9:55 am

mccpi wrote:
Tue Aug 21, 2018 3:34 am
the curve is of a Nokia BL5C, which is a Li-Ion accumulator...not a LiPolymere.
It was illustrative as most batteries will be similar. Most batteries have discharge curves with a slow decline then an over the cliff edge drop as they approach the end of usable charge -

http://www.philohome.com/batteries/discharge-750.gif

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