[EE] LiPo chargers

Discussion:

[EE] LiPo chargers

Neil

2018-11-27 06:28:49 UTC

Hi all,

I'm using an MCP73833-AMI for charging a 1-cell Lipo in a project. This
specific charger is looking for a charge voltage of 4.2V, but the
voltage never gets to over about 4.09V to 4.13V (tested over several
batteries).
I'm not really worried about that last bit of charge, but the charge
status LED never goes out to indicate it's done.
FWIW, some of the batteries I'm using came with chargers whose
indicators go out after they're fully charged, but it's still around 4.1V.

Is this common, or just that I'm picking the wrong batteries? I did see
a couple 4.1V charger ICs options available, but most are 4.2V.

Anyone have a goto charger IC you'd recommend for this? I need small
size and low cost, and 1A should be fine.

Cheers,
-Neil.

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James Cameron

2018-11-27 06:45:19 UTC

Permalink

Charge termination voltage must match the specifications of the
battery. Not all lithium polymer batteries are the same; different
production processes yield different specified termination voltages.

Using a higher termination voltage than specified for a lithium
polymer battery can be exciting.

Post by Neil
Hi all,
I'm using an MCP73833-AMI for charging a 1-cell Lipo in a project. This
specific charger is looking for a charge voltage of 4.2V, but the
voltage never gets to over about 4.09V to 4.13V (tested over several
batteries).
I'm not really worried about that last bit of charge, but the charge
status LED never goes out to indicate it's done.
FWIW, some of the batteries I'm using came with chargers whose
indicators go out after they're fully charged, but it's still around 4.1V.
Is this common, or just that I'm picking the wrong batteries? I did see
a couple 4.1V charger ICs options available, but most are 4.2V.
Anyone have a goto charger IC you'd recommend for this? I need small
size and low cost, and 1A should be fine.
Cheers,
-Neil.
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Neil

2018-11-29 15:12:54 UTC

Permalink

I chose these batteries based on size, and voltage is just specified as
the nominal 3.7V...
https://www.amazon.com/gp/product/B0746JGS4T/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1

Since their charger gets the battery to only 4.1V, is it safe to assume
that that is the voltage I should be charging to? I generally don't
trust the accuracy/tolerance of these really low-cost & cheaply made
products, but I have a few of these chargers and they all charge to the
same voltage. And each one has 4 individual charging circuits, so I can
say that the 4.1V is pretty consistent over a sample size of 12.

Cheers,
-Neil.

Post by James Cameron
Charge termination voltage must match the specifications of the
battery. Not all lithium polymer batteries are the same; different
production processes yield different specified termination voltages.
Using a higher termination voltage than specified for a lithium
polymer battery can be exciting.

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Art

2018-11-29 16:28:31 UTC

Permalink

Neil et al,

I recently investigated LIPO batteries for inclusion into my latest
project.

I thought I'd try a cheap Chinese made charger/protector PCB, which are
based on a Chinese made charger chip, and the completed PCB is available
on ebay for 75 cents each! However, in reading the less than proper spec
sheet for the charging chip, I discovered the chip has float capability
and a trickle charge function!!!

LIPO batteries must not be trickle charged, so I'd encourage all
PICsters to avoid the temptation of buying Chinese chargers from EBAY
based Asian vendors.

==============

In fact, I decided not to use LIPO at all!! My latest project is an
extremely low power unit and LIPO batteries should not be stored fully
charged. Since my PIC project uses 20ua in deep sleep, I would be
effectively storing the battery fully charged because my project might
sit unused for weeks, sometimes months at a time.

However, when my project is needed, it can run at a 30 percent duty
cycle for an entire weekend at a time and uses 50 ma when in active
use....so the higher capacity of the LIPO is desirable.

But......

Rather than mess with any rechargeable battery, I concluded that
disposable alkaline batteries would likely be more appropriate.

Caveat Emptor.

GL to all on the PIClist!

Art

Post by Neil
I chose these batteries based on size, and voltage is just specified as
the nominal 3.7V...
https://www.amazon.com/gp/product/B0746JGS4T/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1
Since their charger gets the battery to only 4.1V, is it safe to assume
that that is the voltage I should be charging to? I generally don't
trust the accuracy/tolerance of these really low-cost & cheaply made
products, but I have a few of these chargers and they all charge to the
same voltage. And each one has 4 individual charging circuits, so I can
say that the 4.1V is pretty consistent over a sample size of 12.
Cheers,
-Neil.

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Neil

2018-11-29 16:44:49 UTC

Permalink

Art,

Although I am using the supplied Chinese charger during development, I
have no intentions of using it in production. For what will be maybe
100 units, it's not worth the frustration to find a Chinese charging IC.

My project needs approx 100mA - 125mA (mostly for a TFT display) when in
use, and I've set it up to completely disconnect the battery when
powered off. For its intended use, I really need a rechargeable battery
and size is very critical. The housing is not a generic box, but a thin
section with approx 7mm height available. I really wanted a 750mah
battery in there, but had to compromise with 500mah. That was probably
the single most tedious part to design.

Cheers,
-Neil.

Post by Art
Neil et al,
I recently investigated LIPO batteries for inclusion into my latest
project.
I thought I'd try a cheap Chinese made charger/protector PCB, which are
based on a Chinese made charger chip, and the completed PCB is available
on ebay for 75 cents each! However, in reading the less than proper spec
sheet for the charging chip, I discovered the chip has float capability
and a trickle charge function!!!
LIPO batteries must not be trickle charged, so I'd encourage all
PICsters to avoid the temptation of buying Chinese chargers from EBAY
based Asian vendors.
==============
In fact, I decided not to use LIPO at all!! My latest project is an
extremely low power unit and LIPO batteries should not be stored fully
charged. Since my PIC project uses 20ua in deep sleep, I would be
effectively storing the battery fully charged because my project might
sit unused for weeks, sometimes months at a time.
However, when my project is needed, it can run at a 30 percent duty
cycle for an entire weekend at a time and uses 50 ma when in active
use....so the higher capacity of the LIPO is desirable.
But......
Rather than mess with any rechargeable battery, I concluded that
disposable alkaline batteries would likely be more appropriate.
Caveat Emptor.
GL to all on the PIClist!
Art

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Art

2018-11-30 08:58:00 UTC

Permalink

Hi Neil,

You are wise not use the Chinese junk for your product, I commend you!
And, totally agree, for exactly the reasons you state. When your name is
on the product, and you care about your reputation, buying sub-standard
Chinese junk is not wise.

I am in the process of designing a PCB for my project, which will fit
inside a 26mm by 46mm by 11mm enclosure (these are outside dimensions).
So, the box is actually smaller inside::>

I don't need a fancy enclosure, and my prototype (beta version) will go
into a salvaged tuner box, from an old (very old) tv. These are no
frills and designed to be used in other larger enclosures (to house
sub-assembly's). The sheet metal is paper thin and is tin plated, so
it's not a fancy enclosure. It is designed to be lightweight, portable
and needs to be extremely rf proof (hence I used the metal box instead
of plastic).

If I do go commercial with the project, the tin plated metal box should
be very inexpensive to produce, and should be adequate for its intended
use...in other words, the enclosure would be deemed adequate by those
who might purchase it.

GL.

Art

Post by Neil
Art,
Although I am using the supplied Chinese charger during development, I
have no intentions of using it in production. For what will be maybe
100 units, it's not worth the frustration to find a Chinese charging IC.
My project needs approx 100mA - 125mA (mostly for a TFT display) when in
use, and I've set it up to completely disconnect the battery when
powered off. For its intended use, I really need a rechargeable battery
and size is very critical. The housing is not a generic box, but a thin
section with approx 7mm height available. I really wanted a 750mah
battery in there, but had to compromise with 500mah. That was probably
the single most tedious part to design.
Cheers,
-Neil.

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Neil

2018-11-30 16:02:03 UTC

Permalink

I never seem to have the luxury of lots of space... everything I design
needs to fit in a very tight enclosure. On this one, dropping from a
standard 1/16" PCB to 1/32" PCB helped a lot.,
This one will be commercial (kickstarter, with a goal of 50-100 units).
I'll send you a link offline to what it is.

Cheers,
-Neil.

Post by Art
Hi Neil,
You are wise not use the Chinese junk for your product, I commend you!
And, totally agree, for exactly the reasons you state. When your name is
on the product, and you care about your reputation, buying sub-standard
Chinese junk is not wise.
I am in the process of designing a PCB for my project, which will fit
inside a 26mm by 46mm by 11mm enclosure (these are outside dimensions).
So, the box is actually smaller inside::>
I don't need a fancy enclosure, and my prototype (beta version) will go
into a salvaged tuner box, from an old (very old) tv. These are no
frills and designed to be used in other larger enclosures (to house
sub-assembly's). The sheet metal is paper thin and is tin plated, so
it's not a fancy enclosure. It is designed to be lightweight, portable
and needs to be extremely rf proof (hence I used the metal box instead
of plastic).
If I do go commercial with the project, the tin plated metal box should
be very inexpensive to produce, and should be adequate for its intended
use...in other words, the enclosure would be deemed adequate by those
who might purchase it.
GL.
Art

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RussellMc

2018-11-30 07:29:52 UTC

Permalink

Post by Neil
I chose these batteries based on size, and voltage is just specified as
the nominal 3.7V...
<https://www.amazon.com/gp/product/B0746JGS4T/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1>
https://www.amazon.com/gp/product/B0746JGS4T/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1
Since their charger gets the battery to only 4.1V, is it safe to assume
that that is the voltage I should be charging to? I generally don't
trust the accuracy/tolerance of these really low-cost & cheaply made
products, but I have a few of these chargers and they all charge to the
same voltage. And each one has 4 individual charging circuits, so I can
say that the 4.1V is pretty consistent over a sample size of 12.
4.1V CV is wholly acceptable - and results in longer cycle life than the

more usual 4.2V.
As that is below the lowest IC programmed Vreg and as the terminate lights
never light it's not obvious what is happening.

The charger IC requires a minimum 0.3v headroom.
[ *Datasheet
<http://ww1.microchip.com/downloads/en/DeviceDoc/22005b.pdf> page 3 section
1.0, supply voltage = *VREG(Typical)+0.3V ]
What supply voltage are you using?

"Trickle" is acceptable at Vmax of < to << of Vmax (nominally 4.2V).
At 4.1V I'd want to be sure that temperature excursions would be accounted
for and at 4.0V you are probably safe to apply voltage constantly.
Constantly applied 4.2V is liable to lead to rapid cell degradation.

It does not sound as if this applies, but: If you are loading the battery
while charging and if Ichg is also supplying this load then if Iload >>
Iterminate_programmed then charging will never terminate.

Russell

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Neil

2018-11-30 15:54:35 UTC

Permalink

4.1V CV is wholly acceptable - and results in longer cycle life than the
more usual 4.2V.
As that is below the lowest IC programmed Vreg and as the terminate lights
never light it's not obvious what is happening.
The charger IC requires a minimum 0.3v headroom.
[ *Datasheet
<http://ww1.microchip.com/downloads/en/DeviceDoc/22005b.pdf> page 3 section
1.0, supply voltage = *VREG(Typical)+0.3V ]
What supply voltage are you using?

Direct 5.0V from a USB charger.

"Trickle" is acceptable at Vmax of < to << of Vmax (nominally 4.2V).
At 4.1V I'd want to be sure that temperature excursions would be accounted
for and at 4.0V you are probably safe to apply voltage constantly.
Constantly applied 4.2V is liable to lead to rapid cell degradation.

I've run several charge cycles at 1C and I can't detect any temperature
increase (as I feel it, not measured). I'm really not concerned about
temperature
And I can live with the battery life at the 4.1V it's getting up to.
Biggest concern is being able to indicate to the user when the charge is
complete.

It does not sound as if this applies, but: If you are loading the battery
while charging and if Ichg is also supplying this load then if Iload >>
Iterminate_programmed then charging will never terminate.

No load during charging. Well, it can be on when charging, but based on
how it will be used (wearable), the user should be charging when it's
powered off.

Russell

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RussellMc

2018-11-27 10:58:25 UTC

Permalink

Post by Neil
I'm using an MCP73833-AMI for charging a 1-cell Lipo in a project. This
specific charger is looking for a charge voltage of 4.2V, but the
voltage never gets to over about 4.09V to 4.13V (tested over several
batteries).

Datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/22005b.pdf

uChip evaluation kit manual:
http://ww1.microchip.com/downloads/en/DeviceDoc/51626a.pdf

uChip Reference Design:
http://ww1.microchip.com/downloads/en/DeviceDoc/51746a.pdf

What thermistor (or what else) is on THERM pin? [data sheet / spec]
(Lack of thermistor MAY alter voltage substantially).

What value of Rprog?
What charge current.
What cell used (datasheet/type/...?)

What package?
Is exposed thermal pad connected to Vss?

____________________

Related

uChip Portable Power Conversion Design Guide

http://ww1.microchip.com/downloads/en/DeviceDoc/30009610F.pdf

Cousin - 73831/2

http://ww1.microchip.com/downloads/en/DeviceDoc/20001984g.pdf

Russell

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Neil

2018-11-29 15:56:31 UTC

Permalink

I'm not monitoring temps, so I have a 10k resistor on the THERM pin as
recommended.
Rprog is 2K ... battery is 500mAH, and for now I'm charging at 1C.

So the batteries on specify the nominal 3.7V... not much else. I've
found similar-sized units on aliexpress but also with not much other
data available.

I'm using the MSOP version, which has no exposed thermal pad.

Cheers,
-Neil.

Post by RussellMc

Datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/22005b.pdf
http://ww1.microchip.com/downloads/en/DeviceDoc/51626a.pdf
http://ww1.microchip.com/downloads/en/DeviceDoc/51746a.pdf
What thermistor (or what else) is on THERM pin? [data sheet / spec]
(Lack of thermistor MAY alter voltage substantially).
What value of Rprog?
What charge current.
What cell used (datasheet/type/...?)
What package?
Is exposed thermal pad connected to Vss?
____________________
Related
uChip Portable Power Conversion Design Guide
http://ww1.microchip.com/downloads/en/DeviceDoc/30009610F.pdf
Cousin - 73831/2
http://ww1.microchip.com/downloads/en/DeviceDoc/20001984g.pdf
Russell

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