How to charge 3.6VDC battery with DC Power Supply

J

jg

Guest
I have a few Rayovac Camcorder 3.6V/2500 mAh batteries that I want to
charge. These were originally charged with a camcorder that I do not
have. However, I have the next best thing. I have a DC Power Supply
(BK Precision 1660A) with both voltage control and current control.
Basically I can set this bad boy to output any volt and current
combination. I have tried charging the batteries at 4.0v and 100mA
and let them charge for about 3 hours. Batteries never got hot (which
to me would indicate that they were never really charged.) When I
first unplug them, they register about 3.6v. However after a day or
so, their voltage drops to 2.6v or so.

So... I am either not charging them up completely or they are no
longer functional. However, these batteries were never put in
production. They are old, but they were still in original packaging
as of a few days ago.

Any help greatly appreciated.

jg
 
"jg" <juangarcia@sacbeemail.com> wrote in message
news:a0bea318-05c8-47bb-8dc0-a61815ecf97e@z10g2000prh.googlegroups.com...
I have a few Rayovac Camcorder 3.6V/2500 mAh batteries that I want to
charge. These were originally charged with a camcorder that I do not
have. However, I have the next best thing. I have a DC Power Supply
(BK Precision 1660A) with both voltage control and current control.
Basically I can set this bad boy to output any volt and current
combination. I have tried charging the batteries at 4.0v and 100mA
and let them charge for about 3 hours. Batteries never got hot (which
to me would indicate that they were never really charged.) When I
first unplug them, they register about 3.6v. However after a day or
so, their voltage drops to 2.6v or so.

So... I am either not charging them up completely or they are no
longer functional. However, these batteries were never put in
production. They are old, but they were still in original packaging
as of a few days ago.

Any help greatly appreciated.

jg
Click to expand...
It would help to know what type of batteries you have.

Tom
 
On Mon, 1 Mar 2010 23:59:19 -0800 (PST), jg
<juangarcia@sacbeemail.com> wrote:

I have a few Rayovac Camcorder 3.6V/2500 mAh batteries that I want to
charge.
Click to expand...
That'll be a Li-Ion battery, judging by the voltage.

I have tried charging the batteries at 4.0v and 100mA
and let them charge for about 3 hours. Batteries never got hot (which
to me would indicate that they were never really charged.)
Click to expand...
Li-Ion batteries don't get very hot during normal use. At such a
gentle charge current, you'd not be able to detect a temperature rise
at all with bare hands. To get the correct charge voltage, you'd have
to check the data sheet, but 4.1V or 4.2V are the normal voltages for
Li-Ion batteries. Be very careful to avoid overcharging them, or
they'll catch fire.

When I
first unplug them, they register about 3.6v. However after a day or
so, their voltage drops to 2.6v or so.
Click to expand...
A certain amount of self-discharge is normal. That looks bit too much,
though.

So... I am either not charging them up completely or they are no
longer functional.
Click to expand...
At 4.0V you are probably not charging them completely, and 100mA for 3
hours is only 300mAh, so that is definitely not enough to completely
charge them.

They are old, but they were still in original packaging
as of a few days ago.
Click to expand...
Li-Ion batteries die of old age. High temperatures or incorrect charge
level shortens life. Ideal storage charge is normally specified at
about 50-60%.

If your batteries are more than 3 years old, they're probably pretty
much dead.
--
RoRo
 
Robert Roland wrote:
On Mon, 1 Mar 2010 23:59:19 -0800 (PST), jg
juangarcia@sacbeemail.com> wrote:

I have a few Rayovac Camcorder 3.6V/2500 mAh batteries that I want to
charge.

That'll be a Li-Ion battery, judging by the voltage.

-- snip --
Click to expand...

Could be three Ni-Cd in series, though.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
 
jg wrote:
I have a few Rayovac Camcorder 3.6V/2500 mAh batteries that I want to
charge. These were originally charged with a camcorder that I do not
have. However, I have the next best thing. I have a DC Power Supply
(BK Precision 1660A) with both voltage control and current control.
Basically I can set this bad boy to output any volt and current
combination. I have tried charging the batteries at 4.0v and 100mA
and let them charge for about 3 hours. Batteries never got hot (which
to me would indicate that they were never really charged.) When I
first unplug them, they register about 3.6v. However after a day or
so, their voltage drops to 2.6v or so.

So... I am either not charging them up completely or they are no
longer functional. However, these batteries were never put in
production. They are old, but they were still in original packaging
as of a few days ago.

Any help greatly appreciated.
Click to expand...
The correct charge cycle depends heavily on the battery type. Chances
are you've either got three NiCd (or NiMH) cells in series, or one LiPo
cell. The charge profile for NiCd and NiMH are quite similar -- with
care you can use the same charging algorithm for both. The correct
charge profile for a LiPo cell is completely different (and completely
wrong) for NiCd/NiMH, and visa versa.

So, your first step is to figure out your battery chemistry. Without
that first step, there is no second step.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
 
jg wrote:
So, your first step is to figure out your battery chemistry. Without
that first step, there is no second step.

They are NiMH. Battery pack is made up of 3 cells. Each one rated at
1.2v, for a total of 3.6v. (I have actually opened up one of the
packs. They are the same height as AA and about 20% fatter.)

So would it be OK to push to 4.2 vdc and set max current to something
like 200mA? I would prefer formulas rather than a straight answer.
(Teach me how to fish.)
Click to expand...
The classic way to charge NiMH batteries is either with a constant
current for a good long time (this works a lot better with NiCd
batteries, but you can get away with it on NiMH if you don't charge at
too high a rate and if you're willing to accept a shortened cell life),
or charge with a constant current until the cell voltages stop rising
(NiCd battery cell voltages actually peak and then drop, NiMH batteries
technically peak, but really discernibly just plateau). Fancy chargers
pulse the current, and measure the cell voltage between pulses, looking
for a peak and/or plateau.

Charging at capacity / 10 hours is the rule of thumb for 'slow charging'
-- so 250mA for your 2500mAh capacity pack. You can 'fast charge' at
higher rates, but _only_ if you're using a peak detect circuit, and what
the fast charge rate can be depends on the particular battery.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
 
"jg" <juangarcia@sacbeemail.com> wrote in message
news:517619b5-7eca-4e54-b462-836f4afd2721@y7g2000prc.googlegroups.com...

So, your first step is to figure out your battery chemistry. Without
that first step, there is no second step.
Click to expand...
They are NiMH. Battery pack is made up of 3 cells. Each one rated at
1.2v, for a total of 3.6v. (I have actually opened up one of the
packs. They are the same height as AA and about 20% fatter.)

So would it be OK to push to 4.2 vdc and set max current to something
like 200mA? I would prefer formulas rather than a straight answer.
(Teach me how to fish.)

---------------------
The cell size is 4/5A, about 1500 to 2000 milliAmphour
Standard charge is 1/10 capacity (150mA) for 14 hours.
It's more than 10 hours because charging efficiency is not 100 percent.

Do not let the cells get over 40 degrees C on charge. Heat is not good to
NiMH
You can charge faster as long as the cells don't overheat.
Faster charge profiles require more careful design, with thermal safetys.
 
So, your first step is to figure out your battery chemistry.  Without
that first step, there is no second step.
Click to expand...
They are NiMH. Battery pack is made up of 3 cells. Each one rated at
1.2v, for a total of 3.6v. (I have actually opened up one of the
packs. They are the same height as AA and about 20% fatter.)

So would it be OK to push to 4.2 vdc and set max current to something
like 200mA? I would prefer formulas rather than a straight answer.
(Teach me how to fish.)

jg
 
On Tue, 02 Mar 2010 08:52:24 -0800, Tim Wescott <tim@seemywebsite.now>
wrote:

Could be three Ni-Cd in series, though.
Click to expand...
It never even struck my mind. Thanks.
--
RoRo
 
On Tue, 2 Mar 2010 11:45:05 -0800 (PST), jg
<juangarcia@sacbeemail.com> wrote:

They are NiMH.
Click to expand...
In that case, forget everything I said in my earlier post.

So would it be OK to push to 4.2 vdc and set max current to something
like 200mA? I would prefer formulas rather than a straight answer.
(Teach me how to fish.)
Click to expand...
NiMH (and also NiCd) cannot be charged based on absolute voltage.
Their voltage is not predictable enough, and also changes very little
as the charge level changes.

There are several ways to charge NiMH batteries. The simplest one is
to charge them with a constant current for a specific amount of time.
You can only use this method if you know the charge level before you
start charging, which, in practice, means you must fully discharge the
battery before you start charging it. If you cannot find the data
sheet, a safe bet is to charge at C/10 (a current corresponding to one
tenth of the battery's capacity, 250mA in you case) for 14 hours. New
batteries should be overcharged considerably the first time in order
to "activate" all of the electrolyte. 24 hours is usually recommended.

You can configure your lab power supply to be a constant current
charger: Set the voltage higher than the battery voltage will ever
reach, but not so high that you make big sparks when you connect the
leads. I'd say 10-12V is OK. Then set the current limit to 250mA and
charge for the specified amount of time. At this charge rate, you
won't ruin the battery if you leave it connected for a couple of days,
but overcharging will slowly kill the battery even at this rate.

If you want to charge partially discharged batteries, you need a more
intelligent charger. As Tim says, watch the voltage while you charge,
and when the voltage stops rising, you're done. This method relies on
the internal temperature of the cells to change, so it will not work
reliably if you charge very slowly.
--
RoRo
 
jg wrote:
---------------------
The cell size is 4/5A, about 1500 to 2000 milliAmphour
Standard charge is 1/10 capacity (150mA) for 14 hours.
It's more than 10 hours because charging efficiency is not 100 percent.

Do not let the cells get over 40 degrees C on charge. Heat is not good to
NiMH
You can charge faster as long as the cells don't overheat.
Faster charge profiles require more careful design, with thermal safetys.

Thanx, what about voltage? More than 3.6v right?
Click to expand...
More than enough to keep the battery charging at the intended current.
I can't recall the exact number for a NiMH cell, but you want
significantly more than 1.25V/cell -- 1.5V/cell is probably the bare
minimum. Set the voltage to 12V and let the current limit do it's job,
maybe.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
 
---------------------
The cell size is 4/5A, about 1500 to 2000 milliAmphour
Standard charge is 1/10 capacity (150mA) for 14 hours.
It's more than 10 hours because charging efficiency is not 100 percent.

Do not let the cells get over 40 degrees C on charge. Heat is not good to
NiMH
You can charge faster as long as the cells don't overheat.
Faster charge profiles require more careful design, with thermal safetys.
Click to expand...
Thanx, what about voltage? More than 3.6v right?

jg
 
On Mar 2, 11:54 am, Tim Wescott <t...@seemywebsite.now> wrote:
jg wrote:
So, your first step is to figure out your battery chemistry.  Without
that first step, there is no second step.

They are NiMH.  Battery pack is made up of 3 cells.  Each one rated at
1.2v, for a total of 3.6v.  (I have actually opened up one of the
packs.  They are the same height as AA and about 20% fatter.)

So would it be OK to push to 4.2 vdc and set max current to something
like 200mA?  I would prefer formulas rather than a straight answer.
(Teach me how to fish.)

The classic way to charge NiMH batteries is either with a constant
current for a good long time (this works a lot better with NiCd
batteries, but you can get away with it on NiMH if you don't charge at
too high a rate and if you're willing to accept a shortened cell life),
or charge with a constant current until the cell voltages stop rising
(NiCd battery cell voltages actually peak and then drop, NiMH batteries
technically peak, but really discernibly just plateau).  Fancy chargers
pulse the current, and measure the cell voltage between pulses, looking
for a peak and/or plateau.

Charging at capacity / 10 hours is the rule of thumb for 'slow charging'
-- so 250mA for your 2500mAh capacity pack.  You can 'fast charge' at
higher rates, but _only_ if you're using a peak detect circuit, and what
the fast charge rate can be depends on the particular battery.

--
Tim Wescott
Control system and signal processing consultingwww.wescottdesign.com
Click to expand...
Thanx, I'll try this over the weekend as I want to be awake to monitor
for heat. Still wondering what the voltage should be though.
 
On Mar 2, 2:05 pm, Robert Roland <f...@ddress.no> wrote:
On Tue, 2 Mar 2010 11:45:05 -0800 (PST), jg

juangar...@sacbeemail.com> wrote:
They are NiMH.

In that case, forget everything I said in my earlier post.

So would it be OK to push to 4.2 vdc and set max current to something
like 200mA?  I would prefer formulas rather than a straight answer.
(Teach me how to fish.)

NiMH (and also NiCd) cannot be charged based on absolute voltage.
Their voltage is not predictable enough, and also changes very little
as the charge level changes.

There are several ways to charge NiMH batteries. The simplest one is
to charge them with a constant current for a specific amount of time.
You can only use this method if you know the charge level before you
start charging, which, in practice, means you must fully discharge the
battery before you start charging it. If you cannot find the data
sheet, a safe bet is to charge at C/10 (a current corresponding to one
tenth of the battery's capacity, 250mA in you case) for 14 hours. New
batteries should be overcharged considerably the first time in order
to "activate" all of the electrolyte. 24 hours is usually recommended.

You can configure your lab power supply to be a constant current
charger: Set the voltage higher than the battery voltage will ever
reach, but not so high that you make big sparks when you connect the
leads. I'd say 10-12V is OK. Then set the current limit to 250mA and
charge for the specified amount of time. At this charge rate, you
won't ruin the battery if you leave it connected for a couple of days,
but overcharging will slowly kill the battery even at this rate.

If you want to charge partially discharged batteries, you need a more
intelligent charger. As Tim says, watch the voltage while you charge,
and when the voltage stops rising, you're done. This method relies on
the internal temperature of the cells to change, so it will not work
reliably if you charge very slowly.
--
RoRo
Click to expand...
Excellent. Thanx Robert, this is exactly the info I was looking for.
I have about 10 of these. Eventually they will find their way into RC
boats. Kids are going to love having the extra batteries.

Thanx again.
 
jg wrote:
On Mar 2, 2:05 pm, Robert Roland <f...@ddress.no> wrote:
On Tue, 2 Mar 2010 11:45:05 -0800 (PST), jg

juangar...@sacbeemail.com> wrote:
They are NiMH.
In that case, forget everything I said in my earlier post.

So would it be OK to push to 4.2 vdc and set max current to something
like 200mA? I would prefer formulas rather than a straight answer.
(Teach me how to fish.)
NiMH (and also NiCd) cannot be charged based on absolute voltage.
Their voltage is not predictable enough, and also changes very little
as the charge level changes.

There are several ways to charge NiMH batteries. The simplest one is
to charge them with a constant current for a specific amount of time.
You can only use this method if you know the charge level before you
start charging, which, in practice, means you must fully discharge the
battery before you start charging it. If you cannot find the data
sheet, a safe bet is to charge at C/10 (a current corresponding to one
tenth of the battery's capacity, 250mA in you case) for 14 hours. New
batteries should be overcharged considerably the first time in order
to "activate" all of the electrolyte. 24 hours is usually recommended.

You can configure your lab power supply to be a constant current
charger: Set the voltage higher than the battery voltage will ever
reach, but not so high that you make big sparks when you connect the
leads. I'd say 10-12V is OK. Then set the current limit to 250mA and
charge for the specified amount of time. At this charge rate, you
won't ruin the battery if you leave it connected for a couple of days,
but overcharging will slowly kill the battery even at this rate.

If you want to charge partially discharged batteries, you need a more
intelligent charger. As Tim says, watch the voltage while you charge,
and when the voltage stops rising, you're done. This method relies on
the internal temperature of the cells to change, so it will not work
reliably if you charge very slowly.
--
RoRo

Excellent. Thanx Robert, this is exactly the info I was looking for.
I have about 10 of these. Eventually they will find their way into RC
boats. Kids are going to love having the extra batteries.

If you don't mind spending the $$ get a peak-detect charger at your
Click to expand...
local hobby shop. Or look around and see if there are any used ones on
Craigs List -- there are probably still some electric fliers that are
converting to LiPo and have an old NiCd only charger around, or who are
upgrading.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
 
On Tue, 02 Mar 2010 15:42:21 -0800, Tim Wescott <tim@seemywebsite.now>
wrote:

If you don't mind spending the $$ get a peak-detect charger at your
local hobby shop. Or look around and see if there are any used ones on
Craigs List -- there are probably still some electric fliers that are
converting to LiPo and have an old NiCd only charger around, or who are
upgrading.
Click to expand...
If you're going to buy a charger that can not do LiPo, make sure you
get it REALLY cheap. For RC hobby, LiPo is the way forward. There are
now batteries on the market that can be charged in 12-15 minutes and
weigh a lot less than NiMH.
--
RoRo
 
"jg" <juangarcia@sacbeemail.com> wrote in message
news:a0bea318-05c8-47bb-8dc0-a61815ecf97e@z10g2000prh.googlegroups.com...
I have a few Rayovac Camcorder 3.6V/2500 mAh batteries that I want to
charge. These were originally charged with a camcorder that I do not
have. However, I have the next best thing. I have a DC Power Supply
(BK Precision 1660A) with both voltage control and current control.
Basically I can set this bad boy to output any volt and current
combination. I have tried charging the batteries at 4.0v and 100mA
and let them charge for about 3 hours. Batteries never got hot (which
to me would indicate that they were never really charged.) When I
first unplug them, they register about 3.6v. However after a day or
so, their voltage drops to 2.6v or so.

So... I am either not charging them up completely or they are no
longer functional. However, these batteries were never put in
production. They are old, but they were still in original packaging
as of a few days ago.

Any help greatly appreciated.

jg
http://www.powerstream.com/NiMH.htm
Click to expand...

http://www.talkingelectronics.com/projects/ChargingNiMH/ChargingNiMH.html

http://www.mpoweruk.com/chargers.htm

http://data.energizer.com/PDFs/charger_appman.pdf

http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf
 
Robert Roland wrote:
On Tue, 02 Mar 2010 15:42:21 -0800, Tim Wescott <tim@seemywebsite.now
wrote:

If you don't mind spending the $$ get a peak-detect charger at your
local hobby shop. Or look around and see if there are any used ones on
Craigs List -- there are probably still some electric fliers that are
converting to LiPo and have an old NiCd only charger around, or who are
upgrading.

If you're going to buy a charger that can not do LiPo, make sure you
get it REALLY cheap. For RC hobby, LiPo is the way forward. There are
now batteries on the market that can be charged in 12-15 minutes and
weigh a lot less than NiMH.
Click to expand...
Yup. The weight isn't as important for boats, but Ni-anything has
pretty much had its day in the sun for electric flying.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
 
Robert Roland wrote:
On Tue, 02 Mar 2010 15:42:21 -0800, Tim Wescott <tim@seemywebsite.now
wrote:

If you don't mind spending the $$ get a peak-detect charger at your
local hobby shop. Or look around and see if there are any used ones on
Craigs List -- there are probably still some electric fliers that are
converting to LiPo and have an old NiCd only charger around, or who are
upgrading.

If you're going to buy a charger that can not do LiPo, make sure you
get it REALLY cheap. For RC hobby, LiPo is the way forward. There are
now batteries on the market that can be charged in 12-15 minutes and
weigh a lot less than NiMH.
Click to expand...
As far as that goes, I've got a Hitec "Multi Charge-A-Matic II" that I'd
_give_ away, but as far as I can tell it's only good for NiCd batteries,
not NiMH (which is why it's collecting dust on a shelf).

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
 
Status Report:
I charged one of the packs overnight for 12 hours. Max current was
set at 250mA. Voltage was set at 10VDC. However, actual voltage
hovered around 4.5V all night. Current control took over. When I
unplugged this morning, pack felt warm to the touch. By no means
hot. Without load, voltage registered at 4.2V. Nice. I will now let
sit for a few days and see how long it holds.

Question:
Based on what I have learned, I should be able to charge these in
series w/o any issues, right? Well, maybe. Given the voltage
unpredictability of NiMH, the voltage drop may not be shared equally
across the packs. However, based on data from last night, Current is
the dominating factor here... so it might just work.

jg
 
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