# How to charge 3.6VDC battery with DC Power Supply

Started by March 2, 2010
```On Tue, 02 Mar 2010 08:52:24 -0800, Tim Wescott <tim@seemywebsite.now>
wrote:

>Could be three Ni-Cd in series, though.

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.

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
```
```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?

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
```
```On Mar 2, 2:05=A0pm, 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? =A0I 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.

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
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

--
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

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
>
> 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

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
>
> 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.

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
>
> 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.

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
```
```On Mar 2, 2:05=A0pm, 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? =A0I 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.

Thanx again.
```
```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?

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
```
```On Tue, 2 Mar 2010 11:45:05 -0800 (PST), jg
<juangarcia@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
```
```On Tue, 02 Mar 2010 08:52:24 -0800, Tim Wescott <tim@seemywebsite.now>
wrote:

>Could be three Ni-Cd in series, though.

It never even struck my mind. Thanks.
--
RoRo
```
```On Mar 2, 11:54=A0am, Tim Wescott <t...@seemywebsite.now> wrote:
> jg wrote:
> >> So, your first step is to figure out your battery chemistry. =A0Withou=
t
> >> that first step, there is no second step.
>
> > They are NiMH. =A0Battery pack is made up of 3 cells. =A0Each one rated=
at
> > 1.2v, for a total of 3.6v. =A0(I have actually opened up one of the
> > packs. =A0They 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? =A0I 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). =A0Fancy 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. =A0You 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

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.
```
```> ---------------------
> 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?

jg
```
```"jg" <juangarcia@sacbeemail.com> wrote in message

>
> 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 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.

```
```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 consulting
www.wescottdesign.com
```
```>
> So, your first step is to figure out your battery chemistry. =A0Without
> 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.)

jg
```
```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.

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
```