Specs for charging nicads

[Mint]

I have a Craftsman 14.4 V. rechargeable drill that uses NiCad
batteries.

It has no ready light, just a charging light.

The manual says it may take up to 6 hrs. to charge.

I left it on overnight.

What are the consequences of that?

It has screws, so I may be able to replace the batteries.

Is there some place that would help me in
determining what a good charger would charge it at?

Thanks,

Andy

 

[Robert Roland]

On Fri, 31 Dec 2010 13:21:01 -0800 (PST), Mint
<chocolatemint77581@yahoo.com> wrote:

I have a Craftsman 14.4 V. rechargeable drill that uses NiCad
batteries.

It has no ready light, just a charging light.

The manual says it may take up to 6 hrs. to charge.

I left it on overnight.

What are the consequences of that?

It depends on the charger. It probably is one of those cheap
almost-constant current chargers. If so, you will have shortened the
life of the battery ever so slightly. If you do it hundreds of times,
the battery will take noticeable damage.

It has screws, so I may be able to replace the batteries.

NiCd is getting hard to find. You could replace them with NiMH, which
would give you more capacity. They are more sensitive than to
overcharge than NiCd, but they are still pretty tough.

Is there some place that would help me in
determining what a good charger would charge it at?

The manufacturer's data sheet for the battery is the final word when
determining the best charging strategy. A good charger lets you select
charge current and ends the charge automatically when the battery is
full.
--
RoRo

 

[Mint]

On Jan 1, 9:07 am, Robert Roland <f...@ddress.no> wrote:

On Fri, 31 Dec 2010 13:21:01 -0800 (PST), Mint

chocolatemint77...@yahoo.com> wrote:
I have a Craftsman 14.4 V. rechargeable drill that uses NiCad
batteries.

It has no ready light, just a charging light.

The manual says it may take up to 6 hrs. to charge.

I left it on overnight.

What are the consequences of that?

It depends on the charger. It probably is one of those cheap
almost-constant current chargers. If so, you will have shortened the
life of the battery ever so slightly. If you do it hundreds of times,
the battery will take noticeable damage.

It has screws, so I may be able to replace the batteries.

NiCd is getting hard to find. You could replace them with NiMH, which
would give you more capacity. They are more sensitive than to
overcharge than NiCd, but they are still pretty tough.

Is there some place that would help me in
determining what a good charger would charge it at?

The manufacturer's data sheet for the battery is the final word when
determining the best charging strategy. A good charger lets you select
charge current and ends the charge automatically when the battery is
full.
--
RoRo

Thanks for the info.

Andy

 

[ehsjr]

Mint wrote:

I have a Craftsman 14.4 V. rechargeable drill that uses NiCad
batteries.

It has no ready light, just a charging light.

The manual says it may take up to 6 hrs. to charge.

I left it on overnight.

What are the consequences of that?

It has screws, so I may be able to replace the batteries.

Is there some place that would help me in
determining what a good charger would charge it at?

Thanks,

Andy

Cordless 14.4V tools usually have a simple charger into which you
insert the battery pack. Most likely, the only charger that is made
for that pack is the one that came with the tool, so you cannot buy
a "better" one. Sometimes, you can improve that charger that came
with the tool by adding a cuttoff circuit to stop the charging when
the battery voltage reaches a predetermined level. That may be worth
doing.

If you are really ambitious, you can design and build what you consider
a "perfect charger", remove the original circuit, and substitute your
own design, using the molded plastic "charging stand" that came with the
tool. That's not worth it just for the sake of making the battery
pack last longer, but it might be worthwhile for the learning
experience.

For your first DIY NiCd charger, I recommend a trickle rate with
automatic termination (or charge rate reduction, if not complete charge
termination), such as the schematic I posted to you in response to
your other post asking about a step down transformer as a battery
charger. The trickle rate is C/10, where C is the mAH rating of the
pack. The target termination voltage is just a bit less than 1.43
volts per cell. For a 14.4 volt pack, that's 12 cells at 1.43 per
cell, or a bit less than 17.16 volts. Note that the charge rate
reduction method in the schematic is intended only for a constant
current circuit such as is shown in the schematic. With the simple
chargers that come with some power tools, a different method is
needed - I'd recommend complete charge termination - ie automatically
disconnecting the charger from the battery.

Ed

 

[asdf]

On Sat, 01 Jan 2011 16:07:32 +0100, Robert Roland wrote:

NiCd is getting hard to find. You could replace them with NiMH, which
would give you more capacity. They are more sensitive than to overcharge
than NiCd, but they are still pretty tough.

NiCd cells can be found in RC shops. They have a lower internal
resistance compared to NiMh cells which makes them more suitable for
motors and stuff drawing high current spikes.

NiMh have also a less pronounced DeltaV voltage drop so that some
chargers could ignore it and countinue charging the cell.
Usually a charger not specifically intended also for NiMh's should be
tested before being let charging NiMh cells unattended.

 

[Mint]

On Jan 1, 10:54 pm, ehsjr <eh...@nospamverizon.net> wrote:

Mint wrote:
I have a Craftsman 14.4 V. rechargeable drill that uses NiCad
batteries.

It has no ready light, just a charging light.

The manual says it may take up to 6 hrs. to charge.

I left it on overnight.

What are the consequences of that?

It has screws, so I may be able to replace the batteries.

Is there some place that would help me in
determining what a good charger would charge it at?

Thanks,

Andy

Cordless 14.4V tools usually have a simple charger into which you
insert the battery pack. Most likely, the only charger that is made
for that pack is the one that came with the tool, so you cannot buy
a "better" one.  Sometimes, you can improve that charger that came
with the tool by adding a cuttoff circuit to stop the charging when
the battery voltage reaches a predetermined level. That may be worth
doing.

If you are really ambitious, you can design and build what you consider
a "perfect charger", remove the original circuit, and substitute your
own design, using the molded plastic "charging stand" that came with the
tool.  That's not worth it just for the sake of making the battery
pack last longer, but it might be worthwhile for the learning
experience.

For your first DIY NiCd charger, I recommend a trickle rate with
automatic termination (or charge rate reduction, if not complete charge
termination), such as the schematic I posted to you in response to
your other post asking about a step down transformer as a battery
charger.  The trickle rate is C/10, where C is the mAH rating of the
pack.  The target termination voltage is just a bit less than 1.43
volts per cell. For a 14.4 volt pack, that's 12 cells at 1.43 per
cell, or a bit less than 17.16 volts.  Note that the charge rate
reduction method in the schematic is intended only for a constant
current circuit such as is shown in the schematic.  With the simple
chargers that come with some power tools, a different method is
needed - I'd recommend complete charge termination - ie automatically
disconnecting the charger from the battery.

Ed

I may do some experiments where I see how long it takes for the
battery to get to 17.16 volts.

I would like to establish a max time.
Then I might be able to attach my charger to a timer.

I guess I would need an ammeter to check the charging rate.

This link has some interesting info.

http://www.angelfire.com/electronic/hayles/charge1.html

Would be interested in your thoughts.

Andy

http://www.angelfire.com/electronic/hayles/charge1.html

 

[Mint]

On Jan 2, 1:34 am, asdf <a...@nospam.com> wrote:

On Sat, 01 Jan 2011 16:07:32 +0100, Robert Roland wrote:
NiCd is getting hard to find. You could replace them with NiMH, which
would give you more capacity. They are more sensitive than to overcharge
than NiCd, but they are still pretty tough.

NiCd cells can be found in RC shops. They have a lower internal
resistance compared to NiMh cells which makes them more suitable for
motors and stuff drawing high current spikes.

NiMh have also a less pronounced DeltaV voltage drop so that some
chargers could ignore it and countinue charging the cell.
Usually a charger not specifically intended also for NiMh's should be
tested before being let charging NiMh cells unattended.

Thanks for the info.

The RC shops also have a gel cell.

I was told that the early ones would explode if charged too long.

Andy

 

[ehsjr]

Mint wrote:

On Jan 1, 10:54 pm, ehsjr <eh...@nospamverizon.net> wrote:

Mint wrote:

I have a Craftsman 14.4 V. rechargeable drill that uses NiCad
batteries.

It has no ready light, just a charging light.

The manual says it may take up to 6 hrs. to charge.

I left it on overnight.

What are the consequences of that?

It has screws, so I may be able to replace the batteries.

Is there some place that would help me in
determining what a good charger would charge it at?

Thanks,

Andy

Cordless 14.4V tools usually have a simple charger into which you
insert the battery pack. Most likely, the only charger that is made
for that pack is the one that came with the tool, so you cannot buy
a "better" one. Sometimes, you can improve that charger that came
with the tool by adding a cuttoff circuit to stop the charging when
the battery voltage reaches a predetermined level. That may be worth
doing.

If you are really ambitious, you can design and build what you consider
a "perfect charger", remove the original circuit, and substitute your
own design, using the molded plastic "charging stand" that came with the
tool. That's not worth it just for the sake of making the battery
pack last longer, but it might be worthwhile for the learning
experience.

For your first DIY NiCd charger, I recommend a trickle rate with
automatic termination (or charge rate reduction, if not complete charge
termination), such as the schematic I posted to you in response to
your other post asking about a step down transformer as a battery
charger. The trickle rate is C/10, where C is the mAH rating of the
pack. The target termination voltage is just a bit less than 1.43
volts per cell. For a 14.4 volt pack, that's 12 cells at 1.43 per
cell, or a bit less than 17.16 volts. Note that the charge rate
reduction method in the schematic is intended only for a constant
current circuit such as is shown in the schematic. With the simple
chargers that come with some power tools, a different method is
needed - I'd recommend complete charge termination - ie automatically
disconnecting the charger from the battery.

Ed


I may do some experiments where I see how long it takes for the
battery to get to 17.16 volts.

Experimenting is a good idea. The length of time will of course
depend upon the state of the battery when you start to charge it.
Obviously, it will take longer to charge a battery that is almost
completely discharged than one that is only haly way discharged.

I would like to establish a max time.

Generally speaking, the max time occurs when you use the so called
"14 hour" charger. Different chargers can have different rates.
For battery packs that tend to get put into a charger and forgoten,
which seems to be what you were talking about in your post, a
"14 hour" charger is desireable (because it won't kill the NiCd pack
quickly), but much less desireable than an automatic charger that
terminates or reduces the charge at the proper point.

Then I might be able to attach my charger to a timer.

You can do that. But it does not prevent the scenario of putting
a battery on the charger when the battery is only discharged a
little bit. Say the battery becomes fully charged after 15 minutes
in your charger, but your timer is set for 6 hours. You get
5 hours and 45 minutes of charging that you did not need.

I guess I would need an ammeter to check the charging rate.

Not if you use the schematic I posted, and select the proper
resistor value for the resistor that connects between the LM317
Vout and adj pins (shown as [15R] in the schematic). To determine
the value, use the formula R = 1.25/I where I is the charging
current you want to use. For example, say you want to charge
at 500 mA. R = 1.25/.500 = 2.5 ohms.

If you want to check the charging rate of a different charger,
an ammeter may mislead you. The charging rate may not be
constant, depending on what type of charger is being used.

This link has some interesting info.

http://www.angelfire.com/electronic/hayles/charge1.html

Would be interested in your thoughts.

He's got the terminal voltage wrong where he says it's 1.5 or 1.6
volts per cell: "Under full charge they require about 1.5V to 1.6V"
However, his method of detecting full charge does not depend on
that voltage, so that error may be irrelevant to his design.
A link to the source code for the PIC program is not posted, so
there's no way to comment on that. The schematic shows 4300
ohms connected across the battery, which would draw about 3.3 mA
from the 14.4V battery if it was installed in the charger and the
power was off. That's not objectionable, unless you consider
a situation where the battery sat in an unpowered charger for
an extended period. It would kill a 14.4V, 1300 mAH pack in 16
days. I don't know why he didn't stuff a FET in there to protect
against that. I don't have the charger, so my remarks are based
soley on what is in the article.

Ed

Andy

http://www.angelfire.com/electronic/hayles/charge1.html

 

[Robert Roland]

On Sat, 01 Jan 2011 23:54:09 -0500, ehsjr <ehsjr@nospamverizon.net>
wrote:

The target termination voltage is just a bit less than 1.43
volts per cell.

For NiCd and NiMH batteries, voltage is a very unreliable way of
detecting full charge. The voltage changes with temperature and also
as the battery ages. In addition, different makes and models will have
slightly varying voltages, so you'll have to calibrate the charger for
each battery.

For lithium-ion and lead-acid, on the other hand, voltage is the
proper way of detecting full charge. A current limit will normally
also be needed to avoid charging too fast.
--
RoRo

 

[Mint]

On Jan 3, 5:11 am, Robert Roland <f...@ddress.no> wrote:

On Sat, 01 Jan 2011 23:54:09 -0500, ehsjr <eh...@nospamverizon.net
wrote:

The target termination voltage is just a bit less than 1.43
volts per cell.

For NiCd and NiMH batteries, voltage is a very unreliable way of
detecting full charge. The voltage changes with temperature and also
as the battery ages. In addition, different makes and models will have
slightly varying voltages, so you'll have to calibrate the charger for
each battery.

For lithium-ion and lead-acid, on the other hand, voltage is the
proper way of detecting full charge. A current limit will normally
also be needed to avoid charging too fast.
--
RoRo

I posted a pic of the circuit board for the 14.4 Volt Nicad battery
charger.

Andy

http://s1127.photobucket.com/albums/l637/bicycle77017/?action=view&current=charger.jpg

 

[ehsjr]

Robert Roland wrote:

On Sat, 01 Jan 2011 23:54:09 -0500, ehsjr <ehsjr@nospamverizon.net
wrote:


The target termination voltage is just a bit less than 1.43
volts per cell.


For NiCd and NiMH batteries, voltage is a very unreliable way of
detecting full charge.

I think you may have missed the context: It's a first DIY
NiCd _trickle_ charger. I'll quote what you snipped from:

"For your first DIY NiCd charger, I recommend a trickle rate with
automatic termination (or charge rate reduction, if not complete charge
termination), such as the schematic I posted to you in response to
your other post asking about a step down transformer as a battery
charger. The trickle rate is C/10, where C is the mAH rating of the
pack. The target termination voltage is just a bit less than 1.43
volts per cell. For a 14.4 volt pack, that's 12 cells at 1.43 per
cell, or a bit less than 17.16 volts."

The charger being discussed was a trickle charger, charging at C/10.
Powerstream indicates full charge of at least 1.41 per cell at 20
degrees C.
http://www.powerstream.com/NiCd.htm

Adding a charge termination circuit that operates at a bit less than
1.43V per cell to the trickle charger to either reduce the charge rate
greatly (the specific example given in the prior post was C/80), or to
terminate it entirely, is better than leaving the pack charging beyond
1.43V per cell. Thus the recommendation of that charge termination
scheme for that charger.

The voltage changes with temperature and also
as the battery ages. In addition, different makes and models will have
slightly varying voltages, so you'll have to calibrate the charger for
each battery.

Nope. You set the termination voltage based on the number of cells in
the pack, and set the charge rate to the mAH rating of the pack divided
by ten. Brand name/model has _nothing_ to do with it. Remember, we're
talking about a first time, do it yourself, NiCd trickle charger,
not the "perfect charger" I mentioned in the paragraph preceeding
the single line you quoted.

For lithium-ion and lead-acid, on the other hand, voltage is the
proper way of detecting full charge. A current limit will normally
also be needed to avoid charging too fast.

Let's get back to the NiCd the OP asked about. If you still
maintain that termination (or charge rate reduction) at a bit less
than 1.43V per cell is not the way to go for the trickle charger
proposed, what alternative termination method do you propose?

Ed

 

[Mint]

On Jan 3, 11:40 pm, ehsjr <eh...@nospamverizon.net> wrote:

Robert Roland wrote:
On Sat, 01 Jan 2011 23:54:09 -0500, ehsjr <eh...@nospamverizon.net
wrote:

The target termination voltage is just a bit less than 1.43
volts per cell.

For NiCd and NiMH batteries, voltage is a very unreliable way of
detecting full charge.

I think you may have missed the context: It's a first DIY
NiCd  _trickle_ charger. I'll quote what you snipped from:

"For your first DIY NiCd charger, I recommend a trickle rate with
automatic termination (or charge rate reduction, if not complete charge
termination), such as the schematic I posted to you in response to
your other post asking about a step down transformer as a battery
charger.  The trickle rate is C/10, where C is the mAH rating of the
pack.  The target termination voltage is just a bit less than 1.43
volts per cell. For a 14.4 volt pack, that's 12 cells at 1.43 per
cell, or a bit less than 17.16 volts."

The charger being discussed was a trickle charger, charging at C/10.
Powerstream indicates full charge of at least 1.41 per cell at 20
degrees C.http://www.powerstream.com/NiCd.htm

Adding a charge termination circuit that operates at a bit less than
1.43V per cell to the trickle charger to either reduce the charge rate
greatly (the specific example given in the prior post was C/80), or to
terminate it entirely, is better than leaving the pack charging beyond
1.43V per cell.  Thus the recommendation of that charge termination
scheme for that charger.

The voltage changes with temperature and also
as the battery ages. In addition, different makes and models will have
slightly varying voltages, so you'll have to calibrate the charger for
each battery.

Nope.  You set the termination voltage based on the number of cells in
the pack, and set the charge rate to the mAH rating of the pack divided
by ten.  Brand name/model has _nothing_ to do with it. Remember, we're
talking about a first time, do it yourself, NiCd trickle charger,
not the "perfect charger" I mentioned in the paragraph preceeding
the single line you quoted.



For lithium-ion and lead-acid, on the other hand, voltage is the
proper way of detecting full charge. A current limit will normally
also be needed to avoid charging too fast.

Let's get back to the NiCd the OP asked about.  If you still
maintain that termination (or charge rate reduction) at a bit less
than 1.43V per cell is not the way to go for the trickle charger
proposed, what alternative termination method do you propose?

Ed

Thanks for everyone's input.

My current charger charges to it's max voltage in about 2.5 hrs.

After 3 hrs, the voltage is still the same.

My battery uses special screws with a protrusion in the center, so I
can't take it apart right now.

It may have 12 cells at 1.2 Volts each.

When I have the funds, I will look at building a better charger than
the Craftsman.

Andy