Trickle charging NiCads

P

pimpom

Guest
I know this is an old topic and I've done a search, but couldn't find a
satisfactory answer to the question: What would be a reasonable charging
current for a NiCad battery (in terms of its mAh rating) under the following
conditions?

1. Battery loading will be infrequent but unpredictable - could be once a
day or a week or more.
2. Unattended charging at or near constant current for 6-10 hours a day,
everyday.
3. Charging circuit needs to be simple - no dv or temperature detection.
Load cut-off will be automatic.
4. Battery service life need not be as long as that with optimum charging,
but should not be drastically shortened.
5. Does not matter if battery power is occasionally unavailable due to
insufficient charging time between (infrequent) loads, but should otherwise
be ready to provide power at any time.

Thanks in advance.
 
whit3rd wrote:
On May 9, 12:23 pm, "pimpom" <pim...@invalid.invalid> wrote:
I know this is an old topic and I've done a search, but couldn't
find a satisfactory answer to the question: What would be a
reasonable charging current for a NiCad battery (in terms of its mAh
rating) under the following conditions?

1. Battery loading will be infrequent but unpredictable - could be
once a day or a week or more.
2. Unattended charging at or near constant current for 6-10 hours a
day, everyday

So, charge at the ten-hour rate from a current source. 800 mAh
battery
(kind of a low-end AA) will want 80 mA for ten hours, roughly,
Problem is, it will be permanently connected to the charging circuit and
will be charged 6-10 hrs a day regardless of whether it is discharged or not
in between charges. Under those conditions, I don't think a C10 charge will
be very healthy for the battery.

so connect a wall-wart with enough volts into a resistor in series
with
the battery, or an unregulated supply with an LM317 + resistor
regulated
current source. The resistor should be sized to R= 1.25V / Icharge,
and suitable to dissipate 1.25 x Icharge watts.
I'm ok with designing the charging circuit to any degree of precision as far
as current regulation is concerned. I just want to avoid a drastic reduction
in useful battery life by constantly overcharging it, while keeping the
circuit simple by omitting a complex full-charge detection.

Perhaps this is a good time to explain the intended application. I want to
make an emergency light using white LEDs that will turn on automatically in
the event of a power failure. Nothing new in that. But this unit will be
connected in parallel with a normal house light that's usually kept on every
night from about 5 or 6 pm to 1-3 am.

The emergency light will sense the state of the light switch even in the
absence of mains power and turn on only if the switch is in the 'on'
position - a fully automatic fit-and-forget operation. I've designed and
tested the circuit but am not sure what level of trickle charging would be a
good compromise.
 
On May 9, 12:23 pm, "pimpom" <pim...@invalid.invalid> wrote:
I know this is an old topic and I've done a search, but couldn't find a
satisfactory answer to the question: What would be a reasonable charging
current for a NiCad battery (in terms of its mAh rating) under the following
conditions?

1. Battery loading will be infrequent but unpredictable - could be once a
day or a week or more.
2. Unattended charging at or near constant current for 6-10 hours a day,
everyday
So, charge at the ten-hour rate from a current source. 800 mAh
battery
(kind of a low-end AA) will want 80 mA for ten hours, roughly,
so connect a wall-wart with enough volts into a resistor in series
with
the battery, or an unregulated supply with an LM317 + resistor
regulated
current source. The resistor should be sized to R= 1.25V / Icharge,
and suitable to dissipate 1.25 x Icharge watts.
 
"pimpom"
I'm ok with designing the charging circuit to any degree of precision as
far as current regulation is concerned. I just want to avoid a drastic
reduction in useful battery life by constantly overcharging it, while
keeping the circuit simple by omitting a complex full-charge detection.

Perhaps this is a good time to explain the intended application. I want to
make an emergency light using white LEDs that will turn on automatically
in the event of a power failure. Nothing new in that. But this unit will
be connected in parallel with a normal house light that's usually kept on
every night from about 5 or 6 pm to 1-3 am.

The emergency light will sense the state of the light switch even in the
absence of mains power and turn on only if the switch is in the 'on'
position - a fully automatic fit-and-forget operation. I've designed and
tested the circuit but am not sure what level of trickle charging would be
a good compromise.

** Most NiCd makers suggest a C/50 rate for constant trickle charging.

But why use NiCds at all??

NiMH cells have lower self discharge rates and less issues like the
formation of "dendrites" that plague NiCd cells left on trickle charge.


....... Phil
 
<ggherold@gmail.com
"Phil Allison"
"pimpom"
I'm ok with designing the charging circuit to any degree of precision as
far as current regulation is concerned. I just want to avoid a drastic
reduction in useful battery life by constantly overcharging it, while
keeping the circuit simple by omitting a complex full-charge detection.

Perhaps this is a good time to explain the intended application. I want
to
make an emergency light using white LEDs that will turn on automatically
in the event of a power failure. Nothing new in that. But this unit will
be connected in parallel with a normal house light that's usually kept
on
every night from about 5 or 6 pm to 1-3 am.

The emergency light will sense the state of the light switch even in the
absence of mains power and turn on only if the switch is in the 'on'
position - a fully automatic fit-and-forget operation. I've designed and
tested the circuit but am not sure what level of trickle charging would
be
a good compromise.

** Most NiCd makers suggest a C/50 rate for constant trickle charging.

But why use NiCds at all??

NiMH cells have lower self discharge rates and less issues like the
formation of "dendrites" that plague NiCd cells left on trickle charge.
I was going to suggest a different battery type also. Why NiCds? If
you don't mind the weight there are also lead acid gel cells. I
haven't done much (read anything) with NiMH. But I thought I read
that they didn't want to be trickle charged. They wanted pulses... I
guess you can make a trickle pulser.


** Trickle pulsing is probably a very neat idea - funny I have never seen
it done other than in the standby-by mode of a pulse type fast Ni-Cd
charger.

The OP could set up a 555 timer, in astable mode, to produce a 1 second
pulse each 30 seconds and have a CCS deliver say 500 mA to the battery
during that pulse. Averages out as 16mA or C/50.

OTOH - emergency systems nearly always use Gell Cells and with good
results. Constant voltage ( current limited) charging is the go with them
and is simple to implement



..... Phil
 
"pimpom" <pimpom@invalid.invalid> wrote in message
news:gu4rii$ru5$1@news.albasani.net...
whit3rd wrote:
On May 9, 12:23 pm, "pimpom" <pim...@invalid.invalid> wrote:
I know this is an old topic and I've done a search, but couldn't
find a satisfactory answer to the question: What would be a
reasonable charging current for a NiCad battery (in terms of its mAh
rating) under the following conditions?

1. Battery loading will be infrequent but unpredictable - could be
once a day or a week or more.
2. Unattended charging at or near constant current for 6-10 hours a
day, everyday

So, charge at the ten-hour rate from a current source. 800 mAh
battery
(kind of a low-end AA) will want 80 mA for ten hours, roughly,

Problem is, it will be permanently connected to the charging circuit and
will be charged 6-10 hrs a day regardless of whether it is discharged or
not in between charges. Under those conditions, I don't think a C10 charge
will be very healthy for the battery.

so connect a wall-wart with enough volts into a resistor in series
with
the battery, or an unregulated supply with an LM317 + resistor
regulated
current source. The resistor should be sized to R= 1.25V / Icharge,
and suitable to dissipate 1.25 x Icharge watts.

I'm ok with designing the charging circuit to any degree of precision as
far as current regulation is concerned. I just want to avoid a drastic
reduction in useful battery life by constantly overcharging it, while
keeping the circuit simple by omitting a complex full-charge detection.

Perhaps this is a good time to explain the intended application. I want to
make an emergency light using white LEDs that will turn on automatically
in the event of a power failure. Nothing new in that. But this unit will
be connected in parallel with a normal house light that's usually kept on
every night from about 5 or 6 pm to 1-3 am.

The emergency light will sense the state of the light switch even in the
absence of mains power and turn on only if the switch is in the 'on'
position - a fully automatic fit-and-forget operation. I've designed and
tested the circuit but am not sure what level of trickle charging would be
a good compromise.
One possibility is to set your charger to charge so many hours per day with
one of the cheapy wall timers. The C/10 or 10 hour rate is often used as an
indefinite charge rate with Nicads, you can leave the charge on all the time
and still have pretty good battery life. You could try a C/10 charger with
a wall timer and set the timer for perhaps 1.5X the usage. For example if
you use 50mA for 10 hours per day you could charge at 50mA for 15 hours per
day. A little error would have minimal effect on battery life.

RogerN
 
On May 9, 8:56 pm, "Phil Allison" <philalli...@tpg.com.au> wrote:
"pimpom"







I'm ok with designing the charging circuit to any degree of precision as
far as current regulation is concerned. I just want to avoid a drastic
reduction in useful battery life by constantly overcharging it, while
keeping the circuit simple by omitting a complex full-charge detection.

Perhaps this is a good time to explain the intended application. I want to
make an emergency light using white LEDs that will turn on automatically
in the event of a power failure. Nothing new in that. But this unit will
be connected in parallel with a normal house light that's usually kept on
every night from about 5 or 6 pm to 1-3 am.

The emergency light will sense the state of the light switch even in the
absence of mains power and turn on only if the switch is in the 'on'
position - a fully automatic fit-and-forget operation. I've designed and
tested the circuit but am not sure what level of trickle charging would be
a good compromise.

 ** Most NiCd makers suggest a C/50 rate for constant trickle charging.

But why use NiCds at all??

NiMH cells have lower self discharge rates and less issues like the
formation of "dendrites" that plague NiCd cells left on trickle charge.

......  Phil- Hide quoted text -

- Show quoted text -
I was going to suggest a different battery type also. Why NiCds? If
you don't mind the weight there are also lead acid gel cells. I
haven't done much (read anything) with NiMH. But I thought I read
that they didn't want to be trickle charged. They wanted pulses... I
guess you can make a trickle pulser.

George Herold
 
Phil Allison wrote:
"pimpom"

I'm ok with designing the charging circuit to any degree of
precision as far as current regulation is concerned. I just want to
avoid a drastic reduction in useful battery life by constantly
overcharging it, while keeping the circuit simple by omitting a
complex full-charge detection. Perhaps this is a good time to explain the
intended application. I
want to make an emergency light using white LEDs that will turn on
automatically in the event of a power failure. Nothing new in that.
But this unit will be connected in parallel with a normal house
light that's usually kept on every night from about 5 or 6 pm to 1-3
am. The emergency light will sense the state of the light switch even in
the absence of mains power and turn on only if the switch is in the
'on' position - a fully automatic fit-and-forget operation. I've
designed and tested the circuit but am not sure what level of
trickle charging would be a good compromise.


** Most NiCd makers suggest a C/50 rate for constant trickle charging.

But why use NiCds at all??

NiMH cells have lower self discharge rates and less issues like the
formation of "dendrites" that plague NiCd cells left on trickle
charge.

I understand that NiMH cells have fewer issues than NiCds. The main reason
for using NiCds is that they're much cheaper and much more easily available
than NiMHs where I live.
 
Phil Allison wrote:
ggherold@gmail.com
"Phil Allison"
"pimpom"

I'm ok with designing the charging circuit to any degree of
precision as far as current regulation is concerned. I just want to
avoid a drastic reduction in useful battery life by constantly
overcharging it, while keeping the circuit simple by omitting a
complex full-charge detection.

Perhaps this is a good time to explain the intended application. I
want to
make an emergency light using white LEDs that will turn on
automatically in the event of a power failure. Nothing new in that.
But this unit will be connected in parallel with a normal house
light that's usually kept on
every night from about 5 or 6 pm to 1-3 am.

The emergency light will sense the state of the light switch even
in the absence of mains power and turn on only if the switch is in
the 'on' position - a fully automatic fit-and-forget operation.
I've designed and tested the circuit but am not sure what level of
trickle charging would be
a good compromise.

** Most NiCd makers suggest a C/50 rate for constant trickle
charging. But why use NiCds at all??

NiMH cells have lower self discharge rates and less issues like the
formation of "dendrites" that plague NiCd cells left on trickle
charge.

I was going to suggest a different battery type also. Why NiCds? If
you don't mind the weight there are also lead acid gel cells. I
haven't done much (read anything) with NiMH. But I thought I read
that they didn't want to be trickle charged. They wanted pulses... I
guess you can make a trickle pulser.


** Trickle pulsing is probably a very neat idea - funny I have
never seen it done other than in the standby-by mode of a pulse type
fast Ni-Cd charger.

The OP could set up a 555 timer, in astable mode, to produce a 1
second pulse each 30 seconds and have a CCS deliver say 500 mA to the
battery during that pulse. Averages out as 16mA or C/50.

OTOH - emergency systems nearly always use Gell Cells and with good
results. Constant voltage ( current limited) charging is the go with
them and is simple to implement


Thanks for your inpuits, everyone. NiMH, lead-acid gel, pulsed and timed
charging are all technically sound ideas. But ATM, I'm committed to the idea
of using one of those compact 3.6V NiCd packs that come with cheap Chinese
import gadgets such as a US$2 rechargeable flashlight.

My circuit uses 1 low-power transistor, one-half of LM393, 3x1N4007, 1 zener
diode, 8 resistors and 2 caps on a 1"x2" pcb, and I want to keep it no more
complex than that.
 
RogerN wrote:
"pimpom" <pimpom@invalid.invalid> wrote in message
news:gu4rii$ru5$1@news.albasani.net...
whit3rd wrote:
On May 9, 12:23 pm, "pimpom" <pim...@invalid.invalid> wrote:
I know this is an old topic and I've done a search, but couldn't
find a satisfactory answer to the question: What would be a
reasonable charging current for a NiCad battery (in terms of its
mAh rating) under the following conditions?

1. Battery loading will be infrequent but unpredictable - could be
once a day or a week or more.
2. Unattended charging at or near constant current for 6-10 hours a
day, everyday

So, charge at the ten-hour rate from a current source. 800 mAh
battery
(kind of a low-end AA) will want 80 mA for ten hours, roughly,

Problem is, it will be permanently connected to the charging circuit
and will be charged 6-10 hrs a day regardless of whether it is
discharged or not in between charges. Under those conditions, I
don't think a C10 charge will be very healthy for the battery.

so connect a wall-wart with enough volts into a resistor in series
with
the battery, or an unregulated supply with an LM317 + resistor
regulated
current source. The resistor should be sized to R= 1.25V /
Icharge, and suitable to dissipate 1.25 x Icharge watts.

I'm ok with designing the charging circuit to any degree of
precision as far as current regulation is concerned. I just want to
avoid a drastic reduction in useful battery life by constantly
overcharging it, while keeping the circuit simple by omitting a
complex full-charge detection. Perhaps this is a good time to explain the
intended application. I
want to make an emergency light using white LEDs that will turn on
automatically in the event of a power failure. Nothing new in that.
But this unit will be connected in parallel with a normal house
light that's usually kept on every night from about 5 or 6 pm to 1-3
am. The emergency light will sense the state of the light switch even in
the absence of mains power and turn on only if the switch is in the
'on' position - a fully automatic fit-and-forget operation. I've
designed and tested the circuit but am not sure what level of
trickle charging would be a good compromise.

One possibility is to set your charger to charge so many hours per
day with one of the cheapy wall timers. The C/10 or 10 hour rate is
often used as an indefinite charge rate with Nicads, you can leave
the charge on all the time and still have pretty good battery life. You
could try a C/10 charger with a wall timer and set the timer for
perhaps 1.5X the usage. For example if you use 50mA for 10 hours per
day you could charge at 50mA for 15 hours per day. A little error
would have minimal effect on battery life.
A charging timer would be superfluous here as the mains line to which it
will be attached is regularly turned on every night during waking hours and
turned off for the rest of the day - a pretty regular cycle. The uncertain
factor is the discharge frequency which is neither regular nor predictable.
It may go for days without being called upon to deliver power. You cite C/10
and someone else cited C/50. That's quite a big difference.
 
"pimpom" <pimpom@invalid.invalid> wrote in message
news:gu6ign$4g8$1@news.albasani.net...
RogerN wrote:
snip

One possibility is to set your charger to charge so many hours per
day with one of the cheapy wall timers. The C/10 or 10 hour rate is
often used as an indefinite charge rate with Nicads, you can leave
the charge on all the time and still have pretty good battery life. You
could try a C/10 charger with a wall timer and set the timer for
perhaps 1.5X the usage. For example if you use 50mA for 10 hours per
day you could charge at 50mA for 15 hours per day. A little error
would have minimal effect on battery life.
A charging timer would be superfluous here as the mains line to which it
will be attached is regularly turned on every night during waking hours
and turned off for the rest of the day - a pretty regular cycle. The
uncertain factor is the discharge frequency which is neither regular nor
predictable. It may go for days without being called upon to deliver
power. You cite C/10 and someone else cited C/50. That's quite a big
difference.
C/50 is a common trickle charge to keep the batteries topped off after they
are peak charged. Back in the day when nicads were the standard
rechargeable battery for cordless phones and the like, most came with
instructions that said to charge before use for around 12-15 hours. These
had c/10 chargers. Nicads can take the overcharging but in my experience I
think they last longer if you don't leave it on the chargers all the time.

RogerN
 
RogerN wrote:
"pimpom" <pimpom@invalid.invalid> wrote in message
news:gu6ign$4g8$1@news.albasani.net...
RogerN wrote:
snip

One possibility is to set your charger to charge so many hours per
day with one of the cheapy wall timers. The C/10 or 10 hour rate is
often used as an indefinite charge rate with Nicads, you can leave
the charge on all the time and still have pretty good battery life.
You could try a C/10 charger with a wall timer and set the timer for
perhaps 1.5X the usage. For example if you use 50mA for 10 hours
per day you could charge at 50mA for 15 hours per day. A little
error would have minimal effect on battery life.
A charging timer would be superfluous here as the mains line to
which it will be attached is regularly turned on every night during
waking hours and turned off for the rest of the day - a pretty
regular cycle. The uncertain factor is the discharge frequency which
is neither regular nor predictable. It may go for days without being
called upon to deliver power. You cite C/10 and someone else cited
C/50. That's quite a big difference.

C/50 is a common trickle charge to keep the batteries topped off
after they are peak charged. Back in the day when nicads were the
standard rechargeable battery for cordless phones and the like, most
came with instructions that said to charge before use for around
12-15 hours. These had c/10 chargers. Nicads can take the
overcharging but in my experience I think they last longer if you
don't leave it on the chargers all the time.
Hmmm. It looks as if there's no definitive answer. Would you say that
something like C/20 would be a reasonable compromise?
 
"pimpom" <pimpom@invalid.invalid> wrote in message
news:gu7991$3or$1@news.albasani.net...
RogerN wrote:
"pimpom" <pimpom@invalid.invalid> wrote in message
news:gu6ign$4g8$1@news.albasani.net...
RogerN wrote:
snip

One possibility is to set your charger to charge so many hours per
day with one of the cheapy wall timers. The C/10 or 10 hour rate is
often used as an indefinite charge rate with Nicads, you can leave
the charge on all the time and still have pretty good battery life.
You could try a C/10 charger with a wall timer and set the timer for
perhaps 1.5X the usage. For example if you use 50mA for 10 hours
per day you could charge at 50mA for 15 hours per day. A little
error would have minimal effect on battery life.
A charging timer would be superfluous here as the mains line to
which it will be attached is regularly turned on every night during
waking hours and turned off for the rest of the day - a pretty
regular cycle. The uncertain factor is the discharge frequency which
is neither regular nor predictable. It may go for days without being
called upon to deliver power. You cite C/10 and someone else cited
C/50. That's quite a big difference.

C/50 is a common trickle charge to keep the batteries topped off
after they are peak charged. Back in the day when nicads were the
standard rechargeable battery for cordless phones and the like, most
came with instructions that said to charge before use for around
12-15 hours. These had c/10 chargers. Nicads can take the
overcharging but in my experience I think they last longer if you
don't leave it on the chargers all the time.

Hmmm. It looks as if there's no definitive answer. Would you say that
something like C/20 would be a reasonable compromise?
It would probably work just fine, nicads have pretty good life even when
continuously overcharged at c/10 but I do get better life out of them by not
overcharging. One charger I have charges at a higher current up to a
certain voltage and then uses peak detection to terminate charge and then
reduces to trickle c/50. You could probably make a design to charge at C/10
at lower voltage and taper off the current as the battery voltage came up.
Perhaps an adjustable voltage regulator and a resistor, that way it would
charge faster after being discharged and charge at maybe c/20 at maybe 80%
charge. For example if you charged a 4.8V pack with a 5.8V power supply and
10 ohm resistor, it would charge at 0.1A with the battery discharged to 4.8V
and the current would approach zero as the pack charge approaches 5.8V.
(assuming at 5.8V the pack was near full charge)

RogerN
 
"RogerN"

Hmmm. It looks as if there's no definitive answer. Would you say that
something like C/20 would be a reasonable compromise?

It would probably work just fine, nicads have pretty good life even when
continuously overcharged at c/10
** That is bullshit.


You could probably make a design to charge at C/10 at lower voltage and
taper off the current as the battery voltage came up. Perhaps an
adjustable voltage regulator and a resistor, that way it would charge
faster after being discharged and charge at maybe c/20 at maybe 80%
charge. For example if you charged a 4.8V pack with a 5.8V power supply
and 10 ohm resistor, it would charge at 0.1A with the battery discharged
to 4.8V and the current would approach zero as the pack charge approaches
5.8V. (assuming at 5.8V the pack was near full charge)

** Such a silly scheme will result in very long charging times AND the
cells will never reach full charge.

There is also the risk of charged cells heating and hence their voltage
dropping and hence the charge rate increasing on and on to destruction.


....... Phil
 
"Phil Allison" <philallison@tpg.com.au> wrote in message
news:76pmg1F1dvh14U1@mid.individual.net...
"RogerN"


Hmmm. It looks as if there's no definitive answer. Would you say that
something like C/20 would be a reasonable compromise?

It would probably work just fine, nicads have pretty good life even when
continuously overcharged at c/10

** That is bullshit.
It's obvious you don't know what you're talking about. Almost every
cordless home device (phone, shaver, etc.) uses c/10 charging for nicads.
You can leave the phone on the cradle indefinately, battery life is not as
good as properly terminated charge but they still last a few years. I know
this to be so, I've had those cordless devices and that is the actual
results, provide better data if you have any.

You could probably make a design to charge at C/10 at lower voltage and
taper off the current as the battery voltage came up. Perhaps an
adjustable voltage regulator and a resistor, that way it would charge
faster after being discharged and charge at maybe c/20 at maybe 80%
charge. For example if you charged a 4.8V pack with a 5.8V power supply
and 10 ohm resistor, it would charge at 0.1A with the battery discharged
to 4.8V and the current would approach zero as the pack charge approaches
5.8V. (assuming at 5.8V the pack was near full charge)


** Such a silly scheme will result in very long charging times AND the
cells will never reach full charge.

There is also the risk of charged cells heating and hence their voltage
dropping and hence the charge rate increasing on and on to destruction.


...... Phil
The right way is peak detection but that doesn't seem to be an option for
this application. If you're going to charge nicads by constant voltage it
would work to limit charge to c/10 and have it taper c/50 at or near peak.
At C/10 nicads won't heat to destruction. Current limited, voltage limited
is what is used on lead acid batteries and they have acceptable charge
times.

My experience is with 28 years of flying R/C model planes and helicopters
where a battery failure means a crash. I've learned most of what I know
about charging from a battery manufacturers former battery expert,
manufacturer information, microcontroller battery chargers, battery charger
chip data sheets and application notes.

RogerN
 
"RogerNutcase"
Hmmm. It looks as if there's no definitive answer. Would you say that
something like C/20 would be a reasonable compromise?

It would probably work just fine, nicads have pretty good life even when
continuously overcharged at c/10

** That is bullshit.


It's obvious you don't know what you're talking about.

** So says a brain dead FUCKING LIAR.


Almost every cordless home device (phone, shaver, etc.) uses c/10 charging
for nicads. You can leave the phone on the cradle indefinately, battery
life is not as good as properly terminated charge but they still last a
few years.

** Much less, in most cases.

SO YOU LIE


You could probably make a design to charge at C/10 at lower voltage and
taper off the current as the battery voltage came up. Perhaps an
adjustable voltage regulator and a resistor, that way it would charge
faster after being discharged and charge at maybe c/20 at maybe 80%
charge. For example if you charged a 4.8V pack with a 5.8V power supply
and 10 ohm resistor, it would charge at 0.1A with the battery discharged
to 4.8V and the current would approach zero as the pack charge
approaches 5.8V. (assuming at 5.8V the pack was near full charge)


** Such a silly scheme will result in very long charging times AND the
cells will never reach full charge.

There is also the risk of charged cells heating and hence their voltage
dropping and hence the charge rate increasing on and on to destruction.



The right way is peak detection but that doesn't seem to be an option for
this application.

** That is no answer at all to my complaints - so you have lost the debate
already.

Clearly, you are know nothing damn fool.


My experience is with 28 years of flying R/C model planes and helicopters
where a battery failure means a crash.

** None of which is even slightly relevant to the original question.


I've learned most of what I know about charging from a battery
manufacturers former battery expert, manufacturer information,
microcontroller battery chargers, battery charger chip data sheets and
application notes.

** Not very interested where you got all your wrong ideas from.

But maker's mostly anonymously authored data sheets, pseudo technical
wankers posing as "experts " for scumbag import operations & ridiculous
software routines embedded in uCs by autistic code scribbling morons are an
* inexhaustible supply * of rechargeable battery bollocks.

Piss off.


...... Phil
 
On May 10, 3:17 pm, "pimpom" <pim...@invalid.invalid> wrote:
RogerN wrote:
"pimpom" <pim...@invalid.invalid> wrote in message
news:gu6ign$4g8$1@news.albasani.net...
RogerN wrote:
snip

One possibility is to set your charger to charge so many hours per
day with one of the cheapy wall timers.  The C/10 or 10 hour rate is
often used as an indefinite charge rate with Nicads, you can leave
the charge on all the time and still have pretty good battery life.
You could try a C/10 charger with a wall timer and set the timer for
perhaps 1.5X the usage.  For example if you use 50mA for 10 hours
per day you could charge at 50mA for 15 hours per day.  A little
error would have minimal effect on battery life.
A charging timer would be superfluous here as the mains line to
which it will be attached is regularly turned on every night during
waking hours and turned off for the rest of the day - a pretty
regular cycle. The uncertain factor is the discharge frequency which
is neither regular nor predictable. It may go for days without being
called upon to deliver power. You cite C/10 and someone else cited
C/50. That's quite a big difference.

C/50 is a common trickle charge to keep the batteries topped off
after they are peak charged.  Back in the day when nicads were the
standard rechargeable battery for cordless phones and the like, most
came with instructions that said to charge before use for around
12-15 hours.  These had c/10 chargers.  Nicads can take the
overcharging but in my experience I think they last longer if you
don't leave it on the chargers all the time.

Hmmm. It looks as if there's no definitive answer. Would you say that
something like C/20 would be a reasonable compromise?- Hide quoted text -

- Show quoted text -
Pimpom, Try googling "battery university". There is a bunch of stuff
there, perhaps some answers to your questions.

George Herold
 
pimpom wrote:
I know this is an old topic and I've done a search, but couldn't find a
satisfactory answer to the question: What would be a reasonable charging
current for a NiCad battery (in terms of its mAh rating) under the following
conditions?

1. Battery loading will be infrequent but unpredictable - could be once a
day or a week or more.
2. Unattended charging at or near constant current for 6-10 hours a day,
everyday.
3. Charging circuit needs to be simple - no dv or temperature detection.
Load cut-off will be automatic.
4. Battery service life need not be as long as that with optimum charging,
but should not be drastically shortened.
5. Does not matter if battery power is occasionally unavailable due to
insufficient charging time between (infrequent) loads, but should otherwise
be ready to provide power at any time.

Thanks in advance.

Simple trickle charger with taper:

Use an LM317 circuit to set the current to C/10. Add a TL431 circuit
on the output, set to the full charge voltage, and designed to steal
current such that the current available to the NiCds drops to ~C/50
or less when the pack reaches full charge voltage.

A partial schematic:

Green
+ ---[LM317]---[D1]---+---[LED]---[R]---+
| |
+-------+------[R]--------+
| | |
[R] | |
| [R] |
Red [LED] | |
| | |
+-------+ [NiCd]
| |
[TL431] |
| |
Gnd ----------+-------------------------+

When green is on and red off, current goes only to battery.
When red comes on, current is "stolen" reducing the charge
rate to ~ C/50 with properly chosen resistors. You don't
need the LEDS, they're just nice indicators. I use 1.43
volts per cell as the full charge voltage. Compute the
parallel R's for ~1.8 volt drop when (C/10 - Iled) flows.

Ed
 
"Phil Allison" <philallison@tpg.com.au> wrote in message
news:76qj3bF1ehni2U1@mid.individual.net...
"RogerNutcase"


Hmmm. It looks as if there's no definitive answer. Would you say that
something like C/20 would be a reasonable compromise?

It would probably work just fine, nicads have pretty good life even
when continuously overcharged at c/10

** That is bullshit.


It's obvious you don't know what you're talking about.


** So says a brain dead FUCKING LIAR.


Almost every cordless home device (phone, shaver, etc.) uses c/10
charging for nicads. You can leave the phone on the cradle indefinately,
battery life is not as good as properly terminated charge but they still
last a few years.


** Much less, in most cases.

SO YOU LIE


You could probably make a design to charge at C/10 at lower voltage and
taper off the current as the battery voltage came up. Perhaps an
adjustable voltage regulator and a resistor, that way it would charge
faster after being discharged and charge at maybe c/20 at maybe 80%
charge. For example if you charged a 4.8V pack with a 5.8V power
supply and 10 ohm resistor, it would charge at 0.1A with the battery
discharged to 4.8V and the current would approach zero as the pack
charge approaches 5.8V. (assuming at 5.8V the pack was near full
charge)


** Such a silly scheme will result in very long charging times AND the
cells will never reach full charge.

There is also the risk of charged cells heating and hence their voltage
dropping and hence the charge rate increasing on and on to destruction.



The right way is peak detection but that doesn't seem to be an option for
this application.


** That is no answer at all to my complaints - so you have lost the
debate already.

Clearly, you are know nothing damn fool.


My experience is with 28 years of flying R/C model planes and helicopters
where a battery failure means a crash.


** None of which is even slightly relevant to the original question.


I've learned most of what I know about charging from a battery
manufacturers former battery expert, manufacturer information,
microcontroller battery chargers, battery charger chip data sheets and
application notes.


** Not very interested where you got all your wrong ideas from.

But maker's mostly anonymously authored data sheets, pseudo technical
wankers posing as "experts " for scumbag import operations & ridiculous
software routines embedded in uCs by autistic code scribbling morons are
an * inexhaustible supply * of rechargeable battery bollocks.

Piss off.


..... Phil
You evidently seem to think you know more than the battery manufacturers
themselves, so please enlighten us.

You claim the cc/cv charging would take very long, that is true, but how
would that readily lend itself to overcharging and thermal runaway?

Your claims of short battery life would be true if we where talking about
NimH, overcharging them destroys them right away.

If you have better ideas, please share them, all you done so far is
recommend other batteries than the OP wants to use.

RogerN
 
"RogerNutcase"

** = brain dead FUCKING LIAR.


You evidently seem to think....

** Total fuckheads like you do not get to sum up anything or anyone.


You claim the cc/cv charging would take very long, that is true, but how
would that readily lend itself to overcharging and thermal runaway?
** First rule of usenet posting is to always post questions and comments
UNDER the words you want to address.

Never re-phrase what another said and then ask them to respond to that.

Cos only lying cunts do that.


Your claims of short battery life would be true if we where talking about
NimH, overcharging them destroys them right away.
** False and irrelevant.


If you have better ideas, please share them, all you done so far is
recommend other batteries than the OP wants to use.

** Totally false and a damn lie - as anyone what reads this thread from the
beginning can see.

YOU are a congenital LIAR Roger.

FOAD.



..... Phil
 

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