LM350K as a charger

[Jason S]

Hi, I need someone who knows a little about LM350 voltage regulators...

I'm referring to the data sheet on this website:
http://www.national.com/ds/LM/LM150.pdf
*** Page 10 - "12V Battery Charger" ***

Can anyone please explain to me briefly how the above circuit works?

I want to charge a small 12V SLA battery. I'm guessing this circuit senses
the battery's condition and perhaps controls the way the LM350 behaves, no?



It specifies a 1N457 diode and a 2N2905 transistor. Both not easily obtained
in Australia. Would a 1N4004 and a PN200 multipurpose do the job,
respectively?



What is the safest way of adding a second LED to represent that charging is
in progress, or is that what the LED is already there for?



One more thing I need to check. I have a 18V DC 1.2A regulated adaptor, but
I want to charge a 12V 1.3A battery (Jaycar part # SB-2480) .... would i
just need to increase the resistance of R7?



Thanks.

 

[Phil Allison]

"Jason S"

I want to charge a small 12V SLA battery.

** Then find a schematic intended for exactly that purpose.

The usual method is to use a *current limited* 13.8 volt DC regulator.

A regulated 13.8 volt supply with a suitable bulb will do at a pinch.




......... Phil

 

[quietguy]

If you google for - electronic circuits for RC models - you will find a number
of circuits for SLA chargers, and some good info about them

David

Jason S wrote:

Hi, I need someone who knows a little about LM350 voltage regulators...

I'm referring to the data sheet on this website:
http://www.national.com/ds/LM/LM150.pdf
*** Page 10 - "12V Battery Charger" ***

Can anyone please explain to me briefly how the above circuit works?

I want to charge a small 12V SLA battery. I'm guessing this circuit senses
the battery's condition and perhaps controls the way the LM350 behaves, no?

It specifies a 1N457 diode and a 2N2905 transistor. Both not easily obtained
in Australia. Would a 1N4004 and a PN200 multipurpose do the job,
respectively?

What is the safest way of adding a second LED to represent that charging is
in progress, or is that what the LED is already there for?

One more thing I need to check. I have a 18V DC 1.2A regulated adaptor, but
I want to charge a 12V 1.3A battery (Jaycar part # SB-2480) .... would i
just need to increase the resistance of R7?

Thanks.

 

[budgie]

On Sat, 22 Oct 2005 15:46:22 +1000, "Jason S" <jst3712@iprimus.com.au> wrote:

Hi, I need someone who knows a little about LM350 voltage regulators...

I'm referring to the data sheet on this website:
http://www.national.com/ds/LM/LM150.pdf
*** Page 10 - "12V Battery Charger" ***

Can anyone please explain to me briefly how the above circuit works?

I want to charge a small 12V SLA battery. I'm guessing this circuit senses
the battery's condition and perhaps controls the way the LM350 behaves, no?

(snip)

If you really want to charge a SLA battery, I'd suggest using a smarter
circuit/device - have a look at the Unitrode (now TI) UC3906 at:

http://focus.ti.com/lit/ds/symlink/uc3906.pdf

One more thing I need to check. I have a 18V DC 1.2A regulated adaptor, but
I want to charge a 12V 1.3A battery (Jaycar part # SB-2480) .... would i
just need to increase the resistance of R7?

That adaptor would be quite suitable for a charger based on the UC3906. There
was a ?SC kit using them - may still be around ay Jaycar, Altronics or
TrickieDickie's.

 

[Franc Zabkar]

On Sat, 22 Oct 2005 15:46:22 +1000, "Jason S" <jst3712@iprimus.com.au>
put finger to keyboard and composed:

Hi, I need someone who knows a little about LM350 voltage regulators...

I'm referring to the data sheet on this website:
http://www.national.com/ds/LM/LM150.pdf
*** Page 10 - "12V Battery Charger" ***

Can anyone please explain to me briefly how the above circuit works?

If we ignore the contribution of the LM301, then the regulator's
output voltage is given by ...

Vreg = 1.25 [1 + R1/(R2 + R3)] = 16.6V

If the output of the LM301 is 0V, then ...

Vreg = 1.25 [1 + (R1||R4) /(R2 + R3)] = 14.0V

The LM301 compares the voltage drop across R2 (76.5 mV) against the
voltage drop across R6 (0.2 x Icharge).

The charger is kickstarted by momentarily disturbing the offset of the
opamp via the Start switch.

I want to charge a small 12V SLA battery. I'm guessing this circuit senses
the battery's condition and perhaps controls the way the LM350 behaves, no?

The circuit attempts to maintain a constant charging current of 383mA.
It does this by sensing the charging current in R6 and adjusting the
charging voltage via the LM301. The regulator voltage is controlled by
varying the resistance at the ADJ terminal of the LM350.

It specifies a 1N457 diode and a 2N2905 transistor. Both not easily obtained
in Australia. Would a 1N4004 and a PN200 multipurpose do the job,
respectively?

Any general purpose PNP transistor (eg BC557) should work OK. A 1N4148
or 1N914 signal diode should be fine in place of the 1N457.

What is the safest way of adding a second LED to represent that charging is
in progress, or is that what the LED is already there for?

The LED lights whenever the charging current is low and goes out when
the current exceeds ~400mA.

One more thing I need to check. I have a 18V DC 1.2A regulated adaptor, but
I want to charge a 12V 1.3A battery (Jaycar part # SB-2480) .... would i
just need to increase the resistance of R7?

I don't see an R7.

In any case I would avoid this circuit for several reasons, the main
one being that it provides no current limiting (other than that
provided inherently by the LM350) in the case of a dead flat battery,
or in the case of a collapsed cell. A better approach is to use a
13.8V constant voltage, current limited charger. WES Components have
one for about $20 to the trade. If you'd like to build your own, then
I can scan the circuit of a commercial SLA charger for you.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

 

[Phil Allison]

"Franc Zabkar"

A better approach is to use a
13.8V constant voltage, current limited charger. WES Components have
one for about $20 to the trade. If you'd like to build your own, then
I can scan the circuit of a commercial SLA charger for you.

** WES have several SLA chargers, the smallest is rated at 0.5 amps and
others are 1 amp and 2.7 amps.

The 0.5 amp (Arlec PS664 ) model is suitable for SLAs rated at 2.5 Ah or
greater.

The OP says he has a 1.3 Ah SLA.

The Jaycar MB-3517 SLA charger ( rated at 350mA) is more suitable.


BTW

Small SLA chargers are cheaper than the cost of the parts to build one.




......... Phil

 

[Jason S]

The OP says he has a 1.3 Ah SLA.

The Jaycar MB-3517 SLA charger ( rated at 350mA) is more suitable.


BTW

Small SLA chargers are cheaper than the cost of the parts to build one.




........ Phil

Yes I know that, but that doesn't apply to me, as I want to incorporate it
into a circuit. I want to be able to control how the charger works. I dont
want to have an external transformer for the charging. I just want a
transformer that can be used for 2 purposes: A charger, and a power supply
for the rest of the circuitry.

 

[Phil Allison]

"Jason S

Yes I know that, but that doesn't apply to me,

** No one gives a flying fuck about YOU - Jason Shithead.

Points of fact are made for the sake of accuracy and to benefit others
reading now or possibly years later.




......... Phil

 

[Jason S]

"Franc Zabkar" <fzabkar@iinternode.on.net> wrote in message
news:ruall1prqt661nnu4chokfee4b7b7oojfo@4ax.com...

On Sat, 22 Oct 2005 15:46:22 +1000, "Jason S" <jst3712@iprimus.com.au
put finger to keyboard and composed:

Hi, I need someone who knows a little about LM350 voltage regulators...

I'm referring to the data sheet on this website:
http://www.national.com/ds/LM/LM150.pdf
*** Page 10 - "12V Battery Charger" ***

Can anyone please explain to me briefly how the above circuit works?

If we ignore the contribution of the LM301, then the regulator's
output voltage is given by ...

Vreg = 1.25 [1 + R1/(R2 + R3)] = 16.6V

If the output of the LM301 is 0V, then ...

Vreg = 1.25 [1 + (R1||R4) /(R2 + R3)] = 14.0V

The LM301 compares the voltage drop across R2 (76.5 mV) against the
voltage drop across R6 (0.2 x Icharge).

The charger is kickstarted by momentarily disturbing the offset of the
opamp via the Start switch.

I want to charge a small 12V SLA battery. I'm guessing this circuit
senses
the battery's condition and perhaps controls the way the LM350 behaves,
no?

The circuit attempts to maintain a constant charging current of 383mA.
It does this by sensing the charging current in R6 and adjusting the
charging voltage via the LM301. The regulator voltage is controlled by
varying the resistance at the ADJ terminal of the LM350.

It specifies a 1N457 diode and a 2N2905 transistor. Both not easily
obtained
in Australia. Would a 1N4004 and a PN200 multipurpose do the job,
respectively?

Any general purpose PNP transistor (eg BC557) should work OK. A 1N4148
or 1N914 signal diode should be fine in place of the 1N457.

What is the safest way of adding a second LED to represent that charging
is
in progress, or is that what the LED is already there for?

The LED lights whenever the charging current is low and goes out when
the current exceeds ~400mA.

One more thing I need to check. I have a 18V DC 1.2A regulated adaptor,
but
I want to charge a 12V 1.3A battery (Jaycar part # SB-2480) .... would i
just need to increase the resistance of R7?

I don't see an R7.

In any case I would avoid this circuit for several reasons, the main
one being that it provides no current limiting (other than that
provided inherently by the LM350) in the case of a dead flat battery,
or in the case of a collapsed cell. A better approach is to use a
13.8V constant voltage, current limited charger. WES Components have
one for about $20 to the trade. If you'd like to build your own, then
I can scan the circuit of a commercial SLA charger for you.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

***
Hi Franc!

Thanks so much for your effort to respond the way you have, question by
question. I admit I made an error with the R7. I actually meant the R6 (0.2
ohm), sorry. I thought the 10W 'R6' had something to do with current
limiting, no? Can't current limiting just be added to it, or is the circuit
in general still 'not-so-good' in your opinion? What were your other
reasons, just out of curiosity?

Anyway, when the LED lights up, does the charging actually stop (to a
certain degree) as well?

Yes, I want to build my own because I want to be able to incorporate it with
other circuits at a later time (that require battery backup), and I don't
want to have an external battery charger plugged into the wall... i know
they exist, and are handy, but it doesn't suit my requirement.

### SCENARIO ###
Incase you don't fully understand the scenario (I dont want the wrong
charger type!), maybe this will give you a better understanding.............
Basically, I intend to have the battery isolated from both the External
Load, and the Battery Charger (separated by relay contacts). The battery is
only used when it is needed (for backup). Instead of having the battery
connected to the charger at all times (keeping it on trickle charge), I
will probably just have a battery voltage checking circuit that monitors the
voltage of the "isolated" battery at regular intervals (baring in mind
batteries self discharge), and if the voltage is getting low (around 11.8V),
a relay will connect the battery to the charger. The charger will do its
job, but when the battery gets full, it either stops charging, or somehow
signals out to the relay driver that the battery is now full and to
disconnect the battery from the charger again.
- Battery Voltage Monitor : "Battery, are you getting low dear?"
- Battery : "Yes! Charge me!"
- [Relay connects battery to the charger]
- [Charging commences]
- ...Time...
- [Charge is complete / Relay disconnects battery from the charger / Fully
charged battery "isolated" again, ready for use].

P.S. Your idea of scanning a commercial SLA charger for me sounds great >
If you have a scan for me, let me know and I'll give you my email address.
But I would need you to briefly explain what the charger does, especially at
the end of the charge cycle. Sorry for the long email... might as well say
as much as I can, instead of emailing back and forth hundreds if times!

Thought I might as well make use of that 18V 1.2A transformer that I can no
longer return now =(

Thanks again, and best regards,

Jason.

 

[Jason S]

"Phil Allison" <philallison@tpg.com.au> wrote in message
news:3s04erFlq14pU1@individual.net...

"Franc Zabkar"

A better approach is to use a
13.8V constant voltage, current limited charger. WES Components have
one for about $20 to the trade. If you'd like to build your own, then
I can scan the circuit of a commercial SLA charger for you.



** WES have several SLA chargers, the smallest is rated at 0.5 amps and
others are 1 amp and 2.7 amps.

The 0.5 amp (Arlec PS664 ) model is suitable for SLAs rated at 2.5 Ah or
greater.

The OP says he has a 1.3 Ah SLA.

The Jaycar MB-3517 SLA charger ( rated at 350mA) is more suitable.


BTW

Small SLA chargers are cheaper than the cost of the parts to build one.

yeh, I believe it - but in my case, I have no option - I need an "onboard
charger".

........ Phil

Thanks for the reply (better than your 'first' one anyway!). But what
happens if I dont want to use an External "plug-in" charger? Is there a
good schematic somewhere I can use (if so, what do you like about it)?
You see, the battery is going to be used as a "backup" battery, and I don't
want to monitor it myself - so the charger should be fully automatic.

 

[Phil Allison]

"Jason S"

Thanks for the reply (better than your 'first' one anyway!). But what
happens if I dont want to use an External "plug-in" charger? Is there a
good schematic somewhere I can use (if so, what do you like about it)?
You see, the battery is going to be used as a "backup" battery, and I
don't want to monitor it myself - so the charger should be fully
automatic.

** Why do you so rudely IGNORE what is said to you ???

Are you a disciple of that Mark Harriss imbecile ???

ALL you need is a voltage regulator with **13.8 volts DC ** output that is
CURRENT limited to around 300mA.
This will charge the 1.3 Ah SLA at a safe rate and then hold the battery
with a tiny trickle of current at 13.8 volts. A 12 volt, 6 watt bulb will do
in series with the 12 volt battery and an LM317 set to 13.8 volts.

This is the standard and preferred method of SLA charging !!!

Get it ???????




.......... Phil

 

[Chris Jones]

Jason S wrote:

"Franc Zabkar" <fzabkar@iinternode.on.net> wrote in message
news:ruall1prqt661nnu4chokfee4b7b7oojfo@4ax.com...
On Sat, 22 Oct 2005 15:46:22 +1000, "Jason S" <jst3712@iprimus.com.au
put finger to keyboard and composed:

Hi, I need someone who knows a little about LM350 voltage regulators...

I'm referring to the data sheet on this website:
http://www.national.com/ds/LM/LM150.pdf
*** Page 10 - "12V Battery Charger" ***

Can anyone please explain to me briefly how the above circuit works?

If we ignore the contribution of the LM301, then the regulator's
output voltage is given by ...

Vreg = 1.25 [1 + R1/(R2 + R3)] = 16.6V

If the output of the LM301 is 0V, then ...

Vreg = 1.25 [1 + (R1||R4) /(R2 + R3)] = 14.0V

The LM301 compares the voltage drop across R2 (76.5 mV) against the
voltage drop across R6 (0.2 x Icharge).

The charger is kickstarted by momentarily disturbing the offset of the
opamp via the Start switch.

I want to charge a small 12V SLA battery. I'm guessing this circuit
senses
the battery's condition and perhaps controls the way the LM350 behaves,
no?

The circuit attempts to maintain a constant charging current of 383mA.
It does this by sensing the charging current in R6 and adjusting the
charging voltage via the LM301. The regulator voltage is controlled by
varying the resistance at the ADJ terminal of the LM350.

It specifies a 1N457 diode and a 2N2905 transistor. Both not easily
obtained
in Australia. Would a 1N4004 and a PN200 multipurpose do the job,
respectively?

Any general purpose PNP transistor (eg BC557) should work OK. A 1N4148
or 1N914 signal diode should be fine in place of the 1N457.

What is the safest way of adding a second LED to represent that charging
is
in progress, or is that what the LED is already there for?

The LED lights whenever the charging current is low and goes out when
the current exceeds ~400mA.

One more thing I need to check. I have a 18V DC 1.2A regulated adaptor,
but
I want to charge a 12V 1.3A battery (Jaycar part # SB-2480) .... would i
just need to increase the resistance of R7?

I don't see an R7.

In any case I would avoid this circuit for several reasons, the main
one being that it provides no current limiting (other than that
provided inherently by the LM350) in the case of a dead flat battery,
or in the case of a collapsed cell. A better approach is to use a
13.8V constant voltage, current limited charger. WES Components have
one for about $20 to the trade. If you'd like to build your own, then
I can scan the circuit of a commercial SLA charger for you.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.


***
Hi Franc!

Thanks so much for your effort to respond the way you have, question by
question. I admit I made an error with the R7. I actually meant the R6
(0.2
ohm), sorry. I thought the 10W 'R6' had something to do with current
limiting, no? Can't current limiting just be added to it, or is the
circuit
in general still 'not-so-good' in your opinion? What were your other
reasons, just out of curiosity?

Anyway, when the LED lights up, does the charging actually stop (to a
certain degree) as well?

Yes, I want to build my own because I want to be able to incorporate it
with other circuits at a later time (that require battery backup), and I
don't want to have an external battery charger plugged into the wall... i
know they exist, and are handy, but it doesn't suit my requirement.

### SCENARIO ###
Incase you don't fully understand the scenario (I dont want the wrong
charger type!), maybe this will give you a better
understanding............. Basically, I intend to have the battery
isolated from both the External
Load, and the Battery Charger (separated by relay contacts). The battery
is
only used when it is needed (for backup). Instead of having the battery
connected to the charger at all times (keeping it on trickle charge), I
will probably just have a battery voltage checking circuit that monitors
the voltage of the "isolated" battery at regular intervals (baring in mind
batteries self discharge), and if the voltage is getting low (around
11.8V), a relay will connect the battery to the charger. The charger will
do its job, but when the battery gets full, it either stops charging, or
somehow signals out to the relay driver that the battery is now full and
to disconnect the battery from the charger again.
- Battery Voltage Monitor : "Battery, are you getting low dear?"
- Battery : "Yes! Charge me!"
- [Relay connects battery to the charger]
- [Charging commences]
- ...Time...
- [Charge is complete / Relay disconnects battery from the charger / Fully
charged battery "isolated" again, ready for use].

P.S. Your idea of scanning a commercial SLA charger for me sounds great
If you have a scan for me, let me know and I'll give you my email address.
But I would need you to briefly explain what the charger does, especially
at
the end of the charge cycle. Sorry for the long email... might as well
say as much as I can, instead of emailing back and forth hundreds if
times!

Thought I might as well make use of that 18V 1.2A transformer that I can
no longer return now =(

Thanks again, and best regards,

Jason.

I don't recommend that you try to determine when the SLAB is in need of
charging by measuring the voltage, since the battery voltage is pretty
constant over a wide range of the possible state of charge. You might find
that when you need it, the battery is only 10% full.

If you want the charger to be off most of the time (e.g. to reduce the
standby power consumption of your installation) then I would suggest just
turn on the charger for 1 hour every week, plus whatever time is necessary
after the battery has been on-load.

I would suggest you buy (or if you insist, build) a normal, voltage
regulated, current-limited SLA charger. Check with an ammeter to make sure
that it does not discharge the battery at all if it is left connected with
the mains switched off. Then put a timer and a relay in the mains to
switch it on for one hour a week as I suggested above. Perhaps one of
those plug-in timers would do. It would even have electrical approval too,
not that this says much about electrical safety...but more about legality
etc.

If you find that your charger =does= draw some leakage current away from the
battery when the mains is off, then you might be able to arrange a relay in
between the battery and charge that is switched on when the charger is on.

Chris

 

[Jason S]

"Phil Allison" <philallison@tpg.com.au> wrote in message
news:3s0q83FltuikU1@individual.net...

"Jason S


Yes I know that, but that doesn't apply to me,


** No one gives a flying fuck about YOU - Jason Shithead.

Points of fact are made for the sake of accuracy and to benefit others
reading now or possibly years later.




........ Phil

oh go and get stuffed u DICKHEAD.

you are really not helping me whatsoever - you think you are, especially by
being so fucking RUDE to a lot of people on here, not just me. Don't take
it out on others just cos you got a miserable life and have a short fuse.
The sort of answer I got from you soooo did not help me. If you had even
bothered to read my questions about the LM350K datasheet in the first
place - whether or not you "approve" of it - you should have answered them
and that is all.
By the way, you really need to control yourself. If people bother you,
ignore them, ok? Don't go calling people a "shithead" n stuff just because
they think you are not helpful enough.... Mister "I know it all".

If I ever post another message in the future, I don't want you to respond to
it ok? I'd rather get no answer than get smart-ass comments from you.

 

[Phil Allison]

"Jason S"

"Phil Allison"


Yes I know that, but that doesn't apply to me,


** No one gives a flying fuck about YOU - Jason Shithead.

Points of fact are made for the sake of accuracy and to benefit others
reading now or possibly years later.



oh go and get stuffed u DICKHEAD.

** You are a ARSE Jason.

A fucking, pig ignorant ARSE !!

you are really not helping me whatsoever

** You are beyond help - Jason.

No one that brain fucked can be helped.

If you had even bothered to read my questions about the LM350K datasheet
in the first place - whether or not you "approve" of it - you should
have answered them and that is all.

** YOU *never* get the right tell others what to do on a Public Forum or
how to answer a query.

Pompous, arrogant, know nothing, autistic fuckwits like Jason are a dime a
dozen.

If I ever post another message in the future, I don't want you to respond
to it ok? I'd rather get no answer than get smart-ass comments from you.

** That guarantees you will get lots from me.

Better go find another NG - fuckhead.




.............. Phil

 

[Ken Taylor]

"Jason S" <jst3712@iprimus.com.au> wrote in message
news:435c4069$1_1@news.iprimus.com.au...

Jason, you'll lose so little by expanding your kill-file by one, you'll
wonder why you didn't do it earlier.

Cheers.

Ken

 

[Phil Allison]

"Ken Taylor"

"Jason S"

Jason, you'll lose so little by expanding your kill-file by one, you'll
wonder why you didn't do it earlier.

** Listen Ken the Kiwi.

I supplied this pig ignorant, autistic imbecile the correct answer to his
query, not once but twice - but he rudely ignored it.

Then the vile anonymous shit for brains publicly abuses me for explaining
the nature of usenet forums to him.

Now some half witted Kiwi shithead called "Ken Taylor" comes along an
supports the vile Jason puke.


Ken - you can go straight into HELL and fucking rot there.



........... Phil

 

[Franc Zabkar]

On Sun, 23 Oct 2005 18:16:24 +1000, "Jason S" <jst3712@iprimus.com.au>
put finger to keyboard and composed:

"Franc Zabkar" <fzabkar@iinternode.on.net> wrote in message
news:ruall1prqt661nnu4chokfee4b7b7oojfo@4ax.com...
On Sat, 22 Oct 2005 15:46:22 +1000, "Jason S" <jst3712@iprimus.com.au
put finger to keyboard and composed:

Hi, I need someone who knows a little about LM350 voltage regulators...

I'm referring to the data sheet on this website:
http://www.national.com/ds/LM/LM150.pdf
*** Page 10 - "12V Battery Charger" ***

Can anyone please explain to me briefly how the above circuit works?

If we ignore the contribution of the LM301, then the regulator's
output voltage is given by ...

Vreg = 1.25 [1 + R1/(R2 + R3)] = 16.6V

If the output of the LM301 is 0V, then ...

Vreg = 1.25 [1 + (R1||R4) /(R2 + R3)] = 14.0V

The LM301 compares the voltage drop across R2 (76.5 mV) against the
voltage drop across R6 (0.2 x Icharge).

The charger is kickstarted by momentarily disturbing the offset of the
opamp via the Start switch.

I want to charge a small 12V SLA battery. I'm guessing this circuit
senses
the battery's condition and perhaps controls the way the LM350 behaves,
no?

The circuit attempts to maintain a constant charging current of 383mA.
It does this by sensing the charging current in R6 and adjusting the
charging voltage via the LM301. The regulator voltage is controlled by
varying the resistance at the ADJ terminal of the LM350.

It specifies a 1N457 diode and a 2N2905 transistor. Both not easily
obtained
in Australia. Would a 1N4004 and a PN200 multipurpose do the job,
respectively?

Any general purpose PNP transistor (eg BC557) should work OK. A 1N4148
or 1N914 signal diode should be fine in place of the 1N457.

What is the safest way of adding a second LED to represent that charging
is
in progress, or is that what the LED is already there for?

The LED lights whenever the charging current is low and goes out when
the current exceeds ~400mA.

One more thing I need to check. I have a 18V DC 1.2A regulated adaptor,
but
I want to charge a 12V 1.3A battery (Jaycar part # SB-2480) .... would i
just need to increase the resistance of R7?

I don't see an R7.

In any case I would avoid this circuit for several reasons, the main
one being that it provides no current limiting (other than that
provided inherently by the LM350) in the case of a dead flat battery,
or in the case of a collapsed cell. A better approach is to use a
13.8V constant voltage, current limited charger. WES Components have
one for about $20 to the trade. If you'd like to build your own, then
I can scan the circuit of a commercial SLA charger for you.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.


***
Hi Franc!

Thanks so much for your effort to respond the way you have, question by
question. I admit I made an error with the R7. I actually meant the R6 (0.2
ohm), sorry. I thought the 10W 'R6' had something to do with current
limiting, no?

R6 sets the charging current according to this formula:

Icharge (mA) = 76.5 / R6

It doesn't actually *limit* the current.

Can't current limiting just be added to it, or is the circuit
in general still 'not-so-good' in your opinion? What were your other
reasons, just out of curiosity?

You could add current limiting to the circuit, but you could achieve
the same end more cheaply using an alternative approach.

One other reason I don't like this circuit is that it charges the
battery as a current source rather than as a voltage source. I think
you'll find that the latter is the more widely accepted approach for
SLA batteries.

Anyway, when the LED lights up, does the charging actually stop (to a
certain degree) as well?

It seems to me that the LED's brightness can vary throughout the
charging process. I'm not quite sure what its exact function is.

Yes, I want to build my own because I want to be able to incorporate it with
other circuits at a later time (that require battery backup), and I don't
want to have an external battery charger plugged into the wall... i know
they exist, and are handy, but it doesn't suit my requirement.

### SCENARIO ###
Incase you don't fully understand the scenario (I dont want the wrong
charger type!), maybe this will give you a better understanding.............
Basically, I intend to have the battery isolated from both the External
Load, and the Battery Charger (separated by relay contacts). The battery is
only used when it is needed (for backup). Instead of having the battery
connected to the charger at all times (keeping it on trickle charge), I
will probably just have a battery voltage checking circuit that monitors the
voltage of the "isolated" battery at regular intervals (baring in mind
batteries self discharge), and if the voltage is getting low (around 11.8V),
a relay will connect the battery to the charger. The charger will do its
job, but when the battery gets full, it either stops charging, or somehow
signals out to the relay driver that the battery is now full and to
disconnect the battery from the charger again.
- Battery Voltage Monitor : "Battery, are you getting low dear?"
- Battery : "Yes! Charge me!"
- [Relay connects battery to the charger]
- [Charging commences]
- ...Time...
- [Charge is complete / Relay disconnects battery from the charger / Fully
charged battery "isolated" again, ready for use].

P.S. Your idea of scanning a commercial SLA charger for me sounds great

Here is the circuit out of a camcorder battery pack, WES code VBV860.

http://www.users.on.net/~fzabkar/vbv860.JPG

It's basically just an LM723 regulator with a TIP41C pass transistor.
Some component values are missing but the principal info is all there.
Note that although the unit is sold as a 6V battery pack for 6V
camcorders, it actually contains four series connected 2.0V SLA cells.
I've had to modify mine for 6V using a 6V SLA brick and some minor
circuit changes. You will need to change some resistor values to
convert it for 12V (13.8V) use.

R4 determines the output current limit, as follows:

Icharge(max) = 0.6V / R4

A value of 0.56 or 0.68 ohm should give you a 1A max charging current.

The potential dividers formed by R16/R17 and R6/R18 determine the
charging voltage.

Transistor Q2 needs to be heatsinked.

FYI, there is a discussion going on at sci.electronics.repair
regarding a homebuilt SLA charger. It uses a Unitrode UC3906 sealed
lead-acid battery-charger IC:

http://focus.ti.com/lit/an/slua115/slua115.pdf

It may be just what you need.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.

 

[Alan Rutlidge]

"Phil Allison" <philallison@tpg.com.au> wrote in message
news:3s3a7gFm98m7U1@individual.net...

"Ken Taylor"
"Jason S"

Jason, you'll lose so little by expanding your kill-file by one, you'll
wonder why you didn't do it earlier.


** Listen Ken the Kiwi.

I supplied this pig ignorant, autistic imbecile the correct answer to his
query, not once but twice - but he rudely ignored it.

Then the vile anonymous shit for brains publicly abuses me for explaining
the nature of usenet forums to him.

Now some half witted Kiwi shithead called "Ken Taylor" comes along an
supports the vile Jason puke.


Ken - you can go straight into HELL and fucking rot there.



.......... Phil

YAWN......
ZZZZzzzzzzZZZZzzzzzzzzzzzzZZZzzzzZZZZZZzzzzzzZZzZZZZZzzzzzzzzzzzZZZZZZ

 

[Phil Allison]

"Alan Rutlidge"

YAWN......
ZZZZzzzzzzZZZZzzzzzzzzzzzzZZZzzzzZZZZZZzzzzzzZZzZZZZZzzzzzzzzzzzZZZZZZ

** Hey netstalker !

Say cheese.




.............. Phil

 

[Jason S]

"Chris Jones" <lugnut808@nospam.yahoo.com> wrote in message
news:11ln58neent2m02@corp.supernews.com...

Jason S wrote:


"Franc Zabkar" <fzabkar@iinternode.on.net> wrote in message
news:ruall1prqt661nnu4chokfee4b7b7oojfo@4ax.com...
On Sat, 22 Oct 2005 15:46:22 +1000, "Jason S" <jst3712@iprimus.com.au
put finger to keyboard and composed:

Hi, I need someone who knows a little about LM350 voltage regulators...

I'm referring to the data sheet on this website:
http://www.national.com/ds/LM/LM150.pdf
*** Page 10 - "12V Battery Charger" ***

Can anyone please explain to me briefly how the above circuit works?

If we ignore the contribution of the LM301, then the regulator's
output voltage is given by ...

Vreg = 1.25 [1 + R1/(R2 + R3)] = 16.6V

If the output of the LM301 is 0V, then ...

Vreg = 1.25 [1 + (R1||R4) /(R2 + R3)] = 14.0V

The LM301 compares the voltage drop across R2 (76.5 mV) against the
voltage drop across R6 (0.2 x Icharge).

The charger is kickstarted by momentarily disturbing the offset of the
opamp via the Start switch.

I want to charge a small 12V SLA battery. I'm guessing this circuit
senses
the battery's condition and perhaps controls the way the LM350 behaves,
no?

The circuit attempts to maintain a constant charging current of 383mA.
It does this by sensing the charging current in R6 and adjusting the
charging voltage via the LM301. The regulator voltage is controlled by
varying the resistance at the ADJ terminal of the LM350.

It specifies a 1N457 diode and a 2N2905 transistor. Both not easily
obtained
in Australia. Would a 1N4004 and a PN200 multipurpose do the job,
respectively?

Any general purpose PNP transistor (eg BC557) should work OK. A 1N4148
or 1N914 signal diode should be fine in place of the 1N457.

What is the safest way of adding a second LED to represent that charging
is
in progress, or is that what the LED is already there for?

The LED lights whenever the charging current is low and goes out when
the current exceeds ~400mA.

One more thing I need to check. I have a 18V DC 1.2A regulated adaptor,
but
I want to charge a 12V 1.3A battery (Jaycar part # SB-2480) .... would i
just need to increase the resistance of R7?

I don't see an R7.

In any case I would avoid this circuit for several reasons, the main
one being that it provides no current limiting (other than that
provided inherently by the LM350) in the case of a dead flat battery,
or in the case of a collapsed cell. A better approach is to use a
13.8V constant voltage, current limited charger. WES Components have
one for about $20 to the trade. If you'd like to build your own, then
I can scan the circuit of a commercial SLA charger for you.

-- Franc Zabkar

Please remove one 'i' from my address when replying by email.


***
Hi Franc!

Thanks so much for your effort to respond the way you have, question by
question. I admit I made an error with the R7. I actually meant the R6
(0.2
ohm), sorry. I thought the 10W 'R6' had something to do with current
limiting, no? Can't current limiting just be added to it, or is the
circuit
in general still 'not-so-good' in your opinion? What were your other
reasons, just out of curiosity?

Anyway, when the LED lights up, does the charging actually stop (to a
certain degree) as well?

Yes, I want to build my own because I want to be able to incorporate it
with other circuits at a later time (that require battery backup), and I
don't want to have an external battery charger plugged into the wall... i
know they exist, and are handy, but it doesn't suit my requirement.

### SCENARIO ###
Incase you don't fully understand the scenario (I dont want the wrong
charger type!), maybe this will give you a better
understanding............. Basically, I intend to have the battery
isolated from both the External
Load, and the Battery Charger (separated by relay contacts). The battery
is
only used when it is needed (for backup). Instead of having the battery
connected to the charger at all times (keeping it on trickle charge), I
will probably just have a battery voltage checking circuit that monitors
the voltage of the "isolated" battery at regular intervals (baring in
mind
batteries self discharge), and if the voltage is getting low (around
11.8V), a relay will connect the battery to the charger. The charger will
do its job, but when the battery gets full, it either stops charging, or
somehow signals out to the relay driver that the battery is now full and
to disconnect the battery from the charger again.
- Battery Voltage Monitor : "Battery, are you getting low dear?"
- Battery : "Yes! Charge me!"
- [Relay connects battery to the charger]
- [Charging commences]
- ...Time...
- [Charge is complete / Relay disconnects battery from the charger /
Fully
charged battery "isolated" again, ready for use].

P.S. Your idea of scanning a commercial SLA charger for me sounds great
If you have a scan for me, let me know and I'll give you my email
address.
But I would need you to briefly explain what the charger does, especially
at
the end of the charge cycle. Sorry for the long email... might as well
say as much as I can, instead of emailing back and forth hundreds if
times!

Thought I might as well make use of that 18V 1.2A transformer that I can
no longer return now =(

Thanks again, and best regards,

Jason.

I don't recommend that you try to determine when the SLAB is in need of
charging by measuring the voltage, since the battery voltage is pretty
constant over a wide range of the possible state of charge. You might
find
that when you need it, the battery is only 10% full.

really? I wasn't aware of that!

If you want the charger to be off most of the time (e.g. to reduce the
standby power consumption of your installation) then I would suggest just
turn on the charger for 1 hour every week, plus whatever time is necessary
after the battery has been on-load.

I would suggest you buy (or if you insist, build) a normal, voltage
regulated, current-limited SLA charger. Check with an ammeter to make
sure
that it does not discharge the battery at all if it is left connected with
the mains switched off. Then put a timer and a relay in the mains to
switch it on for one hour a week as I suggested above. Perhaps one of
those plug-in timers would do. It would even have electrical approval
too,
not that this says much about electrical safety...but more about legality
etc.

If you find that your charger =does= draw some leakage current away from
the
battery when the mains is off, then you might be able to arrange a relay
in
between the battery and charge that is switched on when the charger is on.

Chris

Ok thanks Chris, I'll take that into consideration. Thanks for your reply.

Jason.