charge a 12 vdc sla ftom cars 12 v system ?

[mark krawczuk]

hi, any one got any ideas on how to charge a 12 v sla from a cars 12 vdc
supply ?
i suppose a boost converter circuit to get the voltage up ?
all i need is to charge the 12 vdc sla for a torch. i want to leave it
pretty well connected up permanetly, so its always charged, ready to go ,.
any schematics , links etc....

thanks.
mark k

 

[who where]

On Mon, 1 Feb 2010 10:15:33 +0930, "mark krawczuk"
<krawczuk@adam.com.au> wrote:

hi, any one got any ideas on how to charge a 12 v sla from a cars 12 vdc
supply ?
i suppose a boost converter circuit to get the voltage up ?
all i need is to charge the 12 vdc sla for a torch. i want to leave it
pretty well connected up permanetly, so its always charged, ready to go ,.
any schematics , links etc....

For starters to *properly* manage the charging of SLA/VRLA's you need
something like the old Silicon Chip kit (Altronics K1685). They use
the Unitrode/TI UC3906 controller chip, which has arguably the best
charging regime around. Check out the AppNote by googling for
SLUA115.PDF.

The problem then resolves to providing enough regulating headroom for
the series pass element. Either EA or SC published a design (which
was kitted, don't have the details to hand) to reputedly charge an SLA
from a vehicle supply.

If at all possible, cut your losses and convert the torch to 6 volt
operation, then you just need the standalone K1685 charger. I've been
running a couple of Dolphins for about 14 years using that design with
6V4Ah SLA's, and it DOES look after the batteries. I've only had to
replace ONE in that time.

PS if you do go to 6V, the transistor will require a bit of a
heatsink.

 

[ian field]

"mark krawczuk" <krawczuk@adam.com.au> wrote in message
news:2P-dnf_fUdEyiPvWnZ2dnUVZ_j6dnZ2d@adnap.net.au...

hi, any one got any ideas on how to charge a 12 v sla from a cars 12 vdc
supply ?
i suppose a boost converter circuit to get the voltage up ?
all i need is to charge the 12 vdc sla for a torch. i want to leave it
pretty well connected up permanetly, so its always charged, ready to go ,.
any schematics , links etc....

You don't need huge current - just a slight voltage boost, I'd try a simple
blocking oscillator inverter..

A good starting point might be a salvaged common mode choke (preferably one
with not very large number of turns), one coil from the transistor's
collector to +12 the other coil to the base, the base coil is terminated by
a 10 - 15nF capacitor to GND and a 470k to +12 if it doesn't oscillate first
go, try reversing one of the windings, then reducing the resistor.

For bench testing add an output reservoir electrolytic fed by a fast soft
recovery rectifier from the collector - the voltage will probably be several
times the supply voltage.

Now add a small signal transistor (2N2222 etc) emitter to GND alongside the
BO transistor, collector to base of the BO transistor, the base is connected
via a voltage reference and current limiting resistor (about 2k2 to 10k or
so) to the capacitor/diode junction.

If you can't find a zener diode for the voltage reference that gives the
required float charge voltage (about 13.6 - 13.8V) then use a TL431
adjustable zener + trimpot to set the output exactly where you want it.

Once you've bench tested it, discard the electrolytic and connect the
rectifier to your 12V SLA.

 

[Baron]

ian field Inscribed thus:

"mark krawczuk" <krawczuk@adam.com.au> wrote in message
news:2P-dnf_fUdEyiPvWnZ2dnUVZ_j6dnZ2d@adnap.net.au...
hi, any one got any ideas on how to charge a 12 v sla from a cars 12
vdc supply ?
i suppose a boost converter circuit to get the voltage up ?
all i need is to charge the 12 vdc sla for a torch. i want to leave
it pretty well connected up permanetly, so its always charged, ready
to go ,. any schematics , links etc....

You don't need huge current - just a slight voltage boost, I'd try a
simple blocking oscillator inverter..

A good starting point might be a salvaged common mode choke
(preferably one with not very large number of turns), one coil from
the transistor's collector to +12 the other coil to the base, the base
coil is terminated by a 10 - 15nF capacitor to GND and a 470k to +12
if it doesn't oscillate first go, try reversing one of the windings,
then reducing the resistor.

For bench testing add an output reservoir electrolytic fed by a fast
soft recovery rectifier from the collector - the voltage will probably
be several times the supply voltage.

Now add a small signal transistor (2N2222 etc) emitter to GND
alongside the BO transistor, collector to base of the BO transistor,
the base is connected via a voltage reference and current limiting
resistor (about 2k2 to 10k or so) to the capacitor/diode junction.

If you can't find a zener diode for the voltage reference that gives
the required float charge voltage (about 13.6 - 13.8V) then use a
TL431 adjustable zener + trimpot to set the output exactly where you
want it.

Once you've bench tested it, discard the electrolytic and connect the
rectifier to your 12V SLA.

Surely just plugging into the cigarette lighter socket whilst the engine
is running will charge the battery just fine.

--
Best Regards:
Baron.

 

[Mr.T]

"Baron" <baron.nospam@linuxmaniac.nospam.net> wrote in message
news:hk7gt8$klm$1@news.eternal-september.org...

Surely just plugging into the cigarette lighter socket whilst the engine
is running will charge the battery just fine.

No need to worry about charging current, battery life, or even exploding
batteries then?

MrT.

 

[ian field]

"Baron" <baron.nospam@linuxmaniac.nospam.net> wrote in message
news:hk7gt8$klm$1@news.eternal-september.org...

ian field Inscribed thus:


"mark krawczuk" <krawczuk@adam.com.au> wrote in message
news:2P-dnf_fUdEyiPvWnZ2dnUVZ_j6dnZ2d@adnap.net.au...
hi, any one got any ideas on how to charge a 12 v sla from a cars 12
vdc supply ?
i suppose a boost converter circuit to get the voltage up ?
all i need is to charge the 12 vdc sla for a torch. i want to leave
it pretty well connected up permanetly, so its always charged, ready
to go ,. any schematics , links etc....

You don't need huge current - just a slight voltage boost, I'd try a
simple blocking oscillator inverter..

A good starting point might be a salvaged common mode choke
(preferably one with not very large number of turns), one coil from
the transistor's collector to +12 the other coil to the base, the base
coil is terminated by a 10 - 15nF capacitor to GND and a 470k to +12
if it doesn't oscillate first go, try reversing one of the windings,
then reducing the resistor.

For bench testing add an output reservoir electrolytic fed by a fast
soft recovery rectifier from the collector - the voltage will probably
be several times the supply voltage.

Now add a small signal transistor (2N2222 etc) emitter to GND
alongside the BO transistor, collector to base of the BO transistor,
the base is connected via a voltage reference and current limiting
resistor (about 2k2 to 10k or so) to the capacitor/diode junction.

If you can't find a zener diode for the voltage reference that gives
the required float charge voltage (about 13.6 - 13.8V) then use a
TL431 adjustable zener + trimpot to set the output exactly where you
want it.

Once you've bench tested it, discard the electrolytic and connect the
rectifier to your 12V SLA.

Surely just plugging into the cigarette lighter socket whilst the engine
is running will charge the battery just fine.

--
Best Regards:
Baron.

Just plugging it in to the accessory socket would mean that the SLA would
follow the dips in the car battery's state of charge, such as during
cranking and any other periods of heavy load.

For that reason you'd expect at least one diode in series with the charging
feed. The result of the anti-discharging diode forward volt drop would be
that the SLA was consistently under charged, over a long period of time that
might even result in the cells becoming sulphated.

The rectifier diode in the blocking oscillator I suggested also serves this
purpose.

 

[Baron]

Mr.T Inscribed thus:

"Baron" <baron.nospam@linuxmaniac.nospam.net> wrote in message
news:hk7gt8$klm$1@news.eternal-september.org...
Surely just plugging into the cigarette lighter socket whilst the
engine is running will charge the battery just fine.

No need to worry about charging current, battery life, or even
exploding batteries then?

MrT.

Thats all I do with my 1,000,000 candle power light. Its what 3-4 years
now. Nothing has gone bang, yet...

--
Best Regards:
Baron.

 

[Mr.T]

"Baron" <baron.nospam@linuxmaniac.nospam.net> wrote in message
news:hka5om$dt6$1@news.eternal-september.org...

Surely just plugging into the cigarette lighter socket whilst the
engine is running will charge the battery just fine.

No need to worry about charging current, battery life, or even
exploding batteries then?

Thats all I do with my 1,000,000 candle power light. Its what 3-4 years
now. Nothing has gone bang, yet...

And I bet the lead that came with that one has a limiting resistor built in
which you simply fail to mention.

MrT.

 

[Baron]

Mr.T Inscribed thus:

"Baron" <baron.nospam@linuxmaniac.nospam.net> wrote in message
news:hka5om$dt6$1@news.eternal-september.org...
Surely just plugging into the cigarette lighter socket whilst the
engine is running will charge the battery just fine.

No need to worry about charging current, battery life, or even
exploding batteries then?

Thats all I do with my 1,000,000 candle power light. Its what 3-4
years
now. Nothing has gone bang, yet...

And I bet the lead that came with that one has a limiting resistor
built in which you simply fail to mention.

MrT.

I have no Idea if it has, but I will by tomorrow.

--
Best Regards:
Baron.

 

[Baron]

Baron Inscribed thus:

Mr.T Inscribed thus:


"Baron" <baron.nospam@linuxmaniac.nospam.net> wrote in message
news:hka5om$dt6$1@news.eternal-september.org...
Surely just plugging into the cigarette lighter socket whilst the
engine is running will charge the battery just fine.

No need to worry about charging current, battery life, or even
exploding batteries then?

Thats all I do with my 1,000,000 candle power light. Its what 3-4
years
now. Nothing has gone bang, yet...

And I bet the lead that came with that one has a limiting resistor
built in which you simply fail to mention.

MrT.

I have no Idea if it has, but I will by tomorrow.

Replying to my own post.

There are no resistors in the lead or either of the plugs. However I
did measure the resistance of the conductors that make up the cable by
shorting them at one end and measuring at the other.
Using a digital multimeter on the lowest range (diode test) 0.75ohms the
last digit wandering about.

I therfore conclude that there is only cable and contact resistance !

--
Best Regards:
Baron.

 

[Mr.T]

"Baron" <baron.nospam@linuxmaniac.nospam.net> wrote in message
news:hkfc1v$8b1$1@news.eternal-september.org...

There are no resistors in the lead or either of the plugs. However I
did measure the resistance of the conductors that make up the cable by
shorting them at one end and measuring at the other.
Using a digital multimeter on the lowest range (diode test) 0.75ohms the
last digit wandering about.

I therfore conclude that there is only cable and contact resistance !

And what about between the torch socket and battery?

MrT.

 

[ian field]

"Mr.T" <MrT@home> wrote in message
news:4b6b70e2$0$1783$afc38c87@news.optusnet.com.au...

"Baron" <baron.nospam@linuxmaniac.nospam.net> wrote in message
news:hkfc1v$8b1$1@news.eternal-september.org...
There are no resistors in the lead or either of the plugs. However I
did measure the resistance of the conductors that make up the cable by
shorting them at one end and measuring at the other.
Using a digital multimeter on the lowest range (diode test) 0.75ohms the
last digit wandering about.

I therfore conclude that there is only cable and contact resistance !

And what about between the torch socket and battery?

MrT.

My 2,000,000 candle power 6V/55W 4Ah rechargeable hand lamp has a power
resistor and a diode inside the torch.

I'd have to check the sketch I made for the exact value but I think it was
somewhere in the general direction of 10 - 12 Ohms.

The wall-wart for the lamp has a 7805 with its ground terminal tied to a 2
resistor potential divider across the output to up the regulated voltage.

It also came with a car adapter, but I didn't bother looking inside that.

 

[Baron]

ian field Inscribed thus:

"Mr.T" <MrT@home> wrote in message
news:4b6b70e2$0$1783$afc38c87@news.optusnet.com.au...

"Baron" <baron.nospam@linuxmaniac.nospam.net> wrote in message
news:hkfc1v$8b1$1@news.eternal-september.org...
There are no resistors in the lead or either of the plugs. However
I did measure the resistance of the conductors that make up the
cable by shorting them at one end and measuring at the other.
Using a digital multimeter on the lowest range (diode test) 0.75ohms
the last digit wandering about.

I therfore conclude that there is only cable and contact resistance
!

And what about between the torch socket and battery?

MrT.



My 2,000,000 candle power 6V/55W 4Ah rechargeable hand lamp has a
power resistor and a diode inside the torch.

I'd have to check the sketch I made for the exact value but I think it
was somewhere in the general direction of 10 - 12 Ohms.

The wall-wart for the lamp has a 7805 with its ground terminal tied to
a 2 resistor potential divider across the output to up the regulated
voltage.

It also came with a car adapter, but I didn't bother looking inside
that.

Mine is a 12 volt TH bulb and 12v SLA. Apart from an on/off switch, the
charging socket on the handlamp is wired directly to the battery. It
didn't come with a wall wart. Just the charging cable with a car
adaptor plug on one end and a 5.5x2.5mm jack on the other. In fact I
don't have a clue who the manufacturer is other than "Made in ROC".

--
Best Regards:
Baron.