voltage ok for battery charger ?"

[no one]

hi, i have a 10 amp , 12 volt dc transformer , voltage measured at
rectifier .

with a capacitor across the rectifier , voltage went up to nearly 18
volts .

would this suit the basis for a lead acid car battery charger ok ?

mark

 

[John Tserkezis]

no one wrote:

hi, i have a 10 amp , 12 volt dc transformer , voltage measured at
rectifier .

with a capacitor across the rectifier , voltage went up to nearly 18
volts .

would this suit the basis for a lead acid car battery charger ok ?

No and, sort-of-yes. (what? you were expecting a simple answer?)

The numbers you state give an estimated nearly 13v RMS output at no
load, which is a bit too low for a "simple" directly-connected charger,
and worse still for a series-pass type regulated charger. So in that
case, no.

The yes bit comes from the fact that if you run a switchmode regulated
system, you can step up, and in that case, the transformer *is* good enough.
However, there is nothing off the shelf that does this, so it'll very
much need to be an entirely custom job. Probably more worthwhile as a
learning electronics project, rather than your first preference, a
battery charger.

So it depends on what you want:

A battery charger, or a DIY electronics project?
--
Sorry about your Rectocranial Inversion.

 

[TonyS]

On 19/02/2011 1:09 PM, no one wrote:

hi, i have a 10 amp , 12 volt dc transformer , voltage measured at
rectifier .

with a capacitor across the rectifier , voltage went up to nearly 18
volts .

would this suit the basis for a lead acid car battery charger ok ?

mark

Are you in a hurry?
Have a look around in your shed and find a 6V or so light bulb.
Connect it in series to the battery and you got yourself a sort of
constant current charger.
Never short out them terminals though


Tony

 

[no one]

hi, why cant it be both ????

if you can suggest a suitable step up ic , i`ll do the rest ..... i need
something that would be able to work at least 7 - 8 amps....

thanks,

mark


"John Tserkezis" <jt@techniciansyndrome.org.invalid> wrote in message
news:4d5f4f5b$0$22472$afc38c87@news.optusnet.com.au...

no one wrote:

hi, i have a 10 amp , 12 volt dc transformer , voltage measured
at
rectifier .

with a capacitor across the rectifier , voltage went up to nearly 18
volts .

would this suit the basis for a lead acid car battery charger ok ?

No and, sort-of-yes. (what? you were expecting a simple answer?)

The numbers you state give an estimated nearly 13v RMS output at no
load, which is a bit too low for a "simple" directly-connected charger,
and worse still for a series-pass type regulated charger. So in that
case, no.

The yes bit comes from the fact that if you run a switchmode regulated
system, you can step up, and in that case, the transformer *is* good
enough.
However, there is nothing off the shelf that does this, so it'll very
much need to be an entirely custom job. Probably more worthwhile as a
learning electronics project, rather than your first preference, a
battery charger.

So it depends on what you want:

A battery charger, or a DIY electronics project?
--
Sorry about your Rectocranial Inversion.

 

[John Tserkezis]

no one wrote:

hi, why cant it be both ????

I didn't mean you can't have both. My intention was to mean there are
ramifications if you choose to use that particular transformer.

if you can suggest a suitable step up ic , i`ll do the rest ..... i need
something that would be able to work at least 7 - 8 amps....

And that's where you're not quite making sense.

On one hand you're happy to turn this into a project, (which means
complexity, time and money), on the other hand, you seem to insist on
using that particular transformer, which would mean you save money on a
transformer, but will make your life harder:
I can suggest an SLA charger IC, but while they are usually configured
in a buck configuration (in their appnotes), you could modify at least
some of them for boost too. However, since your transformer will be
either higher AND lower than what the battery needs depending on charge
point and load, a full transformer will probably need to be used.
This is technically doable, but no-one ever would do this because a
suitably sourced power supply would mean a simple (and cheaper) buck
configuration can be used.

At this point, if you need to ask for "a suitable step-up IC", then
this project is either beyond your technical ability, or, near or within
your technical ability but you're just a glutton for punishment.

What you're asking is available off the shelf right now at many shops,
and that would be your cheapest, fastest, and least effort option.

Or, buy a suitable transformer as a new base. Heck, you might be even
able to use a switcher that'll be lighter too. And with the way copper
prices are going, maybe cheaper.

Unless you're a glutton for punishment, in which case, I'm unable to
help you.
--
I'm not on drugs. I am drugs.

 

[Ian Field]

"no one" <krawczuk@adam.com.au> wrote in message
news:v4mdnRXaHKF938LQnZ2dnUVZ_hSdnZ2d@adnap.net.au...

hi, i have a 10 amp , 12 volt dc transformer , voltage measured at
rectifier .

with a capacitor across the rectifier , voltage went up to nearly 18
volts .

would this suit the basis for a lead acid car battery charger ok ?

mark

AFAIK lead-acid battery chargers are wound with too many turns for a normal
PSU transformers, deliberate poor regulation if you like.

The end result is a high off load voltage to get some charging current going
when all the acid is in the plates - leaving nearly non-conducting distilled
water between the plates.

As the battery begins to charge the acid returns to solution in the
electrolyte and the charging current rises.

Your end of charge voltage should not be higher than 14.4V.

If you only have that particular transformer to work with I could suggest
adding series diodes to drop the excess voltage - but that doesn't take into
account variations in mains voltage, or as someone else suggested you can
put a bulb in series.

 

[David Eather]

On 19/02/2011 3:09 PM, no one wrote:

hi, i have a 10 amp , 12 volt dc transformer , voltage measured at
rectifier .

with a capacitor across the rectifier , voltage went up to nearly 18
volts .

would this suit the basis for a lead acid car battery charger ok ?

mark

I'm assuming you have a multimeter.

Can you measure the DC resistance of the secondary (the 12 v side) and
also the AC voltage output of transformer without anything attached
(i.e. bridge rectifer and cap) ?

 

[Ian Field]

"David Eather" <eather@tpg.com.au> wrote in message
newsIKdnaVgs-yOrv3QnZ2dnUVZ_jKdnZ2d@giganews.com...

On 19/02/2011 3:09 PM, no one wrote:
hi, i have a 10 amp , 12 volt dc transformer , voltage measured
at
rectifier .

with a capacitor across the rectifier , voltage went up to nearly 18
volts .

would this suit the basis for a lead acid car battery charger ok ?

mark



I'm assuming you have a multimeter.

Can you measure the DC resistance of the secondary (the 12 v side) and
also the AC voltage output of transformer without anything attached (i.e.
bridge rectifer and cap) ?

ISTR you have to do a vector calculation of DC resistance and the impedance
of the inductance at the mains frequency for it to mean anything worth
knowing.

 

[David Eather]

On 20/02/2011 7:26 AM, Ian Field wrote:

"David Eather"<eather@tpg.com.au> wrote in message
newsIKdnaVgs-yOrv3QnZ2dnUVZ_jKdnZ2d@giganews.com...
On 19/02/2011 3:09 PM, no one wrote:
hi, i have a 10 amp , 12 volt dc transformer , voltage measured
at
rectifier .

with a capacitor across the rectifier , voltage went up to nearly 18
volts .

would this suit the basis for a lead acid car battery charger ok ?

mark



I'm assuming you have a multimeter.

Can you measure the DC resistance of the secondary (the 12 v side) and
also the AC voltage output of transformer without anything attached (i.e.
bridge rectifer and cap) ?


ISTR you have to do a vector calculation of DC resistance and the impedance
of the inductance at the mains frequency for it to mean anything worth
knowing.

I'm still asking the question.

 

[terryc]

no one wrote:

hi, i have a 10 amp , 12 volt dc transformer , voltage measured at
rectifier .

with a capacitor across the rectifier , voltage went up to nearly 18
volts .

would this suit the basis for a lead acid car battery charger ok ?

No. Only useful if the battery is very flat to put some charge into it
or you can find a Dc-Dc battery charger that will use it.

Vin - voltage loss against internal battery resistance = final voltage
on battery. Car batteries typically charge to ~13.5 volts, but sit
around 12.? volts.

 

[Vox]

no one wrote:

hi, i have a 10 amp , 12 volt dc transformer , voltage
measured at rectifier .

with a capacitor across the rectifier , voltage went up to nearly 18
volts .

would this suit the basis for a lead acid car battery charger ok ?

mark

Colin Mitchell has uses a 500mA (0.5Amp) 12 AC ("no-load" rectified DC
~18v?) plug pack to charge a sealed lead acid (SLA)battery in this project.

http://talkingelectronics.com/projects/BatteryCharger-12vSLA/BatteryCharger-12vSLA.html

 

[no one]

hi, secondary side measures : 0.0 ohms !!

primary side measures 8.4 ohms ..

mark k


"David Eather" <eather@tpg.com.au> wrote in message
newsIKdnaVgs-yOrv3QnZ2dnUVZ_jKdnZ2d@giganews.com...

On 19/02/2011 3:09 PM, no one wrote:
hi, i have a 10 amp , 12 volt dc transformer , voltage measured
at
rectifier .

with a capacitor across the rectifier , voltage went up to nearly 18
volts .

would this suit the basis for a lead acid car battery charger ok ?

mark



I'm assuming you have a multimeter.

Can you measure the DC resistance of the secondary (the 12 v side) and
also the AC voltage output of transformer without anything attached (i.e.
bridge rectifer and cap) ?

 

[no one]

ummmm yeah , i had one off them but the wheel fell
off.............................




"David Eather" <eather@tpg.com.au> wrote in message
news:9fGdnYnbV4u3pf3QnZ2dnUVZ_qqdnZ2d@giganews.com...

On 20/02/2011 7:26 AM, Ian Field wrote:
"David Eather"<eather@tpg.com.au> wrote in message
newsIKdnaVgs-yOrv3QnZ2dnUVZ_jKdnZ2d@giganews.com...
On 19/02/2011 3:09 PM, no one wrote:
hi, i have a 10 amp , 12 volt dc transformer , voltage measured
at
rectifier .

with a capacitor across the rectifier , voltage went up to nearly
18
volts .

would this suit the basis for a lead acid car battery charger ok ?

mark



I'm assuming you have a multimeter.

Can you measure the DC resistance of the secondary (the 12 v side) and
also the AC voltage output of transformer without anything attached
(i.e.
bridge rectifer and cap) ?


ISTR you have to do a vector calculation of DC resistance and the
impedance
of the inductance at the mains frequency for it to mean anything worth
knowing.



I'm still asking the question.

 

[Vox]

Vox wrote:

no one wrote:
hi, i have a 10 amp , 12 volt dc transformer , voltage
measured at rectifier .

with a capacitor across the rectifier , voltage went up to
nearly 18 volts .

would this suit the basis for a lead acid car battery charger ok ?

mark

Colin Mitchell has uses a 500mA (0.5Amp) 12 AC ("no-load" rectified DC
~18v?) plug pack to charge a sealed lead acid (SLA)battery in this
project.
http://talkingelectronics.com/projects/BatteryCharger-12vSLA/BatteryCharger-12vSLA.html

couple examples for CAR battery

3A 15V (AC?)Transformer (18v rectified)
using
a.. U1 LM350 Regulator
a.. U2 LM301A Op Amp
http://www.free-circuit.com/car-battery-charger-circuit/

4A 17v (AC?) Transformer
http://schematicwiring.com/simple-electronic-applications/12-volts-car-battery-charger-circuit-schematic-diagram/

 

[David Eather]

On 19/02/2011 3:09 PM, no one wrote:

hi, i have a 10 amp , 12 volt dc transformer , voltage measured at
rectifier .

with a capacitor across the rectifier , voltage went up to nearly 18
volts .

would this suit the basis for a lead acid car battery charger ok ?

mark

Without better info, I'm suggesting this as a cheap way to get some
utility from your transformer.


http://www.filedropper.com/usenetbattery


feed it with rectified, unfiltered DC.

 

[David Eather]

On 21/02/2011 10:37 AM, David Eather wrote:

On 19/02/2011 3:09 PM, no one wrote:
hi, i have a 10 amp , 12 volt dc transformer , voltage measured at
rectifier .

with a capacitor across the rectifier , voltage went up to nearly 18
volts .

would this suit the basis for a lead acid car battery charger ok ?

mark



Without better info, I'm suggesting this as a cheap way to get some
utility from your transformer.


http://www.filedropper.com/usenetbattery


feed it with rectified, unfiltered DC.

if using the transformer in the other thread you should use the 15 volt
taps and change r4 to .1 ohm 5 watt. When adjusting the output voltage
fit a small cap across the output (100uf or more). Also add a thermostat
to the heat sink if you intend to allow charging of very flat batteries.

 

[Ian Field]

"David Eather" <eather@tpg.com.au> wrote in message
news:KcKdnZsoMYHYEP_QnZ2dnUVZ_vidnZ2d@giganews.com...

On 21/02/2011 10:37 AM, David Eather wrote:
On 19/02/2011 3:09 PM, no one wrote:
hi, i have a 10 amp , 12 volt dc transformer , voltage measured at
rectifier .

with a capacitor across the rectifier , voltage went up to nearly 18
volts .

would this suit the basis for a lead acid car battery charger ok ?

mark



Without better info, I'm suggesting this as a cheap way to get some
utility from your transformer.


http://www.filedropper.com/usenetbattery


feed it with rectified, unfiltered DC.

if using the transformer in the other thread you should use the 15 volt
taps and change r4 to .1 ohm 5 watt. When adjusting the output voltage fit
a small cap across the output (100uf or more). Also add a thermostat to
the heat sink if you intend to allow charging of very flat batteries.

Very flat lead acid batteries don't draw much current.