voltage ok for battery charger ?"

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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



Re: voltage ok for battery charger ?"

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 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.

Re: voltage ok for battery charger ?"
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


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Re: voltage ok for battery charger ?"

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 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.

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 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.

Re: voltage ok for battery charger ?"
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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


Re: voltage ok for battery charger ?"
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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) ?

Re: voltage ok for battery charger ?"
hi,  secondary side measures  :    0.0   ohms !!

primary side measures  8.4 ohms ..

mark k


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Re: voltage ok for battery charger ?"
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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.

Re: voltage ok for battery charger ?"
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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



Re: voltage ok for battery charger ?"
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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 /








Re: voltage ok for battery charger ?"
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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.

Re: voltage ok for battery charger ?"
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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.

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