Charging a car battery with 14V AC?

[William Sommerwerck]

"Gary" <garyrsn@gmail.com> wrote in message
news:7fldn7h8irsrfqr9hlgsh92nl9qh682v76@4ax.com...

On Sun, 25 Mar 2012 15:36:44 -0700, "William Sommerwerck"
grizzledgeezer@comcast.net> wrote:

You said something about watching the polarity across
the output of the charger -- what exactly did you mean?

The plus output of the charger goes to the plus terminal
of the battery.

I'm aware of that. I was asking about how the polarity of
the AC output affects how the capacitor should be placed?

AC has no polarity.

Exactly my point. So does it matter how the capacitor is
placed across the output leads?

You wouldn't normally place a capacitor across /any/ device with an AC
output. The only obvious uses that come to mind would be for stability, or
to mop up high-frequency junk. Neither would be likely in a charger.

 

[Dave Platt]

In article <7fldn7h8irsrfqr9hlgsh92nl9qh682v76@4ax.com>,
Gary <garyrsn@gmail.com> wrote:

I'm aware of that. I was asking about how the polarity of the
AC output affects how the capacitor should be placed?

AC has no polarity.

Exactly my point. So does it matter how the capacitor is placed
across the output leads?

No. If it's truly an AC output, the capacitor will explode equally
well with either orientation.

Unless I am missing something here, you're trying to do something
futile... you *cannot* charge a car battery using an AC waveform of
the sort you'd get out of a transformer. The net amount of charge
delivered into the battery will be zero, with or without a filter
capacitor... all you'll do is heat up the battery to no good effect,
and (if you install a filter capacitor) overheat the capacitor and
make it blast its guts out all over the room. This is spectacular but
not terribly useful

You *must* rectify the AC (either half-wave or full-wave
rectification). Once you do so, you no longer have AC - you have a
pulsed DC.

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

 

[gregz]

Dave Platt <dplatt@radagast.org> wrote:

In article <7fldn7h8irsrfqr9hlgsh92nl9qh682v76@4ax.com>,
Gary <garyrsn@gmail.com> wrote:

I'm aware of that. I was asking about how the polarity of the
AC output affects how the capacitor should be placed?

AC has no polarity.

Exactly my point. So does it matter how the capacitor is placed
across the output leads?

No. If it's truly an AC output, the capacitor will explode equally
well with either orientation.

Unless I am missing something here, you're trying to do something
futile... you *cannot* charge a car battery using an AC waveform of
the sort you'd get out of a transformer. The net amount of charge
delivered into the battery will be zero, with or without a filter
capacitor... all you'll do is heat up the battery to no good effect,
and (if you install a filter capacitor) overheat the capacitor and
make it blast its guts out all over the room. This is spectacular but
not terribly useful

You *must* rectify the AC (either half-wave or full-wave
rectification). Once you do so, you no longer have AC - you have a
pulsed DC.

Gary keeps ignoring this.

Greg

 

On Sun, 25 Mar 2012 17:42:53 -0400, Gary <garyrsn@gmail.com> wrote:

On Sat, 24 Mar 2012 10:32:31 -0700, "William Sommerwerck"
grizzledgeezer@comcast.net> wrote:

OK, I will try as you suggest. You said something about watching the
polarity across the output of the charger -- what exactly did you mean?

The plus output of the charger goes to the plus terminal of the battery.

I'm aware of that. I was asking about how the polarity of the AC
output affects how the capacitor should be placed?

I urge you NOT to do this. There is no guarantee this charger will correctly
charge your battery. Find someone knowledgeable to help you. Or pay a
service shop to charge the battery. Or buy a new, working charger.

You're missing the point. Sometimes we play around with old, obsolete
kit, just to see if it'll work.
To cut out a lot of the BS, there is a simple test you can perform.

Set a DMM to the 20VDC range and connect it to the output of the
battery charger. If you get a reading of over 14VDC the charger is
probably good. If you get a reading of a lower voltage, suspect the
charger is bad (unless there is a 6/12 switch). If you get a reading
of 0 VDC, but a reading of 12 -15 VAC, the rectifiers are shorted.

It MIGHT be possible that selenium rectifiers are so leaky that you
would not get a DC reading, but I would doubt it.

PlainBill

 

[Jerry G.]

On Saturday, March 24, 2012 12:12:39 PM UTC-4, Gary wrote:

Hi everyone!

Any reason why AC can't be used to charge a car battery? Reason I'm
asking is that I have an old Fedtro Powerhouse charger
which is outputting AC.

You cannot charge a battery on AC. Battery chargers have to be properly current regulated at the nominal charging voltage for the battery. You do not want to have any kind of battery rupture, and especially a car battery! The acid will do a lot of damage.

Invest in a proper safe battery charger!

Jerry G.

 

[Guv Bob]

"Gary" <garyrsn@gmail.com> wrote in message news:i40sm75vgst4r7m8l000f53evkb70rk1h6@4ax.com...

OK, I will try as you suggest. You said something about watching the
polarity across the output of the charger - what exactly did you mean?

I have rigged up all kinds of circuits as an elec tech, but this would be too risky for me. I would only use a commercial charger and even then would not make any modifications to it. Charging lead-acid batteries always produces hydrogen. Even a little spark or high temp can ignite an explosion which can spray sulfuric acid mist all over. I have never seen an explosion first hand, but have talked to a fellow who is super careful and even he blew one up years ago.

Too many warnings probably, but be sure and connect to the batter first before connecting the charger to the AC source. I also connect the charger to an ext cord, and then (several feet away) connect to the AC receptacle.

FYI, here's a photo of a $25 battery charger I have used for 10+ years. a good investment for other projects.

Battery exploding
http://www.youtube.com/watch?v=d_TnsHu2u4c

Battery getting damaged from improper charging
http://www.youtube.com/watch?v=1APmCDhnuVU

Schumacher 1.5A On-Board Charger Model SE-1-12S. Input 120VAC 4A 60HZ. Output 12VDC 1.5A:
http://imageshack.us/f/205/chargerki.jpg/

 

[Carolee]

On 03/24/12 16:12, Gary wrote:

Hi everyone!

Any reason why AC can't be used to charge a car battery? Reason I'm
asking is that I have an old Fedtro Powerhouse charger
which is outputting AC.

Hopefully your face is in the car battery when it explodes, you stupid
bastard.