Charging a car battery with 14V AC?

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

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

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.

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

Battery getting damaged from improper charging

Schumacher 1.5A On-Board Charger Model SE-1-12S. Input 120VAC 4A 60HZ. = Output 12VDC 1.5A:

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