Unsmoothed car battery charger - is it crap?

[Dave Plowman (News)]

My ancient one has a series resistor to limit the current - and has both mains and DC fuses.

[Michael A. Terrell]

The one I built in the '60s has a Variac to set the charging current, ot float voltage.

[Clot]

[PeterD]

Yes, when religion peddlers come to the door, they make great things to throw.

"But, I didn't see that guy standing there, sorry!"

BTW, don't unpolarized batteries just provide AC? And if that's the case, how do you specifiy 50 or 60 Hz?

[keithw86]

Yes. 0VAC

0VAC 50/60Hz.

Of course, in Spice they can deliver whatever voltage/frequency you want. No need to worry about the little details of thermodynamics either.

[Robert Baer]

...that is how fast it tumbles when thrown?

[Eddie]

I'm the OP. I think mine is over 30 years old.

I took the casing off (rivetted of course) to see the inside:

front

sure looks old!

Eddie

[Eddie]

I'm the OP. Oddly enough when I used my old charger on the almost flat low maintenance battery, the ammeter needle hardly moved at all.

After a few minutes the needle was about midway on the scale where it more or less stayed for a few hours.

What was happening? Didn't see any great rush of current as you might have once had!

PHOTOS: front =

= =

[Eddie]

I was kind of worrying that unsmoothed AC might not be too good for the battery.

[Eddie]

I'm the OP. I think my battery charger is over 30 years old!

I took the casing off (rivetted of course) to see the inside:

front =

= = sure looks dated!

Eddie

[Duncan Wood]

That's what the diodes are for, it never actually alternates.

[geoff]

In message , PeterD writes

The further you drop it, the more it hurts ...

[Peter Parry]

That's fine. It is fitted with an olfactory failure detector so if it goes wrong in the dark you will know all about it.

[Dave Platt]

That sounds like a classic symptom of the battery being badly sulphated.

Lead-acid batteries run on... well, lead and (sulphuric) acid. The electrochemical reaction which produces current, is one in which the lead reacts with the acid. converting the lead to lead sulphate. When you re-charge the battery, the reaction is reversed... the lead sulphate is broken up into lead (metallic) and sulphate ion, which goes back into the electrolyte to once again form sulphuric acid.

The lead sulphate which is formed during discharge has a couple of different crystal forms. The initial deposition of sulphate isn't too difficult to dissolve... but it converts spontaneously to a different crystal form which is hard, difficult to dissolve, and forms an effective insulator.

I think that's what happened to your battery. When you initially tried to recharge it, the plates were covered with a uniform layer of lead sulphate, and were thus well insulated from one another. Very little current could flow. After a few minutes, the relatively high voltage from the old-style charger managed to break down some of the sulphate layer, allowing an increase in the current flow.

There are techniques and devices on the market which are intended to reverse the sulphation of batteries. They usually involve some form of high-voltage pulse charging, sometimes using an inductive "tank" circuit to create very short radio-frequency pulses. This is supposed to break down the insoluble sulphate crystals. Some people swear by these devices, other people swear that they're useless.

Deep-discharging most car batteries (low-maintenance or otherwise) is usually said to be very bad for them. The extensive conversion of lead to lead sulphate (and then back again) damages the structure of the lead plates, and the plates begin to crumble and disintegrate, greatly shortening the battery's lifetime.

[daestrom]

Not *too* many years ago (mid 70's), my dad had to retire his battery charger. The filament for the edison valve finally burned out and there are no replacements.

120 VAC to a transformer with two secondary windings. One powered valve filament, the other when to cathode and positive cable. Negative cable came from plate of the 'valve'.

Worked fine for many years (originally purchased by my grandfather back in the 20's or 30's).

daestrom P.S. Mind you, you did have to keep an eye on the battery and when it started bubbling/boiling, it was time to shut it off (big ole rotary snapswitch on the line side)

[StickThatInYourPipeAndSmokeIt]

You said you saw a diode, so how is it that you forgot that it is NOT AC?

[James Sweet]

It's not unsmoothed AC, it's unsmoothed DC. The battery doesn't care.

[James Sweet]

Of course by then the tube (valve) could have easily been replaced by a modern silicon rectifier.

[JosephKK]

It is actually better than you might expect. It turns out that for battery and plating type reactions pulsed DC actually works better in most cases. It has something to do solution kinetics. And as other posters have noted, you gotta monitor that old thing, and about 4 hours max per session, preferably not more than 1 to 2 hours per session.

[JosephKK]

I can't remember for how long i have known that deep cycling was bas for lead-acid batteries, it is nice to have some insight into the damage process.