Unsmoothed car battery charger - is it crap?

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

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 =

Eddie

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

Ooh, I used to have one of those, don't leave it connected for days or it'll boil your battery.

In message , PeterD writes

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

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.

True, but not a big deal. You might want a new strain relief or grommet on the power cord before you cut the cord by not using one where it goes through the case. The quaint power rectifiers are fine until they are not - if they ever go bad, "modern" replacements are fairly simple to get. You probably have a much better ammeter than you'll get in any "modern" charger.

Nothing wrong with old stuff that works.

If you want a smarter charger, you can start here and add smarts, capacitors, whatever makes you happy - timers, pulsers, voltage regulators, the works. The base it's built on hasn't changed much in 70 years.

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.

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)

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

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

Of course by then the tube (valve) could have easily been replaced by a modern silicon rectifier.

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.

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.

I remember buying an AC Delco battery years ago - and it had a three year unconditional warranty if used on a car, but only one if used in a golf buggy, etc.

I have resurected some batteries that have sit around that initially soak very little input current. I have left it go for a week sometimes. I need to try that with some old gel cells I have. After overcharging them, they partially clear up the sulfation. I mostly use deep discharge batteries in the truck. They seem to hold up better after complete discharge, while the truck sits for long periods. The thicker plates seem to last longer. I keep thinking of hooking up that solar cell charger but never have yet.

greg

Yes, it certainly could have been upgraded. But then you wouldn't get to see the light from across the garage bay :-)

Besides the newer charger had some nice features that are pretty standard now, like reverse polarity protection and trickle finish.

daestrom

They do hold up better, you can still kill them, but deep cycle batteries tend to have solid plates which are much more resistant to damage from sulfation, they do however have a much lower capacity to begin with due to the lower surface area vs the porous plates.

Actually the capicity is similar, it's the peak current that you compromise on.

Selenium rectifiers are still being manufactured (see eg , which refers to a "continuous research and development programme aimed at reliable, lowcost, compact selenium rectifier elements and stacks") but I presume you refer instead to silicon diodes.

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