Old automotive battery charger question

[23hotrodr]

I have an approx. 40 year old 12/6 volt automotive battery charger. When set for 12 volts and not connected to a battery, it reads 12.81 volts. Set to 6 volts and not connected to a battery, it reads 8.1 volts. When I connect to a 12 volt battery, and set for 12 volts and battery fairly well charged I read about 16 volts and the battery starts boiling right away.

Does this seem normal? Should the difference of charger output boltage be that much different when connect to a battery?

Thanks for any info you can provide. -- Mick

[MEXICOWANDERER]

A 5,000 uf electrolytic cap tames those wild swells.

[ktmrfs]

unless you have a true rms voltmeter, the voltage reading from these old (and some newer) battery chargers w/o a battery hooked up is really of marginal use. The old ones used selinium rectifiers and no output filtering, that was the job of the battery. So the unloaded output voltage is NOT DC, nor is it a sine wave.

About all a DC or "peak responding sine wave 60Hz calibrated" voltmeter will tell you is that there is an output voltage.

[MEXICOWANDERER]

I nicknamed new style chargers
CANCEL CHARGERS
If you have to ask - God have mercy on your battery

A Megawatt 36-amp set at 14.0 volts...
Hook it up...
See you tomorrow or the next day.

Cancel culture California legislators know as much about batteries as much as I know about fundraiser dinners at The French Laundry.

[Gdetrailer]

time2roll wrote:
Normal. Now put it in a museum and get a modern charger.

As long as that old charger works and you are not planning to keep it connected and operating 24/7/365, don't bother replacing with a "modern" charger. That old charger will outlast a dozen of the new "modern" ones plus it WILL work on a FLAT battery.

"Modern" chargers are designed to not charge if battery voltage is below 10V (IE "Flat")..

Got a flat car battery or tractor battery that sat over the winter?

Yep, that is where a modern charger will fall flat on it's face and you have to drag another charged battery to the dead one to trick the "smart" charger into charging.. That, is stupid to say the least..

You will not be able to pull my old school charger out of my dead cold hands.. Not even if you offered me 100 smart chargers.

That Transformer based old school charger is pretty much indestructible, rugged and reliable.

Just has one rule to remember, monitor progress and disconnect when done charging.. Pretty simple and works.

[Gjac]

I would keep that old charger for two reasons. If your on board charger does not have an equalizing function that puts out 15-16 volts you can use your portable. What is the output of your onboard charger? Secondly I don't believe the algorithms in these smart chargers fully charge the batteries. I use my 25 year old Magnetek charger to charge for several days after my smart charger says ful and I get several more days of dry camping before batteries reach 50% SOC.

[wa8yxm]

23hotrodr wrote:
I have an approx. 40 year old 12/6 volt automotive battery charger. When set for 12 volts and not connected to a battery, it reads 12.81 volts. Set to 6 volts and not connected to a battery, it reads 8.1 volts. When I connect to a 12 volt battery, and set for 12 volts and battery fairly well charged I read about 16 volts and the battery starts boiling right away.

Does this seem normal? Should the difference of charger output boltage be that much different when connect to a battery?

Thanks for any info you can provide. -- Mick

Does this seem normal.. Absolutely What you are seeing is the fault of your voltmeter I've assorted meters a Peak Reading meter will likelyu show the same voltage all the time. An RMS meter it will vary. and most meters are somewhere in between.

WHY
The old charger is a transformer and either two half wave or one full wave rectifier (Diode, kind of like a one-way check valve for electrons)
A common design had both primary and secondary windings centertapped. For six volt they fed power to the ends of the primary, For 12 volt one end and the center tap. Or two primary windings and series/parallel-ed them (Parallel for 12)

The secondary winding either went through a single diode, 4 diodes in a bridge. or was center tapped each end going through a diode. (All 3 designs work the same).

The output is rectified DC goes from zero to about about 16 (Theory is 16.8 but some loss in the diodes) eitehr 60 or 120 times a second. You meter is averaging or otherwise "Calculating" a reading based on that no load. but with the battery present and charged it sees the peak (16) volts. DO NOT leave this type of charger hooked up longer than needed. Boils battery dry .

[Boon_Docker]

Good to see that someone is really knowledgeable on the use of timers on old school chargers and DC power supplies. 😉 :B

[time2roll]

Normal. Now put it in a museum and get a modern charger.

[23hotrodr]

It's a Schumacher SE-1010. The power cord and the charging cords were in sad shape so I installed new ones. I was just surprised to see the 16 volts when connect to the battery. I never checked the voltage while connected before now. It is a dumb old charger with a power transformer, circuit breaker, 6-12 volt selector switch, amp gauge, and 2 diodes for the dc. I guess it is working as designed.

Thanks for all the knowledge! -- Mick

[Gdetrailer]

Boon Docker wrote:
I think theoldwizard1 meant to say "should use a timer".
Relax man! :B

Absolutely no one ever used a "timer" on the old school chargers as they were typically only used long enough to get a dead battery charged enough to start their vehicle or tractor.

Basically several hrs and at the worst overnight.

Anyone just plugging in and leaving it plugged in for more than that was going to not have much left of the battery..

Some of us old folks were smarter and wiser than modern day folks.

No harm will come to a battery using one of those old chargers as long as you don't leave it running 24/7/365.. No need for using a timer, just use the grey matter between the ears and remember that you were charging a battery..

[Boon_Docker]

I think theoldwizard1 meant to say "should use a timer".
Relax man! :B

[Gdetrailer]

theoldwizard1 wrote:

Gdetrailer wrote:
YES, that is all normal for the old school battery chargers.

Old school chargers (or when using a simple DC power supply) should have a timer. It is very important to make sure the water level is full before starting the charging process.

The boiling is releasing hydrogen which can be explosive in high enough concentrations.

:R

NO, not ALL old school chargers have or had "timers".

Perhaps you can point out WHERE the "timer" is on mine?


Click For Full-Size Image.

You can't, because there is no timer knob on the outside..

And NO, there is NO "timer" inside it either.

That IS pretty much the same charger design that my Dad owned since the 1950s, the internals are the same, a transformer, a rectifier, a self reseting breaker, and the one switch for 6/12V, another in the case of mine for deep cycle/regular.. Those just change what secondary "taps" from the transformer are being used which raises or lowers the voltage.

Now if you are thinking of those 150 lb service station chargers on wheels with 150A starting boost then yeah, those often had a "timer" that you turned which would charge only the time you set it to.. But those were COMMERCIAL chargers, not CONSUMER chargers.

[cooldavidt]

Good for my old 1954 truck too ??

[theoldwizard1]

Gdetrailer wrote:
YES, that is all normal for the old school battery chargers.

Old school chargers (or when using a simple DC power supply) should have a timer. It is very important to make sure the water level is full before starting the charging process.

The boiling is releasing hydrogen which can be explosive in high enough concentrations.

[2oldman]

fourthclassC wrote:
I gotta keep an old "dumb" charger around for batteries that are too depleted for my modern smart charger to work.

Or a known good battery to parallel it with.