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

[JoeH]

Interestingly, on a motorcycle forum I participate in, there was a post yesterday about having a dead battery and that he had a charger on it for a day + and it was still dead. I suggested that he find an old "not smart" charger and try that.... he responded that putting on the old charger worked!

[MEXICOWANDERER]

Don't junk that charger. Send it to someone who understands how to use it. I have sent several hundred pounds of *smart* chargers to recycle centers whom send them to land fills anyway. Transformers in *smart* chargers offer unusable unsalvalvageable voltages.

[wa8yxm]

23hotrodr wrote:
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

Short answer: YES.
First the circuit is a transformer and 1, 2 or 4 diodes
mostly a center tapped transformer and 2 diodes with a center tapped primary as well (The 6/12 switch selects full or half winding on the primary)

No regulation
and as you noticed over charging

Your voltage readings however indicate an RMS type meter so they are wrong.. a Peak Reading meter may show 15-16 volts on the 12 setting which is what you see as the battery charges.

I recommend a recycler for the charger and a new SMART charger.
Mine is a big brother of the Deltran Battery Minder and under that name. 2-4 amps minder, 20 charger 70 Jumper (never got that to work)

[30sweeds]

Kinda off topic but I used to do business with Voltmaster Battery(now Deca) in Corydon Ia. and these guys told me that,at least twice a year,charge the **** out of a deep cycle for 12-15 hrs on manual.Claimed the battery will last twice as long.From my experience,I would say they are correct.Supposed to knock sulfates off the plates.

[Gdetrailer]

30sweeds wrote:
General opinion is you can't leave them hooked up 24-7 like a smart charger.In the auto mode,I can leave mine hooked up as long as I want as the charging rate drops to zero when the battery is fully charged.It will also charge up a stone dead battery.

Old school chargers were never meant to be left on a battery 24/7/365, they were a simple design that was supposed to charge a totally dead battery (like from leaving a door open or headlights on overnight) up to full enough to start your vehicle.

Simple design that just works and typically those chargers are pretty much bullet proof and a fair chance would even survive a EMP blast from a nuclear bomb..

As far as smart chargers, you are very lucky to have one that has a "auto mode", most smart chargers do not have that and require you to push a button to start charging. When charger believes the battery is charged, the unit shuts down and never turns back on unless you disconnect it and then connect and push the start button again..

Not to mention as been stated, most smart chargers will refuse to charge a battery that is considered "dead" as in below 10V..

Now if what you are calling a smart charger that has 5A or less capacity then you have not a smart charger but a battery "maintainer". Those units are like a mini three stage converter and will start charging even if battery is below 10V, they will also drop into "storage mode" to a float voltage of 13.2V when battery is full and they will switch to bulk mode (14.4V) as needed.

I have a 5A version like that that I keep on my backup gen but a "charger" it really isn't, it would take weeks to charge a totally dead battery with 5A of current larger than a lawn tractor battery..

Correct tools for the job makes things easier.

[30sweeds]

I have a 10 amp manual-automatic 6-12V charger similar to Gdtrailer's.I don't know if you would call it "old school" but I bought it in approx 1980.General opinion is you can't leave them hooked up 24-7 like a smart charger.In the auto mode,I can leave mine hooked up as long as I want as the charging rate drops to zero when the battery is fully charged.It will also charge up a stone dead battery.

[red31]

ye ole manual charger will bring the sg into the GREEN, ye newer ones won't.

ye ole manual charger is used to power 12v items that come with alligator clips or cig lighter, ye newer ones won't.

[ferndaleflyer]

My charger was bought at Sears in 1970. It has been used at the race track ever since + here in my home shop. It has out lived at least 3 high $$$$ ones since. It has a timer and a boost setting, 6 volt - 12 volt

[Tom_M1]

Another buzz word is "SOLID STATE". Meaning it has a diode.

[Darklock]

Gdetrailer wrote:

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.

I've had that same charger since the 80's.

[Darklock]

delete quoted wrong post

[time2roll]

Or the 6v/12v switch was in the wrong position and the battery would not charge or was killed.
Or the old charger going at 16 volts was left on too long.
Or the shorted battery with low voltage would charge up just fine until it exploded.

For all you guys the old stuff is generally fine. For the common user the modern charger will help them stay out of trouble.

And if all are so good about batteries how does the voltage get so low that the modern charger does not start? Stuff happens right? Same stuff happens when the 16 volts is applied.... pick your poison.

[Gdetrailer]

Harvey51 wrote:
Thanks for the first post. I was getting our class C ready for some short trips and somehow drained the engine battery. No problem I thought I’ll just use my Black & Decker smart charger. But it refused to charge. After reading the first post I borrowed a dumb charger and got it charged enough for the smart charger to top up.

Kind of make you wonder if the battery industry gave the charger industry some hush money to incorporate that feature into chargers to help sell more batteries?

Smart Charger won't charge the battery so battery must be bad and needs replaced?

Old school chargers sometimes are a bit "smarter" than new technology :B

[Harvey51]

Thanks for the first post. I was getting our class C ready for some short trips and somehow drained the engine battery. No problem I thought I’ll just use my Black & Decker smart charger. But it refused to charge. After reading the first post I borrowed a dumb charger and got it charged enough for the smart charger to top up.