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 > Old automotive battery charger question

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23hotrodr

Iowa

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Posted: 04/01/21 11:57am Link  |  Quote  |  Print  |  Notify Moderator

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


2007 Itasca Suncruiser 35L
2000 Jeep Wrangler

Gdetrailer

PA

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Posted: 04/01/21 12:19pm Link  |  Quote  |  Print  |  Notify Moderator

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

Those old chargers are nothing more than a transformer and a rectifier (diode) with no filtering or voltage regulation. Because they are not filtered or regulated the voltage without a battery will read low (8V DC) and when a load like a battery is connected it will read much higher than normal battery voltage depending on the discharge state of the battery.

The battery acts like a filter capacitor smoothing out the choppy DC voltage from the rectifier an also regulates the voltage to a certain extent.

When you connect a very discharged battery the charger voltage will drop considerably since it can only supply a limited amount of current and when the battery is fully charged the charger voltage will be much higher than normal battery voltage since the battery will be drawing very little amount of current from the charger.

These old chargers are GOOD to have in an emergency backup situation but not good for say 24/7/365 always on situation. The old chargers will boil a battery if you were to leave it connected and turned on for too long.

I keep one of the old ones laying around just in case I run into a very flat battery, newer standalone chargers are "smart" chargers and are designed to not output unless a battery is attached which has enough voltage to trigger the charger on.. Typically 9V or so is required to turn on a smart charger.

If you accidentally ran down your car battery low enough that the lights don't light, a smart charger will not turn on to a charge the battery! That is where the old school chargers shine!

fourthclassC

MA

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Posted: 04/01/21 12:22pm Link  |  Quote  |  Print  |  Notify Moderator

Agree 100% I gotta keep an old "dumb" charger around for batteries that are to depleted for my modern smart charger to work.

bgum

South Louisiana

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Posted: 04/01/21 12:22pm Link  |  Quote  |  Print  |  Notify Moderator

I'll venture to say that I have the same charger with possibly a different name. Bought and used to charge boat batteries.

2oldman

NM

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Posted: 04/01/21 12:36pm Link  |  Quote  |  Print  |  Notify Moderator

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.

theoldwizard1

SE MI

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Posted: 04/01/21 12:36pm Link  |  Quote  |  Print  |  Notify Moderator

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.

cooldavidt

Vancouver

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Posted: 04/01/21 12:51pm Link  |  Quote  |  Print  |  Notify Moderator

Good for my old 1954 truck too ??

Gdetrailer

PA

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Posted: 04/01/21 12:53pm Link  |  Quote  |  Print  |  Notify Moderator

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.


[emoticon]

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

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

[image]
[image]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.

Boon Docker

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Posted: 04/01/21 01:01pm Link  |  Quote  |  Print  |  Notify Moderator

I think theoldwizard1 meant to say "should use a timer".
Relax man! [emoticon]

Gdetrailer

PA

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Posted: 04/01/21 01:25pm Link  |  Quote  |  Print  |  Notify Moderator

Boon Docker wrote:

I think theoldwizard1 meant to say "should use a timer".
Relax man! [emoticon]


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..

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