What kind of battery charger ?

"mowhoong"

** You need to connect a load to the battery when testing the voltage.

A 6 volt lamp would be good.

See what you get then.

.... Phil

3.59 volts is a VERY discharged 6 volt battery and should not be allowed to happen, anything below 6.0 volts needs a charge. The charger detected the battery as less then a 6 volt battery and the only lower setting was 2 volts. You saw for yourself that with some charge to raise the voltage the automatic charger then detected it as a 6 volt battery and proceed to charge it. Without being able to find the specs of your charger it would apeear that its operation is quite correct.

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John G

The fault is in the battery, not the charger. A 6 volt lead acid battery should never be allowed to drop below 5.25 volts. Your battery voltage was too low for the charger to recognize it as a

6 volt battery - not the charger's fault.

Ed

Your 6V battery is dead if its reading 3.59 volts. Get a new one.

Cheers

A car battery that's completely discharged, a fraction of a volt across its terminals, can be fully recharged and will work fine. But a lot of modern chargers will refuse to put current into it. I'm not sure why. You need a power suply or an old fashioned transformer-rectifier charger to bring up a dead battery.

I recently had to kluge a charger from an old 24 volt wall-wart and a ballast resistor. I used a power sander as the resistor. Once it got to 8 volts or so, an electronic charger was willing to take over. Worked fine after that.

John

John

I don't doubt you can raise the EMF but the capacity and internal resistance are ruined by the sulphation.

Cheers

Sulphation results from a battery standing around, discharged, for months. If a battery is drained dead by something like lights being left on, and recharged soon, it will be OK. But a lot of chargers will refuse to charge it, so you take it back to the same auto parts store that sold you the charger, and they *will* tell you that it can't be charged. And they will sell you a new battery. And charge you to dispose of the "dead" one to boot.

People jump dead cars all the time, and that works too.

John

Definitely. I had a dead short to the body through a 15 foot piece of AWG 8. The battery was down to 2 volts when I found it. My battery charger is home brew. A variac, a 30V CT 15 A transformer and a pair of diodes. I set the charge to 5 A, and reset it every 15 minutes till it was up to 12 volts. Then I started the truck to finish the charge. I drove the truck with that battery for four more years.

--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

It really should have charged up in less time than that.

mike

Yawn.....................................................

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You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

I had a kind of opposite experience years ago with a 3.6V NiCd battery for a cordless phone. In those days, there was no local source of such a battery. The internal resistance was so high that a normal charger couldn't put in any useful charge. So, just for the heck of it, I tried coaxing it with my home-built constant current supply. I'd built the supply earlier for testing LEDs, zeners, etc and it could be set to give 0.5-15 mA at up to

45V. To limit the terminal voltage and the resulting battery dissipation, I started out with a low current and gradually increased it as the voltage went down. When it had gone down sufficiently, I let the phone's own charger take over. At first I was skeptical about the result, but the owner used that same battery for years afterwards.

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Funny! :-)

I bet it took a lot of gas to keep that truck running for four years.

John

It sure did. About $25 a week for four years.

--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

To try stop 12V chargers running into 6V battery, or reversed battery.

A good charger might have an over ride for that, pushbutton start?

You'd be surprised how many ways people can damage chargers and lead acid batteries :)

You're right about temporarily flattened batteries, does some damage but no instant kill -- sulphation takes long term undercharge to develop, like lots of short car trips.

Sounds right for common chargers. Battery voltage should come up very quickly, a flat but not sulphated battery accepts current, flat battery that is not accepting current is sulphated, takes some work to restore, usually can't be, another 'it depends'...

Grant.

Or to sell people new batteries. "That battery won't charge" means "it won't charge with the charger I just sold you."

A charger could be smart enough to charge any battery, 6 or 12 volts. Or it could have a switch. Are there any 6 volt batteries still around?

I keep a Lascar power supply around now. That will push enough current into a battery overnight to get a car to start.

Cute little things, handy to have around for all sorts of things.

John

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rs

=A0

Some old tractors still use 6 volt batteries. I think I can buy them up the road at Java Farm Supply.

I heard a report on NPR this morning that no technology ever goes extinct.

George H.

Slave-rowed warships.

John

ever see a Chinese assembly line?