10/2 amp battery charger

I'd take the battery off the charger and use a multimeter to see if the terminal voltage was over 11.5. I'd let the battery sit overnight and see if it was still over 11.5. Why fool with a battery if a cell is shorted?

If the voltage was good, I'd use the multimeter to check the charging current. If it really charges a good battery at 7 amps on the 2 amp setting, that would explain why someone gave it away. I'd check the charging voltage because the charger could damage batteries if it's too high.

Every charger I've had has been like that. Unless you want to pay bigger bucks for a charger with true constant current regulation I think what you have is all you can expect.

** Dead = what ? 10 years old with no voltage on the terminals.

** Not to be trusted, use another DC amp meter to check.

Car battery chargers often use "moving iron" meters cos they are rugged and cheap BUT they also over read the 100HZ/120Hz pulsed current by up to 100%.

** Suspect a shorted cell in the battery.

Use your DMM to see that the voltages are on and off charge.

... Phil

I have similar 2A/10A charger and on mine the meter does not have two different scales for 2A and 10A.

On mine, if it's set for 10A it charges more quickly but it also shuts down the charging earlier. At the 10A rate the green LED indicating fully charged turns on but if I then switch it to 2A it charges some more.

As to voltage, a fully charged lead acid battery, with no load, will be

2.3V per cell x 6 cells = 13.8V. Once it's under load, it's 2.1V/cell or 12.6V. If you have a shorted cell (or more than one shorted cell) it's easy to check because under noload the voltage will be lowered by the number of shorted cells x 2.3V.

An alternator/rectifier/voltage regulator, or battery charger, needs to put out 14.4-14.8V to properly charge a car battery. While people call car batteries "12 volts," they are not 12 volts except under load where they are between 12V and 12.6V.

An article entitled is "Car Batteries Are Not 12 Volts" is available at .

A battery that has just been on a charger or come in from driving may well read 13.8 volts, but it will settle down over a period of hours. A brief load helps it settle faster.

The article points out that it's hard to know the best voltage for an automobile regulator. They all seem to be temperature compensated these days, providing more voltage for a cooler battery. That helps.

A battery used for for a couple of 10-minute drives a day would probably last longer with more charging voltage. A battery on the interstate 10 hours a day would probably last longer with less voltage. How can a car manufacturer predict your driving habits?

I once owned a charger with a switch for conventional or maintenance-free batteries. The maintenance-free does better with more charging voltage.

In the aircraft world they are referred to as a 14 volt system, with

12 cell battery systems referred to as 28 volt.

As for the chargers - a "decent"charger limits the charge current as well as the voltage, so a 2 amp charger will not put out over 2 amps into the battery for trickle charging and will limit the voltage to

14.4 so it will never boil a battery dry.. Most chargers out there fall short of "decent" but there are more and more "microprocessor controlled" 3 stage chargers on the market for approaching an affordable price.

Some will test the battery for shorted cells, indicate the failure, and refuse to charge a defective battery.

I like to see 15.5 when cold.

Another thing to note is that some cars actually pull more current when run ning than when cranking. Surprised the hell out of me to find that out. It was a fairly decent engine but three coils and six fuel injectors would not run on this partly dead battery when the charging system failed. But it wo uld crank. Damndest thing.

Huh, in the old days the radio was the biggest drain, with a vibrator and t ubes and such.

I imagine that's because automobile systems were developed to power a starter from a battery, and, in the days of generators, you could be down to 12 volts on the road.

Aircraft electrical systems were designed primarily to power equipment aloft, without much variation in engine speed.

Neither does mine. Two of you seem to have gotten the impression that my ammeter had two scales, but I don't know where you got that impression.

Thanks for the info.

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And the avionics need to be designed to function optimally at the prevailing operating voltage. Something designed with a 12 volt maximum voltage wouldn't last long at 14 - and in the aircraft world they are nothing if not precise when it comes to specs.

Automobile owners, if told their system was a 14 volt system, would be all bent out of shape to find the resting state voltage to be only

12.6.