hi sages- this may seem like a dumb question. how do you test the performance of a battery charger? i have a sears charger 15 amp with 100amp boost. it has a meter and a rotary switch for 6/12 volt, slow charge, fast charge and boost. it is at least 25 years old, has been used many times and never been opened or serviced. seems to work well. when on would you put some kind of a multi tester across the charging cables? what would you look for? thanks tons bob f

Bob
Is there a problem with it? That being said the open circuit voltage would be 18 VDC or so(some more some less). But the current is what charges the battery. I would measure the voltage of a "dead" battery then connect the charger and see if the Voltage goes up (check it a few times over an hour or so). If the Voltage goes up over time I would say the charger is good.
Just an easy test.
Frank

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hello cuda- i will try what you recommend. now to be clear if i turn the charger on and connect a voltmeter to the cable ends, i should expect the voltmeter to read about 18 volts dc ? thanks bob f

hello cuda- i will try what you recommend. now to be clear if i turn the charger on and connect a voltmeter to the cable ends, i should expect the voltmeter to read about 18 volts dc ? thanks bob f

An open-voltage test may tell you if a charger is sick, but can't tell you for sure it's 100%. You need a load on it (draw significant current) and then look at the voltage. Some modern chargers are quite tricky; some won't really turn on until there's a load with 9V or more already there, but yours is probably too old to have that feature. Generally, the older chargers have little to go wrong inside - a transformer, some diodes, a breaker, and some switches - I have one that is ~60 years old that still works fine.

For currents of a few amps, an old headlight works very well. There are some battery testers that combine a voltmeter with a big power resistor that can take from 20 to 400A for a brief time that could be used for power tests, but the simplest test is to try to charge a very discharged battery; monitor the current and voltage and see how it goes.

Yes BOB
It should measure at least that. I went out and mine had almost 30 VDC when on but not connected to a battery. It then drops to about 14 VDC when you connect it.(i didnt have a dead battery to connect it to).
Frank

_________________
Scrapple: Because a mind is a terrible thing to waste.
73 Duster - Race Car
66 Dart Wagon - DD
178" FED
82 D150
All Slant powered

hi cuda - went out and tested charger without connecting it to battery ; just connected the cable ends to a voltmeter. on slow charge it read 9 1/2 volts and on fast charge it read 11 1/2 volts. later tested it on a battery which read exactly 12 volts. tested each cell with a hydrometer and each read 1.275 specific gravity. when i put the charger on the battery it read 12 1/2 volts. seems charger works but is not perfect. what do you think? bob f