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Tool Talk Discussion Forum

How read an ammeter

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01-24-2023 15:00:46

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I have a battery charger and I would like to know to operate it. I typically charge a battery for the while. I have 10 amp charger but will only register around 3.

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01-25-2023 06:04:49

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 Re: How read an ammeter in reply to mwilke, 01-24-2023 15:00:46  

Get your volt meter out. Amp rate is just that, how much a battery is taking a it charge.

Volts reading is state of charge.
Take a volt reading before and after charging, NOT while the battery is charging,


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01-25-2023 05:01:01

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 Re: How read an ammeter in reply to mwilke, 01-24-2023 15:00:46  
It should be obvious that battery charger ratings are optimistic fraudulent. The only way most battery chargers will produce their rated output current is if the battery is totally dead, and then only for a few seconds before their overload protection trips.

If you open up your charger, you'll probably find NO circuitry to regulate either current or voltage. You'll see a transformer, a couple of diodes and some sort of thermal protection switch. If it has more than one current or voltage range, there'll be a switch that changes which transformer taps are used. But nothing that would actually REGULATE the current or voltage, unlike certain high-end chargers. The current that's applied to the battery by such a charger is not direct current at all, but rather a series of pulses that occur whenever one of its diodes is forward biased. When the battery has a low charge, those pulses will be long, and they will get shorter as the battery charges up. There's nothing you can do to increase the current unless there's a switch to change the current. And if there IS a current switch, it's just changing the transformer output VOLTAGE, which will cause the current pulses to get longer.

Your best tool to go along with a cheap, unregulated charger is a good digital multimeter. You can monitor the battery voltage, which will give you an idea if you're over-charging it or not.

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01-24-2023 19:10:19

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 Re: How read an ammeter in reply to mwilke, 01-24-2023 15:00:46  
One might also add..... ..... ..... . When a battery is shot, it won't accept a charge, and your ammeter will read very low when it's connected to the battery. Any time spent charging will still show it at a low amperage, with no resulting charge.

An old style manual charger will start out at maybe 40amps, then taper off as the charge builds in the battery. When it gets down around 5ish amps, it's time to disconnect it.

A quick charge (40amps) is generally ok for a weak battery that still accepts a charge. Even better, if you have the time, is a trickle charge at 2amps.

The engine start mode (mine is around 200amps) is only when you're really in a hurry, or the battery is in such bad shape that nothing else works. Start mode is only to be used for enough time to turn the motor. Don't leave it in start mode for any longer than necessary.

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01-24-2023 17:14:30

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 Re: How read an ammeter in reply to mwilke, 01-24-2023 15:00:46  
AH , condition and charge on battery .

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01-25-2023 05:51:49

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 Re: How read an ammeter in reply to buickanddeere, 01-24-2023 17:14:30  
Correct, kind of simple if you think about it. Most/all cheaper battery chargers are muti tapped AC transformers with a rectifier to supply DC voltage. The different setting provide different voltages. The ratio of the provided voltage to the battery voltage will determine the current flow. That's why using a lower setting that charges a battery slower and stops charging when the battery reaches just over 12 volts tends to prolong battery life.

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01-24-2023 15:33:30

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 Re: How read an ammeter in reply to mwilke, 01-24-2023 15:00:46  
Only if your battery is severely discharged will you see the charger read the full 10 amps it is rated for. If it has a fair charge the battery won't accept the full 10 amps and your ammeter will read less, such as the 3 you have seen.

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