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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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02-01-2023 09:27:43

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 Re: How read an ammeter in reply to mwilke, 01-24-2023 15:00:46  
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Well, to operate a simple 10A battery charger, you would connect the red-handled clamp to the + terminal on the battery, connect the black-handled clamp to the - terminal on the battery, and finally, plug the charger into a wall outlet.

Really, that's it. No special trick to it.

The charger applies a fixed voltage to the battery, and the Amps shown on the meter depend on the difference between the voltage the charger is applying, and the voltage on the battery. The farther apart the two voltages are, the more Amps will show on the meter. As the voltage on the battery rises and gets closer to what the charger is applying, the Amps will decrease. When the battery is full, the Amps will read zero.

Chargers with a higher Amps rating achieve that by applying a higher voltage to the battery. Remember, the bigger the difference in voltage, the higher the Amps reading on the meter.

One common mistake people make charging batteries is, not leaving the charger on the battery long enough. They will charge the battery for an hour, when it really needs to be charged for 10 hours.
How long to charge a battery? Depends on the rate set on the charger, the capacity of the battery, and the state of charge of the battery. We've already talked about charger rates. Battery capacity is stated in Amp-hours (Ah) and can usually be found either on the battery label or online.

Amp-hours are exactly what they say they are, Amps times hours. You charge a battery at X Amps for Y hours to get XY Amp-hours. A 100Ah battery needs to be charged at 2A for 50 hours to be fully charged from dead, for example. Batteries can be charged at a rate which will charge them in 10 hours, safely, without damage, so the same 100Ah battery could be charged at 10A for 10 hours.

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Tim PloughNman Daley

02-01-2023 01:18:34

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 Re: How read an ammeter in reply to mwilke, 01-24-2023 15:00:46  
What AMMETER are you referring to? On your tractor? GAUGE reads AMPS when charging. Scale goes typically from NEG to POS and at least 20 AMPS up to over 80 AMPS. An AMMETER is not a battery charger. To maintain a charge on your battery, you need a FLOAT CHARGER read on:

ALL batteries and chargers are not created equal. Most bargain-basement units sold have poor lifespans, two years on average, some are bad out the door, so you might think buying a $75 part is a good choice, you will be buying another and another a few years later. Best to invest in a good brand like INTERSTATE, DEKA, EAST-PENN, DURACELL, or EXIDE. If your basic garage trickle charger is left unattended, it can boil out the electrolyte and render it junk. A basic trickle charger can't fix a depleted battery. Research Specific Gravity. You need a good FLOAT CHARGER to leave attached when vehicle is idle. Get the battery tested first at your trusty local shop under load on their machine. You need a good, strong, fully charged battery to:

1. Spin the starter
2. Engage the Bendix
3. Provide voltage to the coil.

As the battery gets weaker, the first thing to fail is your spark. The more current you use to spin the starter, the less you have for the ignition. If your starter motor pulls the battery down much below 5.2 volts (ref: 6-volt battery) turning over is almost a futile effort. 4 Volts is an almost dead unit. It doesn't really matter much if the battery is fully charged until you test it correctly. Simply connecting your trickle charger to the battery won't do anything if it is dead. Just because you have a 6V battery does not mean that your system is wired correctly for the 6V/POS GRN setup. Ditto if a 12V setup as well. One item that is also the usual suspect for non-starting/non-charging is the lack of a fan belt tensioning bracket whether if using 6V and a GEN or 12V and an ALT.

When your vehicle sets idle for more than a week, the battery will start to deplete the lead plates and you lose specific gravity. You can use a HYDROMETER to test Specific Gravity see your OEM Owners Manual. They sell cheap little hand ones at many local auto parts outlets and are usually right on the counter. It resembles a large hypodermic needle and has about a half dozen small colored balls in a solution of Acetone in it. The included chart will tell you how to read the floating balls. A true battery testing unit will give you better results as well as telling if the battery is good or bad. Take to a shop.

The worse thing for battery life is the constant draining and recharging on it. The best solution is to invest in a good float charger like the DELTRAN BATTERY TENDER JR (for 6V). Keep it connected when tractor is idle so the battery maintains a constant full charge and is ready to go when needed. Never just start taking parts off willy-willy and slapping new ones on. Always perform true root cause problem solving methods. Finally, good, correct battery cables are a must. 6 VOLT battery cables require thick as your thumb, HD 00/01 gauge for correct conductivity. On your 6V tractor, the flat, braided ground strap works best. A 12V battery uses smaller gauge cables like what is on your car or truck. A 6V battery requires a GRP 1 AG type for your tractor. 12V uses a GRP 25 or GRP 35 battery. Never use a Deep Cycle, golf cart, or cheapo battery.

99.98% of all non-starting issues are due to incorrect wiring regardless if 6V or 12V. Lack of the GEN or ALT fan belt tensioner is often the root cause of a weak or dead battery - without tension, you will never charge the battery. Once all is right with the world, best to invest in a good float charger like the DELTRAN BATTERY TENDER JR [6V] , $30 avg.


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Tim Daley(MI)

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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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