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Testing an alternator

My kit car has a 45 amp alternator fitted. I have come by a 60-0-60 ammeter in good order. Would it be wise/ safe to connect this ammeter in series between the alternator and the battery then start the engine to use the ammeter as a test gauge? Could I connect it permanently ?

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The short answer is no.
Most amp meters are not designed to carry all of the power the car needs like meters used before 1950.
A better choice is a volt meter.

Posted on Feb 13, 2014


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Posted on Jan 02, 2017

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SOURCE: engine died & wont start no spark ignition coil tested good

try your ignition module in the distributor much more likely. just install rebuilt distributor if that is the problem , if you just replace module the main distributor assem will **** out shortly after.
Make sure you check for broken timing belt also it is one of those two!

Posted on May 27, 2009

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SOURCE: battery test proper voltage, new alternator test

Battery by itself with no cable attach should read 12.4V for low and 13.6V for fully charged.

With both terminal connected a health charging system should read 13.6 to 13.8V

Amp gauge should read positive when chagring and when discharging it should be on the left (negitive side)


Key has to be out of the ign.

Charge battery to the max with terminals off the car.

Test voltage and make sure it's between 12.8 to 13.6V

Check the battery CCA and compare it with a battery load tester.
CCA that read 60% below the sticker is a BAD battery.

Cannect the + terminal.

Carefully touch the negitive terminal to the neg. battery post.

Make sure all doors and light are off

You should get a little spark.

A large spare is equal to a large load.

An amp meter will give you a better idea what the drain is.

A short is hard to find and it will take time.

Work on one fuse at a time until you find the load.

Posted on Jul 17, 2009

  • 103 Answers

SOURCE: chevy cobalt 07 charging fuse/ alternator has been tested good

i have a 05 cobalt SS Superchaged and i bought it new and had to warrenty two batteries and i put another battery n about 7 months ago

Posted on Mar 17, 2010

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How do you hook up amp meter for battery charger

DO NOT CONNECT IT to both poles + - !!! the amp meter have very small internal Ressistance, it blows of :) Connect it like in the picture d640b1d6-15c8-40ff-9dc1-eac0eb3b2a1f.png

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1. Is the lights glowing correctly?
2. check the battery contacts once again re fix them.
3. check the polarity of control unit (Rectifier circuit).
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Battery is good, alternator is good. when car is off the battery is drained

  1. Follow these steps.
    Remove the negative side battery cable from the negative battery terminal.
  2. Connect the black wire to the com input on the multimeter and the red wire to the 10A or 20A input on the multimeter. the meter needs to be able to read at least a 2 or 3 amps for this test to work. Connecting the red wire to the mA input on the multimeter won't work and could damage the meter.
  3. Attach a multimeter(set the dial on the multimeter to measure Amps as per multimeters instructions) between the negative cable and the negative battery post. Wait a few seconds to several minutes for the car to go into sleep mode - i.e. when you make the contact with the ammeter, the cars computer systems "wake up". After a bit of time they will go back to "sleep".
  4. If the ammeter is reading over 25-50 milliamps, something is using too much battery power.
  5. Go to the fuse panel(s) and remove fuses, one at a time. Pull the main fuses (higher amp ratings)last. Perform the same steps for relays found in the fuse panel. Sometimes relay contacts can fail to release causing a drain. Be sure to observe the ammeter after pulling each fuse or relay.
  6. Watch for the ammeter to drop to acceptable drain. The fuse that reduces the drain is the draw. Consult the owners' manual or service manual to find what circuits are on that fuse.
  7. Check each device (circuit) on that fuse. Stop each lamp, heater, etc. to find the drain.
  8. Repeat steps 1&2 to test your repair. The ammeter will tell you exact numbers.
  9. You can also try unhooking the big wire from your alternator. The alternator can sometimes have a shorted diode that can cause amps to flow through the alternator's power cable and through the shorted diode and into the case and through the bolts and back to the negative battery terminal. This will drain a battery in a hurry.Make sure to read the ammeter before and after unplugging your Alternator

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I replaced a battery and an alternator in a 2005 Explorer, Checked voltage after, was getting 14,4 volts, all seemed well, next morning battery was dead, jumped truck, alternator putting out 13.6 volts,...

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It's possible when you took battery cable loose to install ammeter in series, a module may have shut off? Use a jumper wire to keep connection till you get the ammeter hooked up. Just my opinion.

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My 2004 GMC Sierra 1500 has been losing battery charge

Try to locate the cause of the discharge current as below:-

While vehicle electrical system shutdown as for overnight storage, connect an ammeter (with suitable current capacity and sensitivity) across the main ground connection between the battery -ve terminal and vehicle chassis/frame - (-ve of the ammeter to -ve battery terminal post, +ve to vehicle frame),
Carefully disconnect the main battery ground cable from the chassis,
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Occasional dead battery

There are alot of things on newer cars that cause a very slow drain on a battery while your car is off, i.e. radio memory, ecu memory, clock memory, ect. Your battery may still take a charge but wont hold it for as long as your vehicle needs. Batteries are not a one size fits all kind of deal. My advice is to replace your battery with a quality one the correct size and cranking amps your car calls for and see if that fixes your issue. If not then your alternator is not putting out the amps it's supposed to and may be intermittenly not charging.

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