Battery and/or Alternator Testers?

[Crazy Dazz]

Anybody used one of these that they would recommend?

From what I have seen, they seem to fall into the following categories:

1. Extremely cheap "LED" testers, which I assume simply mimic a multi-meter, and are basically pointless. About the only thing they will detect is if your battery has dropped a cell, or your alternator is completely cactus.
2. Basic load testers of around 100 amps. Not really sure how much good that is to test a battery that should be able to put out 4~500A. Again, I suspect they would detect if your battery was complete *****.
3. Electronic testers, which claim to give a comprehensive report, including testing 5~800 CCA. I'm sceptical, as there is no way they could sustain a 500A current without melting.
4. 500A Carbon Pile testers. They at least look the part. Problem is they cost more than a new battery, so for somebody with only a couple of cars, its a bit self-defeating.

I'd also like to know the best way to test an alternator.
(Without buying an $800 tester.) I've tried using a multi-meter, but that can only measure voltage, and is usually ambiguous.

NB: Please don't suggest "go to an auto electrician," as obviously I would already have done that if so inclined.

[commodorenutt]

You only need a multimeter, knowledge of correct voltages, and some intelligence.

To load test an alternator, monitor the voltage while you turn heavy consumers on - headlights + high beam (there's 20-30A right there), rear demister, aircon (to kick in the thermo fan). If the volts drop below about 12.5, then the alternator can't keep up.
Be careful of "smart charge" cars that can throw the figures out - although usually after a starting cycle they'll charge at 14-14.5V for 5 minutes or so.

If you want to actually "dyno test" an alternator & find out what actual amperage it's putting out, you really need a carbon pile.

Most batteries can be tested by watching the voltage when you crank the car. A good rule of thumb is double figures - ie if it stays above 10V cranking it's still reasonable. A healthy battery will normally sustain high 10v to 11v readings while cranking.

[cs123]

For basic in car tests I use a multimeter.

Ideally you will see 13.8 to 14.2 volts from the alternator. Start the car. Put the voltmeter across the battery terminals, measure the voltage.

The turn on accessories likes headlights, ac, demister etc to create electrical load and measure again.

You will generally see the volts lift slightly as the engine RPMs increase off idle.

For basic battery test you can do the same without the engine running. Check voltage with accessories and lights on.

They are just basic tests but show up if you have a problem 99% of the time.

[Crazy Dazz]

I've seen alternators register adequate voltage, and still be unable to charge a battery.

The problem is always in the grey areas. A multimeter can tell you if the battery or alternator is completely cactus, but when neither is, its hard to sus out.

And, to make matters worse, it could be neither. Could be a current drain.

[whitetruck]

A tool called a hydrometer was an easy way to check for a dead cell in a multi cell lead acid battery, I still use one on my deep cycle batteries, however my car batteries are now all sealed making specific gravity tests impossible. I found the voltage tests already mentioned to be the most useful but if I deem it necessary to externally charge the battery I watch the amp meter for normal behavior, it should start out high and fairly rapidly decrease as the batteries resistance increases.

[cs123]

Originally Posted by Crazy Dazz

I've seen alternators register adequate voltage, and still be unable to charge a battery.

The problem is always in the grey areas. A multimeter can tell you if the battery or alternator is completely cactus, but when neither is, its hard to sus out.

And, to make matters worse, it could be neither. Could be a current drain.

I can't comment on that as I would need to be there when you were testing it but IMO is would be pretty rare that you could not diagnose the issue with a meter and knowledge of 2 laws. V=I*R and P=V*I

I can be sometimes hard to pick up an alternator fault and I have seen some where the alternator tested OK but the regulator dropped output when hot.

[aussiblue]

The cheap battery load testers like this http://www.ebay.com.au/itm/BATTERY-L...IAAOSw9eVXVl6m work fine for load testing and the scale on the gauge is calibrated to show the reading for different CCA batteries. They are really only useful when a battery is not holding it's charge and you want to know if the battery is dying or the charging system is at fault; but in those situations it is extremely useful. The carbon pile ones like this don't tell much more (essentially just a current reading) http://www.ebay.com.au/itm/Battery-L...UAAOSwtJZXW3dy
A clamp on AC/DC multimeter is useful as it allows you to more readily test the alternator output by placing the clamp around it's output wire to measure amps. A clamp on meter also allows you to more readily track parasitic drain by moving the clamp along the wiring harnesses from the battery to the drain source. Like this http://www.ebay.com.au/itm/Pro-Serie...EAAOSwv0tVXPP7

Watch out and read the spec carefully before buying a clamp on meter as many like this http://www.ebay.com.au/itm/New-Clamp...kAAOxyf~hRzZ0n while describing themselves as AC/DC clamp on meters, only read AC amp with the clamp function. Jaycar and Altronics both sell suitable clamp on meters such as https://www.jaycar.com.au/400a-ac-dc...meter/p/QM1563 and http://www.altronics.com.au/p/q0968-...c-clamp-meter/

[aussiblue]

Oh and Supercheap have a AC/DC clamp on meter too: http://www.supercheapauto.com.au/Pro...Digital/387596 There cheaper one is AC only.

[X-AHH]

Blue has offered some good advice.

Using a DC clamp meter is a very good way to judge alternator performance. Clamp it on the cable that connects the alternator to the battery and switch everything on that uses power from the battery such as headlights on high beam, a/c on high fan, demister etc

With the engine at around 1500RPM, looking at the clamp meter display, you should be able to see a reasonable amount of current being produced by the alternator up to it's maximum current rating.
The Voltage at the battery should be 14- 14.5V during this test.

[Itsme]

Originally Posted by whitetruck

A tool called a hydrometer was an easy way to check for a dead cell in a multi cell lead acid battery, I still use one on my deep cycle batteries, however my car batteries are now all sealed making specific gravity tests impossible. I found the voltage tests already mentioned to be the most useful but if I deem it necessary to externally charge the battery I watch the amp meter for normal behavior, it should start out high and fairly rapidly decrease as the batteries resistance increases.

Hydrometer test would be one of the best tests for any battery, I was having battery problems with my Ranger when first purchased in which I had ford dealership test my electrical charging system & battery using a load tester & multimeter saying it was ok, then I demanded they do a hydrometer test, funny how it showed up a crook cell with my battery being replaced.

Guys testing of batteries & charging system require various methods, equipment & knowledge/experience

[aussiblue]

Hydrometer test would be one of the best tests for any battery

Only good if it's not a sealed battery and has caps that can be screwed off. Yes you can sometimes rip the sealing caps of sealed batteries, but it's usually not reversible and doing so means you lose the batteries warranty.

[Crazy Dazz]

Hydrometers effectively only measure the acid concentration. A an old cactus battery that is fully charged will still read as good.

I'm curious as to how DC clamp ons work? I thought only AC would generate the requisite field?

[cs123]

Originally Posted by Crazy Dazz

Hydrometers effectively only measure the acid concentration. A an old cactus battery that is fully charged will still read as good.

I'm curious as to how DC clamp ons work? I thought only AC would generate the requisite field?

Current passing though the wire creates a field. AC the field collapses and reverses as the current flow reverses. DC it is constant. Relays, solenoids work on DC field.

If you want to buy a tong meter you should invest in a decent one.

[66 coupe]

just do the old test where you drop the big flat head screwdriver that comes in the stanley kits across the battery terminals, if you get big sparks and the screwdriver partially melts then battery is fine...

[aussiblue]

I'm curious as to how DC clamp ones work? I thought only AC would generate the requisite field?

See https://en.wikipedia.org/wiki/Current_clamp

The Hall effect type is more sensitive and is able to measure both DC and AC,[1] in some examples up to the kilohertz (thousands of hertz) range. This type was often used with oscilloscopes, and with high-end computerized digital multimeters, however, they are becoming common place for more general use.