testing the alternator

[maroon93limited]

Is pulling a bettery cable off while the engine is running still a reliable way to check if your alternator is ok? Threw a new battery in last night after it crapped out, and just for S's and G's took the negative cable off and no noticable drop in idle or anything like that, but sitting at a light with the AC on, boy oh boy does that voltmeter drop a lot. Get going at the green and it gets right back up to normal.

Idling with no load the needle is at about the "M" on the gauge, idling at a stop with the fan or AC on it sits at about the "O".

Am I just being paranoid or is this normal? And like my original question, is pulling a cable a good way to test?

 

[something9000]

pulling the cable and the truck not dying proves the alt. is working but it doesnt mean its working correctly. the best way is to get a volt meter and test it that way with no load then load at idol and around 1200 rpm. alot of autoparts places can test it for free also.

 

[cjmedina]

Simple....

Just measure the battery voltage.

With engine OFF a fully charged battery is about 12.7 Volts


Engine Running is about 1.8 volts above the base voltage....

 

[brokenarrow]

Oops sorry wrong thread

 

[osteologation]

Simple....

Just measure the battery voltage.

With engine OFF a fully charged battery is about 12.7 Volts

Engine Running is about 1.8 volts above the base voltage....

This only proves the regulator is functioning. I've had windings break that will still put out 14 volts but only 30 amps.

 

[FIND]

Just go to walmart or some shop that sells batteries (like a parts store or an automotive repair facility) and ask them to test your battery and charging system. They have a tool that hooks up to the battery that will test the battery (load test and such), voltage drop at starting (to test your starter) and alternator (including diode ripple).

Most of them will do it for free because they want to sell you something if what you have is no good.

 

[Roadrunner777]

The price of load testers has dropped over the years, they are out there for under $30... might get one just to have in the shop.

 

[cjmedina]

LOL you already have a load tester by turning al the accessories on at ounce! Then check the regulator output at the battery and with the engine off!!!

 

[red94ex]

mines is doing the same thing, for some reason i wanna say its the volt regulator or the alt brush...?

 

[waskly]

Is pulling a bettery cable off while the engine is running still a reliable way to check if your alternator is ok? Threw a new battery in last night after it crapped out, and just for S's and G's took the negative cable off and no noticable drop in idle or anything like that, but sitting at a light with the AC on, boy oh boy does that voltmeter drop a lot. Get going at the green and it gets right back up to normal.

Idling with no load the needle is at about the "M" on the gauge, idling at a stop with the fan or AC on it sits at about the "O".

Am I just being paranoid or is this normal? And like my original question, is pulling a cable a good way to test?

a battery is used to regulate, stabilize voltage in the vehicle, with out the batter, even a dead one, you cant maintain voltage and the spikes make it do odd things, so your test is inconclusive.