Alternator tests

[Paulstewart20]

Hi, Tried searching for alternator posts but nothing came up close to what I want to know. What volts should the alternator be kicking into the battery Im currently getting 12.20 when on tick over its also a brand new battery and when blower and lights are on it drops to 11.70 volts, watched a couple of you tube clips and they say power should be 12.6 when ignition is off and 13-14 volts when engine is running is this right or are clios diffrent.

 

[dann2707]

Yes should be 14v when the car is running mate, could be a few things.
Check your earths
Usually the alternator that's dead though

 

[JamesBryan]

14.5 mine is.

Sounds like it's dead, but test it on the live of the alternator and earth to the body of it or something metal.

 

[Paulstewart20]

Cheers I did this showed the same voltage

 

[Paulstewart20]

Yes should be 14v when the car is running mate, could be a few things.
Check your earths
Usually the alternator that's dead though

Checked continuity across the earths and its all good

 

[JamesBryan]

Cheers I did this showed the same voltage

Dead then.

 

[Paulstewart20]

Is it possible the tensioner is not applying enough strain? it is spinning the alternator but maybe its slipping slightly I might mark it with a pen and see if they line up again after a run.

 

[JamesBryan]

Possibly, although you'd tend to hear it slipping.

Not sure that marking it would work as for every full revolution the belt does, the alternator pulley would do x amount of turns. Meanwhile the marks would only line up once every certain revolution.

 

[Paulstewart20]

Possibly, although you'd tend to hear it slipping.

Not sure that marking it would work as for every full revolution the belt does, the alternator pulley would do x amount of turns. Meanwhile the marks would only line up once every certain revolution.

ah yeah fair one, I did just swap it with my spare alternator but only getting 12.4 volts with this one its just enough to remove the battery and stop light of the dash but looks like I need a new one.

 

[dann2707]

Checked continuity across the earths and its all good

It's no good doing continuity across the earths, you want to check the resistance across them or do a voltage drop test.

 

[Paulstewart20]

It's no good doing continuity across the earths, you want to check the resistance across them or do a voltage drop test.

how do you do that?

 

[Paulstewart20]

I tried below and it seemed to fluctuate widely but if I go from neg to the strut bolt its a good reading, Im gonna sand it all down and see what happens, just wanted to check that below is correct. tia


If your accessory still doesn’t work properly after redoing the grounds, you will need a voltmeter or multimeter to trace the wiring. Set the voltmeter to read ohms (resistance) and probe the battery’s negative stud and ground connection on the accessory (the ground terminal on an amp, for example). If you have a reading less than five ohms, the ground is okay.

If the resistance is okay but the accessory still isn’t working right, set the voltmeter to DC current (voltage). Turn the accessory on and retrace the grounding path as you did before. The voltage should be no greater than .05 volts under load. If you find a point where voltage is present, then you need to add a bonding strap or find a new grounding point so no voltage is present at any of the grounding points.

If the reading is higher, you need to probe the grounding path between the accessory and the battery. Starting at the battery, run the voltmeter probe from the battery to the first grounding point, usually a fender on muscle cars and trucks. Continue to where the fender attaches to the main body, and from there to the accessory. If you find a point of high resistance (over five ohms), you will need to attach a bonding strap or wire between the panels or parts where resistance is highest.