Technical Batery/Alternator test

[majakozmo]

Hi,
I bought a new battery (old one was already KO).
Because of the power steering light ON (for about 1 month already), I have decided to do a battery test.

I did it in the following sequence and got the following battery voltage:

1. engine off > 12,5V
2. engine on (900rpm) > 14,1V
3. engine on (900rpm) + heater, rear demister, headlights, radio > 12,5 V
4. engine on (2000rpm) + heater, rear demister, headlights, radio > 13,5V
5. engine on (3000rpm) + heater, rear demister, headlights, radio > 13,5V
6. once I turned off all, i.e just engine on 900rpm the voltage stays on 13,5V

note: With engine on (900rpm) the voltage on alternator was 6,03V

The voltage does not looks OK to me. What is your opinion?
Is the 14,1V in step 2 OK? ( I have read somewhere that it should be enough, but I'm not sure)

Thank you.

 

[a1ant]

Hi mate

To charge the battery, the alternator voltage output has to exceed a minimum charging voltage. This minimum charging voltage is 13.8v across the battery terminals, or at the output of the alternator. A single lead-acid cell starts to charge at anything over 2.25 volts. Since a 12 volt battery has six cells, any 12 volt lead-acid battery needs at least 13.8v to start to charge. This voltage will be enough to fully charge or maintain the battery on a trickle charge, but charging time will be very long at 13.8v.
To fully charge in reasonable times, the alternator output must be 14.2v to 14.5v as measured across the battery terminals. Charging voltages over 14.7v can prematurely dry the battery by boiling out electrolyte.

Have a look at THIS guide

Alan

 

[maggers]

Your voltages look fine but I'd query where the 6.03v one came from. Steering light on is usually a fault with the torque sensor on the column, do a search as I know some people have managed to fix it but if not a new column is needed.

 

[PuntoHowTo]

The 6 volt reading is likely a differential voltage between to positives Ie the earth was already elevated to 7ish volts and the positive was at 12-13volts so the meter was showing the difference

 

[majakozmo]

I am glad the battery and alternator are ok
I will check the steering column.
Thank you all for your inputs.

 

[fingers99]

I am glad the battery and alternator are ok
I will check the steering column.
Thank you all for your inputs.

As I see it, the battery is fine. The alternator is dying.

But try it at 3,000rpm, see if the full load voltage improves.

 

[s and b]

As I see it, the battery is fine. The alternator is dying.

But try it at 3,000rpm, see if the full load voltage improves.

i agree but would be cleaning possibly replacing main power lead from alt to starter to battery first
had a few now where high resistance clamped cables cause poor flow

 

[Ziggy122]

i agree but would be cleaning possibly replacing main power lead from alt to starter to battery first
had a few now where high resistance clamped cables cause poor flow

i'd seriously do the clean option first as well

Its cheap for a DIY too!

Just remember to have battery removed while doing so - prevent sparky sparky and shock shock....

While your there - clean the earths too!
poor earths = Poor voltage
poor cables = Poor voltage

the voltages imo look low, but with punto alternators been stupidly cheap from scrappies and easy DIY fit, i'd try it

Ziggy