Bung battery, or alternator?

[diss7]

I usually drive the te27 once a fortnight, give or take. Usually starts straight away, plenty of cranking power.

Went to give it a drive yesterday and battery was dead flat. Checked the terminals were all okay, and checked the cells. Were a little low so topped them up. Then jumped it off the hilux, and as I walked around the front of the car I noticed the lights were on. Old car = no indication on the dash that the lights are on, or buzzer.

Took it for a 30 minute drive to put some juice back into the battery. Went to start the car again this morning, and it didn't have enough power to turn the motor over. (And yes, I made sure I hadn't left the lights on again!)

Have I ruined the battery? I didn't purchase the battery, so unsure of age, but it looks to be an okay battery. I jumped the car again, and remembered the car has an AMP gauge. It reads +50 to -50, and while the car was running it was reading only slightly above 0, say about +5. Is this measuring the current across the battery, or the current being generated from the alternator? I don't recall what this gauge read before all of this.

I went to go and get another battery, but then I saw that batterys are now $150+ (last time I bought a battery it was $50) so decided I want to check that it is the battery that is at fault!

I'm pretty sure it is the battery at fault. It would be a coincidence if the alternator shit itself at the same time.

[xsspeed]

Got a multimeter?

[hsmidy]

running a battery down like that is not good for it, what you want to do is put it on a pulse charger and that will bring it back to life (or atleast your best bet, if not a pulse charger a CTEK)
Chances are you alt is sweet as, doesnt matter how long you drive around charging your batt if it isnt accepting charge.

[sergei]

I would say alternator is fine if running you get 5A coming into battery.
That is what normal charge should be like.
If alternator was completely poked the car would stall once you would remove the jumper leads.

The battery will not charge fully if you take it for a spin for 30 min.

Say you have 30Ah battery, to charge it fully from flat you need 6+ hours of 5A current charge.

You will need to charge it with battery charger for 10 hours or so.

I hope you haven't put tap water, as that will kill the battery in long term.

[Grrrrrrr!]

5 amps is a bit low if the engine was at revs (ie, above about 2k rpm) and the battery was flat enough to need a jump. Even a small alternator will put out 30+ Amps into a flat (but not shagged) battery.
Which means one of two things, your alternator is weak, or your battery is toast. It could even be both. Or the gauge is stuffed, but thats reasonably unlikely.

[diss7]

Thanks for the ideas.

I bought a new battery and it started straight up. Stopped and started it a couple of times, no worries.

I'll see how it goes in the next couple of days.

Gauge could be bung, its 40 years old!

[pc]

$16 for a cheap multimeter from Dick Smiths. Worth buying if just for future use.

[sergei]

$16 for a cheap multimeter from Dick Smiths. Worth buying if just for future use.

Don't buy Dick Smiths multimeter get to Jaycar and get one of these:
http://jaycar.co.nz/productView.asp?ID=QM1440

Alternatively if you are on cheap side:
http://jaycar.co.nz/productView.asp?ID=QM1523

[diss7]

I'll get one tomorrow. Explain how I can check if the alternator is functioning correctly a-please..

[Grrrrrrr!]

check battery voltage before starting car... should be about 12ish volts. If it less than that the battery is flat or poked.

Start car, get it up in revs a little, check battery voltage again. Should be around 13.8-14V if alternator is working and battery isn't too flat. Even if battery is flat it should rise a volt or two from what it was before you started the car.

[xsspeed]

^ yep. If alt is poked you will see the battery dropping voltage slowly while the motor runs

[diss7]

Got a multimeter and read 12.5 across the battery. Once started read 13.7 at idle.

Thanks for the help.

[hsmidy]

just a note just because you are getting 14 odd volts doesnt necesarily mean that your alt is a minter your can in some alts drop a phase and still put out 14v but the current it can produced really drops off. multimeter and an inductive clamp(ammeter) will let you know the true state of your starting charging systems

[Babz]

^+1 but it is more then likely the battery. The fact that you are getting 12.5v when not started (which is the about the right voltage) only indicates that the battery does not have enough starting current to turn the starter motor.

[Scottie]

just a note just because you are getting 14 odd volts doesnt necesarily mean that your alt is a minter your can in some alts drop a phase and still put out 14v but the current it can produced really drops off. multimeter and an inductive clamp(ammeter) will let you know the true state of your starting charging systems

Do you mean if the diode pack craps out and the Alternator produces alternating current instead of DC?

[Grrrrrrr!]

tthat would only happen if the diodes failed closed circuit, normally they burn out and fail open circuit, basically the same effect as cutting an alternator output wire. You get lumpy DC instead of smooth DC and sod all current.

[sergei]

1 Diode blown. Voltage was normal, current was sufficient, very noisy DC:


What normal looks like:

[diss7]

Got a multimeter and read 12.5 across the battery. Once started read 13.7 at idle.

Thanks for the help.

I bought a new battery, and then measured and got these results. These were not the readings on the old battery

[blindnz]

1 Diode blown. Voltage was normal, current was sufficient, very noisy DC:


What normal looks like:

Have you just changed the time base and v/div.... </troll>