No charge! What to check first?

bakers · Oct 15, 2013

Hi all,

My Son got to work this morning and the battery had died!

He mentioned yesterday that when he put full beam on the radio went off! I should have twigged something was wrong.

Anyway it's dead, miles from home, I'm off over later with jump leads etc.

Question is, it seems there is no charge, guess it could be a number of things, what should I check first.

Any suggestions welcome!

Steve

bakers · Oct 15, 2013

It's a 200tdi by the way

martyc · Oct 15, 2013

Test for voltage at the battery with the engine not running, then test again with it running. The first will prove the battery is dead (no charge) or if it's some electrical fault, and the second will prove if the alternator is working or not

bakers · Oct 15, 2013

Thanks, will give that a try, assuming I get it running

Bromsgrove Defender · Oct 15, 2013

Take a multimeter with you to check the alternator.

But to be honest it could just be a knackered battery

Loose or corroded terminals. Loose earth strap.

If your really unlucky it could be shorting out somewhere. ..

Shifty1962 · Oct 15, 2013

Take a spare battery. It will be enough to get you home as a diesel will run once started so long as the fuel solenoid is energised.

goldypurple · Oct 15, 2013

check the alternator belt also if loose will not charge enough, or it be be missing

Oldseadog · Oct 15, 2013

Does the charge light come on?

If not, it could be as simple as changing the bulb in the dash, without which the alternator will not charge.

timtheenchanteruk · Oct 15, 2013

Oldseadog said:
Does the charge light come on?

If not, it could be as simple as changing the bulb in the dash, without which the alternator will not charge.

Saw this the other day too, and wondered why? and if it is because it needs a flow to ground, how come swapping it to an LED doesnt cause an issue, it usually does in these things.

trax · Oct 15, 2013

timtheenchanteruk said:
Saw this the other day too, and wondered why? and if it is because it needs a flow to ground, how come swapping it to an LED doesnt cause an issue, it usually does in these things.

iirc, when you turn on your ignition, it sends power down the bulb to the alt which powers the fields. You need them to be energized.

timtheenchanteruk · Oct 15, 2013

hmmm, but if an LED is fitted (as I have) a resistor is in place, so the voltage/current is dropped from the usual 12V, but mine charges fine??? im confused.

unless the exiter only needs a fraction of a volt to get going??

the_wolf · Oct 15, 2013

Anyone willing to test that theory? I'd be interested to know if its true, surely a bulb doesn't control the alternator?

Also (slight thread hijack here) but to settle an argument, if my engine was running (200tdi) and I disconnected the battery would it cease to run or would all be ok?

trax · Oct 15, 2013

timtheenchanteruk said:
hmmm, but if an LED is fitted (as I have) a resistor is in place, so the voltage/current is dropped from the usual 12V, but mine charges fine??? im confused.

unless the exiter only needs a fraction of a volt to get going??

so from how i understand it.

the alt coil is an electromagnet. the amount of current going to the field coils (non rotating bit) changes the strength of the magnet which works with the rotor coil to make leccy.

the alt controls the output (hopefully 14.4v) by changing the amount of current going to the field coil and it does that by using current generated by the alt. (self sustaining or it might amplify the current)

so if i'm right, yep the led might be allowing less power, but it only needs to get the alt started, then it self sustains at normal levels.

the_wolf said:
Anyone willing to test that theory? I'd be interested to know if its true, surely a bulb doesn't control the alternator?

Also (slight thread hijack here) but to settle an argument, if my engine was running (200tdi) and I disconnected the battery would it cease to run or would all be ok?

should keep running, but you'll probably overcharge and damage something. mate did it to his 2.25 petrol to test the alt was working.. the nutter

blue beasty · Oct 15, 2013

What about the fuel solinoid?

trax · Oct 15, 2013

blue beasty said:
What about the fuel solinoid?

alt would still be chucking out 14.4v and powering it. I've not done this btw, just guessing and what my mate did.

the_wolf · Oct 15, 2013

trax said:
so from how i understand it.

the alt coil is an electromagnet. the amount of current going to the field coils (non rotating bit) changes the strength of the magnet which works with the rotor coil to make leccy.

the alt controls the output (hopefully 14.4v) by changing the amount of current going to the field coil and it does that by using current generated by the alt. (self sustaining)

so if i'm right, yep the led might be allowing less power, but it only needs to get the alt started, then it self sustains at normal levels.

should keep running, but you'll probably overcharge and damage something. mate did it to his 2.25 petrol to test the alt was working.. the nutter

Overcharge what? Doesn't the engine run off the alt anyway. Obviously battery is kept topped up and when engine is off electrics run off battery. Surely with the battery disconnected the alternator isn't charging anything but is still providing power to the fuel solenoid?

trax · Oct 15, 2013

the_wolf said:
Overcharge what? Doesn't the engine run off the alt anyway. Obviously battery is kept topped up and when engine is off electrics run off battery. Surely with the battery disconnected the alternator isn't charging anything but is still providing power to the fuel solenoid?

not sure, i'm just a self taught monkey. but doesn't the battery prevent power surges. so i have no idea what will happen to electrical equip / voltage regulators and all that.

sp00k · Oct 15, 2013

In the case of cars, the battery also has a special function in that it acts as capacitor. It dampens down surges that would otherwise damage sensitive electrical gear. It also supplies any high loads (temporarily) that the alternator cannot cope with on it’s own. I guess in an emergency you could run from the alternator alone - with simple defender electrics you might get away with it.

SteNova · Oct 15, 2013

Deffo needs a lamp to make it charge, it was the one thing we had to keep working when building banger racers

No charge! What to check first?

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Leaks an prone to bits dropping off

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