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Discussion Starter · #1 ·
Ever since I fitted a Jaycar digital Voltmeter I've noticed that when starting my Patrol, the alternator takes 30 seconds to a minute to begin charging.

In fact I'm not sure if its time or RPM related, because sometimes it won't begin to charge until it gets above 2000rpm. Is this normal, or is it a sign that there's trouble on the horizon? I've had the volt meter fitted for 12 months and its been doing it pretty much the whole time.

It never fails to charge, but sometimes it takes a short drive (eg. 200m) before it cuts in. Ideas?
 

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Does the alternator/battery warning light in the dash come on when you turn the ignition on and then go out once the engine has started?
 

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GU 2007 Cab Chassis Leafie, 6.5L Chev diesel, manual, slide on Tommy Camper on back
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Hi @AfricanGQ, the voltage output of the alternator sufficient to charge the battery (around 14-15 volts) should appear at the alternator terminal even at idle.
What it wont make much of at idle rpm is current (amps).
You say your voltmeter takes a while to show charging is happening, like 30-60 seconds.

If you turn the key to ON but not Start, does the voltmeter come on?
What does it show before the engine starts?
Does this voltage seem to gradually rise after you turn the key to on - or does it immediately show battery voltage at a steady reading?
After the engine starts, does the voltmeter show a gradual rise up to charging voltage, or does it suddenly kick up?

Can you check if this is occurs after fixed amount of time regardless of engine rpm (or is it related to rpm)?
Maybe you could do an experiment, time from engine start to voltmeter volts kicking up when you leave the car idling, then repeat for some different revs (still parked).
Is it a fixed time, or does rpm affect the time. Let us know.
 

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Mine does the the same mate. Once started produces no power until i give it a rev and excite the alternator. Once i do that light goes out and begins charging. Been doing it for years. Kind of enoying. I but it down to the aftermarket alt possibly having wrong size pulley maybe to make right revaluations to excite. But im no expert.
 

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Happens on my factory alternator too.

Somebody said it was caused by sticking brushes, but I don't really know.

It's not hard to give it a rev, and cheaper than a new/rebuilt alternator.
 

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Discussion Starter · #7 · (Edited)
Hi @AfricanGQ, the voltage output of the alternator sufficient to charge the battery (around 14-15 volts) should appear at the alternator terminal even at idle.
What it wont make much of at idle rpm is current (amps).
You say your voltmeter takes a while to show charging is happening, like 30-60 seconds.

If you turn the key to ON but not Start, does the voltmeter come on?
What does it show before the engine starts?
Does this voltage seem to gradually rise after you turn the key to on - or does it immediately show battery voltage at a steady reading?
After the engine starts, does the voltmeter show a gradual rise up to charging voltage, or does it suddenly kick up?

Can you check if this is occurs after fixed amount of time regardless of engine rpm (or is it related to rpm)?
Maybe you could do an experiment, time from engine start to voltmeter volts kicking up when you leave the car idling, then repeat for some different revs (still parked).
Is it a fixed time, or does rpm affect the time. Let us know.
12.6/7 volts before starting - can drop slightly (0.2-0.3v) after cranking & while the engine is running, after time / short drive it suddenly jumps up to 14.1 +/-. Both time & rpm factors seem to be random - never the same. Once it starts charging, it doesn't stop, even at idle. The rpm seems only to effect when it first begins to charge. After that, it still maintains 14v unloaded at 800rpm no problems.
 

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Discussion Starter · #8 ·
Happens on my factory alternator too.

Somebody said it was caused by sticking brushes, but I don't really know.

It's not hard to give it a rev, and cheaper than a new/rebuilt alternator.
Thanks for the feedback - good to know I'm not alone! Was afraid it was a sign the alternator was on the way out...
 

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Discussion Starter · #9 ·
Mine does the the same mate. Once started produces no power until i give it a rev and excite the alternator. Once i do that light goes out and begins charging. Been doing it for years. Kind of enoying. I but it down to the aftermarket alt possibly having wrong size pulley maybe to make right revaluations to excite. But im no expert.
Thanks for the feedback - as far as I know mine is original, I bought my rig with 262k on the clock, used for towing a caravan only before I got it. Its still possible it's been changed, but unlikely.
 

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GU 2007 Cab Chassis Leafie, 6.5L Chev diesel, manual, slide on Tommy Camper on back
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12.6/7 volts before starting - can drop slightly (0.2-0.3v) after cranking & while the engine is running, after time / short drive it suddenly jumps up to 14.1 +/-. Both time & rpm factors seem to be random - never the same. Once it starts charging, it doesn't stop, even at idle. The rpm seems only to effect when it first begins to charge. After that, it still maintains 14v unloaded at 800rpm no problems.
It sounds like the alternator doesnt have sufficient excitation at the battery voltage on starting.
The way I understand it is at starting, the battery volts are connected to the rotor to kickstart the alternator into being able to make electricity (AC), which is regulated to the ~14V DC. Once that voltage is getting made this is fed back to the alternator rotor for the excitation supply. At some point it is self sustaining. This rise in alternator output voltage is also what turns off the "battery/charge" lamp.

Here is the wiring diagram for the TD, with the yellow highlight showing the path of battery volts to the "L" terminal of the alternator (L for Lamp).
Besides the ignition switch and the 10A fuse - you can see a light globe (the battery/charge lamp) and a resistor around it.
As a suggestion if you wanted to, you could replace the lamp unit.
It's resistance may have increased with age, which would reduce the alternator excitation current on starting.
(Which may explain why you car needs time or rpm before the alternator kicks in and starts making a useful voltage for charging).
This is just a theory, no sure fire fix of your issue.

Otherwise, as the other posters have mentioned, maybe you just live with it.

530508
 
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