Author Topic: Voltage at startup  (Read 1398 times)

Offline Alex

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Voltage at startup
« on: August 16, 2010, 07:59:42 pm »
The car's running really well at the moment, but as always I've got a few questions!

My volt meter is showing a significant drop at startup that makes me question if there's a problem with the electrical system somewhere.

The volt meter plumbed into the ignition switch, so from what I can tell with my multimeter there's a 1V difference between the reading on the gauge and the voltage between the battery terminals.

However.

If I start the car after it's been sat overnight or after work the voltage drops to 11V on the gauge (so 12V, ish, across the terminals) and the battery light comes on. It'll sit at idle like this, though sometimes it'll stall after 30 seconds or so.

If I blip the throttle to about 2,000rpm the voltage shoots up to 12.5V on the gauge (13.5V? across the terminals) and stays there instead. It doesn't drop down afterwards, even when the engine returns to idle, and doesn't seem to stall if it's left.

I've got my suspicions that the alarm is draining the battery tbh, but I'm wondering if the battery is sick.

The starter motor seems a little reluctant to turn sometimes, like it's full of honey or something. A mate of mine on Practical Classics reckoned that was a battery issue.

It does seem to be charging properly though, and the alternator's been replaced a few years back. All my earth straps are new, and they're greased at the terminals to stop water/rust getting in.

Any ideas?
« Last Edit: August 16, 2010, 08:01:21 pm by Alex »

Offline Yoof

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Re: Voltage at startup
« Reply #1 on: August 16, 2010, 08:08:52 pm »
Voltage reg on the alternator often require a quick blip to start charging, especially if they're aftermarket ones.


Offline Alex

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Re: Voltage at startup
« Reply #2 on: August 16, 2010, 08:19:50 pm »
Aha so that's normal then?

Is a little voltage drop expected too?

I'm so obsessive about everything I really shouldn't be able to watch my engine closely!

Offline GAF2

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Re: Voltage at startup
« Reply #3 on: August 16, 2010, 08:25:56 pm »
mines exactly the same small blip of throttle and light goes out, never had any bother because of it.

cheers grant

Offline Yoof

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Re: Voltage at startup
« Reply #4 on: August 16, 2010, 09:40:45 pm »
Dependant on engine temp and under bonnet temp, circa 10v under cranking is normal.

Offline Alex

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Re: Voltage at startup
« Reply #5 on: August 16, 2010, 10:37:43 pm »
Happy days :)