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None of us are normal Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 25 Jun 2009 03:38:29
In Reply to: What's normal range for voltage readings on EDU?, Noel, Wed, 24 Jun 2009 17:50:04 Members do not see ads below this line. - Help Keep This Site Online - Signup |
This is a really complex question.
The first thing to do is to get a voltmeter and measure the voltage on the battery, and compare it to the voltage on the EDU. The EDU is not a precision instrument, and I often see as much as a 0.4 volt difference between it and the true battery reading. The voltage difference (error) can also change with time and temperature.
Much over 14.2 is a bit high - it can be a sign of a bad Voltage Regulator. If the VR is going south (or North, in this case), it should be replaced. If the voltage goes too high, it can damage the electronics, not a happy event.
So - measure the voltage on the battery while monitoring the EDU. The easiest way is with the hood open, connect the meter so you can see it through the gap between the hood and the dash, and sit in the seat. You are going to want to see the voltage (and voltage error) with the car at idle, and at 2500 RPM or so. Just rev the engine - no reason to have to be moving or load the engine. The alternator can produce more voltage at higher RPM, so it's the VR's job to control that (regulate). If the voltage at the battery really is jumping up to 14.5 at mid-RPMs (2500 or so), I'd replace the VR. If you blip it up higher (3-4K rpm) and the voltage keeps going up, that's a sign of a bad VR. If it goes up 0.1 volts, no problem; if it goes up by 0.5 volts, not good - replace the VR.
The voltage depends on a lot of things- engine speed, how good the VR is, electrical loads (AC on, brake lights, cabin fan, etc.) and underhood temperatures. The VR is temperature compensated - the hotter it is, the lower the output voltage should be. Charging a battery causes heat; you want to charge the battery slower if it is hot under hood, and the only way to charge it slower is to keep the voltage down. So you might see 14.2 V with a cold engine, but 13.4 (or less) when it gets toasty under hood. I've even seen 'normal' readings of 12.8 on a scorching day stuck in traffic, when you can smelt iron under the hood.
So get a meter, and compare the readings to the EDU. The EDU may very well be lying.
posted by 192.249.47...
, Thu, 25 Jun 2009 03:38:29 <-- Viewing This Message, Thu, 25 Jun 2009 08:55:32
, Wed, 24 Jun 2009 18:48:35
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