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Not an issue Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 8 Oct 2008 17:55:02
In Reply to: General charging question - '95 Aero, Lawrence, Wed, 8 Oct 2008 08:39:25 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The EDU voltage reading is taken a lot more seriously than it deserves. Or at least it causes a lot more concern than it should.
First, the EDU display is not a precision instrument. As Aom mentioned, if you really want to know, stick a voltmeter on the battery and compare that to the EDU reading. I've seen EDUs reading as much as 0.4 volts off.
The voltage is a function of a lot of things. Besides the EDU accuracy, there is engine speed, electrical load, Voltage regulator variation, and underhood engine temperatures.
Ignoring the EDU accuracy, a voltage regulator is not a precise device. It's job is to keep the voltage above 13.0 and below about 14.2. Each one is different. Next, the voltage changes with engine speed - more speed, more voltage. Now, it's the VR's job to crank the voltage back down as the RPMs increase. But it isn't perfect. As the electrical loads change, the voltage changes. Again, the VR tries to keep the voltage steady, but it doesn't need to be very precise - again, above 13.0 and below about 14.2 is OK.
Lastly, underhood temps. The VR has a temperature adjustment. Batteries create heat when they charge. To keep the battery from cooking, the VR drops the voltage as underhood temps rise. So you'll typically see a higher voltage when a car is first started on a cold day then after the car has been running a while and things are toasty in the engine bay.
Bottom line - if the voltage is above 13.0 volts (12.6, actually), the battery is charging. Anything much over 14.3 is going to cook the battery if it stays that way.
What's normal? When the car is underway, above 13.0 and below 14.2 is just fine. 13.6 isn't inherently better or more virtuous than 13.3, or should feel ashamed when faced with 13.9. More is not better. The voltage will vary, and worrying over it isn't a good idea. And with a warm car idling at a light, with a lot of electrical loads, like headlights, brake lights (brake lights take a LOT), blower motor, and maybe the A/C cycling, the voltage might drop to 12.8. That's just fine. The battery might not be charging much, but it is still doing fine, and you won't spend 5 hours that way.
posted by 76.219.9...
, Wed, 8 Oct 2008 17:55:02 <-- Viewing This Message
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