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Re: I think I will roll on 1/2" plywood and do it from top Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 14 Nov 2002 09:02:14
In Reply to: I think I will roll on 1/2" plywood and do it from top, Daren, Wed, 13 Nov 2002 20:34:40 Members do not see ads below this line. - Help Keep This Site Online - Signup |
I'm a little confused by what you gave for voltage readings. When you first start the car, the EDU displays and holds the cranking voltage, which is usually in the 9-11 volt range. If you hit the info button, or drive the car a hundred feet or so, the EDU changes to the actual battery voltage.
To get a true indication of alternator output, start the car, hit the info button to 'beep it around' back to volts, and rev the engine to 2K rpm or so. This makes sure the VR has enough juice (from the revving) to get the field coils under control.
There are a lot of variables. The EDU is not a precision meter. Always check it against a known good digital meter. Next, voltage output does vary as a function of a lot of things. It's harder for the VR to achieve full output at idle than at speed. The electrical load has a big effect - is the defroster, seat heater, headlights, or fan on HI? Is your foot on the brake? (Brake lights take a lot of current). Lastly, how hot is it under hood? The VR is temperature compensated - it puts out less voltage when hot than when cold. That's because batteries can't be charged as quickly when hot. A VR may put out 13.3V on a hot day, and 14.2 on a cold morning.
Basically, if the VR is putting out 13.3 or more when the car is going down the road, I'd count it as OK. If it starts drooping into the 12.7V range at a light, it's not a good sign, but wouldn't be out of the question if the defroster is on, headlights on, fan on high, seat heater cooking, and your foot on the brake.
As to the voltages you're seeing, that's the VR, not the battery. A fully charged battery sits at 12.6 volts or so. When you run the car, the alternator provides (or should provide) all the current necessary for the car, with some left over to charge the battery. The only way to charge a battery is to provide a higher voltage than the battery (to get current to flow IN), the Alternator runs about 13+ volts.
The best way to check a battery is to make sure it's fully charged - drive the car around for 20-30 minutes, where the alternator is working and providing 13+ volts. Then get a Specific Gravity meter from any autoparts store. It's just a clear plastic body with a rubber squeeze bulb. You pop the cover off the battery cells, and suck some electrolyte out of each cell, one at a time. It will tell the specific gravity for each cell. The SG determines how much sulphuric acid and lead sulphate is in the electrolyte, which determines the state of charge of the cell. If 5 out of the 6 cells are good, get a new battery. One bad cell is death for a battery. A SG meter is about $12 and well worth it.
posted by 192.249....
, Wed, 13 Nov 2002 14:53:36, Thu, 14 Nov 2002 09:02:14 <-- Viewing This Message
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