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Re: Low Voltage at start Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Fri, 14 Sep 2001 09:47:46
In Reply to: Low Voltage at start, Tom 9KT, Fri, 14 Sep 2001 09:13:26 Members do not see ads below this line. - Help Keep This Site Online - Signup |
As a 'feature' of the system, the EDU captures the low voltage level during engine start. This can be used as an indication of battery /starting system health. BUT, and this is a big BUT, unless the voltage is very low, use it as a RELATIVE measure.
Huh? What? Basically - every car is different, so bad for one may be normal for another. Get to know the car, and if you see that voltage creeping down, take that as a time to act.
The EDU isn't an accurate instrument - I regularly see 0.3 volt variation between actual battery voltage and the reading. Also, exactly 'when' that voltage is captured makes a BIG difference in the reading, and that not only varies from car to car, but to some extent from start to start. Lastly, battery temperature has a big effect - expect lower start voltages if the battery is cold.
Here's some rules of thumb- 10 volts and above is great, 9.0 volts and up is OK, and 8.0 volts and up may be a concern. But that varies from car to car. My '88 shows voltages in the mid 9's, and that's OK for that car. Once it drops below 9.0, the battery is dead. But my '92 has shown a startup voltage of 8.1 - 8.5 since new. A new, fully charged battery is maybe 8.3 or so. 8.1 is OK on a cold day, and I've even seen high 7's.
So as a guess, I'd say 9.5 is fine. If you want to be sure, buy an inexpensive ($15 or so) Specific Gravity gauge for your battery. It's a clear plastic body with a squeeze bulb on top. You stick the hose into each battery cell and suck up battery acid to fill the body. A needle shows the state of charge for that cell. Do it for each of the 6 cells.
But get to know what your car does, and react if something changes. And 0.1 volt isn't a big change.
I wish I could simply say "9.5 is good, anything below 9 is bad", but it just isn't that straightforward. But it's important to remember that the EDU gauge can be used as a guide, not an absolute. Don't start sweating over every 0.1 volt, or that if it reads 12.8 when you're sitting at a light it means you need a new alternator.
Good luck!
posted by 140.157....
, Fri, 14 Sep 2001 09:47:46 <-- Viewing This Message
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