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Unread 05-01-2007, 04:51 PM   #1
irwinsr5
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Default Volt meter / Battery Voltage

I've tried searching on this subject but can't find much information about it so I apologize if it is a repost.

I am in the process of getting / installing a volt meter inside the 4runner to obviously tell me how much charge is left in my battery (seems stupid toyota didn't do this). I was just wondering if anyone knows how much power the battery needs to turn over the engine. I remember someone saying they didn't want to let their second battery get below 11V although for actually starting the engine is this a high or low estimate?
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Unread 05-01-2007, 05:45 PM   #2
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See this link and scroll down a bit to see the state of charge table, showing how much capacity is left at what voltage of the battery.

http://www.windsun.com/Batteries/Bat...ery%20Voltages

For voltmeters you might want to check these out

http://www.cyberdynegauges.net/voltmetersproduct.php

Or you can opt for something simpler and cheaper.
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Unread 05-01-2007, 05:57 PM   #3
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Do you know how much charge it takes to start the engine?

Or is roughly 10.5 (a little about 0% charge) enough to turn over the enginer
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Last edited by irwinsr5; 05-01-2007 at 06:01 PM.
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Unread 05-01-2007, 07:50 PM   #4
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Quote:
Originally Posted by irwinsr5 View Post
Do you know how much charge it takes to start the engine?

Or is roughly 10.5 (a little about 0% charge) enough to turn over the enginer
I doubt 10.5V will do it. Pending on the battery, but I wont go below 11.7V or so. With all the electronics it is better to have a bit more charge.
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Unread 05-07-2007, 10:54 PM   #5
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I've been thinking about similar things and I ran across this page, which has good info about how to accurately measure state-of-charge for a car battery and also the tables to convert voltage to state-of-charge:

http://www.uuhome.de/william.darden/carfaq4.htm

the trick is, after charging the battery (i.e. running the engine) or putting significant drain on it you have to wait a while before the voltage reading is an accurate reflection of the charge in the battery. You also can't trust it at all during actual charging/disgacharging activity due to the fact that the voltage "boosts" a little while charging and sags while discharging. I think these are the reasons Toyota doesn't include any sort of built-in battery guage...it just wouldn't be accurate under typical use.

for instance, you could turn the high-beams on for 5 minutes after stopping the engine and then let it sit for 10 minutes...then you would get an accurate reading.
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Unread 06-02-2007, 04:28 PM   #6
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Because my Scan gauge is only looking at the 12 volt bus for the engine I wanted a way to watch my second battery. I bought one of these off of ePay



I have not decided where to mount it and it requires a 5 volt source (easy to do) but it is small. I got mine in a bid for $15 shipped.

http://cgi.ebay.com/Mini-Green-LED-D...QQcmdZViewItem
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Unread 06-02-2007, 04:50 PM   #7
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Nice find!!
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