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getting a 15v rating on a 12v system


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still_walkin 
Silver - Posts: 644
Silver spacespace
Joined: April 18, 2007
Location: California, United States
Posted: December 04, 2009 at 7:13 AM / IP Logged  
I have a 1993 cadillac deville and it has a 800cc 1000c battery big 3 zero guage all stock and a 250a alt I got from highoutput alt.com . The alt was 240 but I had it beefed up after I broke it . So I'm messing wit my sitnger digital led read out on my battery and the car is on headlights on and I'm getting 14.25 thn 14.50/14.75 it jumps around then hits 15.01 for like two seconds then goes back down. Is this a good thing seeing how I haven't wired the system in yet. Post your thoughts thanks
1993 sdv
Alpine 4x6 6x9 5 1/4 swr-10d4
alpine v60
12.5 VGA flip down
Nettop pc w/10" touch screen
78nova
5-re audio 5x7 ,10" sub &
Xtx-500.5
"Take the faceplate off get the jumperpack"
blackcivichatch 
Copper - Posts: 229
Copper spacespace
Joined: January 27, 2009
Location: Missouri, United States
Posted: December 04, 2009 at 11:47 AM / IP Logged  
I know that I wouldn't be complaining about gettin 15 volts. But if its jumpin around like that when youre just idling and no system on, it sounds like somethin might not be right.. Does you alt have an internal voltage regulator?
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yimke 
Copper - Posts: 417
Copper spacespace
Joined: June 23, 2009
Location: Nebraska, United States
Posted: December 04, 2009 at 12:24 PM / IP Logged  
Ya check your voltage regulator. It sounds like it is working because it jumped it back down, but it might be going out because it spiked like that.
still_walkin 
Silver - Posts: 644
Silver spacespace
Joined: April 18, 2007
Location: California, United States
Posted: December 04, 2009 at 2:27 PM / IP Logged  
It has a internal voltage reg. in the alt.
1993 sdv
Alpine 4x6 6x9 5 1/4 swr-10d4
alpine v60
12.5 VGA flip down
Nettop pc w/10" touch screen
78nova
5-re audio 5x7 ,10" sub &
Xtx-500.5
"Take the faceplate off get the jumperpack"
still_walkin 
Silver - Posts: 644
Silver spacespace
Joined: April 18, 2007
Location: California, United States
Posted: December 05, 2009 at 7:19 AM / IP Logged  
So I go out there last night and check the voltage after I crank and start the car I get a steady 15.89 and I'm thinkin my alts gonna die on me or my battery is gonna explode. So after work I check it with a regualr voltmeter and the battery cable and get these results below. I think those battery post are designed to boost your voltage from your orginal numbers giving you false numbers. Is there another way to boost your voltage .
Car off
Stinger batt post 13.70
Regular voltmeter12.80
Car on
Stinger 15.04
Volt 14.40.
What you all think.
1993 sdv
Alpine 4x6 6x9 5 1/4 swr-10d4
alpine v60
12.5 VGA flip down
Nettop pc w/10" touch screen
78nova
5-re audio 5x7 ,10" sub &
Xtx-500.5
"Take the faceplate off get the jumperpack"
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: December 05, 2009 at 9:41 AM / IP Logged  
It sounds like you have a voltage drop between the battery and the alternator's sense wire.
That shouldn't happen if it is a single-wire alternator - ie, (excluding the obvious ground/chassis & battery B or B+ heavy connections) it only has a charge-lamp connection aka D+.
If it's a 3-wire - typically Ig (+12V), L (charge lamp), & S (Sense), the S should be taken to the battery.   
If it's a 2-wire - ie, L = charge lamp & S or I or Ig = +12V - then the latter S has to be connected to the battery +12V.
Instead of powering S from whatever power wire, insert a relay.
Actuate the relay with the power wire (ie, to #86 with #85 to chassis) and use #30 & #87 to connect the battery +12V to the alternator's S terminal.
FYI - battery 13.7V sounds like a typical 12V battery with its post-charge "surface charge". It should drop to ~12.7V after a some minutes with a reasonable load.
14.4V is a healthy maximum charge voltage (long-term - meaning not higher, but may drop to 13.8V "float voltage" once the battery is charged). This is expected wherever the alternator gets its "Sense" voltage from.   
Erratic voltmeter readings may be due to normal AC fluctuations on the supply. Digital voltmeters tend to be "sample & hold" - ie, whatever instantaneous voltage (spike/dip). (That's another instance where where "True-RMS" meters are required.)   
Analog meters tend to show an average (of any variation).
A "true-average" can be shown with an RC filter for the voltmeter.
still_walkin 
Silver - Posts: 644
Silver spacespace
Joined: April 18, 2007
Location: California, United States
Posted: December 05, 2009 at 11:27 AM / IP Logged  
They are both digital and I took the numbers from the battery . The battery is a double post. I took the readings from the top post. And these numbers came right when the car is off and right when it was started
1993 sdv
Alpine 4x6 6x9 5 1/4 swr-10d4
alpine v60
12.5 VGA flip down
Nettop pc w/10" touch screen
78nova
5-re audio 5x7 ,10" sub &
Xtx-500.5
"Take the faceplate off get the jumperpack"
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: December 05, 2009 at 12:22 PM / IP Logged  
So which voltmeter is showing the correct voltage?
The Volt indication is fine.
The Stinger reading is too high for a battery.
still_walkin 
Silver - Posts: 644
Silver spacespace
Joined: April 18, 2007
Location: California, United States
Posted: December 05, 2009 at 3:26 PM / IP Logged  
That's what I was thinking too when I first installed the terminals I used a regular digital meter and got around those numbers so I'm gonna rule out and ignore those stinger numbers and try another meter and see what I get
1993 sdv
Alpine 4x6 6x9 5 1/4 swr-10d4
alpine v60
12.5 VGA flip down
Nettop pc w/10" touch screen
78nova
5-re audio 5x7 ,10" sub &
Xtx-500.5
"Take the faceplate off get the jumperpack"
DYohn 
Moderator - Posts: 10,740
Moderator spaceThis member has made a donation to the12volt.com. Click here for more info.spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spacespace
Joined: April 22, 2003
Location: Arizona, United States
Posted: December 05, 2009 at 7:23 PM / IP Logged  
Forget about those crappy indicators built into your equipment which may or may not read correctly and test your system with a real volt meter.
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