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12v regulator


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sarbein 
Member - Posts: 6
Member spacespace
Joined: November 16, 2006
Location: Greece
Posted: November 16, 2006 at 1:26 PM / IP Logged  
hi all,
when i start my car the starter needs a lot of current to operate.So for 3-4 seconds,until the car starts normally,the voltage drops down to 0V and rises up to 12V very quickly because of inductive phenomenon.
I want to construct a voltage regulator 12v or 12,8v maximum input, to 12v output with 2A circuit current maximum.The circuit in normal operation demands 100mA.So ideal stable output is 12v/100mA!
This circuit will provide a small GPS modem..
if someone has a schematic circuit would help me a lot!!
thanks in advance..
kgerry 
Platinum - Posts: 3,455
Platinum spaceThis member consistently provides reliable informationspace
Joined: February 07, 2004
Location: Saskatchewan, Canada
Posted: November 16, 2006 at 2:15 PM / IP Logged  

go to an electronics wholesaler and ask for a 12 volt + v reg...

but keep in mind that a regulator regulates it's supply voltage... so if supply drops out so will it's regulated output.....

you may want to look at a gel cell battery or alarm backup battery ......

Kevin Gerry
Certified Electronics Technician
MECP First Class Installer
Owner/Installer
Classic Car Audio
since 1979
sarbein 
Member - Posts: 6
Member spacespace
Joined: November 16, 2006
Location: Greece
Posted: November 16, 2006 at 2:41 PM / IP Logged  
thanks kgerry!!
sarbein 
Member - Posts: 6
Member spacespace
Joined: November 16, 2006
Location: Greece
Posted: November 16, 2006 at 4:03 PM / IP Logged  
Just a moment kgerry
I agree that a regulator regulates it's supply voltage,but when the suplly drops out,this msec,can i use a capacitor with a large discharge constant in order to keep my output voltage to 12v?
Then the spike of 12V comes again and recharge my capacitor..this repeats 2-3sec until my car starts operating normally..
If i make a mistake please correct me.
KPierson 
Platinum - Posts: 3,527
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Joined: April 14, 2005
Location: Ohio, United States
Posted: November 16, 2006 at 5:18 PM / IP Logged  

You're going to need a pretty large cap to supply a 100mA device at 12vdc for 4 seconds.

I'm not sure why you need the voltage regulator at all though.  Most voltage regulators will need ~+2vdc above their output to actually work correctly, meaning you will need about 14vdc constantly to provide a solid 12vdc out.

I like the idea of using a small back up battery system.

Kevin Pierson
Ween 
Platinum - Posts: 1,364
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Joined: August 01, 2004
Location: Illinois, United States
Posted: November 17, 2006 at 10:30 AM / IP Logged  

hi,

just use a diode (1N4001 or similar) on the power lead and a large value capacitor across the power leads of the device.  used to have to do that with some older radar detectors to have them power up properly.  i'd start with 10000 microfarads and go from there...shouldn't take up much space.

hope this helps

mark

master5 
Silver - Posts: 1,123
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Joined: October 10, 2006
Location: United States
Posted: November 17, 2006 at 11:25 AM / IP Logged  

What kind of vehicle is this? Perhaps you need a better battery or starter?

If this vehicle requires that much current to start and nothing is defective I would think the best way around is a small back up battery, isolated during crank. I would not trust a cap to perform this function although it might work as well. But the current demands for the small GPS modem seems like a prime candidate for a b/u battery in this case.

I don't believe a regulator will do much if the voltage is actually dropping down to zero as you state, that is not really it's purpose.

master5 
Silver - Posts: 1,123
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Joined: October 10, 2006
Location: United States
Posted: November 17, 2006 at 11:30 AM / IP Logged  

Oh wait...you didn't mention, where are you measuring this "zero" volts? You might just need to connect the GPS to an ignition wire. If you have it on an ACC wire it will read zero during crank. That is normal. This may not be the problem but  trying to check out all possibilities.

"normally,the voltage drops down to 0V and rises up to 12V very quickly because of inductive phenomenon"

I don't think this has anything to do with inductance, but if everything else is normal it is current draw issues.

Good Luck

sarbein 
Member - Posts: 6
Member spacespace
Joined: November 16, 2006
Location: Greece
Posted: November 18, 2006 at 3:59 AM / IP Logged  
Thanks master5 for your reply!!!
I will try to use a detector (diode-capacitor)as ween said.
The problem is that i don't want to use a battery.Otherwise i wouldn't have problem because battery would save me during crank..
I hope that the combination 1n4001 and 10000ěF will work properly!!!
Thank you ALL!!!12v regulator -- posted image.
master5 
Silver - Posts: 1,123
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Joined: October 10, 2006
Location: United States
Posted: November 18, 2006 at 12:23 PM / IP Logged  

Ok, keep us posted.

Best of luck.

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