New Poster here,,, need help with circuit design

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jhowle
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New Poster here,,, need help with circuit design

Post by jhowle » Thu Dec 09, 2010 11:53 pm

hello, i am new to these forums. This sight was recommended by a local computer store.

Anyhow, I am big in to car computers and I have one installed in my car but i am seeking help with a small project. As I am sure most of you all are aware the voltage in a car varies from 11 to 14.4 volts. With my car it doesn't have a voltmeter on the dash and what I would like to build is a circuit that does two things a/ regulates my car voltage to 12VDC at 10 amps for my Car PC and screen and filters out altinator noise b/ has a volt meter circuit with an LCD or LED display to show the voltage being output by the rgulator.

My reasons for wanting to built this is because when i first crank my car it takes a minute or two to charge the battery back up above 12 and if i turn it on when the voltage is low i get some erros with my car pc. it uses a simple DC/DC power supply and subsequently i recieve that high pitch whistle in the back ground which increases in pitch the more the engine RPM's increase. I'm and aircraft mechanic by trade and i'm very skilled with a soldering iron. if anyone can help me with a parts list and a basic schematic i will be forever in your debt. :arrow:

dyarker
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Re: New Poster here,,, need help with circuit design

Post by dyarker » Fri Dec 10, 2010 2:46 am

Car voltage to anode of diode that can handle, say, 15A. Cathode to SLA battery which feeds DC/DC converter.

Diode prevents car cranking from loading the SLA voltage down, so computer can be started before car engine. SLA also acts as a d_mned big capacitor, soaking up the whine. When engine is running, alternator provides current for computer and recharges the SLA.

Getting the voltage from ignition switch ACC position (or relay controlled by ACC) would prevent the computer from running down car battery if you accidentally leave computer on when engine is off.

Make only one negative return connection to chassis. All computer, or devices connected to computer, should have their negative/common wired back to DC/DC supply. This eliminates ground loops.

Cheers,
Dale Y

jhowle
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Re: New Poster here,,, need help with circuit design

Post by jhowle » Tue Dec 14, 2010 3:40 am

Sweet, I appretiate the help. When i installed the car pc, at first i used the ignition circuit from the car but after a short time I put in a switch on the side of my center console and ran a wire from battery to this switch then to the ignition line for the carpc power supply. I decided to do this because i wanted to be able to run the PC independednt of the car electrical system. Awhile back I had a memphis audio high current system installed and I have a 2 gauge power wire from the battery to power the amp via a 120amp ANL fuse. This is the same place I'm getting the power for my CarPC.

When I put in the CarPC, i used my skills for wire repair since I serve in the USAF as an Aircraft mechanic on F-15E's and I used some wire mesh wrap and wrapped my RCA cable and PC power wires and then I grounded one end of the mesh to the chassis with a Zenor Diode. This reduced the altinater noise dramatically but you can still hear it.

If you could, could email me a basic schamitc of a regulator with the circuitry for an LCD read out included in the circuit. If it's a matter making it worth your while i can do so. thanks in advance

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dacflyer
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Re: New Poster here,,, need help with circuit design

Post by dacflyer » Tue Dec 14, 2010 2:30 pm

alt. noise can be from many things.. but mostly from bad grounding of items..
had a weird noise from my car radio, i thought well the antenna is grounded to chassis of the car, and the radio is grounded, cause that's power return. well i found out later on that if i bumped the side of radio the noise would go away..later after much checking, i found out the noise was cured when i grounded the case of the radio..
perhaps that may help you out also with your dc/dc power supply.. also the power in your car should be about 13.5 - 13.8 volts average..
just 12 volts is not a good voltage if car is running.. that's a low to no charge indicator, but your an AP mechanic, so you know that ;)
you might want to try a large cap near the alt. output if need be.

on ebay you can find ready made LCD or LED volt meters for cheap in many styles. and colors.

jhowle
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Re: New Poster here,,, need help with circuit design

Post by jhowle » Wed Dec 15, 2010 10:35 pm

Hmm, thats a good suggestion. I will have to try it, I should tell you though that my car PC replaced the car radi all together. The only thing in my Dash is a 7" PC touch screen. When the car audi installer put in the audi system they grounded the amp with the same 2 gauge wire and at a point 8"'s from the amp. I have always wondered if how they did it was the best way to go. They used basically a gold plated bracket with self tapping screws into some raised framework under my passenger seat. Would it be better to attempt to run a ground for the amp straight to the battery or just simply solder the 2 gauge ground wire to the chassis. I have even thought about running the amp ground and hooking it to the engine block and then making a 2 gauge ground lead and adding a ground wire from engine to chassis.

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