CD Rom PSU output in Car - diyAudio
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Old 28th August 2004, 06:00 AM   #1
cwteoh is offline cwteoh  Malaysia
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Default CD Rom PSU output in Car

I am fixing a CDROM in my car for CD player (Just for fun), CDROM needs +12V 1.5A and +5V 0.9A power. So I use 7812 and 7805 regulators with 2'' by 3'' inches heatsink in a small plastic case for each CDROM PSU output voltage.

At both 7805 and 7812 input pin I connected a ceramic 0.33uF Cap and Elna 2200uF ap at the both output pin. I am not sure it will work in my car or not. The heatsink not really hot for first 1 hour in air-con environment. Not sure what will happen when the CDROM is connected to my car amp (not live test yet).

Is anyone have this experience about this?
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Old 28th August 2004, 10:18 AM   #2
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the 7812 might shut off...as it has only a 1A limit...maybe u could get a 3A part...
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Old 28th August 2004, 10:50 AM   #3
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I wouldn't bother using a 7812 at all - if you feel that your car voltage might be a tad high while it's being charged by te alternator, simply insert a 3A diode in series with the +12V DC supply.

As for the 7805, mount it on a decent heatsink (±100mm square aluminium with vertical fins) or better still, feed it's output into the base of a power transistor (still using a heatsink), such as a 2N3055 and take the output from there. Suggest you do a Google search for examples of such a regulator.

-Eric
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Old 28th August 2004, 11:32 AM   #4
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he might be using a regulator to reject the noise that might appear from an alternator...not sure though
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Old 28th August 2004, 11:44 AM   #5
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Yes, or he could use a simple Pi-network (cap-choke-cap) to achieve the same affect. Better still to kill any Alternator noise at source by simply placing a cap (±0.5uF) across the alternator.

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Old 30th August 2004, 02:58 AM   #6
cwteoh is offline cwteoh  Malaysia
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do you guys think this PSU will damage my car battery? what yours opinion?
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Old 30th August 2004, 03:10 AM   #7
cwteoh is offline cwteoh  Malaysia
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just find out my 7812 spec. Model # is 78T12 CT regulator 12V 3A.
Should be OK for the CDROM?
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Old 30th August 2004, 07:44 PM   #8
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Should be fine, but your voltage output might be a bit low however, because your input is not that high to start with. You should still use a heatsink for the device.

-Eric
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Old 1st September 2004, 01:12 AM   #9
cwteoh is offline cwteoh  Malaysia
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you are right... I am applying a 3x3 inches heatsink for each regulator. testing will be done by this week...
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Old 1st September 2004, 12:07 PM   #10
Immo_G is offline Immo_G  Australia
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As long as you have a fuse I can't see a way to damage the car's power system. Not sure how gain would work out though, I've driven a car amp off PC, and its stupidly high ( had windows volume control on 1%, anything higher was too loud) .
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