Here's the deal.
I will try the CB with the computer supply, and I will make full observations about noise caused in all surrounding equipment by the switching supply.
Then I will come right here on this thread and make a tech report.
It won't be today, though. I am working on carrier current at the moment, and I'm getting carried away in the current of life.
Keep in mind, the new PC power supplies communicate with the mother boards and monitor the supply voltages and it's cooling fan, along with monitoring the computer temperature and it's cooling fans, particularly the CPU fan and spins it up when needed for better cooling during heavy CPU (microprocessor) usage..as well as any fan that may be on the buss processor CPU. There is also an "interlock" loop that has to be connected, as well as the on/off function.
Even the older PC power supplies had a loop connection made through the power connector on the mother board, so that will have to have a jumper as well.
Good luck!
RFB
Do a Google search for "convert PC power supply". There are a ton of hits, including videos, on how to use an ATX supply as a standalone power supply.
The only minor complication seems to be that the supply needs a minimum load to keep the switcher circuit alive. Typically, it is a 10 ohm, 10 watt resistor connected across the +5V line to ground. Once the switcher is operating, all the voltages come alive.
A jumper or switch is needed across two wires to simulate the signal from the PC that turns on the supply.
A 3.3V sense wire back to the supply is available for connecting to the final destination 3.3V distribution on the motherboard to compensate for resistive losses in the interconnect. It may be connected directly to the 3.3V output when that output isn't used, or you don't care about the precise level of the 3.3V at the final load location.
Otherwise, the supply is just a supply. There are no other exotic functions. CPU temperature monitoring and CPU fan speed control are functions implemented on the motherboard and are not controlled by the ATX supply.
These supplies are designed to comply with the Intel design guide documents such as http://www.formfactors.org/developer/specs/PSU_DG_rev_1_1.pdf and previous documents. To get that coveted "Intel Inside" sticker, all components must comply with Intel design guides.
There are bad switching supplies and good switching supplies when considering conducted and radiated RFI caused by the switcher circuit. ATX supplies have RF filtering on the line side and the load side. Do a Google search for "ATX power supply schematic" to get a sampling of the input and output filtering. Intel mandates compliance with FCC, Euro and Canada regulations.
The reason why PC motherboards have all those capacitors is to suppress on board "ground bounce" transients due to all the very high speed digital IC drivers on the board. The capacitors aren't there to filter switching noise from the power supply.
All considered, a PC ATX power supply converted for bench power supply use is an upscale and VERY inexpensive solution.
No debate on a PC power supply being (somewhat) of an upscale to a real bench power supply or a power supply built for a specific purpose...say isnt that what a PC power supply is..built for a specific purpose!
Ive used them too, in many applications. But I have also realized that even a PC power supply cannot be adjusted for various voltage and current needs. Not everything needs 12 volts at 10 amps, or 5 volts at 25 amps, or 3 volts at 5 amps. Even the PC power supply with those capabilities, you cannot vary the current and have a safety feature like that in a bench supply where if you build something to only use a certain amount of current, the bench supply trips and shuts down the voltage and current, while the PC supply, tends to just shove voltage and current into the device, and will do so even more because as far as the PC supply is concerned, it simply sees more demand like it would in a computer and kick up it's current and voltage regulation capacity.
Next to blowing a fuse or blowing up the circuit under test, that's about all the protection your gonna get.
It may have the approval of the FCC as far as noise, but that approval is CLASS A Computing device approval. That doesn't mean its necessarily a good thing for powering devices other than a computer.
And I never said the power supply controls the fan. I said the mother board communicates with it via voltage sensing and current sensing, as well as temperature sensing. If the fan in that PC supply starts to flake out, the mother board will know this and start shutting down the computer. If there was no communication, even on the simplest level, the mother board would have no idea there is a problem and would continue to operate. That was a very common problem in older PC's when the power supply fans flaked out and people sitting there wondering why their computer fried.
But if it were that simple to use salvaged PC supplies, why would the PC supply need any converting?? A bench supply doesn't need any converting.
Just my 2 cents.
RFB
I would not use a PC power supply for anything other than its intended purpose, namely to power a PC. There are just too many unknowns regarding load protection,stability, control lines, and probably things I haven't thought about..
There are many wall wart, inline, and enclosed 12 volt switchers available on the surplus market in the $10 to $30 range. Only purchase one which will work down to zero current however. The question remains about the current draw of an automobile radio and this would probably depend a bit on the audio output power one is intending to produce.
My first guess is that a 5 Amp unit would work. This would give an input power of 60 watts which would probably suffice for indoor listening volume.
Last year I purchased a 12V 43 Amp surplus OEM supply which adjusts nicely up to 13.8V and has over current and over voltage shutdown protection. It cost about $75 but I needed it for a non radio purpose. I am not recommending this for general bench work because the high current capability can be dangerous but only offer this as an example of what is out there.
Neil
An old point of confusion I have had for many years is mention of "13.8VDC" in discussions about automobile related power supply.
If automobiles have 12VDC power systems, what is the significance of 13.8V?
An operational lead acid battery with six cells (nominal 12V) will have 13.8 V when fully charged and so will the auto DC supply. 13.8 V comes from the battery characteristics.
When in doubt I have used the DC voltage measurement to assess the battery and charging system. If the battery is around 11 V engine off and goes up to 14 V running then the alternator is OK and the battery is weak. If the voltage does not come up to 14 V then the alternator is suspect. This is not the best way to test things but it is a starting point.
Neil
"If automobiles have 12VDC power systems, what is the significance of 13.8V?"
Vehicles electrical systems take quite a bit of current, even when it's just the ignition system for the engine in operation. These days with electronic ignition, the current draw is somewhat less compared to the old point contact and coil system. But even the newer systems still use either a single or an array of step up transformers to produce the high voltage for the spark plugs by means of switching the DC voltage into the transformer, where it is stepped up and produces the high voltage to produce the spark.
Now imagine all that happening at 5,000 times per second on 8 cylinders! If one were to measure it with a meter or ignition check system that could only see switching at a very low rate, it would appear to be like a dead short across that DC supply. This is why the vehicles can generate up to 14 or 15 volts out of the alternators at around 60 to 80 amps of current! That poor alternator must not only provide the necessary current constantly to keep the vehicle electrical system going, but also to maintain a charge on another load, the battery.
A fully charged battery will need to provide at least 400 amps of start current to turn that starter motor to crank the engine, and at the same time, still provide current for the ignition system to fire the plugs, and provide voltage and current for the on-board ECU systems and all those fancy lit up indicators on your dash board.
Neil is correct, the typical run voltage of a vehicle 12 volt system is around 13.8 volts. The alternator has a stator winding and a rotor winding. The stator winding is the winding on the outside of the rotor and is what produces the electrical voltage and current. The rotor also has a coil, which is fed about half of the DC voltage in the system to produce the magnetic field for the stator to produce electricity when the rotor rotates. Alternators produce an AC voltage, which is rectified internally in the alternator by a dual pair full bridge rectifier system. Regulation takes place inside the alternator by varying the rotor voltage, which is monitored and controlled by the vehicle computer system. Older systems relied on either a voltage regulator within the alternator or an external resistor divider network to maintain proper rotor voltage so the alternator would not produce over-voltage when the engine RPM increases, such as that during acceleration. The regulators also increase the rotor voltage when the RPM winds down during braking, or when loads are removed from the system such as turning off the lights, A/C etc.
Even with the alternator doing it's thing, it cannot supply the vehicle's entire voltage and current requirements, especially when all of the electrical systems are turned on, such as during night time driving with lights and other accessories, car radio, thump amps, air conditioner compressor electromagnetic lock pulley, and these days, dvd players, lcd screens and all kinds of other stuff. During these and even light load conditions, the entire vehicle electrical system splits the work between the alternator and the battery sources. While doing all that, the system must keep at least a decent charge on the battery at all times so that the next time it is required to start everything up, there is enough voltage and current to get everything going all over again.
RFB
It all began with horses. Now we have these elaborate systems that seem like science fiction in your description, but there it is: the common car!
Thank you for the engineering blueprint.
Gentlemen of the broadcast industry of Part 15
I havent solved my question yet about where is or do new car radios have an AM antenna trimmer but the discussions under the post are interesting to read anyway.
From my own past experience if you want a noisless power supply for running a car radio in the house use a 12 volt battery, storage or Sealed 12 volt battery. Any swithcing power supply devlopes tons of hash, many ohters just have too much hum, I know if its regulated and filtered you may not have hum. At anyrate, you dont want your radio connected to the power line in anyway shape or form for lowest possible electrical hash, interferance,or what ever. Ive done all of the differet types of power supplies for car radio in the home and for AM reception, a battery wins every time. Charge it up, then disconnect the charger, you have plenty of time for operation. Thats all I have to say. I have broadcasting to do so cant take the time to write much more, time to change the 8 track tape in the chain.
Radio Joe
Or you can use a solar panel array to power the radio, and charge a battery for night time use. A steering diode prevents current draw of the solar panel pulled by the battery, and it allows the solar panel isolation from the battery, blocking current flow in the opposite direction but maintains the flow in the other. Adding a voltage regulator will keep the solar panel from over voltage production and prevent over-charging.
Have fun with them 8 Tracks! I used to have a 20 slot 8 Track player where all of the 8 Track tapes were slid into slots in a circle, and the whole works rotated from one tape to another, working from the short aluminum tape contact which was used to close the contacts so the deck would change tracks. Was a nifty deck. I called it "FRED".
RFB