ahh, I see now.
I was kind of flipped around. SO how about a DPDT switch, once flipped it would connect the doubled 5VSB (say around 12v now) to the Car's ignition, and at the same time connect the 12v+ (the main circuit so 34 amps) to the HU Constant and main draw. All of this done after the PS has been turned on by shorting the PS On to the ground. Then with a simple Cap like you suggested to hold the voltage for that instant.
Or maybe that switch won't work and a simple relay to do all that would be necessary.
You can use a small 9.6V NimH battery (8 cells) and run the memory wire from that. You will need a diode from the +12V line, and also a 100 ohm resistor in series with the diode, and run it to the + battery terminal. That will trickle charge the battery with about 20mA while the computer is on, and when the computer is off, the battery will keep your memory. The diode is very important so the battery does not drain through the computer PSU when it's turned off.
I'd also HIGHLY recommend building a filter for the +12V to the Head Unit, because the power is NOISY in a computer due to the different devices inside the computer. I'd recommend a toroid filter or two with at least 10000uf or better of capacitors after it.
The power inside a computer is nowhere near as clean as the power in a car, it has to be filtered if running some type of amp from that source, or you will hear noises in your speakers from typing, moving the mouse, disk access, etc.
Well, first off, thanks!
Next, the PS is connected only to the HU, no other devices installed. Also, Computer Power Supplies are arguably the cleanest DC power I can purchase. So I am not sure any filtration is necessary. Especially considering Car's are often argued to have horrible DC. I mean, other than the regulator on the alternator, while the car is running no other filtration is put on the power being pulled. (This is what I have learned, and could very well be completely wrong)
As far as the memory goes, I think a simple 5 volt doubleing circuit will do the trick. I tested with a friends voltage supply, it has a digital read out and variable voltage output, the HU turned on around 8-9 volts, 10 volts consistantly. Tomorrow night I hope to check the amperage being pulled at 10v.
If the 5V VSB can be doubled to 10v and keep the memory, a simple DPDT switch can switch the 10v from constant on the HU to the ignition, while at the same time switch the 12v from the PS to the constant on the HU.
I am going to have to see if a simple rocker will be fast enough. Perhaps a small capacitor will be needed. If so, would I need to parallel the capacitor across the switch, or put it in series in the 10v VSB?
Thanks once again for your help.
ALso, an update, I was able to turn everything on tonight and listen to some CDs on my Tang Band W3-871s fullrangers. The sound was easily comparable to My Parental Units' all-in-one HT reciever. (No surprise there I guess)
i suggest trying without the extra filtering first either way
having played with auto electronics a fair bit from time to time it is certainly not clean power, especially with the motor actually running. with crappy car audio gear you can sometimes hear noise from the revs increasing (like a high pitched whine increasing with revs) and stuff like that - good quality car audio gear filters that out perfectly as it is.
Alright, so my last question is with the switching, what capacitor if it is necessary is recommended? Like a voltage rating and uF.
I purchased a on-on DPDT rocker switch, rated at 20 amps at 12v, more than enough for this application. I should be wiring it up to see if it works sunday.
like i said before i had make somethng like this.
and ive cleaned up the noises from power supply with ans choke and an cap ( i guess it wass 10000uF but o dont remenber)
its not to filtrate the noises like a car make. is that theses power supplys have high frequence noises.
there is no hum on my amp. but there was something like a white noise on it. before the choke and the cap.
i alsow have insulated the fan from the 12V cos it makes a rathle on the sound. try out with noting if you like. but if you see that you need filtering. Do it :)
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