Alright, Gonna make my own power supply.

crazydemon · 01-12-2004, 12:03 AM

Seems like the best solution, plus I might learn something along the way.

My plan is to use the LM2677 Adjustable regulator to regulat the voltage to 12V, 5V and 3.3V. Each line will be able to supply 5A, which I think should be enough. If not, I may use the 10A version of the IC instead.

To get the -12 and -5V, i will also use an LM2587 with a simple inverting circuit to get -12V. From there, a negative linear voltage regulator shoudl provide the -5V. I should be able to get away with this since the -12, and -5V lines do not require any 'real' power.

One thing Im wondering about is the way this will function with conjunction to an ATX motherboard. Using a relay, I can activate this power supply, but how will the motherboard deal with this? With all the rails live, will it still function properly and stay off before the power button is pressed? Do I need to create any kind of communication between the power supply and the MBD?

Also, since all of the voltages will be regulated, should I also regulate the incoming voltage to 12V to help even out the spikes? Seems like over-protection too me.

Thoughts?

weekendowel · 01-12-2004, 01:07 AM

What do you think will happen when the voltage of the battery sinks below 11 Volts or something when you start your car?

meddler · 01-12-2004, 03:16 AM

don't bother regulating the input, thats what the LM2677 is for. You don't need to regulate power twice. There will also be a voltage drop due to the regulation, I think it is 3V, so you will need to give the circuit 15V to get 12V out. (It has been a while since I have looked at the data sheet so I could be wrong). You will also have to consider what weekendowel said. When you start your car, your power supply will brown out due to the fact that your battery voltage can drop to as low as 8V during cranking. If this doesn't worry you then it should be ok. You should be able to do a search for ATX specs on google, that will answer your question about turning on the power supply.

crazydemon · 01-12-2004, 06:19 PM

about restarting when the car is cranked? doensn't bother me at this point, may think of something later.

As for having only 12V input when the car is off, a simple relay by passing the 12V line regulator trigered by the ignition shoudl solve the problem.

I can use the live 12V line that is triggered by ignition to trigger a relay that would switch the input of the pc to the regulator, instead of simply feeding off the battery when the car is off.

Here's what seems like a simple solution to the reboot problem.
Connect a small 12V rechargable battery via a charge circuit to the main 12V line. Connect this devide in close proximity to your PC and install a diode that would only allow current to pass to the carPC system, but not from it. THis way, when you crank the car, the system will temprarily feed from the local 12V battery rather then the main power source. When all is good, this battery will quickly be recharged to normal conditions.

If the diode is not sufficient, a simple SCR or relay circuit may also be built.

crazydemon · 01-15-2004, 10:46 PM

I've been searching for a while on ATX specifications, and although Ive found some information, im still not 100% clear on how I will be able to integrate this power supply to ATX requirements.

If you can provide some links, I would be greatful.

Would it work if I simply connected all of the rails to the motherboard? Does the motherboard NEED to send signals to the PSU, or is that just for advanced power feateres, sleep, standby, and such?

Thanks again.

MikeH · 01-16-2004, 06:48 AM

Crazy.....Here's the ATX spec.

Vineet Singh · 01-17-2004, 12:54 PM

Quote: Originally Posted by crazydemon

about restarting when the car is cranked? doensn't bother me at this point, may think of something later.

As for having only 12V input when the car is off, a simple relay by passing the 12V line regulator trigered by the ignition shoudl solve the problem.

I can use the live 12V line that is triggered by ignition to trigger a relay that would switch the input of the pc to the regulator, instead of simply feeding off the battery when the car is off.

Here's what seems like a simple solution to the reboot problem.
Connect a small 12V rechargable battery via a charge circuit to the main 12V line. Connect this devide in close proximity to your PC and install a diode that would only allow current to pass to the carPC system, but not from it. THis way, when you crank the car, the system will temprarily feed from the local 12V battery rather then the main power source. When all is good, this battery will quickly be recharged to normal conditions.

If the diode is not sufficient, a simple SCR or relay circuit may also be built.

Should work in theory, but using a 12v battery, your voltage will be variable to a point (maybe 1-2v) to the amount of current you draw, I'm under the impression that 'puters really only like stable voltages (and stable OS's

).

You could figure out a 2 stage switching powersupply, perhaps something similar to 2 parallel laptop 5a @ a settable 12-22v, or a single highpower one from targus, feeding the circuit you mentioned above. Run that whole thing off the 12v seperate battery, and just feed the charge current through a beefy diode or SCR like you mentioned. The laptop targus supply is very efficient (85%? higher?). It produces almost no heat.

This is exactly why I used a laptop as my car computer. In fact, this would be the closest thing to what you are proposing

My setup, I have a 5v dc tiny relay running off the keyboard port, which in turn switches on a 12v 30a relay which turns the power on to all the amps, the laptop converter, and the audigy usb nx sound card, which is powered by a regulated 5v powersupply I built last night (this supply can handle 2.5a, so today I will make it run a powered USB hub as well).

The circuit for the 5v side of the AVCLAN is based of the LM117 IC series, more specifically, the LM317T P+. It has a small aluminum box, which also serves as the heat sink for it. It has protection diodes, and capacitors to reduce ripple, and keep it clean when the car is running. It's basically the same circuit as page 14 - Adjustable Regulator with Improved Ripple Rejection

http://www.national.com/ds/LM/LM117.pdf

But some of the capacitor values are a little different, and the adjustable resistor is switched out to two 1.5k resistors in parallel to provide 750ohms to the vadj line. I really needed 735-740ohms to produce 5.10v, so I found two that were on the low side of their tolerance, make sure you test final voltage before plugging stuff in. The audigy nx has virtually no noise induced by this powersupply, and it does draw about 1.1amps.

When the laptop shuts down/hibernates/standsby (via tiny momentary switch in dash), it shuts power to all the things not in the laptop, including power to charge it's own battery (so to actually turn on, it should have some charge left at all times).

crazydemon · 01-18-2004, 05:36 PM

Thanks, I've read the ATX specs before, and I understand it in theory, but I dont quite understand how the MB controls the PSU using the TTL line in practice.

Seems like a MB varies the voltage over this line which should be picked up by the PSU and vary the line voltages accordingly.

It's just not very clear how this can be inplemented into the kind of PSU I'm talking about...