As an electronics nonexpert, the only idea I have is to get a second power supply. That should work fine. Of course, an electronics whiz could probably tell you a better way to do it.
Anyone used a dc-dc psu (mine is a home made one) with a high capacity hard disk?
I am trying to upgrade my tiny 1Gb in car disk to a 6.4gb one but cannot get the unit to boot with the 6.4gb in.
Looking at the Seagate site it mentions that the 1Gb drive only requires 1.2A to startup while the 6gb require 2.2A.
Any suggestions for me to try?
The PSU runs with the standard Maxim chips...
Perhaps it would not be bad idea add some extra capasitors to output of your suply, it would not hurt
How did you design your 12V section? Which Maxim chips did you use? What current did you design your 12V section for?
My player uses a 6.4G Quantum fireball, I also used the MAX regs for 5,-5 and -12. The 12V reg I origionaly used was an LM7812 in a TO3 case. Mine has been working fine even with the 1A 12 reg, however I had alot of weird **** happening with the drive (noise related I think) when I changed the position of the noise suppressor. With the suppressor at the computer end of the power in, there was less static noise but the system wouldn't boot and a clicking noise at about 2 hz was comming from the speakers. Then I noticed a mechanical noise a the same frequency comming from the HDD. I ended up putting a reasonable sized smoothing cap across the input of the PSU, this fixed it. This has probably got nothing to do with the problem you are experiencing but then again it might help. Also the power ratings on my HDD are 5/12V 650/720mA.
I would suggest using a different regulator for the +12V. You can get LM350 regulators in a TO-3 case that can source 3, 5, or 10 Amps depending on how much you want to spend and what type you get.
My guess is the 2Hz "ticking" you heard was your 1A regulator going in and out of an overload state (i.e. providing 12V and then shutting down, powering up again, shutting down, and so on...) If your drive says it takes 2A to start up and you're only using a regulator rated at 1A, then the regulator might not be able to handle the load. Plus don't forget the motherboard draws current from the 12V line too.
Adding additional capacitors on the output won't increase the maximum current source rating on the regulator. Capacitors can provide short bursts of power when needed, but spinning up a hard disk isn't very "short" on the scale of ns and ms.
Just some ideas...
Yorba Linda, California
M²PC Phase IV - *** PENDING ***
GrahamS, I have to agree with jjohnson. Upgrade the current capacity of your +12VDC. One of the sites I visited used Motorola MC78T12CT +12VDC regulators. They are rated at 3A a piece. I am currently in the planning stages of my PSU and am designing my +12VDC with 2 of these paralled together. Just put a .1 ohm resistor at the end of each MC78T12 to balance their outputs. jjohnson's idea works also!
so teasinglet it go, but must still answer.
Problem is not dc/dc, it is too low outputpower or just poor design of dc/dc.
Just like picking too lowpower dc/ac inverter.
My original proposal of adding more caps to output, is easy to test and in some cases solution, but if problem is poorly designed system or system needing too much power too early, you need something else.
Basicly you should not let power go to pc-board before you have all sytems working with full power.
For all those using linear regulators for the +12V supply, be sure to use LOW DROPOUT regulators!
'Regular' linear regulators require about 1.5VDC input above the output of the regulator, so if you are using a plain vanilla 12V regulator, it needs 13.5V to give you 12V out. If the input drops below 13.5V, your 12V output drops.
Low dropout regulators can take an input closer to the output voltage, but still they need usually 0.4 to 0.6V above the output.
Take a volt meter and measure the output of existing 12V regulators when you hear the tick tick tick. You may be running into a problem where you don't have enough voltage coming in and your 12V line is sagging.