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Topic: ATX Breakout Suggestion (Read 21290 times) previous topic - next topic

Re: ATX Breakout Suggestion

Reply #15
The fuses are ment to protect the circuitry and _not_ the PSU.

When you are using fuses it is common to use selectivity (1:1 translated from the dutch selectiviteit) The idea is that the fuse the closest to the problem will pop and the remaining of the stuff keeps wokring. For example normal households over here are fused 25A, 50A or 63A (depends on the connection to the grid) where the mains-cable enters the house, each electrical circuit is fused 10A or 16A. Electrical equipment are fused even lower. Even when the electrical powerplant is capable of supplying several MA (mega amperes).

If you need more Amperes from the PSU, please design an alternative pcb as the tracks on this aren't desgined for lots of current (they are beefy but not calculated/rated for large currents). Also the wires (mine are less teh 1mm2) cant supply large currents. PLease be wise enough to use fuses in your design though.

Re: ATX Breakout Suggestion

Reply #16
The tracks on the board are about 5 mm wide and those short runs in open air would be able to handle 12-15 amps without going more than 30 degrees C above ambient.  A bit hot yes, but not too bad. 

According to Daves experiments on his blog this could be increased to considerably more (double?) by removing the soldermask over the tracks and put a good helping of solder on top of the tracks.

Still, most people only need an amp or two so the PCB fulfills that need.  For larger currents cheap banana plugs and the most likely thin wiring is not suitable anyways.  For really large currents a proper PSU should have sense-wires that will compensate for the voltage losses in the cables and contacts - something that the PC PSUs are sadly lacking.

Re: ATX Breakout Suggestion

Reply #17
Can someone offer a good inexpensive source for the red and black terminals? Digikey or Mouser? Everything seems pretty pricey.

Re: ATX Breakout Suggestion

Reply #18
My best bet has been ebay, aliexpress, etc
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Re: ATX Breakout Suggestion

Reply #19
I'd like to see a 9v section of the board.
I'm not an electronics expert, but I can solder.
Is there a voltage regulator to provide 9v without much heat?

Re: ATX Breakout Suggestion

Reply #20
[quote author="Royalblu"]Can someone offer a good inexpensive source for the red and black terminals? Digikey or Mouser? Everything seems pretty pricey.[/quote]

i have ordered a few double (black + red currently on a homemade power supply) from newark/farnel they were <$3.00 ea pomona brand too.

Re: ATX Breakout Suggestion

Reply #21
A 9 volt linear voltage regulator in the 78xx series  would not generate too much heart if connected to the 12 volt rail on the PSU.  But a small heatsink out just a piece of metal might be required if you will pull more than half an amp from the 9 volt.

The standard output voltages of the 78xx is of course 5 volt using the 7805 and 12 volt with the 7812. But there are also 7806, 7809 and 7815 for 6, 9 and 15 volts.

An example of a suitable regulator is this: http://my.element14.com/stmicroelectron ... dp/1087089

Re: ATX Breakout Suggestion

Reply #22
[quote author="ian"]I couldn't find any bigger (let alone 15A and cheap) surface mount poly fuses on Mouser, neither could our sourcers in Shenzhen. We could explore through hole for a future version. If you a link to an alternate SMD part I'd be happy to check it out too.[/quote]

Digikey has a 3A 24V PTC fuse in SMD in stock, but I can't link to it since I have a new account.

Digikey P/N: MF-LSMF300/24X-2CT-ND

The through-hole stuff has somewhat higher holding currents, and a fair number are available if you're willing to drop the voltage spec from 18V to 16V, up to about 15A. MF-R1100, 16R1100GF, AHRF1500, etc.

-R C

Re: ATX Breakout Suggestion

Reply #23
Thanks. I found this at mouser and will pick some up on my next order:
http://nl.mouser.com/ProductDetail/Bour ... 22Y%252bnU
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Re: ATX Breakout Suggestion

Reply #24
Hi Ian I couldn't find specs for the V2, but from what i see from the Kicad screenshot you are going to add VADJ, are you going to use lm317/lm337?, there will be current measurement points or a micro to do that?

If I may, i would suggest to replace the lm317 with a LT3083 or LT1083, and instead of using a potentiometer(assuming that is what your going to use) use a digital potentiometer. Why all this?, the LTx083 will let you shutdown the Vadj output just shorting to ground the ADJ pin. So if we also are able to measure the current(i'm assuming that a current sense resistor will be there) we can drive the LDO and have CC and CV using an external micro to drive all.
Otherwise you could add and leave unpopulated a low pass filter +opamp to ADJ pin so if someone want can drive the LDO using an external micro.


Re: ATX Breakout Suggestion

Reply #26
I am fairly committed to the 1.25 amp limit as a feature - about the same as your project gets from a TO220 7805. However, clearly the community wants more :) I guess I will pop a through-hole fuse footprint on the next version to make it easier to pop on a big cheap polyfuse.
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Re: ATX Breakout Suggestion

Reply #27
Polyfuses that are used for this are 15volts 1.25 amp, I havent understood yet how these works, if I buy 30volts 1.25 amp polyfuses instead, will that be bad?
i would guess the fuse reacts to the wattage, 15x1.25, so if I buy 30volt it would be 30x1.25, which is considerably higher.
Will that be seriously bad if i do that? (I found cheap ones on ebay... :) )

Re: ATX Breakout Suggestion

Reply #28
It is the maximum breakvoltage (when the fuse is tripped)

It shouldn't matter. These fuse are basicly ptc (positive temperature coefficient) resistors. When lots of current flows through them, thry get hotter, temperature gets up inside. When the temp is too high (because of the current) the resistance will be infinite which is an open connection.

Re: ATX Breakout Suggestion

Reply #29
Since the ATX PSU connector and the board have holes to bolt the connector down, would you care to suggest appropriately-sized hardware for this?  Or zip ties, perhaps?  Or do you recommend against this?

Should the load resistor be flat against the board?  (The power supply I took out of an old Gateway Pentium 2 machine needs the load resistor to start up.)  I am planning on putting it in the sick-of-beige case for it.

I'm trying to resist suggesting a small breakout board for the PSU's additional connectors that plug into the disk drives. :-)

Anyway, thank you for this design, it looks nice and will be very useful.