A1200 Additional power via floppy connector

[Hodgkinson]

Hi there,
After rebuilding my A1200D, I’ve recently begun having issues with the A1200 PSU coughing out and restarting the system whenever additional devices are powered up (These devices draw power from the A1200 via the floppy drive power connector).

As a result, I’ve had to convert an ATX PSU for the A1200, and im wondering whether there is any detriment to feed power into the A1200 from both the normal PSU connector and the floppy header?
Even though I’ve now rewired all the additional devices to be powered directly from the ATX PSU, I've noticed that the voltage drop across the A1200 from the power connector to the floppy connector is fairly large considering the normal voltage operating range for TTL devices, and im wondering whether adding a second supply path might just help bring the voltage within the A1200 up a little.

Hodgkinson.

[motorollin]

Hodgkinson wrote:
im wondering whether there is any detriment to feed power into the A1200 from both the normal PSU connector and the floppy header?

I wouldn't recommend it. Two separate power supplies going in to the same circuit is asking for trouble. Why not just cut the A1200 power connector off of your PSU and wire it on to the ATX PSU? I did this and it worked perfectly when connected to the A1200 standard power socket.

Hodgkinson wrote:
Even though I’ve now rewired all the additional devices to be powered directly from the ATX PSU, I've noticed that the voltage drop across the A1200 from the power connector to the floppy connector is fairly large considering the normal voltage operating range for TTL devices, and im wondering whether adding a second supply path might just help bring the voltage within the A1200 up a little.

An ATX PSU should be more than powerful enough by itself. There's no need to supplement the power with the A1200 PSU and risk damage to one or both of the PSUs. Also, I wouldn't recommend using the floppy connector for power. You lose the 3.3v supply, which results in certain parts of the board not functioning (sound, some ports etc).

--
moto

[ZeBeeDee]

Would it not be more prudent to get (or construct) an external box of some kind to house all these extra devices and have them powered from an independent supply?

[Hodgkinson]

Ooops, sorry, I didn’t mention that the ATX PSU is already converted to power the A1200 via the conventional power socket. The original A1200 PSU is no longer used.

Im just wondering whether connecting the PSU to power the A1200 via two different paths would be safe to do - With the aim being to reduce the supply resistance to the A1200 and boost the supply voltage a little.

Hodgkinson.

EDIT: The independant devices include commercial devices such as a printer, frame grabber, USB desk lamp, and barcode reader pen. Im trying to arrange for everything to be powered from the same source - Its much neater, more efficient on sockets, and reduces the risk of devices being blown up at power on if devices arn't powered up in the correct sequence.

[doctorq]

Im just wondering whether connecting the PSU to power the A1200 via two different paths would be safe to do - With the aim being to reduce the supply resistance to the A1200 and boost the supply voltage a little.

I have used my A1200T for years with a power setup like that, and haven't busted anything yet.

[ZeBeeDee]

Hodgkinson wrote:

EDIT: The independant devices include commercial devices such as a printer, frame grabber, USB desk lamp, and barcode reader pen. Im trying to arrange for everything to be powered from the same source - Its much neater, more efficient on sockets, and reduces the risk of devices being blown up at power on if devices arn't powered up in the correct sequence.

It might be neater and more efficient but after reading the above edit, my first thought was 'if one goes bang, they'll all go bang'

I'd rather use 8-way extension sockets ...

[Hodgkinson]

True...But when AT or ATX PSU's go bang they have a habit of destroying themselves rather than the computer that they're connected to...Just take a look in a blown up PSU and you'll know what I mean...

As I was saying, is there any detriment to feeding the A1200 with power, from the same power supply, via two different paths?

EDIT: I don't acutally have any plug-in PSU's for the additional devices anyway, so I need to power them from somewhere...

[rkauer]

Hodgkinson wrote:
True...But when AT or ATX PSU's go bang they have a habit of destroying themselves rather than the computer that they're connected to...Just take a look in a blown up PSU and you'll know what I mean...

As I was saying, is there any detriment to feeding the A1200 with power, from the same power supply, via two different paths?

EDIT: I don't actually have any plug-in PSU's for the additional devices anyway, so I need to power them from somewhere...

 It's OK to feed the motherboard via the standard socket and the floppy power pin header (if the PSU is the same). I do it to mine and it runs OK, with little voltage dropout. Specially heavy power-hungry accelerators would be benefited for a loss-less power rail (like 040 accelerators or PPC).

 For feed other devices, just put (or leave untouched) the original 4-ways Molex connectors.

 Trust me, I have a degree in electricity!

 @Moto: the Amiga don't use the 3.3V rail anywhere! Just +5V, +12V and -12V.

[Tenacious]

Two seperate feed-in points for +12, -12, +5 and Gnd may very well work.  I, however,  would be concerned about creating "loops" in these rails.  Loops can be a source of electrical noise and cause intermittant behavior.  Typically, engineers and circuit board designers are strongely encouraged to provide one point source for all the power rails and avoid loops at all costs.

If the stock 1200 power connector is not enough for the MB and an accelerator (it sure should be), you could try to add copper to those main traces and connect the PS there.

A much simpler solution might be to power the HD, floppy, CDRom, etc, directly from the PS; reducing the current that must flow throught the MB and it's original connector.

[actung_bab]

go for it mine been powered that way since the blizzrd ppc cards came out and used to run the machine 24 /7 running bbs
never had bit of trouble.

 :-)

[Hodgkinson]

Thanks for the advice!

I’m not actually experiencing problems with voltage drop; I just thought it might be a good idea anyway. I'll have a think about the circular rail problem and the effects it might cause.

Re running hardware directly from the PSU, that's exactly what I've been doing. All the additional devices (Except for 2.5" HDD) have now been retrofitted to be powered directly from the PSU, and If I ever get a Blizzard SCSI controller for the 1230IV (Hint...), all the SCSI HDD's and CD-ROMs slung outside of the case will draw their power directly from the PSU.

Hodgkinson.

[rkauer]

 I am aware of the redundant power rail issue.

 But it appears only in high current/high frequency devices (like peecees, nowadays).

 And this method alleviates the current inside the motherboard, even with the cycling power issue.

[Hodgkinson]

But it appears only in high current/high frequency devices (like peecees, nowadays).

And this method alleviates the current inside the motherboard, even with the cycling power issue.

Agreed. I think I'll give it a try - Reducing the power flowing through any one part of the motherboard can't be a bad thing.
Now all I have to do is to make a female-female molex connector (Has anyone seen these for sale in PC shops? :crazy: )

Regards,
Hodgkinson.