Power from PSU to A1200 floppy-connector - safe?

[Hewitson]

I suggest not drawing much current from the floppy port. The tracks are thin and will burn up if too much current is drawn.

[Sandro]

Originally Posted by Hewitson

The tracks are thin.

thats one of the reasons there is less voltage in the zone of the power connector compared to other distant zones in the motherboard

those thin tracks increase resistance and lowers voltage, also there lot of filters and resistances disturbing the voltage and amperage
I think the A1200 motherboard is bad designed or not designed to add lot of periphericals

The idea of add power to the floppy port is good and safe as you can see in the link the trick is recommended by PHASE 5 to stabilize their turboboards...the trick adds more power to the A1200 accelerator port because the floppy plug is near it

[vitux]

I see there are contradictions.
I do not know what to do, I'm going crazy

[fitzsteve]

Hewitson is referring to drawing power from the floppy connector, for example running fans/3.5in HDD's in addition to the floppy drive by way of a splitter as this can draw too much current and burn the tracks.

This thread is discussing the adding of power in order to stabilize the accelerator which is tried and tested by many users, or you can run additional power lines under the Motherboard.

I doubt your issue with the Voodoo card is in any way related to adding power via the floppy connector, surely your Busboard takes it's power directly from ATX the PSU?

[demolition]

Originally Posted by fitzsteve

Hewitson is referring to drawing power from the floppy connector, for example running fans/3.5in HDD's in addition to the floppy drive by way of a splitter as this can draw too much current and burn the tracks.

This thread is discussing the adding of power in order to stabilize the accelerator which is tried and tested by many users, or you can run additional power lines under the Motherboard.

Well, if you can't draw much current one way, then the other way isn't going to be much better.

If you connect power to the floppy connector and you have an expansion card which uses a lot of power, it could potentially draw a large percentage of that from the floppy connector.
I think there's no clear answer to it since it depends on several things. I'd rather prefer to improve the power lines by soldering a wire on the bottom side between the output side of the power supply filter and a place close to the expansion connector. That would be the safe way to go.

[vitux]

fitzsteve, yes, yes
the Vodoo should be Vodoo own problem, or problems with my power supplies, or perhaps P8P9 connectors of Mediator.(although seem to go well with the ppc only)
To me, the PPC, work do well when I connect floppy cable to the motherboard, but this only happens to me with one of my power supplies, with another, no.

demolition: yes yes,
but unfortunately I have no knowledge of electronics and soldering

I need try with the other voodoo (which I have) (NOT) or a virgeS3
I need to test with more power supplies.
as a last option, sending a workshop.

[Sandro]

Originally Posted by demolition

Well, if you can't draw much current one way, then the other way isn't going to be much better.

If you connect power to the floppy connector and you have an expansion card which uses a lot of power, it could potentially draw a large percentage of that from the floppy connector.
I think there's no clear answer to it since it depends on several things. I'd rather prefer to improve the power lines by soldering a wire on the bottom side between the output side of the power supply filter and a place close to the expansion connector. That would be the safe way to go.

this is a good idea.. a direct 5v cable from power connector to floppy connector, I would another direct cable to pins 41/42 ide port

my A1200 when is connected to composite video and the floppy drive is in use the image in the screen start to flash a bit...seems there is a fall of power in the 5v line and is not related to power supply Im using an Antec sp350w atx
is a fall of power due a buggy motherboard design which is limiting 5v amperage anywhere

[Stedy]

Hi,

The best solution to reliably power an A1200 or other wedge Amiga, is to cut the power lead as short as possible or wire a picoPSU inside the machine.

The standard A500/A600/A1200 power lead is say 1.5 metre long and uses 18 AWG cable (I struggle to tell cable size by looking at it), this has a rating of around 4A and will drop approx 250mV @ 4A. Most 5V TTL devices operate from 5V, +/- 250mV, you can see that at full load, the Amiga power lead will drop +5V below the lower limit, assuming the PSU supplies a nominal 5V with no load.

An ATX PSU and most modern high current PSUs, have remote sense wires on the 20/24 pin ATX connector, you may see extra wires on the +5V(red wire) and +3V3 wires (orange wires). This regulates the output converter , based on the load and compensates for the drop in the cable loom, which on an ATX power connector is 30cm. The picoPSU is great as it is so small and has no cable loom, hence can regulate easily.

I tried and failed (and slapped my forehead afterwards), to power a processor card from the +5V drive connector, I only needed 4A but the drop through the cable was too much that it tripped the monitors on my (non-Amiga) PowerPC card, before causing damage.

I measured the current of an A1200 with Apollo 040, it uses 2.4A continuous not a lot by today's standard but as I used an ATX PSU and a short Amiga power lead, I had 4.90V on the Amiga. To get closer to 5.00V, I would have to wire directly to the A1200 power connector with short (25-75mm) wire of 14 AWG or better.

Adding extra power via the floppy connector can cause ground loops. This can affect the Audio and Video outputs as you can have large currents flowing where they should not.

So in summary:

1) Connect to the A1200 mainboard using short wires direct from the PSU, is there is no bus board.
2) If there is a bus board, use short, thick wires to the Amiga power connector from the bus board. I like the EC3 connectors, used for Radio control cars, high current, low contact resistance.
3) Consider locating a pisoPSU inside the Amiga
4) Power HDDs and optical drives direct from the ATX connector.

You can probably tell I've spent too much time playing with power supplies

[TomCrazy]

In addition to what Stedy points out, I would like to address another reason to why it's not a good idea to supply power to the floppy disk drive connector.

The A1200 motherboard has inductors, capacitors and ferrite beads at the power input jack that are filtering the voltages before they reach other components on the motherboard. Since these filtering components are not available at the floppy power connector (after all, it's meant to deliver power to the floppy drive, not receive power), supplying power at the floppy connector would almost be like bypassing the power filter circuitry completely at the power input jack. It will be equivalent to completely bypassing the inductive part of the power input filtering stage and adding some series resistors to the filter capacitors.
This can very much lead to higher noise, higher ripple and higher instability on the supply lines for the board.

Looking at the schematic, we can find a 1000 µF, a 220 nF and a 10 nF capacitor hooked up in parallel on the 5V supply line, right after the input jack. These are working together in order to reduce voltage fluctuations due to sudden current changes on the board (CPUs operating, moving actuator arm in a physical HDD etc), while also suppressing noise, ripple and other unwanted properties of the supply voltages in order to clean them out as much as possible.
These components that are doing this filtering are not present at the floppy input connector. Futhermore, the floppy connector is located very far from the power input jack, which makes the situation even worse.

I certainly do not think that supplying power to the floppy connector could harm the Amiga as long as the PSU is working as it should and powering on without any overshoot, but supplying power at the floppy connector could cause instability issues due to increased noise floor, fluctuation in the supply voltage, higher ripple etc.

I would not be afraid of killing my motherboard by supplying additional power to the floppy connector since the motherboard is not very likely to get damaged by this. However, I would never do it anyway since that would be asking for trouble. In some cases it might work, in some cases it might not. And, even though it seems to work at first, doing something that has a certain potential of creating problems is generally not a very good idea.

[roy bates]

a busboard also bypasses the amiga 1200 normal power connector as its not used in tower converted 1200's with busboards.

if anyone has noticed the motherboard is powered through the expansion slot.(the other end of the amiga)

but then agaian peaple are talking about powering extra equipment from the motherbaord.

[vitux]

PicoPSU What model do you recommend me?
the largest, how many Amp provides in +5 v?

[demolition]

According to the manual, the 120W version can do 4.8A continuous without a fan, 6A cont. with a fan and 8A peak on 5V. This should be plenty unless you have a very demanding Amiga.

[vitux]

It's for a Amiga in the tower, with PPC060, Mediator, Voodoo, DVDROM, HDD, fans, some neons a minimonitor :-)

[demolition]

Well, that might classify as a demanding Amiga.

Then I'd probably go for the 160W version which will do 8A cont/10A peak, and make sure that there's some airflow over it to keep it cool.

[roy bates]

im curios,why would you want to use a pico supply in a tower.

isent there room for a atx supply at a far higher rating.

[Mad-Matt]

My Amiga still uses Floppy connector for supplementary power and has been for nearly 15 years (however long the bppc has existed). Also around the time of the BVision release an option to add extra 5v via the Bppc fan connector was presented for anyone with power troubles. Id did help me as normally the Power led would dim/flicker abit when ppc was working hard, but was nice bright and stable with the extra power added.

However, some time later when I decided not to use the fan connecter as an input anymore, I noticed it no longer supplied power to the fan either so I have to power the fane external now. So I don't recommend adding 5v to fan connector to anyone even if it did help in the shorterm.

[vitux]

roy bates, Mad-Matt.
That's the reason I seek some form of stable 5v to not have to use the floppy cable.
Stedy I understand that recommends using a picoPSU. "The picoPSU is great as it is so small and has no cable loom, hence can regulate easily."
(I'm no expert or skilled at soldering)
However it seems little power even in the 160w. Also would need a lot of wire splitters

[Stedy]

@Vitux,

I don't know the full power consumption of your system to advise further. Older GPUs are very power hungry (40-60W), compared to more modern parts (<5W in some modes). The mediator has P8/P9 connectors, just buy an ATX to AT power adaptor, http://amigakit.leamancomputing.com/...roducts_id=306 and use a regular ATX power supply.

As stated by TomCrazy and Roy Bates, the original Amiga power input has filtering capacitors, based on the long power lead of the original PSU. If you have a multi-layer PCB, it will help immensely in delivering power. You could add more decoupling capacitors, then you need to consider in-rush currents easily 100A or more!

@Thread

My A1200+Apollo 040 & HDD uses 13.2W (2.4A@5V, 0.1A@12V) of power. I would not want to draw more than 25W through the main board as I do not know how the PCB has been designed. Above 25W(around 5A on +5V), you need better, regulation of the +5V line or else you may get unexplained crashes. My previous advice stands.

Designing high power 68040/68060+PowerPC and PCI bus boards for the A1200 is a tricky job, you have to give credit to Elbox for what they have done.

[theshinyknight]

I was looking for a solution to use a PSU on the amiga, without the square connector, and let me tell you: the idea to plug a power source where instead you should have a load (an item that takes electricity), it is never a good idea.

Fundamentally, a circuit is built to have input and output, and there is a reason: the current flow. In a simple circuit, the current flow may be irrelevant, but in a computer, which works with diodes and transistors, the current flow is important, because some chips are designed to get the electricity in one way, and block it in the opposite way.

Just picture inverting the cables on your distribution box in your car: the engine will continue to go for example in the cylinder sequence 1-6-2-4-3-5, but you cause the spark in the opposite order, killing the car.

The Amiga was already not designed for many of the things that we do with it, so at least let's put the power where it should go The board itself is pretty simple, but I would not power mine from the floppy connector for sure; plus you skip the valuable filters on the V-in (altho if you use a good power supply, the filtering is not that important...AC adapters nowadays are much better than the ones made 20 years ago).

You can do it but I don't think that it is a good idea; I used a picoPSU , with an ATX connector soldered on the bottom of the amiga board; in this way it is not intrusive and the power goes in from the right place It is enough to power my 1200 with expansion board, floppy, hd and cd rom

[demolition]

Originally Posted by theshinyknight

the idea to plug a power source where instead you should have a load (an item that takes electricity), it is never a good idea.

Fundamentally, a circuit is built to have input and output, and there is a reason: the current flow. In a simple circuit, the current flow may be irrelevant, but in a computer, which works with diodes and transistors, the current flow is important, because some chips are designed to get the electricity in one way, and block it in the opposite way.

That's not really relevant in this case, since the two supplies are connected without any diodes or transistors inbetween. The only problem could be the tracks being too narrow to handle the current flowing along a different route than designed, although since they are the same power source externally it will regulate itself along with the resistance. I think generally it will lower the current on most current tracks on the PCB to connect the PSU to the floppy connector as well, maybe except near the floppy power connector.

As you also mention, skipping the filters on the input is not generally a good idea, so that is a reason not to do it.