External NuBus power supply?

[olePigeon]

As many of you are aware, my little IIci just doesn't have the juice to run much more than 8MBs of RAM and a 25MHz 040 Radius Rocket.

So I was wondering if it would be possible (well, not just possible, but relatively easy?) to provide an external source for +5V power to the NuBus slots on a IIci. There's plenty of room inside, and I've been experimenting with different ways of mounting an LC power supply next to the existing IIci Power Supply.

I'm pretty tight on cash right now because of reduced hours at work which is why I haven't attempted to buy a Quadra 700 power supply yet, so I'm working with what I have. My technical abilities are limited to a dremel and soldering iron.

Any comments on the technical feasibility of this idea?

 

[Bunsen]

Well, the simplest mod I can think of would be to gang the +5V lines from each power supply together, by soldering [ * edit: see below] the two wires together, and feeding into the existing IIci connector/s. In theory, that should sum the current capacity on the +5V feed of both supplies. That, or using the LC supply to drive the HD and floppy, leaving the IIci supply to run the logic board and Nubus - or vice versa, if the +5V rating on the LC supply is actually the higher of the two.

Are both supplies switched, and/or soft power-on compatible? If switched, it would be a good idea to gang them both to a single switch so they come on together. If soft-power, I'd suggest joining the soft-power-on lines. It's also probably a good idea to gang the ground line/s so they are both on the same 0V floor.

* Thinking further, I would say using a screw terminal "chocolate-block" for connections is probably better than soldering - it allows you to non-destructively experiment with different set-ups - and a simple way to adapt (say) an ATX supply at a later date. They're cheap, and as long as they are screwed down tightly and not subjected to cable strain, as secure as a solder joint. Connect the motherboard/drive plugs to one side, and both power supplies to the other. You can even label each line on the white plastic.

[YMMV. No warranty implied. Information supplied for entertainment porpoises only. Offer not vaild in Delaware.]

 

[bigmessowires]

I've never tried that, but is putting two PSU's in parallel safe? If one puts out a slightly higher voltage than the other, you'll end up with current flowing *in* to one of the PSU's, which might be very bad.

 

[Bunsen]

Hmm, I've never considered that. I suppose if you wanted to be extra-sure, you could put a diode on each line, to ensure that current only flows in one direction (away from each supply). I -think- you'd need to put them in reverse on the -ve lines.

Any voltage difference would be very small though, so any back current should be too (I -think-)

Giving each supply seperate tasks (ie, motherboard+Nubus on one, drives on the other) avoids the whole issue, so it might be the better bet.

 

[PackingTape]

I think the diode would be bad because of the voltage drop. (maybe someone who knows more about electronics can help me out here ) I agree the separate supplies for different tasks might be the better way to go.

 

[bigmessowires]

Here is a semi-relevant link: http://www.weidmuller.ca/system/files/webfm/downloads/pdfs/literature/PS06_Parallel_Operation_of_Switchmode_Power_Supplies.pdf

Long story short: it may not work the way you intended, but probably won't explode.

 

[olePigeon]

First, thanks for all the suggestions.

I have an idea, but I don't know if it'd work. I may have access to NuBus connectors at my local surplus store (I'm going to go check today.) What about soldering a molex connector directly to the voltage pins on the card, disabling the pins underneath so they don't connect to the motherboard, then just plug it directly into the LC power supply? Give it its own dedicated power supply. Avoid modifying the motherboard or splicing the power supply all together, and make the modifications to the card itself.

 

[Trash80toHP_Mini]

If you're willing to clip the wires to the Mobo connector off your IIci PSU inside the case at about the halfway point you're all set. Using that connector/& wire stubs, you can easily adapt just about ANY ATX or AT PSU . . .

. . . and it'll fit into your IIci. :approve:

You can even restore the IIci PSU to its current config at a later date if you'd wish to do so.

Workable PSUs can be found curbside or for a few bucks inside a junker at a thrift store.

 

[Bunsen]

Do you have an external, powered SCSI hard drive or drive case?

The first thing I would try (as it's the least destructive) is to see if the IIci+Rocket will boot from an external drive. Either clone the startup disk / system folder to the external, or remove the internal HD altogether and put it in the external case. Then, unplug the power leads to the floppy and internal HD (if it's still there), power up the external drive, and boot.

If that works, then it shows that the IIci PS has enough grunt to run the logic board + Rocket, so you can then hook up the LC supply to run the floppy + HD and be done

I may have access to NuBus connectors at my local surplus store (I'm going to go check today.)

Oooh } How many, and at what price?

What about soldering a molex connector directly to the voltage pins

AND at least one ground/earth.

on the card, disabling the pins underneath

How?

so they don't connect to the motherboard, then just plug it directly into the LC power supply?

Where does the added Nubus connector come in here? Does it sit between the Rocket and the motherboard Nubus socket? If so, will you still be able to close the case with the added height on the Rocket?

I do like the idea of a self-powering Rocket mind you

 

[olePigeon]

Do you have an external, powered SCSI hard drive or drive case?

I gave that a go with similar results to just leaving the HDD in. I can't remember if I could have more RAM or not.

I may have access to NuBus connectors at my local surplus store (I'm going to go check today.)

Oooh } How many, and at what price?

I found two male connectors and a whole box load of female connectors. They were 90 cents each I believe.

on the card, disabling the pins underneath

How?

Looking at the NuBus connector, I think I can straighten the pins and pull them out of the housing so there're no pins at all that would connect to the motherboard's slot. I would then solder the molex cable directly to the board's 5v thingy, and the ground to the ground pin.

Where does the added Nubus connector come in here? Does it sit between the Rocket and the motherboard Nubus socket? If so, will you still be able to close the case with the added height on the Rocket?

I think I misspoke. I meant to have an extra NuBus connector so that when I'm done fiddling, I can put a new one back on so the card still works. I'll be making some permanent changes to the NuBus connector itself and I wanted the card to still be in working condition if my idea doesn't pan out.

I do like the idea of a self-powering Rocket mind you

If I have time, I'm gonna give it a go this weekend.

 

[olePigeon]

7100 power supply didn't work. Still chocking unless I put absolute minimum amount of RAM in my computer and Radius Rocket.

Hopefully I can get some help, and attempt an ATX power supply transplant. Now that I have two compatible power supplies, I think I'll just gut one of them and stick the innards of the ATX power supply inside. Maybe even a mini-ITX power supply, they still go up to 200w.