Installing Dual Power Supplies

This page has all the info I have collected on installing dual power supplies
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Rick sent me some news that he was having trouble with his 6500 and had an idea on how to fix it. He installed a second power supply to help alleviate the load on the original supply! Very ingenious. Thanks for the info Rick. Read below on how he did it.

[Hi Tom,

With all the past talk of the 6400/6500 fan being noisy and for some odd reason, my optical mouse not working properly, I decided to look to the cause of both problems. The computer power supply. With a:

Sonnet G3/400 Mhz processor
Voodoo 2000 3D graphics card (PCI slot)
Entegra USB card (PCI slot)
Internal Zip drive
Internal ethernet card (comm II slot)
Apple Video card (Video slot)
Apple TV card (TV card tray)
128 megs of RAM
Stock CD-ROM Drive
Stock 6500 mother board
7200 RPM 12 Gig HD
Internal stock floppy drive

the power supply was being sucked for every milliamp it could supply. This was causing freezes, the optical mouse stopped working, fan got noisy, ethernet froze and a host of other erratic problems over time. I don't believe that Apple ever intended for this computer to get all its slots filled at one time, especially an accelerator in the cache card slot. So the answer was to add another power supply to run the devices that required the most current. These included the,

7200 RPM 12 gig Hard disk drive
Internal Zip drive
Internal stock floppy
Internal stock CD-ROM

Motors are notorious for creating "noise" when starting up and then pulling a constant and inconstant current while operating. So with the information below I added a separate disk drive power supply to handle all the motorized drives in the machine. This left the relief to the stock power supply to supply the proper currents and voltages for the motherboard and all its attached cards.

First, you need to purchase a small disk drive power supply from an electronics shop (Jameco, Digikey, surplus, etc.) The power supply must provide +12 volts and + 5 volts with common grounds. The +5 volts should be rated for at least 5 amps and the +12 for about 1 amp. The higher the better. But there is a trade off. My power supply measures 6 inches long and 3 inches wide. The more power the power supply has, the bigger it will be and you won't be able to get it into the computer. I mounted mine directly on the stock power supply, but anywhere that does not interfere with the motherboard movement and connections is fine. You must also purchase a male Molex connector. These are the connectors that plug into the stock HD. Some power supplies will come with them attached. The way Apple has internally connected up all the drives, means you may only have to disconnect at only one drive. Apple was generous enough to provide multiple connections of Molex wire and connectors (on my machine anyway). Also, don't get the connections backwards or you will burn up the HD. The red lead on my machine is for +5V and the yellow (sometimes orange) is +12 volts. Both black leads are ground. Check with a volt meter if your not sure. As you can see by the pictures, (sorry for them being a bit blurry) you will have to open up the stock power supply to get at the monitor connection plug. You connect the 115vac input for the second power supply to the relayed controlled monitor plug. You must do this so the computer will turn off both power supplies when shutting down. I am not responsible for any problems or disasters that occur while adding this power supply.

Since adding this power supply, my optical mouse has never failed on power up as it did in the past. The fan is quiet, and the HD seems faster. If you have never done this type of work before, then don't ! Get some one who knows their way around a schematic and electronics. If not you may regret it later.]

Here are some images Rick sent me. I will try to elaborate as much as possible for each image. Click here for my instructions on removing your stock power supply.

This one shows the second supply he bought to connect to the original supply. I don't know if he took it out of the case or if it came this way? It's safer to leave it in a case if possible!

This is an image of the stock 6400/6500 power supply opened up ready to connect the AC power from this supply to the second supply. This is needed so both supplies will turn on automatically when you power up your Mac. Note the location of the red arrow I drew. This is where the AC connection will be made.

This image is a close up of where the AC wires are to be soldered onto the original supply. Those two solder posts are connected to the switched relay that is activated when you power up your Mac. I don't know if it will be safe to also run a monitor off of this plug as well though? This is the inside of the AC outlet that was normally intended for the monitors power cord.

This image shows the wires being passed through from the original supply to the second supply. I'll have to check but I think that hole is already in the original case?

Here is another picture with everything completed except reinstalling the supplies.

You'll have to imagine that the second supply sits between the original supply and the IDE HD. The fan shown faces the mother board.

Other ideas that come to mind are to remove the stock speaker box if not used and place the second supply down there. There is plenty of room for another supply down there but if you bought one with an enclosure then you might have trouble facing the fan out the 6400/6500's case?

The best idea may be to buy a power supply with a case and leave the entire second supply out side next to your 6400/6500. Then all you have to do is run one cable inside to the HD's and no other hacking need be involved. In fact you can even connects its AC plug to the original power supplies AC outlet from the out side just like you where plugging a monitor into your Mac. This makes for the easiest install and works as advertised without the hassle. It won't be as neat leaking as you'll have another device on your desk but its the easiest and safest to perform


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This page last updated 3/9/2001