Modify USB ZipDrive power input source - query

[Ouabache]

I have a USB Iomega zip drive (100MB) that uses both an external power supply and USB cable. Subsequent models of the same drive take power (5V) directly off the USB from the PC. I wish to modify my zip drive to make it a bus-powered device. The external PS measures +5V open circuit. The spec on the external PS transformer is 5Vdc, max 1A

Does the ZipDrive require the use of the 5V USB line to make the data read/write operations to a zipdisk? [/color](the other 3 lines are data+, data- and ground)
Is it recommended to isolate the newly modified 5V line (to Zipdrive PS input) from the line that already goes to Zipdrive circuitry? If so, how?
How can I find out if the PC can supply sufficient current thru USB port for new total load (both Zip's PS and data circuitry)?
(If total current draw is an issue, Iomega may have designed their upgraded model, taking that into account).

glossary of selected abbreviations:
PS - power supply
Zip - Iomego zipdrive
USB - universal serial bus (original, not
2.0)

 

[imabug]

The max current draw allowed on the USB bus is 500 mA. It's quite likely that the new USB Zip drives are built with motors that draw less than this. Older ones with external power supplies probably have motors that draw more than this.

 

[Ouabache]

I haven't been able to locate any specs on current drawn by each of these models. I will put my model on the bench and directly measure the current drawn during read/write operations.

If it turns out that the draw is less than 500mA, are there other considerations that should be addressed, such as isolating the newly modified 5V line (to Zipdrive PS input) from the line that already goes to Zipdrive circuitry?

Does the ZipDrive require the use of the 5V USB line to make the data read/write operations to a zipdisk?