I am using 2 full PCI Xem systems in one computer, each with 4 16-port modules attached.
I’m wondering if I simply need the 2 power supplies for the end 2 modules on each card, for a total of 4 power supplies
…OR…
if I should use a total of 6 power supplies… 2 on the end 2 modules of the first card, and 4 (one on each module) on the second card.
If the issue is power through the PCI cards, then I’m ok using just 2 power supplies on the end 2 modules of each card. But if the issue is power from the computer, then I might need the total of 6 power supplies.
There is no set recommendation when it comes to how many power supplies are needed, as this can vary depending on the amount of power provided from the host systems PCI bus and the amount of serial usage at any given time (i.e. 64 ports running 19200 simultaneously).
In typical implementations where 4 Ports Em modules are attached, an external power supply is needed on the 2nd module in the chain only. However, if strange behavior is seen on the ports during higher usage (one direction of data, missing data, etc…), it would be a sign that additional power is needed (on the 3rd module).
Be careful, too much power can produce bad results too. Only add external power supplies as needed.
Actually, the situation has become more complex with some of the newer servers.
In some servers, customers have reported that when using the same model servers, and using 2 Xem host adapters with 4 16em modules connected to each host adapter, they had to use 6 power supplies with some servers and 8 power supplies with others for all of the serial ports to function correctly.
The old rule of thumb of using power supplies only on the 3rd and 4th ports modules apparently can no longer be relied upon due to motherboard design changes.
The bottom line is you will have to experiment as the number of power supplies required will vary.