| Title: | DEChub/HUBwatch/PROBEwatch CONFERENCE |
| Notice: | Firmware -2, Doc -3, Power -4, HW kits -5, firm load -6&7 |
| Moderator: | NETCAD::COLELLA DT |
| Created: | Wed Nov 13 1991 |
| Last Modified: | Fri Jun 06 1997 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 4455 |
| Total number of notes: | 16761 |
Hello ,
I have a question regarding the input power to the DECHUB 900.
We sold four hubs to a customer who asked for a UPS on each hub due
to the remote location of each hub. DECsite ordered a 1.5KWatt UPS
for each hub. The hubs are fully poulated and have four power supplies
in each for redundancy. Everything was working fine until the power
went down ....... Guess what happened ..... None of the hubs stayed
up. We had the impression that the UPS would hold the load but
apparently it didn't. There is some confusion here as to the stated
Electrical Specifications
Input current: Less than 10 Amps.
What is this implying ? 9 Amps at 220 Volts gives us 1980 Watts.
However it is rated at less than 1100 VA ...
Can anyone recommend what size UPS we should have installed. Possibly
our Networking group did not take into account the inefficiencies of
the UPS 1.5 KW (Must certainly be around 1.2 KW) and the HUB itself.
Is there a clear specification which will help us know exactly how
much power the HUB draws when it has one,two,three or four power
supplies inserted.
Regards,
Confused Technician.
| T.R | Title | User | Personal Name | Date | Lines |
|---|---|---|---|---|---|
| 2612.1 | VA rating is critical, not watts! | NETCAD::B_MACARTHUR | Thu Aug 24 1995 13:21 | 44 | |
HUB Electrical Specifications:
Input Voltage: 88VAC - 264VAC (Design Range)
Input Current: 13.7A - 6.8A (these are worst case numbers for each
voltage range...low line in each case)
Input VA: 1200VA for either range! This is the critical specification
when sizing a UPS, not watts. I've tested a 1250VA UPS (APC Model
1250RM) with a fully loaded hub and it works fine. My guess is that
there was either a problem with the UPS you selected, or the
Volt-Ampere (VA) rating was too low (again, watts don't mean anything
here, the critical spec is VA).
To answer your other questions, the rating of "less than 10A" for
input current implies that at a nominal line voltage of 115 or 120 VAC,
the HUB will draw less than 10A. In the 240VAC range, the current will
be approximately half that value (5A). Here's some other numbers that
may help:
Output Power (max) = 420 watts
Efficiency (worst case) = 58% or .58
Power Factor (worst case) = .6
420/.58 = 724 watts AC input (worst case)
724/.6 = 1206 Volt-Amperes (worst case)
1206VA/120VAC = 10.05A
1206VA/88VAC = 13.7A
1206VA/240VAC = 5.02A
1206VA/176VAC = 6.85A
This example shows you how to calculate input current at different
input voltages. The key here is the VA rating.
Give me a call or send mail if you have further questions.
Bob
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