Section VIII
Trouble-Shooting Guide
006-0006504 02/27/18
Rev R
54 of 56
UPS-3000 Guide
www.synqor.com
▪ A newly started load disturbs the existing UPS loads.
A common problem can occur when the UPS is running and powering one or more loads
connected to its AC OUTPUT, and then an additional load of the AC OUTPUT is turned on.
If this newly started load draws a large surge current at start-up, it can cause the current
limit of the UPS’s AC OUTPUT to be triggered, and the AC OUTPUT voltage will then drop.
This drop could cause the existing loads to be disturbed. Furthermore, if the voltage drops
far enough, the UPS will turn off it AC OUTPUT and initiate a new start-up sequence (after
0.1 seconds). This latter action would cause the power flow to the existing loads to be
interrupted.
If this disruption of existing loads is a problem, then the solution is to make sure the
loads that display this start-up surge characteristic are all started first, or that all loads are
started at the same time.
•
Cable wire resistance is too high:
As mentioned in the section “Power Cables Wire Size”, the resistance of a power cable’s wires
gives a voltage drop from the upstream to the downstream end of the cable. This voltage drop,
if large enough, will cause the either UPS to determine that the voltage at its AC INPUT or its
DC INPUT is below its minimum specified value, even though the corresponding voltage at the
source of AC or DC power is within the specified range.
This problem is particularly possible for the DC INPUT, since the DC INPUT current is so high (as
much as 124 A at full power) and the DC INPUT voltage is so low (as low as 22 V).
The phenomenon that may be displayed is the following.
▪ Assume the AC INPUT source is not present, but the DC INPUT source is.
▪ The UPS, before it turns on, does not draw any power or current from the DC INPUT, and
therefore the voltage drop across the DC INPUT cable is zero.
▪ The UPS sees that the voltage at the DC INPUT is within its specified range, and enables its
outputs.
▪ As the load then draws power, the UPS begins to draw current from the DC INPUT cable. This
current causes a voltage drop to appear across the cable.
▪ If the voltage at the DC source is close to, but still above, its 22 V minimum, but the voltage
drop across the cable is large enough for the voltage at the DC INPUT of the UPS to fall below
22 V, then the UPS will determine that the DC INPUT is out of range and will switch over to
drawing power from the internal Battery Pack.
