MPC 1250, Operator'S Manual, Page: 43 / 44

Section VIII Trouble-Shooting Guide
006-0007207 MPC-1250DC Guide Rev F 43 of 44 03/03/2022 www.synqor.com
▪ 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 MPC 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 65 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 MPC, 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 MPC sees that the voltage at the DC INPUT is within its specified range, and enables
its outputs.
▪ As the load then draws power, the MPC 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 MPC
to fall below 22 V, then the MPC will determine that the DC INPUT is out of range and will
shutdown.
▪ Since the MPC no longer draws current from the DC INPUT, the voltage drop across the DC
INPUT cable goes back to zero volts.
▪ After a while, the MPC decides the DC INPUT voltage is back within its proper range, and
begins to draw a current from the DC INPUT.
▪ The cycle above repeats itself for a total of three times, at which point the MPC stops
trying to draw power from the DC INPUT for one minute. After this one minute another set
of 3 cycles are repeated, followed by another stop for one minute, and so on.
This same problem can also occur for the AC INPUT if the voltage at the AC source is close to the
specified 80 Vrms minimum limit. In this case the MPC will try ten times before stopping for a
one minute interval.
The solution to this problem is to make sure that the cable has wires of sufficient diameter, or
“gauge” for the length of the cable. The longer the cable, the bigger diameter the wire should have.
See the section “Power Cable Wire Size” for recommended cable wire sizes.