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TB269 Rev1 Voltage ratings of DC drives and DC Power Supplies
Many new DC motors are rated 180VDC as it allows direct rectification of line voltage eliminating the need for a step down transformer
 Newer CENTROID DC drives can now operate at high DC voltages
When determining the operating voltage of a DC drive it is extremely important to select a voltage that is NOT
higher than the voltage
rating of the lowest voltage rated motor connected to the drive  Modern drives use switching output electronics that subject the motor to
the full DC supply voltage at various frequencies and duty cycles  Therefore the DC supply voltage must not be greater than the
voltage rating of the motor to prevent insulation breakdown a burnt commutator due to arcing and exceeding the maximum motor
speed
Running a DC motor at less than the rated voltage will not damage the motor  The reduced voltage mostly limits the top speed of the
motor if voltage reduction is extreme then the maximum motor current may also be limited  Matching the motor drive voltages
and current produces the optimum performance result
After determining the required DC voltage for the drive the necessary AC voltage to be rectified can be calculated as follows
AC voltage = DC voltage / 1 414
This calculation is based on the peak or no load DC voltage and full bridge rectified single phase AC voltage
Examples
1 120VDC motors and drive are selected The AC voltage needed = 120 / 1 414 which equals 84 86VAC
2 180VDC motors and drive are selected The AC voltage needed = 180 / 1 414 which equals 127 29VAC
3 110VAC is readily available what DC voltage would be produced?
     DC voltage = AC voltage X 1 414 which equals 155 54VDC
Example 3 illustrates an important reason many new DC motors are rated 180VDC as it allows direct rectification of line voltage
eliminating the need for a step down transformer  A step down transformer would be required for the drive in example 1 to provide less
than 84 86VAC to allow for variations in the main voltage
The full bridge rectifier being used must also be considered  It must be capable of handling the full voltage and current of the drive and
motors plus the ripple current of the filter capacitor All of our DC bridge boards produced can handle 180 VDC but the capacitor HAS
to be checked Older CENTROID cap and bridge kits were shipped with 160 vdc caps  So the big cap would have to be changed for a
250 vdc rated unit the bridge board can be retained if you plan on directly rectifying 110 vac
The filter capacitor provides current to the drive when the AC voltage is between peaks and helps absorb the pulses caused by the
drive's switching electronics  It is critical that the capacitor can handle the working voltage and current with plenty of margin for
transients and effects of aging
The Cap in our Cap and Bridge combo has been replaced with a unit that will operate at up to 180VDC The capacitor should be
labeled 12000uF 250volt Before powering up
confirm the 250volt voltage rating  If the capacitor does not have this voltage rating DO
NOT
apply more than 83VAC to the cap bridge unit
Check the serial number of the following drives to determine if it has been produced to operate up to 180VDC
DC1 beginning with serial number 91
DC3IOB beginning with serial number 453
ALLIN1DC beginning with serial number 538
Note If you cannot locate the drive serial number another way to tell if the drive is 180 volt version locate the largest electrolytic
capacitor on the drive circuit board Three axis drives will have three of these single axis drives will only have one The capacitor
should be labeled 100uF 250volt  If the capacitor does not have this voltage rating DO NOT
operate the drive above 120VDC
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Document History
Rev1 Created on 2012 09 27
by #326