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IBM 5155  -  Power Measurements


General

The IBM 5155's power supply is rated at 114 Watts. Expressed that way, the wattage is misleading. For example, it does not mean that 114 Watts of power can be drawn from the +5V line if no power is drawn from the other lines. Each of the output voltage lines has its own power rating, that must not be exceeded. Click here to see those ratings.


Power measurements

The power consumption figures shown below were determined by measuring current consumption from the power supply.

Current consumption was measured using a digital multimeter and altered power cables. Of those cables, the cable used to measure motherboard current and expansion card current is shown on this link.

Because of 1. the limitations of measuring complex current consumption using a digital multimeter, and 2. small variations between units, the figures shown below should only be used as a guide.



IBM 5155 MOTHERBOARD  (which actually, is an early 5160 motherboard)

If your motherboard has the optional 8087 math coprocessor fitted, see note 1.

  Measured
AMPS
- Normal		 Measured
AMPS
- Peak		 Calculated
WATTS
- Normal		 Calculated
WATTS
- Peak		      Comment
+5 V 1.38 A 1.45 A 6.9 W 7.25 W  Peak occurs on application of power. No 8087 math coprocessor.
- 5 V 0 0 0 0  Motherboard passes this through to expansion connectors.
+12 V 0 0 0 0  Motherboard passes this through to expansion connectors.
-12 V 0 0 0 0  Motherboard passes this through to expansion connectors.
      = 6.9 W = 7.25 W  



CRT UNIT

       Comment
+12 V A sticker on the CRT unit has "13.0 V" and "1.4 A".
A label on the PSU indicates that the connector (P12) that supplies the +12V to the CRT unit, is rated at 1.5A
Probably best to assume that the CRT unit will consume up to 18 W peak.



5155 KEYBOARD

  Measured
AMPS
- Normal		 Measured
AMPS
- Peak		 Calculated
WATTS
- Normal		 Calculated
WATTS
- Peak		      Comment
+5 V 0.13 A 0.13 A 0.65 W 0.65 W  
      = 0.65 W = 0.65 W  



IBM COLOR GRAPHICS ADAPTER  (CGA)

  Measured
AMPS
- Normal		 Measured
AMPS
- Peak		 Calculated
WATTS
- Normal		 Calculated
WATTS
- Peak		      Comment
+5 V 0.65 A 0.65 A 3.25 W 3.25 W  
- 5 V 0 0 0 0  Circuit diagram indicates nil use.
+12 V 0 0 0 0  Passed through to the two Berg connectors. See note 2.
-12 V 0 0 0 0  Circuit diagram indicates nil use.
      = 3.25 W = 3.25 W  



IBM 5.25" DISKETTE DRIVE ADAPTER  (360KB FLOPPY CONTROLLER)

  Measured
AMPS
- Normal		 Measured
AMPS
- Peak		 Calculated
WATTS
- Normal		 Calculated
WATTS
- Peak		      Comment
+5 V 0.4 A 0.4 A 2 W 2 W  
- 5 V 0 0 0 0  Later version of the adapter. See note 3.
+12 V 0 0 0 0  Circuit diagram indicates nil use.
-12 V 0 0 0 0  Circuit diagram indicates nil use.
      = 2 W = 2 W  



MAGNETIC PERIPHERALS 360KB FLOPPY DRIVE, MODEL 9248 01

  Measured
AMPS
- Normal		 Measured
AMPS
- Peak		 Calculated
WATTS
- Normal		 Calculated
WATTS
- Peak		      Comment
+5 V 0.45 A 0.51 A 2.25 W 2.55 W  Peak occurs during activation of spindle motor.
+12 V 0.42 A 1 A 5 W 12 W  Peak occurs during activation of spindle motor.
      = 7.27 W = 14.25 W  





Note 1 At power on of the computer, and whilst idle, the 8087 draws about 1 W. [source: my measurement]
When the 8087 is being used (a program is using it), the 8087 draws up to about 3 W. [source: 8087 datasheet]
   
Note 2 A cable from the CRT unit plugs into the 4-pin Berg connector, accessing the composite video signal, but not the +12 volts.
   
Note 3 IBM 5155s were fitted with the later version of the adapter, and that version does not use minus 5 volts.
Click here to view the difference between the early and later adapters.