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IBM 5150  -  Power Measurements


General

The IBM 5150's power supply is rated at 63 Watts. Expressed that way, the wattage is misleading. For example, it does not mean that 63 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 5150 MOTHERBOARD  -  '16KB-64KB' VERSION

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 1.31 A 1.32 A 6.55 W 6.6 W Peak occurs on application of power. No 8087 math coprocessor.
- 5 V 0.001 A 0.001 A 0.005 W 0.005 W Used by 4116 RAM chips, and cassette circuitry (specifically chip U1). Available on expansion connectors. See note 2.
+12 V 0.04 A 0.055 A 0.48 W 0.66 W Used by 4116 RAM chips. Available on expansion connectors.
-12 V 0 0 0 0 Available on expansion connectors.
      = 7 W = 7.26 W  



IBM 5150 MOTHERBOARD  -  '64KB-256KB' VERSION

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 1.3 A 1.45 A 6.5 W 7.25 W Peak occurs on application of power. No 8087 math coprocessor.
- 5 V 0 0 0 0 Used by cassette circuitry (specifically chip U1). Available on expansion connectors.
+12 V 0 0 0 0 Available on expansion connectors.
-12 V 0 0 0 0 Available on expansion connectors.
      = 6.5 W = 7.25 W  



IBM KEYBOARD

  Measured
AMPS
- Normal		 Measured
AMPS
- Peak		 Calculated
WATTS
- Normal		 Calculated
WATTS
- Peak		      Comment
+5 V 0.1 A 0.11 A 0.5 W 0.55 W Peak occurs on application of power.
      = 0.5 W = 0.55 W  



TANDON TM100-2 FULL HEIGHT FLOPPY DRIVE

  Measured
AMPS
- Normal		 Measured
AMPS
- Peak		 Calculated
WATTS
- Normal		 Calculated
WATTS
- Peak		      Comment
+5 V 0.29 A 0.38 A 1.45 W 1.9 W Peak occurs during activation of spindle motor.
+12 V 0.34 A 0.9 A 4 W 10.8 W Peak occurs during activation of spindle motor.
      = 5.45 W = 12.7 W  



IBM MONOCHROME DISPLAY AND PRINTER ADAPTER  (MDA)

  Measured
AMPS
- Normal		 Measured
AMPS
- Peak		 Calculated
WATTS
- Normal		 Calculated
WATTS
- Peak		      Comment
+5 V 0.75 A 0.75 A 3.75 W 3.75 W  
- 5 V 0 0 0 0 Circuit diagram indicates nil use.
+12 V 0 0 0 0 Circuit diagram indicates nil use.
-12 V 0 0 0 0 Circuit diagram indicates nil use.
      = 3.75 W = 3.75 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  





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 1 mA. Calculated by noting voltage drop (about 10 mV) over a 10 ohm resistor.
   
Note 3 The early version of the IBM diskette drive adapter uses minus 5 volts, but not the later version.
That is reflected in the first 5150 Technical Reference, which indicates that minus 5 volt use includes "and analog circuits in the diskette adapter phase lock loop.",
That text was removed in later editions of the Technical Reference.
Click here to view the difference between the early and later adapters.