SD Card reader / writer current draw.

I’ve got an interesting situation with my SD card reader / writer.

When the device is powered up it draws about 6 mA. However, once the first write has taken place then this drops to 0.6mA and stays there. I have more than one of these and they all behave the same. I may be wrong but to me this doesn’t seem normal?

I’ve attached some example code which is basically the datalogger demo with the sensor reading code removed and delay introduced.

/*
  SD card datalogger
 
 This example shows how to log data from three analog sensors 
 to an SD card using the SD library.
 	
 The circuit:
 * analog sensors on analog ins 0, 1, and 2
 * SD card attached to SPI bus as follows:
 ** MOSI - pin 11
 ** MISO - pin 12
 ** CLK - pin 13
 ** CS - pin 4
 
 created  24 Nov 2010
 updated 2 Dec 2010
 by Tom Igoe
 
 This example code is in the public domain.
 	 
 */

#include <SD.h>

// On the Ethernet Shield, CS is pin 4. Note that even if it's not
// used as the CS pin, the hardware CS pin (10 on most Arduino boards,
// 53 on the Mega) must be left as an output or the SD library
// functions will not work.
const int chipSelect = 4;
// Some variables for timing
long previousMillis = 0;        // will store last time the sensors were read
long interval = 60000;          // interval at which to read sensors (milliseconds)

void setup()
{
  Serial.begin(9600);
  Serial.print("Initializing SD card...");
  // make sure that the default chip select pin is set to
  // output, even if you don't use it:
  pinMode(10, OUTPUT);

  // see if the card is present and can be initialized:
  if (!SD.begin(chipSelect)) {
    Serial.println("Card failed, or not present");
    // don't do anything more:
    return;
  }
  Serial.println("card initialized.");
}

void loop()
{
  unsigned long currentMillis = millis();
  if(currentMillis - previousMillis > interval) 
  {
    previousMillis = currentMillis;   

    // make a string for assembling the data to log:
    String dataString = "123456";

    // open the file. note that only one file can be open at a time,
    // so you have to close this one before opening another.
    File dataFile = SD.open("datalog.txt", FILE_WRITE);

    // if the file is available, write to it:
    if (dataFile) {
      dataFile.println(dataString);
      dataFile.close();
      // print to the serial port too:
      Serial.println(dataString);
    }  
    // if the file isn't open, pop up an error:
    else {
      Serial.println("error opening datalog.txt");
    } 
  }
}

dannable:
When the device is powered up it draws about 6 mA. However, once the first write has taken place then this drops to 0.6mA and stays there. I have more than one of these and they all behave the same.

I may be wrong but to me this doesn’t seem normal?

Why does this seem not normal?

The SD Card Physical spec (1.0.1) allows for 15mA averaged over 1 second at power-on. Then current drops until a read or write occurs.

The time delay before the first read is a minute. That’s a lot of power going to ‘waste’?