Last updated: 12 April 2010
Sent:	Thursday, April 8, 2010 11:08:05
From:	Ludwig Krijgshaftig (
Your site contains a number of items on powerpacks used with telescopes.
In discussing the capacity of batteries the actual power drawn by the
scope is also discussed. I have seen mentioned an average of 2A (at 12V)
for the telescope and much more when using dew heaters.

As I was curious, I have done some measurements for my ETX-125PE, with
and without dew controller and heater. The dew controller I have is a
Kendrick Digifire 10 and with the ETX I only use a Kendrick 5" Premier
Heater with the controller setting at 40%.

Current measurements were done with a Fluke 112 multimeter. These are
the results:
Scope in standby/startup: 150mA
Scope slewing RA: 230mA
Scope slewing RA and Dec: 550mA
Scope tracking: 130mA (strangely this is lower than at standby/startup)
Dew controller in standby: 30mA
Dew controller in programming mode: 730mA (this is only when making
setting adjustments)
Dew heater (5" at 40%): 540mA (this is not an average, but the max when
actually heating)

During most of an observing session the usage is therefore only 130 + 30
+ (540 * 0.4), which comes down to about 380mA.

Anyone interested may use these figures to estimate how long a
batterypack will last when used with this or similar equipment.

Kind regards,

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