The current draw of the EQ8 with different motor controller versions

The measurement of the current draw of the EQ8 was made with an oscilloscope. Thereby the dynamic process with different axis movements could be recorded and illustrated.

The current draw of the EQ8 mount with motor controller software V2.08 in tracking mode is about 500mA. The software version v2.08 was the delivery status of my mount in July, 2013.

The current draw of the EQ8 mount with motor controller software V2.09 in tracking mode is about 1500mA. The software version V2.09 was offered for download from August 16, 2013. It should eliminate occasional problems (wrong pulses) on the autoguider port. However, the current of the RA motor during normal tracking also was rised from 500mA to 1500mA. So beside the torque also the running noise was clearly increased. And the maximum operating times of an accumulator supply was shortened to about one third.

The current draw of the EQ8 mount with motor controller software V2.09_LP in tracking mode is again about 500mA. This software version V2.09_LP was offered for download from August 21, 2013 as an alternative for version V2.09. The difference to previous version V2.09 is the decreased current draw of the RA motor during normal tracking. So the mount is again nearly inaudible during normal tracking like it was in the delivery status. And the reduced current draw allows again longer operating times with accumulators as with the V2.08.

The current draw of the EQ8 mount with motor controller software V2.10 in the tracking mode is the same as of version V2.09_LP with about 500mA. The software version V2.10 was offered for download from February 2014. It differs from the version V2. 09_LP by a reduced acceleration and deceleration when slewing the axes with high speed. As shown in the diagram this is achieved by ramp control. The current was increased during fast and constant slewing for both axes in comparison to previous versions. Probably because the maximum goto speed was reduced from 1000x to 800x. Also an improvement of the autoguiding performance was realized with this software version. The Firmwareloader software reports this version as 02.0A.04.

My simple and very small power supply for the EQ8

In the data sheet of the EQ8 mount the manufacturer requires a DC source in the range of 11 - 16 Volts with a load capacity of at least 4 Ampere. My measurements of the dynamical current draw showed that the current draw during full acceleration of both axis after a Goto command really reached 3.8 Ampere for a short time. So the power supply must be able to deliver this current without a voltage drop below 11 Volts, indeed measured direct at the mount. So all used cables and connectors should be of suitable quality. Otherwise a malfunction or a damage of the stepping motor end phase could occur. Too low operating voltage will be shown as a blinking LED on the mount head.

So a sufficient power supply should be able to deliver the peak current of 3.8A for a short time and for the times of axis movements the according smaller currents. Actually I did not expect that the small power supply from the EQ6 is also able to supply the EQ8. But measurements with the switching power supply on the EQ8 and many observation nights confirmed that this switching power supply is also sufficient for the EQ8 operating.

The little switching power supply (W x H x D) 34 x 75 x 43 mm for 15,- Euro with 12 Volt nominal output voltage and 2A nominal output current (24W) is sufficient for the power supply of the EQ6 and EQ8.

My measurement values are showing why this switching power supply is sufficient. This relative small switching power supply can deliver up to 4.7A for some seconds without a shut down. And a current output in the range of 4A is possible even for more than 10 minutes without overheating and shut down because of this. This is absolutely sufficient for the practical operation of the EQ8 mount. An another big advantage of switching power supplies is the integrated thermal overload protection and short current protection. In case of an error the device immediately makes a shut down to protect itself or a supplied electronic. And if the error is removed the supply will be continued without any fuse change. With this switching power supplies I have mad only good experience in the last ten years.

The change of the output voltage during a load change from idle to 4 Ampere. This is the double of the nominal current value of the switching power supply. The short drop of the voltage below 11 Volt for a duration of only 4ms is no problem for the motor controller of the EQ8.

The change of output voltage during a load change from doubled nominal output current to idle.

The current curve shape during a short. The diagram of this measurement shows that also extrem high current peaks are no problem for some milliseconds for this switching power supply.

The angle plug for power supply was soldered on a new short cable. The plug case has been rotated so that the cable outlet is on the side now.

EQ8 Mount - Pages overview

Page #1 - History, decision and purchase of the Skywatcher EQ8 mount

Page #2 - Mobile setup of the EQ8 mount with Newton telescope

Page #3 - Current draw and power supply of the EQ8 mount (this page)

Page #4 - Detailed images of the EQ8 mount

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