SOME LX90 & ETX POWER REQUIREMENTS Last updated: 23 December 2007

Sent:	Saturday, December 22, 2007 02:04:16
From:	John Hall (john_d_hall@hotmail.com)
Back in 2002, I made some measurements of the power requirements of an 8
inch LX90.....

In normal use, slowly tracking the sky, it was about 140mA.
Slewing with a single axis was about 300mA.
Slewing with both axis together was about 450mA.
The 'peak' current, both axis slewing up to full speed was about 600mA.

I measured this using a laboratory power supply, set to 12V. The
readings fluctuated somewhat, so these are average values.

My guess is that the Meade 1.5A power supply has a healthy reserve, to
accommodate additional accessories etc. I would be surprised if the ETX
telescopes need more than the LX90.

I hope that helps you.

Regards,
John.

And more:

Curiosity got the better of me - I've just made some measurements with
my ETX-90 (non-PE) so that we can compare them with the LX-90.....

When the 'scope is aligned and tracking an object, it takes about 200mA.
Slewing with both axis at full speed, it takes about 530mA.
The highest peak I saw was 610mA.

I measured this using a digital multimeter and the power source was an
NP7 gel cell (7Ah sealed lead-acid type) which was giving about 12.6V.

It is difficult to make truly accurate measurements because the current
fluctuates rapidly. I guess this is due to the way the motors are
'pulsed' by the Meade controllers. So it is possible that the real peaks
are a little higher than I've seen here. Ideally, I suppose you need a
power supply with good, fast regulation to cope with the peaks. So the
result you get probably depends on the 'quality' of your power supply,
not just its rated current.

Incidentally, these measurements and my original ones with the LX-90,
were made indoors at about 20 Celsius. I don't know if the current might
increase at lower outside temperatures? Worth considering anyway.

Yes, best wishes for Christmas and the new year, and also to Mike
Weasner and the rest of the "ETX community".

Regards,
John.
(United Kingdom - never enough clear skies here!!)

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