HEQ5Pro power consumption

[louie_the_fly]

Can someone tell me what the power figures (amps &/or watts) are for a Skywatcher HEQ5Pro mount when running on 12 volts DC? I'm trying to get all my power requirements sorted so I can design a power pack. I will want to run the mount, dew heaters (15 watts max total), laptop, and some auxillary LED lighting. I couldn't find the info I need in the Skywatcher literature.

:thanx:

[Astro_Bot]

The HEQ5 Pro draws only a little less than the EQ6 Pro. If you design for an EQ6/NEQ6 Pro, you'll have your HEQ5 Pro covered.

I measured EQ6 Pro power draw some time ago and found:

Sidereal Tracking = 11W
Max. Slew Rate = 22W


Here are a couple of related threads:
Batteries (http://www.iceinspace.com.au/forum/showthread.php?t=94663)
EQ6 Power Cable (www.iceinspace.com.au/forum/showthread.php?t=103031)

[RobF]

Hi Stewart,

From measurements off my HEQ5Pro:

On, but parked: 0.35A
Tracking: 0.63A
Slewsing 800x both RA and Dec: 1.12A


I'd think the laptop and dew heaters would be the main thing you'd need to be watching if running away from 240V.

[RobF]

This was a gel battery, about 12V power supply - astrobot suggested that should be given too :)

[Steffen]

I found that the power draw of the HEQ5Pro's slewing very much depends on the mechanical alignment of the gears. If you tighten the gear mesh and axial play of the worm in order to minimise backlash and noise you will inevitably put more strain on the motors and make them draw more current, perhaps much more (I have yet to measure it but the shortened battery life tells the story).

This is why I'm looking forward to putting in the belt mod kit I received from 1parsec, it should reduce backlash and noise without unduly increasing friction.

Cheers
Steffen.

[RobF]

Be interesting if it does save some power Steffen. Hope your post your experiences with the kit too.

[Astro_Bot]

Thanks for the additional info. Some people like to run their mounts on ~15V (via an A/C adapter) instead of ~12V, which will mean a difference of around 20% in current draw (and hence a 20% difference in battery life calculations, if the wrong voltage was assumed).

---------

Regarding power vs gearing, I guess following on from the other thread (and interesting topic you raise!) ...

To my way of thinking, an imbalance on any axis (e.g. if "pushing up" - as some people like to set up their mount that way) or the stiffness of grease (temperature/age), or age of bearings or payload weight will increase mechanical load, and hence draw more power*, and is likely to be the cause of more variance in power draw than differences in mechanical efficiency of gearing (e.g. gears vs belt).

Although belt drives are theoretically more efficient than transfer (spur) gears (IIRC), the losses aren't dramatically different - using some remembered numbers for cars as an example, a belted CVT has mechanical efficiency around 95%, whereas a manual gearbox has efficiency around 90% (albeit with lots of assumptions about the range of input power and torque). I'd be academically interested if there are decent figures for efficiency of spur gears vs belts as might be found in a mount. I stumbled across these figures, but don't know if they're that reliable:

http://www.eng-tips.com/viewthread.cfm?qid=74637

This is also an interesting article, though it has only qualitative info on drive efficiency:

http://www.dfmengineering.com/news_telescope_gearing.html

In an EQ mount, the final worm drive is likely to be the most lossy mechanical component in either case, since worm drives (IIRC) typically have only ~70% efficiency, though it'll depend on the ratio.

For batteries, there are so many other variables, it'd be hard to say that shortened battery life would be caused primarily by gear adjustment (assuming they are not tightened to the point of binding). Temperature, initial charge and standing time, payload, balance set up, etc. Nevertheless, gear adjustment might have an effect. I'd be interested in a controlled experiment.

When I measured power draw on my EQ6 Pro, I had it carefully balanced with my typical payload of (at that time) 13kg. I suppose I should actually measure power draw with different payloads and a slight imbalance, to see if there's a noticeable difference. It'd be interesting to see if the practice matches the theory.



* It's been a long time since I did DC motor theory, but IIRC (a big assumption!), increasing mechanical load reduces back EMF at any given instant due to increased lag, which increases net voltage and current supplied to motor and hence increases motor power input and mechanical power output, which reduces lag ... or something like that. It's a pretty neat self-correcting system, if operated within its design limits, with the general relationship that increasing load increases power drawn.

[1parsec]

Hi Louie,
I've just took the following current measurements for a NEQ6 and HEQ5 mounts. Both mounts have been converted to belt drives.
I used a bench power supply with the supply voltage set to 12.0 vdc. The readings did float around 100mA or so these are averages.


___________Tracking ____RA Slew ______Dec Slew ____RA+Dec Slew

NEQ6 ______700 mA _____800 mA _____1150 mA ______1300 mA

HEQ5 ______700 mA _____740 mA _____1050 mA ______1100 mA


Dave

[RobF]

Thanks Dave

That's incredibly useful info for anyway planning a dark sky camping trip where batteries are the only option.

[louie_the_fly]

Hi everyone. Sorry about not getting back sooner. We've had a pretty hectic time here with things other than astronomy taking priority.

Thanks to everyone for all the info. It is exactly what I was after. I'll bank it for when we get a chance to get the scope out again.

Cheers. Louie