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Mount performance and supply voltage

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#1 Michael Covington

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Posted 22 October 2021 - 09:01 PM

I recall reading that Sky-Watcher (or somebody!) recommends that their mounts run on 13.5 V (or something like that) rather than 12 V, because they perform better (in some way).   (Obviously NOT above the specified maximum voltage, which is probably 14.)

Questions:

Was it Sky-Watcher or somebody else?

Do the mounts that this applies to have servo motors or stepper motors?

What was the performance improvement?

There's a theoretical reason why raising the supply voltage to a stepper motor that is being microstepped might improve its performance, but I'm curious as to exactly what was recommended, and by whom.  References to other threads here are welcome.

Thanks!



#2 OzAndrewJ

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Posted 22 October 2021 - 09:27 PM

Gday Michael

Pretty sure SkyWatcher is the one who recommended higher voltage

and the mounts use steppers.

That said, the boards we had circuit diags for ( Early EQ8 ) indicate

they have an onboard boost converter to raise the stepper voltage as required

( and it has a 2 voltage setting, if i did the math right it can output 16V or 45V ),

so my guess is the 13.8V in gives that setup a bit of headroom and lowers the

current draw at the power in socket.

 

Andrew Johansen Melbourne Australia


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#3 Ayaan Hashim

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Posted 22 October 2021 - 10:29 PM

Astrobiscuit on youtube for some mounts?- https://www.youtube....h?v=4rCyC3_YIME



#4 bobzeq25

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Posted 22 October 2021 - 10:30 PM

The thing I saw came from this guy.

 

https://www.youtube....yC3_YIME&t=942s

 

Here's the thread.  It was somewhat contentious, and there was no resolution.  I found the idea somewhat idiosyncratic.   Skywatcher themselves recommends 11-16V.  That range is consistent with my experience with my iOptron CEM60.  Note that I have really solid wiring/connectors.

 

https://www.cloudyni... mount voltage


Edited by bobzeq25, 22 October 2021 - 10:31 PM.

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#5 rgsalinger

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Posted 22 October 2021 - 10:38 PM

When I bought my Astro-Physics Mach 1 AP recommended the Pyramid family of 13.8 volt power supplies. That way, you're pretty much guaranteed to end up at the mount with more than 12 volts. I used that supply with my AZ/EQ6 and nowadays with my CEM120EC2 as it the idea of starting a little higher than 12 volts made sense to me. In fact, the only time I can recall having a power supply problem was when I use a cheap 10 amp 12volt supply because it was handy when setting up my friends EQ6R. The mount went "nuts".

 

So, across a lot of mounts it would seem that being a little high is the way to go.  I'd always make a call if I was buying a mount to the vendor to double check what they recommend. 


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#6 Raginar

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Posted 02 November 2021 - 01:48 AM

When I bought my Astro-Physics Mach 1 AP recommended the Pyramid family of 13.8 volt power supplies. That way, you're pretty much guaranteed to end up at the mount with more than 12 volts. I used that supply with my AZ/EQ6 and nowadays with my CEM120EC2 as it the idea of starting a little higher than 12 volts made sense to me. In fact, the only time I can recall having a power supply problem was when I use a cheap 10 amp 12volt supply because it was handy when setting up my friends EQ6R. The mount went "nuts".

 

So, across a lot of mounts it would seem that being a little high is the way to go.  I'd always make a call if I was buying a mount to the vendor to double check what they recommend. 

I seem to remember Losmandy being the same way.  



#7 MCinAZ

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Posted 02 November 2021 - 04:17 PM

  Many mounts can benefit from higher-than-12 V inputs, and any well designed mount designed for 12 V nominal operation will tolerate at least a few volts above that simply because "12 V" lead acid automotive batteries source 13.8 V or so when fully charged. A-P and Losmandy mount controllers (and probably almost all others) internally regulate the supply voltage to lower values -- 3.3 and/or 5.0 V are typical -- for the control functions but tie the high side of the motor drives to the external supply voltage. In general, motors operate more efficiently at higher voltages, so as long as the motor is rated for more than the maximum voltage applied, increasing that value is a good thing.

 

  The maximum operating voltage may be limited by the regulators in the controller more than the motors themselves. In any case, abide by the manufacturers specifications and all should be well.


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#8 ngatel

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Posted 02 November 2021 - 08:00 PM

Many mounts can benefit from higher-than-12 V inputs, and any well designed mount designed for 12 V nominal operation will tolerate at least a few volts above that simply because "12 V" lead acid automotive batteries source 13.8 V or so when fully charged. A-P and Losmandy mount controllers (and probably almost all others) internally regulate the supply voltage to lower values -- 3.3 and/or 5.0 V are typical -- for the control functions but tie the high side of the motor drives to the external supply voltage. In general, motors operate more efficiently at higher voltages, so as long as the motor is rated for more than the maximum voltage applied, increasing that value is a good thing.
 
  The maximum operating voltage may be limited by the regulators in the controller more than the motors themselves. In any case, abide by the manufacturers specifications and all should be well.


Actually car batteries are 12.6 volts fully charged. Deep cycle lead acid batteries 12.7 - 12.9 if properly charged with a 4-stage charger.

All my 12 volt equipment works fine with 14.4 volts, except my mini PC. If the voltage goes much over 13 volts it shuts down (by design). Something to think about.
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#9 Michael Covington

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Posted 02 November 2021 - 09:32 PM

12.6 V -- normal output voltage of a fully charged lead-acid battery (it is stable at this voltage for a long time as it is discharged)

 

12.9 V -- output voltage of a freshly charged lead-acid battery for perhaps the first hour or less
 

13.1 V -- highest voltage from a very freshly charged lead-acid battery for the first few minutes

13.8 V -- nominal voltage of a running car's 12-volt electrical system (to charge the battery); correct supply voltage for CB radios, etc., that are designed to be powered by a running car


Edited by Michael Covington, 02 November 2021 - 09:33 PM.

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#10 Sacred Heart

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Posted 02 November 2021 - 11:14 PM

The Losmandy power supply is in the 15 volt range.   Joe



#11 OldManSky

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Posted 03 November 2021 - 08:49 AM

"In general, motors operate more efficiently at higher voltages, so as long as the motor is rated for more than the maximum voltage applied, increasing that value is a good thing."

 

I have no doubt that is the case -- that motors (which kind, servos or steppers or something else?) operate "more efficiently" at higher voltages.

 

I have, though, not yet seen actual evidence that supplying a higher voltage to particular mounts provides better tracking performance -- which is the claim Michael is asking about, and the claim from an online video that generated much of the discussion.

 

Yes, absolutely -- don't let the voltage supplied to a mount drop below the mount's spec voltage.  It won't work well if you do that.  If your power supply drops when you connect items using power to it, get a better power supply.

 

But intentionally increasing voltage to get better performance in some way?  I'm highly skeptical.  :)


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#12 Michael Covington

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Posted 03 November 2021 - 01:11 PM

The specific phenomenon I have in mind is this.  Stepper motors, when microstepped, don't have equal torque at all of the microsteps.  As a result, they lag slightly behind the intended position for part of the cycle, then get ahead of it for the other part.  (Someone posted, somewhere on Cloudy Nights recently, a link to technical literature about this.)  The oscillation *should* be small enough to ignore.  I'm thinking it would increase if the voltage available to the motor were lower.  But I have not looked at all the IC specifications, etc., to see if the motor is powered by unregulated input voltage.

Anyhow, that's why I asked the question, and what I really want to know is not the theory, but the observed performance of mounts.

I would not supply more than the rated maximum voltage, that's for sure.  That is probably 14 volts for most brands (I know it is for iOptron, and, IIRC, Celestron).  

At the same time, the nature of batteries being what it is, there seems to be no reason to supply less than 12.6 volts.

If the mount regulates its voltage, then it might be that the extra voltage is just turned into heat, and helps keep dew off your mount :)


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#13 ngatel

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Posted 03 November 2021 - 01:30 PM

"In general, motors operate more efficiently at higher voltages, so as long as the motor is rated for more than the maximum voltage applied, increasing that value is a good thing."

 

I have no doubt that is the case -- that motors (which kind, servos or steppers or something else?) operate "more efficiently" at higher voltages.

 

I have, though, not yet seen actual evidence that supplying a higher voltage to particular mounts provides better tracking performance -- which is the claim Michael is asking about, and the claim from an online video that generated much of the discussion.

 

Yes, absolutely -- don't let the voltage supplied to a mount drop below the mount's spec voltage.  It won't work well if you do that.  If your power supply drops when you connect items using power to it, get a better power supply.

 

But intentionally increasing voltage to get better performance in some way?  I'm highly skeptical.  smile.gif

Agree.


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#14 OldManSky

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Posted 03 November 2021 - 01:40 PM

At the same time, the nature of batteries being what it is, there seems to be no reason to supply less than 12.6 volts.

If the mount regulates its voltage, then it might be that the extra voltage is just turned into heat, and helps keep dew off your mount smile.gif

Unless you're not using batteries... 

I have my DC power supply (12V 30A) plugged into mains.  It's output is adjustable -- I set it to 12.3V.  With the very small drops in my system, no power plug is getting less than 12.2V.  

 

The dew prevention is a positive, I guess! 



#15 ngatel

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Posted 03 November 2021 - 01:42 PM


At the same time, the nature of batteries being what it is, there seems to be no reason to supply less than 12.6 volts.

 

Quality regulated AC to DC power supplies are going to keep the voltage constant.

 

However when it comes to batteries, there are some considerations. When a load is applied to a stationary battery, the voltage will drop. There is a relationship between the battery's AH capacity and the amount of the load. For example, if I run my camper's microwave (which I never do, but have tested) via the inverter, after a period of time the measured voltage at my 225 AH battery bank drops considerably. When the battery voltage gets down to 10.5 volts the inverter shuts off. After a few minutes the battery voltage goes up, but not to the full charge level of 12.7 to 12.9 volts.

 

When running a mount via a battery, battery capacity and applied loads need to be taken into consideration. Many people say a lead-acid battery should not go below 50% of its state of charge (or 50% of its AH capacity). Why is this? Take a look at the chart below, and also realize that many Li-ion and LiFePo4 manufacturers quote lead acid re-charge cycles assuming the lead-acid batteries are being discharged down to 20%.

 

State-of-Charge-Chart-Typical-Internet.jIf you want to use a Li-ion or LiFePo4 battery, check out the specifications. My Li-on batteries are fully charged at 12.6 volts. My LiFePo4 battery bank starts at just over 14 volts. If I run the scope and accessories all night long on my 48AH LiFePo4 battery, consuming 20 AH, in the morning the battery bank is still over 13 volts.




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