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Power packs and voltage conversion / Skywatcher NEQ6

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#1 John Tucker

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Posted 13 June 2018 - 12:54 PM

Fairly recently I purchased a Skywatcher NEQ6 mount and a fairly high end lithium battery pack to drive it.  Unfortunately I'm having a lot of trouble that I believe to be related to the voltage of the lithium battery dropping from its fully charged, low load value of 11.5 volts to something just below 10.  The mount manufacturer strongly recommends a power source capable of delivering at least 4 amps at 11.5 to 16 volts. 

 

I hate to replace the battery because I spent a fair bit on the lithium pack and aside from the voltage shortfall it is a nice unit.  It's specs say it will deliver 180 watts from the DC port, which would be about 15 amps at 12 volts.  There is an AC outlet on the unit that the specs claim will deliver 100  watts at 120 volts, which is about 8 amps.  Its a big manly battery with 150 watt hours of storage, it is just falling short on the voltage by 10 to 20%, and this shortfall is catastrophic for my purposes.  

 

Am considering

 

1. Buying a AC power supply for the telescope and plugging it into the battery AC outlet.  It seems ludicrous to convert DC to AC and then back to DC, but I think the battery probably has the capacity to do that and still deliver 12+ volts at 4 amps. Like I said, its a big manly battery.  

 

2. There are voltage converters online that will convert 12 volts DC to 15 volts DC, which I think would covert my 10 or so volts to about 12.5 volts.  I'd just have to pull out the old soldering iron and put it inline on my power cord.  

 

 

Thoughts on this?  Anyone with similar experience?  I worry a little bit about the AC power supply approach because I destroyed a Meade LX200 mount using a nominally 12 volt AC converted purchased on Amazon.  Apparently the quality of these varies widely and they can have voltage spikes. Wife probably won't throw for another $1700 mount. 

 

Thanks

 

JT

 

 [attachment=1071072:Capture.JPG][attachment=1071079:Capture.JPG]


Edited by John Tucker, 13 June 2018 - 01:08 PM.


#2 Chuckwagon

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Posted 13 June 2018 - 02:23 PM

The battery is probably a 3 cell lithium design, so if each cell were 3.8v full capacity, you're only getting 11.4v total.  So right off it is a bit low on volts.  Then, 150 watt-hour is only around 13 amp-hours at 11.4v.  So it really isn't a very beefy battery.  Using the 120v outlet will give you even less capacity, as the 120v conversion is wasteful.  (Also, watts=amp x volts, so 100 watts = .83 amps x 120v, which is quite a bit less than 8 amps, so the 120v outlet isn't intended to run anything very power hungry.  Unless you meant 1000w.  :)  )

 

A buck converter/voltage regulator would likely work fine, but with conversion loss it' likely your capacity is never going to be more than 10 amp-hours or so.  That's probably enough to run just the mount for an evening or two, depending on how much slewing you do and how long your night runs.

 

So I'd say investing $10 to $15 on a converter is probably worthwhile, but I'd likely get a higher capacity main battery and use this unit as a secondary supply or backup to the main.

 

If you want more power, there are tons of threads discussing batteries, costs, chemistries,etc., and I'm sure you'll be able to find enough info to make a choice.

 

Cheers


Edited by Chuckwagon, 13 June 2018 - 02:25 PM.

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#3 John Tucker

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Posted 14 June 2018 - 07:05 AM

The battery is probably a 3 cell lithium design, so if each cell were 3.8v full capacity, you're only getting 11.4v total. So right off it is a bit low on volts. Then, 150 watt-hour is only around 13 amp-hours at 11.4v. So it really isn't a very beefy battery. Using the 120v outlet will give you even less capacity, as the 120v conversion is wasteful. (Also, watts=amp x volts, so 100 watts = .83 amps x 120v, which is quite a bit less than 8 amps, so the 120v outlet isn't intended to run anything very power hungry. Unless you meant 1000w. :) )

A buck converter/voltage regulator would likely work fine, but with conversion loss it' likely your capacity is never going to be more than 10 amp-hours or so. That's probably enough to run just the mount for an evening or two, depending on how much slewing you do and how long your night runs.

So I'd say investing $10 to $15 on a converter is probably worthwhile, but I'd likely get a higher capacity main battery and use this unit as a secondary supply or backup to the main.

If you want more power, there are tons of threads discussing batteries, costs, chemistries,etc., and I'm sure you'll be able to find enough info to make a choice.

Cheers



#4 John Tucker

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Posted 14 June 2018 - 07:37 AM

Thanks for the comments.  Will definitely go with the voltage stepup adapter.  Will let you know how it goes. 



#5 Phil Sherman

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Posted 14 June 2018 - 01:46 PM

I have a similar issue with my Atlas mount when running it from a 12V SLA battery. At the start of an evening's observing all was well but at the end of the night, when I also needed to use the battery to power the laptop, the voltage dropped to the point where the mount was complaining.

 

My solution was to use a buck/boost converter to keep the voltage at 13.2v. I've had no issues since starting to use it.


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#6 John Tucker

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Posted 14 June 2018 - 05:39 PM

I have a similar issue with my Atlas mount when running it from a 12V SLA battery. At the start of an evening's observing all was well but at the end of the night, when I also needed to use the battery to power the laptop, the voltage dropped to the point where the mount was complaining.

 

My solution was to use a buck/boost converter to keep the voltage at 13.2v. I've had no issues since starting to use it.

Aside from the noise, did you notice any issues with GoTo alignment?  I've been having all kinds of problems. I was under the impression that GoTo alignment was usually pretty smooth if you had the polar alignment correct and accurately placed the tube in home position before starting, but I had my polar alignment spot on the other night (as demonstrated by several 3 min exposure photographs) and the GoTo was wildly off.  Especially toward the end of the night after I'd repeated the alignment a few times trying to get it better, you could just look at the OTA and tell it was pointing 20 degrees or more off from the target. 


Edited by John Tucker, 14 June 2018 - 05:39 PM.


#7 carolinaskies

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Posted 15 June 2018 - 12:46 PM

In the short term that converter will allow you to continue to use the battery. But in the long run you'll want to look for a better Battery Solution if you plan to run extensively and don't want to be hassled by constantly needing to recharge or swap batteries around.

Personally I don't think running the mount under voltage is a good thing. I would want to ensure that I was powering it towards the top end of the voltage rating say around 14.5v so that by the time my observing session was over I might have only discharged to just above 12 volts. Mounts definitely will start to do wonky things when the voltage and amperage drop into weak ranges.
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#8 John Tucker

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Posted 15 June 2018 - 01:16 PM

In the short term that converter will allow you to continue to use the battery. But in the long run you'll want to look for a better Battery Solution if you plan to run extensively and don't want to be hassled by constantly needing to recharge or swap batteries around.

Personally I don't think running the mount under voltage is a good thing. I would want to ensure that I was powering it towards the top end of the voltage rating say around 14.5v so that by the time my observing session was over I might have only discharged to just above 12 volts. Mounts definitely will start to do wonky things when the voltage and amperage drop into weak ranges.

I freely admit I don't know what I'm doing here, but its a 150 watt hour/12 amp hour battery.  Assuming the mount runs at about a third of maximum draw continuously, should be good for a minimum of 6 hours. 

 

The larger of the two Celestron Power Tanks (I'm aware of their terrible reputation) is about 200 watt hours and being a lead acid battery shouldn't be discharged more than half, so about 100 usable watt hours.  A car battery is about 480 of which 240 is useable, so about 60% larger than what I have. 

 

What am I missing?



#9 wargrafix

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Posted 15 June 2018 - 01:39 PM

https://www.amazon.c... power station\

 

What about this one? Its effective 15 Amp Hours



#10 John Tucker

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Posted 15 June 2018 - 03:11 PM

https://www.amazon.c... power station\

 

What about this one? Its effective 15 Amp Hours

Ooooh, I like that.  Thanks.



#11 Chuckwagon

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Posted 15 June 2018 - 04:20 PM

What am I missing?

Probably not much.  smile.gif  But if you want to get a better understanding of some of the issues involved with batteries in general, and why this seems so confusing for so many folks, read this article;

 

http://batteryuniver...n_with_voltages

 

They do a good job of explaining how various battery chemistries typically deliver power.

 

It is because of the differences in nominal charge values that you see power packs that are listed as 12v, but only have 11.1v or less of true output.  A 3 cell design, like the one Wargrafix linked, would need to have a voltage regulator to step the voltage up to a true 12v.  And since so many makers list ratings based on a single cell's capacity (for example, 50,000 mAH at 3.7v, but only 16,750 mAH at 10.89v, which would drop even further if it were stepped up to 12v) it can be difficult to get an accurate idea of how much true capacity the power source can provide.

 

Most of these lithium based solutions that people recommend around here do work, at least well enough for the folks recommending them.  But I think there is enough variation in how well various mounts work with different voltages, that I'd shy away from any solution that I didn't see working on the exact same setup I use.

 

Plus, I don't mind the extra weight of a lead-acid battery, so I prefer to use the tried and true, more standard, and less over-hyped approach.  You can get a 35AH deep cycle SLA(AGM) battery for about $50.  That would easily get you two 8-hour nights of constant 1 amp draw (without dropping below 12v) between recharges without discharging the battery below 50%.  That type of usage would allow you use the battery for around 600 discharge/recharge cycles before the full charge capacity would drop to 60% of new.  If you recharged after every night, you could extend that to 1200 cycles.  So while the lithium based solutions likely have 3 or 4 times that many cycles, they also tend to be 3 or 4 times as expensive, and the true capacity is 30-40% less.

 

So I'm still waiting for the solutions to become less expensive and better designed.  smile.gif


Edited by Chuckwagon, 15 June 2018 - 04:33 PM.

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#12 carolinaskies

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Posted 15 June 2018 - 04:35 PM

That second listed battery generator has a much better output at 12 volt and also had 19 volt available depending on which Port you were using and the raining on that 12 volt was 5 amp which is more than enough to run them out and it does have a 15 amp hour rating. So it's better than the original one listed. The problem we have right now is that most of these lithium ion battery generators are insanely expensive on the open market. So the choice of the sealed lead acid battery is more economical. For those that are going to be observing only a few hours I think the lithium-ion isn't a bad option but for those who are out Imaging for 6 or more hours a night they definitely are more maintenance heavy and having to recharge them for the next use. Along with the inconsistent ratings as was described above it makes it difficult to have to do the math to figure out what is the true capability.

For recreational use these are fine but for a dedicated system I definitely would suggest building a more robust box that will not only Power the mount but any accessories placed on it including do heaters cameras Etc.
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#13 t-ara-fan

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Posted 16 June 2018 - 03:18 PM

 when I also needed to use the battery to power the laptop

Your laptop (and mine) draws about 5A from the battery. As you say, at the end of the night.  That makes the output voltage of the SLA battery drop a lot. 

 

How big is your battery?  My 33Ah SLA was too small, the 75Ah is a lot better.  Now I have both, I can dedicate the 75Ah to the scope, cameras, dew heaters etc, and keep the 33Ah just for charging my laptop.



#14 John Tucker

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Posted 20 June 2018 - 10:54 PM

I picked up this voltage booster from Amazon, attached it to a small board with screws and using a staple gun, immobilized the input and output wires so when they were tugged on they wouldn't pull out of the device.  

 

Adjusted voltage to 14.7 volts and it seems to maintain that quite nicely.  Was also able to purchase the female cigarette lighter connector and the 2.1 x 5.5 connectors from Amazon to make this all easily assembled and dissembled.  

 

 https://www.amazon.c...0?ie=UTF8&psc=1

 

 https://www.amazon.c...0?ie=UTF8&psc=1

 

 https://www.amazon.c...0?ie=UTF8&psc=1


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#15 dirac

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Posted 06 July 2018 - 01:06 PM

Aside from the noise, did you notice any issues with GoTo alignment?  I've been having all kinds of problems. I was under the impression that GoTo alignment was usually pretty smooth if you had the polar alignment correct and accurately placed the tube in home position before starting, but I had my polar alignment spot on the other night (as demonstrated by several 3 min exposure photographs) and the GoTo was wildly off.  Especially toward the end of the night after I'd repeated the alignment a few times trying to get it better, you could just look at the OTA and tell it was pointing 20 degrees or more off from the target. 

Polar alignment has nothing to do with pointing accuracy. Polar alignment will improve tracking. An excellent 3 star alignment will improve your pointing accuracy. If you do a 20 star alignment then you'll have a much better model of the sky and your pointing accuracy will be very good. I'd suggest doing a 20 star alignment instead of just 3 dum stars. 



#16 John Tucker

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Posted 06 July 2018 - 06:53 PM

But if yor polar alignment is off by 5 degrees, your OTA in home position is pointing in a direction 5 degrees different that what your GoTo software is assuming when it starts slewing to the first GoTo alignment star. And when it slews to the second, its guesding its location based on two previous points, the first star and the incorrect home position directionality, when it looks for the second.

People tell me they're unrelated, but when I finish a 3 star alignment the SynScan handset gives me a measurement of how far off the polar alignment is.

#17 Phil Sherman

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Posted 07 July 2018 - 10:26 PM

Your laptop (and mine) draws about 5A from the battery. As you say, at the end of the night.  That makes the output voltage of the SLA battery drop a lot. 

 

How big is your battery?  My 33Ah SLA was too small, the 75Ah is a lot better.  Now I have both, I can dedicate the 75Ah to the scope, cameras, dew heaters etc, and keep the 33Ah just for charging my laptop.

I use a 17AH SLA battery for short sessions. Full night sessions require swapping out the battery for a 100A flooded cell lead acid one. When I run the computer from the 17AH battery, I'm usually using my old ASUS netbook which runs directly from the 12V battery. When I use that computer, I use its fully charged internal battery until it's discharged then I plug in the external battery and remove the laptop's battery to prevent charging it from the external battery. This power source swap usually occurs less than an hour before the end of the session.

 

It's easy to swap batteries because they're connected to the power distribution box using PowerPole connectors. This completely eliminates any possibility of reversing the polarity when changing batteries. An alternative to Power Pole connectors is to use XT60 connectors which are used by the model aircraft enthusiasts.



#18 Luna-tic

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Posted 08 July 2018 - 09:55 AM

Aside from the noise, did you notice any issues with GoTo alignment?  I've been having all kinds of problems. I was under the impression that GoTo alignment was usually pretty smooth if you had the polar alignment correct and accurately placed the tube in home position before starting, but I had my polar alignment spot on the other night (as demonstrated by several 3 min exposure photographs) and the GoTo was wildly off.  Especially toward the end of the night after I'd repeated the alignment a few times trying to get it better, you could just look at the OTA and tell it was pointing 20 degrees or more off from the target. 

 

Most likely, with the mount running on a marginal voltage, it's losing its alignment. Most mounts draw very little current during tracking, but slewing, since it is driving the motors at high speeds, draws much more current; During high current loads, you get a voltage drop, and if it drops below whatever the minimum is that the mount requires to operate, it can lose its flash memory, or stop altogether.

 

Even when a battery is rated at a sufficient nominal voltage, such as 13.4-14 VDC like most lead-acid batteries, they still have a rating for a deliverable current above which, you get a voltage drop if the current drain is too high. The rating will say something like "12volts @ 2.5 amps", meaning the battery is capable of delivering 2.5 amps while maintaining 12 volts. A higher current drain may cause the voltage to start dropping, to a point where it drops below the minimum required by the appliance to operate. This is also why the LiPo you're using, with its lower nominal voltage, fails in its task under high load conditions, such as slewing, or the combined use of running the telescope and a computer. And once the battery has been drained to near its rated amp/hour capacity, voltage drop becomes the norm under even lower current drain. LiPo batteries will stop working altogether once they drop to a certain voltage.

 

For practical purposes, one of the popular lead-acid "jump starter" systems will run a mount all night, along with a dew heater or a laptop, and they are relatively inexpensive. Downside is bulk and weight, too bad you can't get them without the little compressor and other junk we don't need. I have one and can run my EQ6R-Pro all night, with a moderate amount of slewing while observing many objects in different parts of the sky. For long-duration tracking during AP, you should get about the same amount of time or better. I would never power both my laptop and telescope from the same source unless it were a high capacity marine deep-cycle type, with a lot of reserve. I also have the smaller Celestron LiFePO Power Tank, which will easily run my AVX for two nights. I haven't yet tried it on the Skywatcher yet due to cable incompatibility.

 

One other thing; voltage convertors usually come with a price. If you have, say, a battery with a nominal voltage of 10.4VDC, capable of 3 amps at that voltage, and you place a convertor in the system to bump up that voltage, you'll get a drop in deliverable current inverse to the increase in voltage (resistance of the system remaining the same). So, if that decrease in current availability is less than needed by the connected appliance, you'll still get a voltage drop when current drain is higher. That's electricity, irrespective of battery type.


Edited by Luna-tic, 08 July 2018 - 10:05 AM.

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#19 John Tucker

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Posted 08 July 2018 - 12:04 PM

Thanks.  I measured the no-load voltage of the battery at 12.5 volts. It's supposed to be able to deliver 15 amps at peak but I don't think it was maintaining 12 volts at load because it screeched and stopped at high slew speeds once the battery ran down a bit. Seems to be behaving better so far with a step up adapter to 14 volts.

 

Selling a mount that wants 13 or 14 volts to work optimally seems a little awkward.  But I guess its a matter of what you're optimizing against.



#20 Luna-tic

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Posted 08 July 2018 - 07:44 PM

To know for sure, you'd have to measure voltage at the telescope connection under full load (high-speed slewing) to know how much drop you're getting. If the battery is capable of delivering 15 amps at 12VDC, you probably have a little leeway with the stepper, but  I can't imagine the scope requiring more than 5 amps to operate.


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