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Portable Power. Calculating requirements

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#1 CanadianLoki

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Posted 14 February 2021 - 08:17 AM

Portable power question. I am getting mixed information. I've watched numerous videos that explain how to add up the power requirements for all your devices and then buy a battery/build your power box to suit your needs. Doing this (unless I'm way off)  I figure for an overnight session (say 8-10 hours) I would need close to 1,600 watt hours or 80-100 amp hours at 12V to be on the safe side. I want to image at remote dark sky locations so need everything powered by batteries. Then I see people posting about Jackary or similar power banks that are WAY under the requirements (like 17 amp hours) and saying how they work for them.  My equipment is an HEQ5 mount, cooled ASI camera, ASIAIR Pro, EFW and EAF (both low draw). Dew heaters will be powered by USB brick and no laptop (ASIAIR Pro). Anyone with similar setup that uses these pre-made power solutions that can attest to whether they really can supply enough juice for hours?

 

Item              Volts       Amps       Watts         Hours         Watt Hours
ASIAIR            12            6              72             10                   720
ASI 294mm     15            3              45             10                   450
ASI EAF           12          0.5              6              10                   60
ASI EFW            5             1              5              10                    50
HEQ5 Pro        15             3             45              10                   450
    
     1730 total watt hours / 12V = 144 amp hours?

 

this would get expensive for a LiFePO4 battery. Any help/feedback would be appreciated. I also not against having 2 smaller light weight battery solutions if it makes more sense.



#2 davidmalanick

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Posted 14 February 2021 - 08:33 AM

I believe it is 13.5 Amp Hours.



#3 CanadianLoki

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Posted 14 February 2021 - 08:35 AM

I believe it is 13.5 Amp Hours.

Thanks. Unfortunately your answer is too short for me to understand the logic behind it. Can you elaborate?



#4 davidmalanick

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Posted 14 February 2021 - 08:43 AM

http://www.omnicalcu...ttery-amp-hours

 

http://deepcyclebatt...tery-amp-hours/



#5 astrohamp

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Posted 14 February 2021 - 08:58 AM

For me I had a Kill-A-Watt meter on hand already that I attached all my AC powered astro tech to, including computers, monitor(s), fans... and operated the set up a number of nights. Instant and accumulated power displayed.

Know that all the AC-to-DC power converters have losses meaning they use more power then deliver.  This actually helps when adding a fudge factor for total consumption.

The rule of thumb for true deep cycle "lead" batteries (AGM/SLA) is to only use 50% of capacity to maintain long cycle life, the 1000-2000+ cycles some advertise.  I worked hard with my choices to try and keep full on power use less then 120w.  This pushes my 100AH AGM battery very hard into the 250-500 cycle zone.  My choice.  YMMV


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#6 pcaritj

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Posted 14 February 2021 - 08:58 AM

I think your math is right. (One of the battery calculators above will probably confirm that.) Where I think you're going wrong is with your inputs. Your requirements seem closer to peak consumption for the various devices you'll have connected than to average. But the average (given your patterns of use) is what you need for capacity planning. For example, an ASIAIR may require a 6A/12V power supply,  but I would be very surprised if it actually *used* 6A on a consistent basis (or ever), unless you are pushing a lot of power through a dew heater. I don't own an ASIAIR, but given what it is, I'd expect average power consumption to be a fraction of that. 

 

Others with more experience may be able to give a more general answer, but here is an example:

 

I have a Losmandy G-11 mount, ATIK 314L+, two smaller ZWO cameras,  an Astroberry, EFW, and EAF. That will generally run for most of the night on this 213Wh battery.



#7 Avgvstvs

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Posted 14 February 2021 - 09:22 AM

Forget the Maths

Just buy the biggest power supply you can afford


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#8 daveco2

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Posted 14 February 2021 - 09:44 AM

I agree with pcaritj about the average power draw.  Most of the equipment spends most of its time idling, even the camera cooler.

Otherwise, your math is correct.

I have a 70Ah LiFePO4 battery in a PowerWerx box (photo attached) and it's still going strong after 6 hours with this load:

1. Laptop

2. CEM40

3. ZWO asi2600

4. ZWO 2" EFW

5. Pegasus FocusCube

6. Small LED lamp

7. Dew heaters (3 small)

 

After outfitting the battery box with all the connectors and meters I wanted, total price came to about $1,000.  My partial justification is that it's

useful to run my router and computer in a power outage, like the one we just had.  Weight of box, including charger, 24 lbs.

Attached Thumbnails

  • box isometric photo.jpg

Edited by daveco2, 14 February 2021 - 09:51 AM.

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#9 Sandy Swede

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Posted 14 February 2021 - 10:08 AM

I think your math is right. (One of the battery calculators above will probably confirm that.) Where I think you're going wrong is with your inputs. Your requirements seem closer to peak consumption for the various devices you'll have connected than to average. But the average (given your patterns of use) is what you need for capacity planning. For example, an ASIAIR may require a 6A/12V power supply,  but I would be very surprised if it actually *used* 6A on a consistent basis (or ever), unless you are pushing a lot of power through a dew heater. I don't own an ASIAIR, but given what it is, I'd expect average power consumption to be a fraction of that. 

 

Others with more experience may be able to give a more general answer, but here is an example:

 

I have a Losmandy G-11 mount, ATIK 314L+, two smaller ZWO cameras,  an Astroberry, EFW, and EAF. That will generally run for most of the night on this 213Wh battery.

From what I can discern, the ASIAIR Pro has a max amp draw of 6.  However, I don't think it would last long at a continuous 6 amp draw.  I bet that baby would get hot.  Yes, connecting 4 dew heaters at 1.2 amp each port would not be a good configuration. 

 

 

Watts = Amps x Volts 



#10 CA Curtis 17

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Posted 14 February 2021 - 10:15 AM

Your numbers are seriously inflated.  I am not sure where you got them, perhaps from the power bricks supplied for some of them but these are never the actual power drawn by the device they power.

 

I made extensive measurements of my astrophotography rig plus all of the different mounts I have and run days and days of tests at my home observatory and out in the field actually taking images and can assure you that your rig will not consume anything like what you have listed.  Here is a summary of the current at 12V for multiple mounts during tracking and high speed dual axes slews.  You do not need to size you total power for the HS slews as those only occur during setup and not during the imaging session.  But, you do have to take the HS slews into account when sizing the total current capacity and cable size of your setup.

 

Now, for the other components, I carefully measured the current and power used by each in my setup.  While mine are not identical to yours, unless you have some very exotic camera, focuser, etc. expect your numbers to be similar to mine.  In my case, my Jacker power supply is regulated and puts out 13.1V so you can simply multiply the numbers in the table by 1.1 (13.1V/12V) if you power supply is regulated at 12V.  Most are higher than that and typical lead acid batteries are not regulated but start at ~12.8V and fall of to ~11.8V where they are dead.  You can find the full details of my measurements and how long my Jackery lasted using different versions of my setup in my review on my web site.  Just scroll down till you see the review of the Jackery solar generator.

 

While my measurements do not include the ASIAIR since I do not own one, it is simply the equivalent of my Pegasus power/USB hub and a Raspberry Pi combined.  I took a look at its specs and it say it takes 2-6A at 12V.  That means it is including power to you camera, EAW,EAF, mount and its own Raspberry Pi at 6A.  You do not need to double count the currents.  6A x 12V = 72W will be the top end of the power you need if you use the full capacity of the ASIAIR.  The EAW and EAF will draw less than 0.5A and only when you engage them which will be infrequently.  Even though I have not measured your mount exactly, I am sure it will not draw more than 0.5A when tracking.  If your camera is uncooled, expect it to draw less than 0.5A at 12V.  If cooled assume 2A at maximum cooling.  What I don't know is how much power the Raspberry Pi uses itself, but I am guessing less than 35W at 12V.  So, if using a cooled camera I would estimate:  3+ 2 + 0.5 + 0.02 + 0.02 ~ 6A or 72W total. The 1000Wh Jackery or similar will give you 10 hrs.   If using an uncooled camera then 3 + 0.5 + 0.02 + 0.02 ~ 4A or 48W.  The Jackery 500Wh or similar will give you 10hrs.

 

 

Let us know if you have more questions.

 

Curtis

Attached Thumbnails

  • Mount Power Measurements.png
  • Screen Shot 11-01-20 at 09.32 AM.PNG

Edited by CA Curtis 17, 14 February 2021 - 10:30 AM.

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#11 CanadianLoki

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Posted 14 February 2021 - 10:18 AM

I think your math is right. (One of the battery calculators above will probably confirm that.) Where I think you're going wrong is with your inputs. Your requirements seem closer to peak consumption for the various devices you'll have connected than to average. But the average (given your patterns of use) is what you need for capacity planning. For example, an ASIAIR may require a 6A/12V power supply,  but I would be very surprised if it actually *used* 6A on a consistent basis (or ever), unless you are pushing a lot of power through a dew heater. I don't own an ASIAIR, but given what it is, I'd expect average power consumption to be a fraction of that. 

 

Others with more experience may be able to give a more general answer, but here is an example:

 

I have a Losmandy G-11 mount, ATIK 314L+, two smaller ZWO cameras,  an Astroberry, EFW, and EAF. That will generally run for most of the night on this 213Wh battery.

thanks. this is what I'm hoping to read. I don't mind DIY but it often comes out more $ as I always want to do it right the first time and go big. Perhaps I am relying too much on max and should be looking more at average but that's why I'm hoping people like you who own these pre-made options chime in and post actual usage experience. Cheers!



#12 CanadianLoki

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Posted 14 February 2021 - 10:53 AM

Your numbers are seriously inflated.  I am not sure where you got them, perhaps from the power bricks supplied for some of them but these are never the actual power drawn by the device they power.

 

I made extensive measurements of my astrophotography rig plus all of the different mounts I have and run days and days of tests at my home observatory and out in the field actually taking images and can assure you that your rig will not consume anything like what you have listed.  Here is a summary of the current at 12V for multiple mounts during tracking and high speed dual axes slews.  You do not need to size you total power for the HS slews as those only occur during setup and not during the imaging session.  But, you do have to take the HS slews into account when sizing the total current capacity and cable size of your setup.

 

Now, for the other components, I carefully measured the current and power used by each in my setup.  While mine are not identical to yours, unless you have some very exotic camera, focuser, etc. expect your numbers to be similar to mine.  In my case, my Jacker power supply is regulated and puts out 13.1V so you can simply multiply the numbers in the table by 1.1 (13.1V/12V) if you power supply is regulated at 12V.  Most are higher than that and typical lead acid batteries are not regulated but start at ~12.8V and fall of to ~11.8V where they are dead.  You can find the full details of my measurements and how long my Jackery lasted using different versions of my setup in my review on my web site.  Just scroll down till you see the review of the Jackery solar generator.

 

While my measurements do not include the ASIAIR since I do not own one, it is simply the equivalent of my Pegasus power/USB hub and a Raspberry Pi combined.  I took a look at its specs and it say it takes 2-6A at 12V.  That means it is including power to you camera, EAW,EAF, mount and its own Raspberry Pi at 6A.  You do not need to double count the currents.  6A x 12V = 72W will be the top end of the power you need if you use the full capacity of the ASIAIR.  The EAW and EAF will draw less than 0.5A and only when you engage them which will be infrequently.  Even though I have not measured your mount exactly, I am sure it will not draw more than 0.5A when tracking.  If your camera is uncooled, expect it to draw less than 0.5A at 12V.  If cooled assume 2A at maximum cooling.  What I don't know is how much power the Raspberry Pi uses itself, but I am guessing less than 35W at 12V.  So, if using a cooled camera I would estimate:  3+ 2 + 0.5 + 0.02 + 0.02 ~ 6A or 72W total. The 1000Wh Jackery or similar will give you 10 hrs.   If using an uncooled camera then 3 + 0.5 + 0.02 + 0.02 ~ 4A or 48W.  The Jackery 500Wh or similar will give you 10hrs.

 

 

Let us know if you have more questions.

 

Curtis

wow, that's great info. By the sounds of your review I could likely get away with a 500Wh unit. I run a cooled camera but plan on running dew heaters through a usb bank mounted under the scope if I can.



#13 CA Curtis 17

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Posted 14 February 2021 - 11:33 AM

The wild card in my estimates is how much power the ASIAIR itself uses to power its internal Raspberry PI.  Since I do not have one, I cannot measure it myself.  My BeeLink mini-pc only used ~19W so maybe the ASIAIR will use similar instead of the 35W.  Keep in mind, you can run these Lithium units down to about 20% SOC without shortening the life of the unit which is a heck of a lot better than a wet lead acid battery.  So estimate only 400Wh as useable power from a 500Wh unit.  For 8 hrs you should be able to draw 50W and be safe.  If you were to use the Jackery or similar for the dew heaters as well, you would have to move up to a higher capacity power source.

 

This is the problem with so much equipment.  The key is to stay d.c. and not use inverters, turn the camera cooling to the minimum necessary, use only the dew power needed to keep dew at bay (this is good practice anyway to avoid creating air turbulence by overheating the optical tube), use some reflectix around the dew heater to direct all the heat to the OTA instead of to the air, use short cables with higher gauge wires (18AWG instead of 20 or 22) to minimize power loss due to cable resistance, etc.  For those using a pc turn off all unused software, turn down the screen brightness or use a headless mini-pc or NUC.

 

Good luck

Curtis


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#14 astrohamp

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Posted 14 February 2021 - 02:39 PM

Measure twice...buy once. 

 

At least until you add considerably more tech to your set up, or used up the life cycle of the current battery(s).



#15 pcaritj

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Posted 14 February 2021 - 02:46 PM

I suppose that if you *really* wanted to be sure, you could connect your setup through an ammeter and see how much power it actually draws. Most decent multimeters could probably do the job. Then it's just a matter of adding a suitable margin (120%?) and multiplying by hours. 


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#16 mtc

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Posted 14 February 2021 - 09:07 PM

I went thru the calculations/estimate phase on this thread.. big difference between max and actual values...
https://www.cloudyni...wer-options-pps

Hope this helps.

#17 Linwood

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Posted 14 February 2021 - 09:39 PM

I suppose that if you *really* wanted to be sure, you could connect your setup through an ammeter and see how much power it actually draws. Most decent multimeters could probably do the job. Then it's just a matter of adding a suitable margin (120%?) and multiplying by hours. 

This.

 

You need to do math for everything that may run at the same time, with the max they can draw, to calculate your MAX amperage which determines wire size, fusing, power supply capacity, etc. 

Then you need to let it sit and run normally for a while with a meter and measure averages.  They will be VERY different, e.g. filter wheels, focusers, etc. have like a 1% duty cycle, and essentially do not count for amp hours.  Computers are likely to run at maybe 20% (well, unless you leave a planetarium running with high frame rate updates).  

 

Basically you need to figure out what "normal" is, and it's hard to look that up, you need to be normal for a while and measure. 



#18 rgsalinger

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Posted 15 February 2021 - 01:09 AM

Unless you enjoy projects don't over think this.

 

Just get a kill-a-watt meter and do a 10 hour imaging run where you have AC power available. Note how much power you used. Run any dew heaters at 20 percent all night long as they really are the big variable. Now, just buy a battery pack large enough to run all night long plus 25 percent. The last thing that I would worry about is catering for "peak power". Just give yourself the same 25 percent of headroom and you'll be fine.  

 

If you have the budget, then the Goal Zero Yeti's are simply the best power option that money can buy. (You can save a bundle on a DIY LIPO pack if you know what you are doing). 

 

FWIW, I have not been imaging portably for a while now, but I still have all of the wiring and accessories to do portable imaging (new portable mount coming soon). What I did was to use stuff from https://powerwerx.com/ (cheaper knockoffs are available) with some old 16 gauge speaker cable and a lead acid battery pack. (I'll go LIPO next time around for a number of reasons).

 

Rgrds-Ross 



#19 CA Curtis 17

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Posted 15 February 2021 - 01:21 AM

 

If you have the budget, then the Goal Zero Yeti's are simply the best power option that money can buy. (You can save a bundle on a DIY LIPO pack if you know what you are doing). 

 

Ross, with all due respect I have to disagree. 

 

Look at the technical specifications of the Goal Zero power stations carefully compared to others like the Jackery.  First, both use LiNMC for light weight.  Both have regulated voltage output.  Both have MPPT charge controllers built in for easy solar re-charging.  Both have pass through charging. Both have several USB output ports and pure sine wave AC outputs. Both have 2 year warranties, although my Jackery increases that to 3 years when you register the product.  An so on.  Very little difference of significance based upon these attributes. 

 

Now, here is where they differ.  Cost per unit of Amp-Hour (or watt-hour if you prefer).  The Goal Zero 505Wh specifies 505 watts (46.9Ah) only at 10.8V.  Nothing we use wants to work at 10.8V.   Let’s figure out how many Ah at 12.7V which is the voltage of a fully charged lead acid battery.  That would be 40Ah or 508Wh.  At a base cost of $699.95 you are paying $17.5 per Ahr at 12.7V.  Next, look at the Jackery 518Wh unit.  It specifies 518Wh at 21.6V and 24Ah.  Don’t ask me why all of these solar generator companies use these different voltages and not 12V or 13V for consistency.  Anyway, the Jackery will supply 40.8Ah at 12.7V which is 518Wh.  The price is $500 so you are paying $11.41 per Ahr at 12.7V.  You can do the calculation at any voltage you like, the Jackery will come out to be 30% cheaper.

You can do the same calculations for the Goal Zero 200Wh  ($20.4 per Ah) and 1500W ($16.93 per Ah) models to compare with the closest comparable Jackery  models, 240Wh ($12.17 per Ah) and 1002Wh ($11.41 per Ah).   For these models the Jackery is even a better buy by comparison.

I see absolutely no reason to buy the Goal Zero over the Jackery.  And Jackery has an excellent reputation on Amazon. 

 

Now there are other very good solar generators out these besides the Jackery that have comparable tech specs and competitive price points, but I have only had hands on experience with the Jackery and feel quite comfortable recommending it.  I would certainly recommend it over the Goal Zero given the significant cost differential

 

Regards,

Curtis



#20 rgsalinger

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Posted 15 February 2021 - 02:05 AM

You are right that the Jackery 500 is much cheaper than the Goal Zero 500 and is clearly a better buy. I don't know much about their product - quality or company.I'm getting a portable mount, hopefully at the end of this mount and I'll give the Jackery a try. The pricing is compelling. 

 

FWIW, don't ever trust Amazon recommendations - too many are paid for by the vendors - big problem what Amazon has.  

 

I have two Goal Zero 3000 Yeti's powering my MX+ and my CEM120EC2. They have been running off the grid for almost two years now without a hitch. When I was setting them up the support was excellent which was helpful to me because I had never done anything like this before. It's hard to keep on top of alternatives when you have something that works as well as my power packs do. One of them even has a lead acid battery attached (100AH) for some additional capacity. 

 

Rgrds-Ross



#21 Linwood

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Posted 15 February 2021 - 06:58 AM

Unless you enjoy projects don't over think this.

 

Just get a kill-a-watt meter and do a 10 hour imaging run where you have AC power available. Note how much power you used. Run any dew heaters at 20 percent all night long as they really are the big variable. Now, just buy a battery pack large enough to run all night long plus 25 percent. 

The only thing I'd adjust in this is that dew heat is heavily dependent on location. Here in the swamp we call Florida I would have to plan on 100%.  There are probably dry areas where near zero is "normal".   But it's exactly as above -- figure out normal, and measure it, don't deal with maximums for battery capacity.


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#22 Lasko

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Posted 15 February 2021 - 01:29 PM

Look at the technical specifications of the Goal Zero power stations carefully compared to others like the Jackery.  

I would second this.  The Ground Zero looks perfectly fine and no reason to think it doesn't work.  Comparing the 200x with the Jackery 167Wh unit that I use, it is very similar down to practically the same connector setup.  The real difference is the cost which is about half.



#23 mtc

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Posted 16 February 2021 - 03:10 PM

I have a 50Ah LifePO4 battey in a converted toolbox and get a full 10 hours runtime - with everything running (outside temp ~32F):

Sirius EQ-G Mount

DewHeater-Scope
DewHeater-Finder
Arduino-Focuser
USB Hub
533MC-Pro with TEC Cooler (at max power)

1290MM-mini

300W inverter for Laptop AC power (running: NINA, PHD2, EQMOD, Stellarium)

 

My nominal battery draw is 52W, 4A

 

powerbox-outside-mini.jpg


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#24 CA Curtis 17

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Posted 16 February 2021 - 07:25 PM

I have a 50Ah LifePO4 battey in a converted toolbox and get a full 10 hours runtime - with everything running (outside temp ~32F):

Sirius EQ-G Mount

DewHeater-Scope
DewHeater-Finder
Arduino-Focuser
USB Hub
533MC-Pro with TEC Cooler (at max power)

1290MM-mini

300W inverter for Laptop AC power (running: NINA, PHD2, EQMOD, Stellarium)

 

My nominal battery draw is 52W, 4A

 

attachicon.gifpowerbox-outside-mini.jpg

Just so that I am clear, are you saying that the 52W includes the power draw for you laptop through an AC inverter?  Seems low to me if including a laptop running software to control the mount and an imaging and guiding application.  What laptop are you using and how long does the battery last without power from the inverter? 



#25 rgsalinger

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Posted 17 February 2021 - 01:45 AM

Well, if the laptop screen is kept off and the laptop is modest (and it can be) the power draw might not be very much for most of the night. Personally I was more dubious about the cooler running "at max power" because there's no reason to cool that chip to less than -10C and that would be a very low power draw on a cold night. 

Rgrds-Ross




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