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Mini PC vs Battery Capacity Help

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#1 Vinnyvent84

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Posted 02 March 2024 - 07:55 AM

Firstly, I hope I’m posting this in the right area - seemed like the best fit but if not I apologize.

I have a question that my simply brain simply is struggling to figure out please!

I have a mini PC that when plugged into my jackery at peak usage is consuming about 55w. It averages about half that or less but let’s just use the number of 55w for this assumption. It runs on a one of those larger laptop type transformer plugs with a DC plug into the mini pc. On Amazon under power section it states: 19V-3.42A 57W Input: 100-240V AC, 50/60Hz , Output: 19V 3.42A.


With the above information if I have a 24,000mah with 140w output battery and run that mini pc at 55w approximately how long would that battery last? I have tried using different calculators and it seems like 4 hours or so but I can’t help but feel like I’m wrong. Can someone sanity check me? Thanks in advance!

#2 Migwan

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Posted 02 March 2024 - 08:28 AM

55w / 19v = 2.89A       24Ah / 2.89A = 8.3h

This assumes 100% efficiency in converting AC voltage to DC voltage, which isn't so.   I don't happen to know what percentage a "transformer" consumes, but from experience, it won't pull Ah down to anywhere near 4 hours. 


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#3 Migwan

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Posted 02 March 2024 - 08:33 AM

By the way, the draw of the PC will be significantly less when the battery is fully charged.   


Edited by Migwan, 02 March 2024 - 08:33 AM.

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#4 Vinnyvent84

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Posted 02 March 2024 - 08:43 AM

55w / 19v = 2.89A 24Ah / 2.89A = 8.3h
This assumes 100% efficiency in converting AC voltage to DC voltage, which isn't so. I don't happen to know what percentage a "transformer" consumes, but from experience, it won't pull Ah down to anywhere near 4 hours.



Thank you very much. This is great news as I was just hoping to get a solid 4 hours which seems by your info I most definitely will. Thank you so much!

#5 Charlie B

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Posted 02 March 2024 - 08:47 AM

55w / 19v = 2.89A       24Ah / 2.89A = 8.3h

This assumes 100% efficiency in converting AC voltage to DC voltage, which isn't so.   I don't happen to know what percentage a "transformer" consumes, but from experience, it won't pull Ah down to anywhere near 4 hours. 

Depends on the battery type.  If lead-acid, you likely cannot discharge more than 50% and maintain voltage.  The 12V to 19V converters are usually around 90% or greater efficiency.  I use a 100AH LiFePo battery, which is both light and capable of being discharged below 50% and maintain voltage.

 

Regards,

Charlie B  


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#6 descott12

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Posted 02 March 2024 - 08:52 AM

don’t we need to know the voltage if the battery? are we assuming 12 volts? because an amp hour at 12v is not the same as an amp hour at 6. i think we should do the calculation in watt hours instead
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#7 Charlie B

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Posted 02 March 2024 - 09:32 AM

don’t we need to know the voltage if the battery? are we assuming 12 volts? because an amp hour at 12v is not the same as an amp hour at 6. i think we should do the calculation in watt hours instead

I did assume 12 V because of the 24AH battery. I suppose a golf cart 6V battery could be used, 

 

Regards,

 

Charlie B


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#8 Vinnyvent84

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Posted 02 March 2024 - 09:37 AM

Depends on the battery type.  If lead-acid, you likely cannot discharge more than 50% and maintain voltage.  The 12V to 19V converters are usually around 90% or greater efficiency.  I use a 100AH LiFePo battery, which is both light and capable of being discharged below 50% and maintain voltage.

 

Regards,

Charlie B  

 

 

don’t we need to know the voltage if the battery? are we assuming 12 volts? because an amp hour at 12v is not the same as an amp hour at 6. i think we should do the calculation in watt hours instead

 

 

I did assume 12 V because of the 24AH battery. I suppose a golf cart 6V battery could be used, 

 

Regards,

 

Charlie B

Thank you all for taking a look 

 

here is the battery I’m looking at 

 

https://a.co/d/1Fvn1DD



#9 descott12

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Posted 02 March 2024 - 09:46 AM

Thank you all for taking a look 

 

here is the battery I’m looking at 

 

https://a.co/d/1Fvn1DD

That looks like a 5 volt battery as it is all USB outputs. I don't believe this is what you want or need. The specs should always include voltage AND mAH or watt hours so you know exactly what you are getting.


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#10 Vinnyvent84

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Posted 02 March 2024 - 10:01 AM

That looks like a 5 volt battery as it is all USB outputs. I don't believe this is what you want or need. The specs should always include voltage AND mAH or watt hours so you know exactly what you are getting.


Hmmm. Fair enough. I was looking at the single port USB-C puts out up to 140 watts and people are using it to power MacBook pros. So I figured surely if I use the single port only with a 100w USB-C to DC cable it shouldn’t be an issue on a mini Pc that maxes out at 55w under constant heavy load (which is rare).

#11 Vinnyvent84

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Posted 02 March 2024 - 10:19 AM

That looks like a 5 volt battery as it is all USB outputs. I don't believe this is what you want or need. The specs should always include voltage AND mAH or watt hours so you know exactly what you are getting.

so I just did a check again on the site and it does state it’s 28 Volts (5amps / 140w). 
 

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Edited by Vinnyvent84, 02 March 2024 - 10:20 AM.


#12 Charlie B

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Posted 02 March 2024 - 10:35 AM

Thank you all for taking a look 

 

here is the battery I’m looking at 

 

https://a.co/d/1Fvn1DD

This is definitely not what I was thinking about.  My battery charges my PC, runs my mount, camera, dew heaters, etc. 

 

Regards,

 

Charlie B 


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#13 Vinnyvent84

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Posted 02 March 2024 - 10:47 AM

This is definitely not what I was thinking about. My battery charges my PC, runs my mount, camera, dew heaters, etc.

Regards,

Charlie B



Oh no definitely not you have a full blown rig. I down own a dew heater yet just the Celestron aluminum dew shield. So since my evolution has an internal battery I just wanted something to power the mini PC attached topside to the scope. I want to try my hand at EAA. I currently have a 678mc and since it’s uncooled it just plugs into the mini pc. I can make a 3D printer holder for that battery and clip it to the evolution handle which now means no cords coming to the ground so that’s the basic rationale behind looking at this.

#14 arbit

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Posted 02 March 2024 - 11:11 AM

It's not very clear what voltage the mAH is rated at.

Typically for LiPo the nominal voltage would be 3.7V. That means around 100WH, or just under 2 hours for a 55W load.

The specs do say 28V, but for that to be the basis for 27AH would mean a capacity of 756WH, which is huge, and incidentally inconsistent with the images saying, for example, charges an S23 4.2 times (which would imply around 80 to 90 WH). Typical large laptop batteries are 70WH or so in PCs, so 750WH capacity means 10 charges, while the claim (for Macbook M1) is 1.4 charges.

Overall, might be safer to assume a 100WH capacity.

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#15 Cliff Hipsher

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Posted 02 March 2024 - 08:56 PM

Forget the numbers and fancy math.  

 

What you really need to know is how many watts of power the entire rig is consuming during an imaging run.

 

For example my GEM45 rig pulls ~27 watts with 2 12VDC dew heaters @50% (I don't like USB powered heaters. They waste USB ports, they complicate cable management, and they are horribaly inefficeient), camera cooling set to -10C, tracking is on and the camera is taking 10 second darks.  So since the mount is drawing 27 watts that comes out to  27watts per hour or 27Wh.

 

To get a 10 hour run I need a power source that is rated higher than 270Wh.  I currently use a power station that is rated at 320Wh which gives me a 2 hour buffer to allow for Polar alignment and operator errors..

 

To get these numbers I use an in-line power analyzer.  The hard part is setting up the cables.  Keep in mind that you MUST have all of the loads connected in paralle. Air power distribution makes that part easy.



#16 descott12

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Posted 02 March 2024 - 09:38 PM

  So since the mount is drawing 27 watts that comes out to  27watts per hour or 27Wh.

 

To get a 10 hour run I need a power source that is rated higher than 270Wh.  I currently use a power station that is rated at 320Wh which gives me a 2 hour buffer to allow for Polar alignment and operator errors..

 

 

This was sort of my point. The mA hours is meaningless. It is watt hours that matters.



#17 Cliff Hipsher

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Posted 02 March 2024 - 10:33 PM

This was sort of my point. The mA hours is meaningless. It is watt hours that matters.

Advertising agents like to put the big numbers and the wattage first because the average schmoe knows diddly about electricity and numbers like 20000mAh and 300 Watts elicits a "Oh Look! A Ball!!" response and out comes the plastic..



#18 WadeH237

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Posted 04 March 2024 - 11:28 AM

Thank you all for taking a look 

 

here is the battery I’m looking at 

 

https://a.co/d/1Fvn1DD

From the information at that link, it is literally impossible to know the actual capacity of the battery.  Any capacity stated in amp hours (or any fraction of) is meaningless without knowing the voltage at which it's measured.

 

That capacity could be rated at 12 volts.  It could be rated at 5 volts.  It could be rated at 24 volts.  It could be rated at 3.2 volts (the nominal voltage of LiFePO4 cells), or it could be rated at 3.8 volts (the nominal voltage of lithium ion cells).  The capacity of the battery would vary wildly, based on which answer is correct.

 

If you can find a battery rated in watt hours, instead of amp hours, it would be possible to determine the actual capacity.

 

But in this case, it looks like the seller is far more interested in flashy pictures and quotes, than actual information.  I would avoid this battery like the plague - for any purpose. 


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#19 Vinnyvent84

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Posted 04 March 2024 - 01:44 PM

From the information at that link, it is literally impossible to know the actual capacity of the battery.  Any capacity stated in amp hours (or any fraction of) is meaningless without knowing the voltage at which it's measured.

 

That capacity could be rated at 12 volts.  It could be rated at 5 volts.  It could be rated at 24 volts.  It could be rated at 3.2 volts (the nominal voltage of LiFePO4 cells), or it could be rated at 3.8 volts (the nominal voltage of lithium ion cells).  The capacity of the battery would vary wildly, based on which answer is correct.

 

If you can find a battery rated in watt hours, instead of amp hours, it would be possible to determine the actual capacity.

 

But in this case, it looks like the seller is far more interested in flashy pictures and quotes, than actual information.  I would avoid this battery like the plague - for any purpose. 

So it actually is stated in the product details of that page, I took a screenshot for you below, its located at the very bottom. It states its 28v but as other users here explained that seems dubious considering the math doesnt add up on how many charges it provides for different items in the description. 

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  • Screenshot 2024-03-04 at 1.41.31 PM.png


#20 WadeH237

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Posted 04 March 2024 - 02:10 PM

So it actually is stated in the product details of that page, I took a screenshot for you below, its located at the very bottom. It states its 28v but as other users here explained that seems dubious considering the math doesnt add up on how many charges it provides for different items in the description. 

I don't know what to make of that 28v number.  It's completely nonsensical.  I am sure that those USB outputs are 5v.

 

They absolutely no not say anywhere that the 27000mah number is the capacity at 28v - and honestly, I would be shocked if that were actually the case.  If they actually had 27000mah at 28v, they would have a 63 amp hour battery at 12v.  Elsewhere, they state the weight at 1.56lb.  For reference, I have a 105 amp hour LiFePO4 battery at 12v, and it weighs about 20lb.  If they could achieve 63 amp hours at less than 2lb, they'd be shouting it from the mountain tops.  They'd also have the number "750 watt hours" in a 100 point font.  They'd likely be candidates for a Nobel prize.

 

Working backwards, the energy density of my battery is about 5.25 amp hours per pound.  If they have about the same energy density, they'd have about 8 amp hours at 12v.  And actually, I think that actually tells us the voltage at which the capacity is rated.  If they are using Li-ion batteries, the nominal cell voltage is 3.7v.  27 amp hours at 3.7 volts is the equivalent capacity of 7.9 amp hours at 12v., and that's not likely a coincidence.

 

So what these marketing shysters are doing is to use the nominal single cell voltage to produce the highest plausible capacity in amp hours.  Then they are tossing about some other voltage numbers for who knows what reason.  Certainly the 28v number has no technical significance whatsoever.  The cynical person in my suspects that they are trying to mislead their customers.

 

I maintain that the best thing to do is to run far and fast away from this product.  And do not even consider buying a battery where they don't either give you a capacity in watt hours (which is likely about 95 watt hours) or amp hours at 12v (which is around 7.9 amp hours at 12v).  Without that information, you are literally buying something where they are hiding the single most important specification.

 

Oh, and to answer your question in the very beginning of the thread (based on my inference above), if you are using 55 watts, this battery would have an expected life of just over 100 minutes.

 

What you really want is something like this.  That would give you around 9 hours of use at your 55 watt rate.




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