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Power Options (For OCD Personality)

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#1 HSTeach

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Posted 16 September 2021 - 10:58 AM

Hello,

I was wondering if anybody can help me with power options for my AVX mount and ASI Air Pro.  I am using a ZWO 385 camera (Doesn't really need power)  I understand that I need 12v/2a for the AAP and 12v/3a for the AVX mount.  Is there a small portable battery pack that can handle this?  Also, can I run one 5.5/2.1mm cord from the battery and split it into two male ends to feed the AAP and AVX?.  I have read that the mount and AAP would best be served with separate power supplies/cords.

 

Ultimately, I am trying to keep a clean power setup with minimal cords and smallest possible battery size.  I only do EAA for several hours and don't need power for the whole night.  I see that the Powertank pro might work but wanted to get more input.

 

Thanks,

Phil



#2 lzagar

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Posted 16 September 2021 - 11:33 AM

Phil,

 

I use this rechargeable battery.

 

https://www.amazon.c...J/ref=emc_b_5_i

 

It comes with a dual power cable and recharger and has plenty of power for both your mount and camera.  It also has a 5 volt USB port.

 

Lee


Edited by lzagar, 16 September 2021 - 11:34 AM.

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#3 c8se

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Posted 16 September 2021 - 11:49 AM

I use a harbor freight portable battery @ 12v/ 17 Ah.  That would power your system for approx 3.5 hrs.  It has two 12 v cigarette ports and one 5 v USB port, work light (white), and charger.  I’ve used mine for over 1.5 yrs and still going strong, just keep it topped off. $50.



#4 AaronH

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Posted 16 September 2021 - 07:34 PM

Just pay attention to battery chemistry.

 

I have two lithium battery packs...

 

One has conventional Lithium cells, and has voltage that starts at 12.6V, but drops to 9V as it discharges. I don't ever let it get more than half-discharged, because i don't want voltage to drop below 11V, in case devices get unhappy. However, some mounts don't like anything at all below 12V, which would be very limiting for this kind of battery.

 

The other battery pack has LiFePO4 cells. It stays at 12.8V the whole time until it's empty and voltage drops off a cliff.

 

The LiFePO4 battery is bigger, higher-capacity, and more expensive. However, I feel more comfortable using it due to its stable voltage.


Edited by AaronH, 16 September 2021 - 07:40 PM.

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#5 ks__observer

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Posted 17 September 2021 - 01:47 AM

Just pay attention to battery chemistry.

 

I have two lithium battery packs...

 

One has conventional Lithium cells, and has voltage that starts at 12.6V, but drops to 9V as it discharges. I don't ever let it get more than half-discharged, because i don't want voltage to drop below 11V, in case devices get unhappy. However, some mounts don't like anything at all below 12V, which would be very limiting for this kind of battery.

 

The other battery pack has LiFePO4 cells. It stays at 12.8V the whole time until it's empty and voltage drops off a cliff.

 

The LiFePO4 battery is bigger, higher-capacity, and more expensive. However, I feel more comfortable using it due to its stable voltage.

 

Second Edit:

 

So looking at the graph in the link below, a lead acid will drop below 12v around the 50% discharge point, and a lithium around the 80% discharge point.

https://www.zwerfcat...ium-hybrid.html

 

LiFePO4 appears you can discharge down to around 90%:

https://www.batteryp...rge-curves-faq/

 

And it seems these numbers are roughly accurate but dependent on temperature and discharge rate.

https://www.batteryp...rge-curves-faq/

 

I just picked up this lithium-ion power bank that I am hoping will run my system:

https://www.amazon.c...product_details

 

But now you got me thinking about the LiFePO4 and if there is a significant benefit to upgrading to a LiFePO4.

 

 

Sorry the graph I looked at was for the Lithium-Manganese -- not lithium-ion.

According to the graph in the link below, lithium and LiFePO4 both drop off the clip around the same 90% capacity-used point -- though LiFePO4 is supposedly the flattest curve.

https://www.batteryp...rge-curves-faq/

It seems you can probably safely run lithium down to around 20% and maintain voltage needed for one's mount and systems.


Edited by ks__observer, 17 September 2021 - 02:14 AM.


#6 AaronH

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Posted 17 September 2021 - 02:37 AM

Lead-acid batteries discharge in a fairly linear fashion. But they usually start with an open-circuit voltage (OCV) of around 13-14V, then by the time they get much below 12V, you really want to charge them.

 

"12V" lithium ion battery packs usually start with an OCV of 12.6V (3 x 4.2V), then quite quickly drop down to around 12V. They then very gradually, over the main part of their discharge curve, trend towards 11V or so (around 3.6V per cell), then drop off rapidly. This is fine for many devices, and I've used batteries like this with no worries, provided I don't run them too low. But their characteristics can particularly be an issue with mounts like the EQ6-R, which really demand a minimum of 12V. Even at 80% capacity, these batteries can start causing issues with picky devices.

 

"12V" LiFePO4 cells start with an OCV 14.4V (4 x 3.6V), but extremely quickly drop to around 12.8V (4 x 3.2V), and just stay there, with only a few percent variance as they discharge. Then the voltage drops off a cliff as they're just about flat.


Edited by AaronH, 17 September 2021 - 02:52 AM.

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#7 AaronH

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Posted 17 September 2021 - 02:44 AM

So looking at the graph in the link below, a lead acid will drop below 12v around the 50% discharge point, and a lithium around the 80% discharge point.

https://www.zwerfcat...ium-hybrid.html

That article is almost certainly talking about LiFePO4 batteries (they're the main type sold as "lithium" lead-acid replacements). The discharge curve matches that for LiFePO4 chemistry.

 

EDIT:

 

Here's an article with a rough Li-ion vs LiFePO4 discharge curve comparison (about two thirds of the way down):

https://techmoment.n...vs-lithium-ion/

 

You'll be fine with a Li-Ion battery pack for most purposes. I used one for most of this year until I picked up a bigger LiFePO4 one.

 

The only things to consider are:

- If you're using a larger Synta mount like an EQ6, then it can be very picky about low voltage. It's not going to be happy if it drops below 12V.

- Don't run your battery down to flat. Don't do this anyway, regardless of (memoryless) battery chemistry.

- The "charge" indicator can be rough and ready. "Half charge" can actually mean "almost flat" on many battery packs.


Edited by AaronH, 17 September 2021 - 03:15 AM.

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#8 ks__observer

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Posted 17 September 2021 - 09:20 AM

Great info -- thanks!

I use an EQ6R.

I found a graph for Lithium-Ion that is encouraging -- hits 12V at 30% capacity at 0deg C and hits 12v at 25% capacity for 10deg C (50deg F):

https://www.research...fig1_322836042 

 

I hope to run some tests of my own soon on my set-up.



#9 Rickycardo

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Posted 17 September 2021 - 12:03 PM

Anyone use a Jackery product? I'm looking at those for remote power for a small laptop until my AAP+ comes. I know they're expensive I'm wondering about how good they are.



#10 CA Curtis 17

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Posted 17 September 2021 - 03:36 PM

I have used Jackery's 500 and 1000Wh solar generators over the last year and would have no problem recommending them.  Yes Jackery is one of the more expensive solar generator manufacturer's but when you look at the components inside you will see they are very high build quality and have been around for a dozen years.  In contrast, there are lots of battery tear down videos which show how poorly manufactured some of the cheap solar generators or bare lithium batteries are made.  There are also some less expensive ones which seem to be very well made based upon the tear down videos I have seen.  Check before you buy.

 

I have tested several different LiNiMnCoO2 solar generators and LiFePO4 batteries over the last year plus both in my home observatory and in the field.  I have shared a lot of what I found in the presentation I gave on The Astro-Imaging Channel back in June.  Skip ahead to ~ 31min into the presentation to see the part about Li batteries and solar generators.

 

A few comments relative to the information in some of the above posts:

 

1.  First, all of the solar generators and lithium batteries I have seen on the market have a Battery Management System (BMS) imbedded inside.  If you find one that does not, avoid it.  The BMS is in there to protect the battery from misuse, damage, fire etc.

 

2.  Because of the BMS all solar generators and lithium batteries are designed to be discharged until the BMS shuts down the output.  This will happen when 100% of the manufacturer's capacity specification has been reached.  There is no need to shut the power supply down at 80% or 90% of capacity.  The BMS will not let the individual cells inside be discharged below a safe minimum to prevent damage to the cells and loss of longevity of the battery/solar generator.  In other words, while most NMC power sources specify 500+ full discharge cycles and most LiFePO4 power sources specify >= 2500 full discharge cycles, you will not reduce the number of cycles by running the power source until the BMS shuts it down.  But yes, you can increase the number of discharge cycles of lithium batteries by stopping before full discharge.  But think about how long it will take you to use 500 full discharge cycles.  Remember, these batteries are only spec'd for a 10 year lifetime.  Also, if you use the full capacity for the 500+ cycles, the battery will not be dead, but will have had its capacity reduced to ~ 70 to 80% of its original value.  So, it will still have life.

 

3.  While the discharge curve of NMC cells falls off faster than LiFePO4, all of the power sources using NMC that I am aware of, such as the Jackery solar generators, regulate the output voltage.  As an example, I measured the output voltage of the Jackery 500 from 100% SOC until 0% SOC with a power load of 60w.  The output voltage started at 12.9V and finished at 12.8V when the BMS shut the output down and the Jackery's LCD showed 0% capacity left.  This is not unique to the Jackery 500.  This is how they are designed to work.

 

4.  I have just measured the voltage discharge curves of two different LiFePO4 batteries which commonly are not voltage regulated.  I tested one from Battleborn and the other from Bioenno Power.  The Battleborn 100Ah battery maintained the voltage above 12V until it discharged to 95% of its full capacity.  Interestingly, that happened after delivering 105.5Ah of power wihich is 5.5% above the battery's spec.  It happens because Battleborn builds their batteries with cell packs that exceed the rated spec by ~ 4 to 8%.  The Bioenno 50Ah battery maintained the voltage above 12V until it discharge to 91.5% of its full capacity.  Measurements were at room temperature which was ~ 85 degrees F.  

 

5.  I have also used a Talentcell battery like the one Lee linked to above.  Mine is 8.5Ah capacity and has been used when I need much less energy such as when I am using a very simple EAA setup for outreach.  As pointed out, they have some convenient output options including 5V, etc.  It is hard to find complete details on the small form factor Talentcell batteries so it is not clear which chemistry they use except in the few they indicate are LiFePO4.  I have seen the inside of one of their batteries and it did have a BMS as I expected.

 

Hopefully this helps others thinking about lithium power solutions.

 

Best Regards,

Curtis


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#11 AaronH

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Posted 17 September 2021 - 09:27 PM

This is the Li-Ion device I have that runs down to a fairly low voltage as it discharges:

https://www.jaycar.c...centre/p/MB3748
 

Jackery devices aren’t widely available here in Australia, so it was the most reasonable alternative I could find at under AU$200 street price when I was just looking for a simple unit to run an AZ-GTi and OSC camera, but it does suffer from voltage drop as it discharges. To be fair, the manual makes this clear: “The 12V DC output ranges between 9V~12.6V … due to chemical characteristics of the battery”. In retrospect, I should have just invested in a better unit to begin with.

 

Better-made devices likely have better internal circuitry to avoid these issues, so I started looking at those, but availability is a problem here. Then I noticed that affordable LiFePO4 options have now hit the market, so I just went for that option when it was time to upgrade.

 

This is the particular unit I upgraded to. It didn’t look to shabby for AU$550 (US$400), and has worked well:

https://www.snowys.c...h-power-station

 

That said, if I was in the US, I would have just gone for a Jackery option. They seem tried and tested by plenty of users.


Edited by AaronH, 17 September 2021 - 09:31 PM.



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