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Looking for battery for telescope to replace FLA that is too small

Linwood

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Jan 5, 2022
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Hi. New here, and I hope it is OK to ask about just batteries and not solar.

I do occasional astronomy from dark sites without power. I set up a Group 27 Lead Acid deep cycle battery and for a while it was adequate, but I am reaching the point where my nightly usage is way over what it can provide. Due mostly to imaging in a swamp (Florida, US) I have a lot of dew strips to keep equipment clear, and it plus computer and router and such add up to about 7-8A draw at 12(ish) volts, and since Florida winters are when I image, that's about 12-14 hours (to allow some set up time and tear down).

So if I should draw 50-60ah from the battery I'm pushing double that. I got low voltage alarms the last time by about midnight.

I do not want to build my own battery from cells (I have too many incomplete projects already).

I'm looking at pre-made 150ah LiFePO4 batteries. I could drop them into my current battery box I think literally without modification. The existing meter I have on it is a watt hour meter, so I think I can use that for a SOC indicator (vs voltage), and I think it physically fits. I should be able to draw 90-100ah from it on a full night without issue, and I would return home and be able to recharge at leisure (or even if remote would find power and do so at 20A or so with plenty of time even if I image the next night).

200ah batteries are a lot larger and I think bigger than I need; 100ah is cutting it too close I think. Using two or more to combine seems a complication I do not need, plus makes using a battery box for transport a bit more complicated.

So first question: Is that a sane approach?

150ah pre-made are less readily available, but I found one from Eco-Worthy that is relatively inexpensive. I cannot find many reviews, but what I find is not bad. Anyone have any specific thoughts on that?

Or a recommendation of others?

The Battleborn (as an example, but some well known brands also) is about 2.5x as expensive. Reviews indicate it has better waterproofing and cold charge protection, neither are really an issue for me.

Most (seemingly) independent youtube reviews focus on Chins, Zooms, and a few others, I can find none for this. Or any 150ah ones (other than Battleborn and similar).

So... I welcome any general guidance.

Linwood
 
Welcome to the forums!

I do occasional astronomy from dark sites without power.
I'm so sorry to hear that! Between mosquitos, nocturnal alligators, the hobby's enchanting operational hours, humidity, and your friends expecting images to look like they came from Hubble it takes a real love to stick with it. ;)

I set up a Group 27 Lead Acid deep cycle battery and for a while it was adequate, but I am reaching the point where my nightly usage is way over what it can provide.
You could just get a second LA battery and put it in parallel to double your hours.

I'm looking at pre-made 150ah LiFePO4 batteries.
Will has a number of tear-down videos on these, the good news is the biggest complaint is typically the low-temperature cutoff ... which shouldn't bother you since they can be recharged inside where it's warm. So you just need something where the insides aren't substandard junk.

So first question: Is that a sane approach?
For the battery yes. For the hobby, not too sure... perhaps you can post some of your images? ;)

I cannot find many reviews, but what I find is not bad. Anyone have any specific thoughts on that?
It's hard to trust the reviews on sites like Amazon or youtube for batteries, most don't know what they're talking about. I'd stick with one of the ones Will took a cutoff saw to where you can see the inside build quality.

The Battleborn (as an example, but some well known brands also) is about 2.5x as expensive.
Battleborn is supposedly good quality... also has a 10-year warranty (so do Chins). Sok has a seven-year warranty.

I do not want to build my own battery from cells...
Will builds one of his Milk crate batteries from cells in less than 15 minutes. The cheapest way to go and the best quality you can get because you know you built it with quality parts. You don't have to use a milk crate, you can get battery boxes (or use the one you already have).
 
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I'm so sorry to hear that! Between mosquitos, nocturnal alligators, the hobby's enchanting operational hours, humidity, and your friends expecting images to look like they came from Hubble it takes a real love to stick with it. ;)

For the battery yes. For the hobby, not too sure... perhaps you can post some of your images? ;)

Thank you, @svetz, for the thoughts.

Hobby first: Yes, it can be challenging, but hobbies with no challenge seem rather pointless. You asked to see photos, here are what I have so far (in about 1.5 years):

https://www.captivephotons.com/Photography/Astrophotography/

Certainly takes longer to accumulate images than shooting birds. :)

You could just get a second LA battery and put it in parallel to double your hours.

Will has a number of tear-down videos on these, the good news is the biggest complaint is typically the low-temperature cutoff ... which shouldn't bother you since they can be recharged inside where it's warm. So you just need something where the insides aren't substandard junk.

It's hard to trust the reviews on sites like Amazon or youtube for batteries, most don't know what they're talking about. I'd stick with one of the ones Will took a cutoff saw to where you can see the inside build quality.

Using a second LA battery - yes, twice the weight/size to haul, but a possibility.

Reviews: I was not particularly trusting Amazon (though ones with a few hundred reviews for pricy stuff are probably less likely to be fake), but more the youtube testing/tear-down ones.

Is Will the Will Prowse? Yes, I've seen many of his, and that is one place I was looking for what seemed objective advice.

I have not seen any Eco-Worthy from him, nor any from vendors that had 150ah (other than Battle Born). Honestly before I pay Battle Born prices (at 2.5x as much) I will probably go with the second LA.

Battleborn is supposedly good quality... also has a 10-year warranty (so do Chins). Sok has a seven-year warranty.

SOK seems to skip from 100 to 200, no 150 (many of the brands do). I thought Battle Born had one but their web site right now shows none, so maybe I imagined it. I think it's the 150 aspect that is throwing me, lots of brands with 100ah reviewed to choose from, not so much 150.

Will builds one of his Milk crate batteries from cells in less than 15 minutes. The cheapest way to go and the best quality you can get because you know you built it with quality parts. You don't have to use a milk crate, you can get battery boxes (or use the one you already have).

Thank you for that pointer, I had not seen it and that is a definite possibility, and has a bit of unexpected synergy. At home (not at dark sites) i have a hand truck with three milk crates semi-permanently mounted, with all the counterweights and power supplies and cables I need for the back yard, so I can roll it out all at once. I do not use it at a dark site, but adding a battery "crate" would feel very familiar. I may look into that, especially since he had a recommended BMS.

My main reluctance is the physical packaging, to have something I can pack up and take with, and handle easily. It is why the drop-in Group-27 size of the 150's is attractive as well, that battery box I built works just fine. But a Milk Crate would work just fine also.

But before I leave the 150 behind -- any specific advice, or tear down videos I missed, on Eco-Worthy? Are they well known? Good/bad?
 
I did a more careful measurement last night of my lower-power telescope setup, and on a relatively dry night (more relative humidity means more power for dew heaters), and got 48ah. Adding in 2 more amps for the larger dew heaters on my larger scope as an estimate I'm at 76AH, which considering the dark site (in the everglades) is always more damp, is getting me in the 85ah range at a guess.

Considering there's a lot of variability in all this, from relative humidity to how much the computer works (plate solving, focus runs, etc.) I still think 100ah is cutting it too close, even ignoring that running 90ah out of a 100ah battery is not great for it, the last thing I want is to run dead at 30 minutes before dawn and not be able to complete (I shoot flats at dawn, which are necessary for calibration, so I'm not so much losing a few shots as losing the ability to calibrate all shots).

So I really think I'm on the 150-200ah path.
 
... You asked to see photos, here are what I have so far (in about 1.5 years):
My God! It's full of stars!! Bowman jokes aside, You've got some serious skills ... it's definitely not crazy and I thank you for braving all those dangers and sharing. Wow! Now I need to figure out how to follow you.

Is Will the Will Prowse?
Yes. He runs these forums.
I may look into that, especially since he had a recommended BMS.
Check his DIY Solar Blueprints. Will keeps them updated as he replaces components as he finds better quality/prices. Techniques in the videos don't go out-of-date, but actual hardware does.
My main reluctance is the physical packaging, to have something I can pack up and take with, and handle easily.
Some of the battery boxes made for boating have great handles and come in standard sizes.

You can find plain jane ones to ones with USB ports, power meters, overcurrent protection, etc.

Heck, design your own with red led lights and fund your hobby selling them at the dark site, you can't be the only one in need of more power ; -)
71-aC+zNX8L._AC_SL1500_.jpg
But before I leave the 150 behind -- any specific advice, or tear down videos I missed, on Eco-Worthy? Are they well known? Good/bad?
Sorry, about all I know of the Ecoworthy is they don't make their own stuff (not even the weather instruments), they resell. On the upside, they seem to have an eye for price and quality on the weather instruments at least, a lot of people like them. The amazon comments said they had a split warranty for the battery, 1 year and 5 years based on what happened. Considering it takes longer to charge one up than build it from the big rectangular cells I'd go that way (I built one the hard way with those cylindrical cells, see Peak Jump Start before I knew better, but it has a nice case with power meter, switches, lights, USB, and aligator clamps).
 
I would get a pair of 100Ah drop ins from one of Will Prowse’s reviewed sellers. That way you have a huge cushion, and selection.
Personally… I would order several premade 100Ah cell bundles, and a jbd BMS, and bolt together a 200Ah pack that fits in the box you have, and be done with it.

I think it was battery depot, or similar that sells the packs.
 
Thanks for the compliments on the images, that's almost all from my back suburban yard with a LOT of light pollution. You just have to take a LOT of images and combine them together. They get better by the square root of the number of images.

I would get a pair of 100Ah drop ins from one of Will Prowse’s reviewed sellers. That way you have a huge cushion, and selection.
Personally… I would order several premade 100Ah cell bundles, and a jbd BMS, and bolt together a 200Ah pack that fits in the box you have, and be done with it.

I think it was battery depot, or similar that sells the packs.

I'm just starting to read about how to build and BMS's... if I go 8 cells for 200ah (2x4 connections at 12v) do I need two BMS's, to have the proper balance control? I understand with the drop-ins that I can just parallel them, but it had me wondering about 8 75ah cells for 150h also. Or even 12 x 50.

Also, how relevant during discharge (at 10a or so over 12-14h) is airflow for cooling (I am in florida so some nights may be in the 75F range, never below about 40F). Was thinking of some of the Rigid (Home Depot) stackable cases, I have a bunch of those now for telescope parts, etc. I think I could get some of the 180ah on one of his recommended sites, lay them in 2 stacks, and have plenty of room for a BMS as well. That they stack and fasten together is very convenient, can make towers of cases in the back of the SUV (counterweights on the bottom and they won't fall over).

I could open them up for charging to have better airflow, but due to all the dew would not really want them open at night.
 
Airflow for cooling cells comes into play with high amperage discharge… your load is minimal, and won’t cause much heating at all. Don’t worry about it. Now, when it’s in the 90’s at night, battery degradation can be an issue, but aside from filling the box with ice packs, or installing it in a refrigerator (which would need more batteries) there isn’t much that can be done about it.
 
@Linwood, don’t overlook the fact that LiFePO4 have at least 80% of their capacity useable as opposed to 50% with your FLA.

I might suggest starting with a 100 Ah and see if that works.

If not you could easily parallel another 50 Ah to get exactly where you want to be.

Either way, your back will appreciate the lighter load. ?

FWIW, I run LiFePO4 in a shipping container in AZ at times with temps above 100 degrees F. This is for an off grid Amateur radio station. At times I also discharge it below freezing (NEVER charge it that way).

My oldest LiFePO4 is about 7 or 8 years old and I don’t perceive any performance degradation despite this occasional abuse.
 
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I would get a pair of 100Ah drop ins from one of Will Prowse’s reviewed sellers. That way you have a huge cushion, and selection.
Personally… I would order several premade 100Ah cell bundles, and a jbd BMS, and bolt together a 200Ah pack that fits in the box you have, and be done with it.

I think it was battery depot, or similar that sells the packs.
Ok, I found the source for the cell packs.

 
So my best guess right now is I'm around 80ah which is your 80%, so no room for error really.

But some simple minded questions:

If I have drop in batteries, I assume I need to parallel them when fully charged, not wait for one to run mostly down and parallel? Won't I have a high current draw as the more-discharged sucks power from the more charged? Or is their flat discharge curve such that this is moot?

And I assume I should separate to charge? I.e. not build them together in a box?

I'm leaning more toward a solution that's larger thank I need rather than smaller, if I can't hit the sweet spot; less need to revisit.
 
Ok, I found the source for the cell packs.
Wow, that is pretty cheap. This is making me think also if I get a USB version I can probably build a little ESPhome device to record battery status in MQTT; i already have that integrated with the telescope gear for tracking weather, so I could track SOC (or can I with the BMS?) and shut down at 85% or some such, i.e. gracefully shut down the telescope using its automation.
 
So my best guess right now is I'm around 80ah which is your 80%, so no room for error really.

But some simple minded questions:

If I have drop in batteries, I assume I need to parallel them when fully charged, not wait for one to run mostly down and parallel? Won't I have a high current draw as the more-discharged sucks power from the more charged? Or is their flat discharge curve such that this is moot?

And I assume I should separate to charge? I.e. not build them together in a box?

I'm leaning more toward a solution that's larger thank I need rather than smaller, if I can't hit the sweet spot; less need to revisit.
What he meant by 80% is for lithium maximum use life is around 80% for lead acid, maximum use life requires a maximum 50% discharge…
Meaning your 80Ah lead acid can only discharge 40Ah before damage to the battery…
With lithium, a 100Ah pack can safely discharge 80Ah before cycle life gets impacted…
 
What he meant by 80% is for lithium maximum use life is around 80% for lead acid, maximum use life requires a maximum 50% discharge…
Meaning your 80Ah lead acid can only discharge 40Ah before damage to the battery…
With lithium, a 100Ah pack can safely discharge 80Ah before cycle life gets impacted…
I understood. And I'm saying last night's measurements put me right at about 80% of the 100ah LiFePO4 that are readily available. But my observing kit has grown a lot over the last year. I would like to say I am maxed out, but... well, things happen. So I do not want to plan for 80AH (100ah capacity), I think it cuts too close. The now room for error comment related to "error in planning how much I need" not "how much I can draw from it".

And yes, I had about a 110ah LA and realized very quickly first time out it would not make it through the night, or not survive repeated use even if it did.
 
Wow, that is pretty cheap. This is making me think also if I get a USB version I can probably build a little ESPhome device to record battery status in MQTT; i already have that integrated with the telescope gear for tracking weather, so I could track SOC (or can I with the BMS?) and shut down at 85% or some such, i.e. gracefully shut down the telescope using its automation.
They also sell the individual cells… same price which is annoying. But you could buy the cells, and some nickel strip and a spot welder, and make up whatever size bank you need… bolt up their BMS and have a custom sized battery ready.
 
May I ask about this drawing, any issues or major things I am omitting?

This is based on these batteries (160ah x 4): https://www.electriccarpartscompany.com/163ah-calb-batteries-l173f163b

And this BMS: https://overkillsolar.com/product/bms-120a-4s-lifepo4/

And drawn roughly to scale. I imagine a sheet of plywood the size of the case, put one pair of batteries under, one over, strapped somehow to it, with the BMS and terminals on top. That way nothing can shift during handling of the case. I'll cut a hole for powerpole connectors going out (fused), and nothing else needed, no inverters, etc. Just 12v out is all (I may add a buck converter to keep it up near 13.8 or so, as the mount is happier with a couple more volts). Maybe foam on the bottom to give it vertical support against the top foam.

I'll open it to charge, but leave it closed in use.

I read about active/passive balancing, but I assume passive in the BMS is fine for new cells. Is there anything else needed, or is it just this simple?

It looks like with a blue tooth module I get SOC and BMS info on my phone, so no explicit gauge needed, and I do not really see a need for an on/off switch.

One thing I like about this is I have 4 of these cases already, adding a 5th to the stack takes no additional floor space in the SUV, plus they are easy to handle, I have about 40# in one now for counterweights without problems, and this is going to be lighter than that.


casebuild.jpg
 
As long as you build the cells in a compressed manner, or use flexible bussbars between the cells that would be an easy build.
 
Ah, I am very glad I asked. Though now I am confused. What I read seems to imply I must always compress these rectangular cells or risk delamination (https://www.currentconnected.com/learning-center/lc-stor/llfp-comp/), but you said "or" use flexible bussbars (I was thinking of just some #6 or so copper cable with lugs).

I will not have room for a compression rig on each pair, the case is pretty thin.

But why did you say "or", are there times I do not need compression?
 
As long as you build the cells in a compressed manner
Isn't compression overkill for this? I think compression is for "hypermiling" when you have lots of cells, from the wiki:

In experiments, Lithium-ion capacity fade after 1200 cycles for 0, 5, and 15 psi compression was found to be: 11%, 8.8%, and 8.4%.
So, lithium ion data, but compression only buys you 2.6% less fade over 1200 cycles? So not worth it for 4 cells IMO.
In the batteries Will cuts apart, I haven't seen any compression, just room for expansion (there's a ~6% volume change for 0 to 100% SoC, flexible, diagonal bus bars, or compressible separators between cells reduce the strain on terminals ).

... I'm saying last night's measurements put me right at about 80% of the 100ah LiFePO4 that are readily available.
I wouldn't worry about draining your LFPs to 90%, at your low C-rate the degradation isn't that many cycles. Assuming you cycled them once per night, 2800 cycles is still over 7 years (they don't stop working, capacity just drops a little year over year), so 15 years if you do cycle every other night. By then calendaring aging may have caught up to them. Everyone's a bit different, but here's a generic & conservative chart to give you some ideas....

tumblr_nvv9j0IgIc1qa2swjo1_1280.gifv
 
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