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Old 05-04-2021, 08:21 AM   #1
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LifePo4 280Ah for 620$

Hey,
I know that some people just want plug n play, but if you donít mind just a bit more tinkering you can save a lot of $.

Here are some links for 280Ah LifePo4 batteries

https://m.aliexpress.com/item/100500...source=admitad

Here is the BMS link

https://overkillsolar.com/product/bms-120a-4s-lifepo4/
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Old 05-05-2021, 09:21 AM   #2
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Doesn't have to be fancy to be effective

This is my battery setup. Nothing fancy and after a 1.5 years they are still testing at 100%. This is a 200Ah LifePo4 set up. Very similar to the one you can now get for less money. The industry is moving very fast and it doesn't make any sense in spending thousands of dollars on batteries that will be eclipsed by new tech in the next 5 to 7 years.
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Old 05-10-2021, 08:46 PM   #3
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Too bad I just received two 100 AH LiFePo batteries from Renogy ($1600 for the pair). Otherwise I might have gone this route. Looks like a great option. Maybe next time for me. I am sure I will like the Renogy batteries, but the cost difference is significant.
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Old 05-11-2021, 02:36 PM   #4
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Looks to me like 280 ah. at 3.2 volts. At 12.8 volts, that would be 70 ah. Does that still look like a good deal?

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Old 05-11-2021, 03:18 PM   #5
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Looks to me like 280 ah. at 3.2 volts. At 12.8 volts, that would be 70 ah. Does that still look like a good deal?

Bruce
Not correct.

Batteries wired in series add their voltage but amp-hrs stay flat, so 4 of them in series would be 12.8V and still 280ah.
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Old 05-11-2021, 03:41 PM   #6
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Not correct.

Batteries wired in series add their voltage but amp-hrs stay flat, so 4 of them in series would be 12.8V and still 280ah.
Note that the somewhat-confusing site is showing 4 modules of the 3.2v batteries for $471 (plus the BMS, to get the OP's $620) so at the price from the original post it would be 4 of the things to wire up in series and make a 12v array.
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Old 05-11-2021, 03:57 PM   #7
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Not correct.

Batteries wired in series add their voltage but amp-hrs stay flat, so 4 of them in series would be 12.8V and still 280ah.
Sorry. I'll pay more attention next time.

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Old 05-11-2021, 05:27 PM   #8
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Originally Posted by AstroBruce View Post
Sorry. I'll pay more attention next time.



Bruce


Hey there,

If you want some more info check out mobile-solarpower.com. This guy has really helped me understand how these packs work.

Crazy that you can get so much product for very little money these days. It will continue like this for a very long time!
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Old 05-11-2021, 07:24 PM   #9
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Crazy that you can get so much product for very little money these days. It will continue like this for a very long time!
There is a huge downside to "rolling your own". When you go with one of the recognized brands, you're paying for the R&D that they've put into the logic and electronics of their Battery Management Systems...and you're paying for the advanced materials of construction--in particular, the separator membranes.

When a cell fails internally (for example, a short between anode and cathode) it turns into a molten ball of inextinguishable fire. Before it gets to that point, you want the membrane to melt closed and stop the chemical reaction...but before that, you want the BMS to recognize any problems and shut down the reaction prophylactically. I've run experiments in the lab as well as observed the aftermath of real-world lithium batter failures. I'm impressed how much heat these things can generate! Personally, I would sleep better knowing the batteries under my bed can only fail in a safe condition.

I'm not saying "don't go with a build-your-own-battery-system". Indeed, you can save money and build something that exactly conforms to the space you may have available. Instead, be sure to understand exactly what technology you're buying and be sure you know how it all plays together so you can consciously manage your risk profile.
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Old 05-11-2021, 08:16 PM   #10
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There is a huge downside to "rolling your own". When you go with one of the recognized brands, you're paying for the R&D that they've put into the logic and electronics of their Battery Management Systems...and you're paying for the advanced materials of construction--in particular, the separator membranes.



When a cell fails internally (for example, a short between anode and cathode) it turns into a molten ball of inextinguishable fire. Before it gets to that point, you want the membrane to melt closed and stop the chemical reaction...but before that, you want the BMS to recognize any problems and shut down the reaction prophylactically. I've run experiments in the lab as well as observed the aftermath of real-world lithium batter failures. I'm impressed how much heat these things can generate! Personally, I would sleep better knowing the batteries under my bed can only fail in a safe condition.



I'm not saying "don't go with a build-your-own-battery-system". Indeed, you can save money and build something that exactly conforms to the space you may have available. Instead, be sure to understand exactly what technology you're buying and be sure you know how it all plays together so you can consciously manage your risk profile.


If you have information about any battery failures with LifePo4 cells paired with a great BMS I would like to know.

I run this configuration and if I have missed something in my research please let people know about any problems.
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Old 05-11-2021, 08:59 PM   #11
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Originally Posted by Humboldt Air View Post
If you have information about any battery failures with LifePo4 cells paired with a great BMS I would like to know.

I run this configuration and if I have missed something in my research please let people know about any problems.

TL;DR
If you're happy with your safety analysis, then go for it.


The Longer Version
My comments should only be construed as a general warning; I have no specific knowledge on these particular batteries or the BMS, so I cannot comment on them.

In pre-COVID days when we could still travel freely throughout the world, I volunteered on the technical team for a global contest (for both high school and university entrants) to see who could devise the most energy-efficient mode of transportation. One class of this competition was battery-powered vehicles, and the students either had to build their own batteries (or purchase on the market) and had to build their own motor controllers. Part of my duties was to ensure the Li-battery entrants were safe to operate, so we did a detailed inspection of every vehicle. In particular, we made sure the students understood the technology they were playing with. If was fair game to use a battery with a built-in BMS, but they had to be able to explain how it worked--physically and electronically. If they could convince me they knew their system, then they could get out on the track. Due to limited budgets, many schools opted for cheap (i.e. offshore) batteries and BMS. We had to disqualify many of them, because they could not produce documentation on their systems--in many cases, the manufacturers or sellers did not make this information available. Occasionally, we would disqualify a team even with full documentation if their setup was deemed too risky, from an HSE perspective. Because of this experience, I am acutely aware that it may be hard to procure sufficient documentation to be able to verify BMS and Li-ion cell configurations are bounded within the envelope of safety for the intended application.

As for public LI-ion battery failures, the ill-fated Auxiliary Power Unit in Boeing 787 Dreamliner comes to mind. While those batteries used a slightly different chemistry, nether Boeing nor the FFA could identify the failure modes that grounded the entire 787 fleet for quite awhile in the last decade. There is evidence that sometimes a single cell would fail (short circuit) and then heat up the entire battery, causing other cells to outgas. They found some irregularities with the BMS operation. They even suspect some the the battery-powered APUs could have been wired incorrectly. (These potential root causes are mostly independent of battery electrochemistry, so these are relevant data for this discussion.)

While we will never know how the Boeing lithium ion batteries failed, you can be sure that the battery chemistry, components, and construction were analyzed and tested to understand their operating windows. The BMS would have been tested and modeled and pushed to failure during design. The APU itself would have had to have performance guarantees. But yet, somehow these systems failed--multiple times! If it can fail an American-made commercial aircraft with all their built-in redundancies, it can fail anywhere.

Humboldt, you seem to have researched your product pretty well. If you're convinced you're safe, then go camping and have fun. As for me...as fun as it would be to build a home-brew Li-ion battery system for my Airstream when it's time to replace my AGMs, I will most likely purchase whatever products have been proven in the marketplace at the time I'm ready.
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Old 05-11-2021, 09:45 PM   #12
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Quote:
Originally Posted by jaybauman View Post
TL;DR

If you're happy with your safety analysis, then go for it.





The Longer Version

My comments should only be construed as a general warning; I have no specific knowledge on these particular batteries or the BMS, so I cannot comment on them.



In pre-COVID days when we could still travel freely throughout the world, I volunteered on the technical team for a global contest (for both high school and university entrants) to see who could devise the most energy-efficient mode of transportation. One class of this competition was battery-powered vehicles, and the students either had to build their own batteries (or purchase on the market) and had to build their own motor controllers. Part of my duties was to ensure the Li-battery entrants were safe to operate, so we did a detailed inspection of every vehicle. In particular, we made sure the students understood the technology they were playing with. If was fair game to use a battery with a built-in BMS, but they had to be able to explain how it worked--physically and electronically. If they could convince me they knew their system, then they could get out on the track. Due to limited budgets, many schools opted for cheap (i.e. offshore) batteries and BMS. We had to disqualify many of them, because they could not produce documentation on their systems--in many cases, the manufacturers or sellers did not make this information available. Occasionally, we would disqualify a team even with full documentation if their setup was deemed too risky, from an HSE perspective. Because of this experience, I am acutely aware that it may be hard to procure sufficient documentation to be able to verify BMS and Li-ion cell configurations are bounded within the envelope of safety for the intended application.



As for public LI-ion battery failures, the ill-fated Auxiliary Power Unit in Boeing 787 Dreamliner comes to mind. While those batteries used a slightly different chemistry, nether Boeing nor the FFA could identify the failure modes that grounded the entire 787 fleet for quite awhile in the last decade. There is evidence that sometimes a single cell would fail (short circuit) and then heat up the entire battery, causing other cells to outgas. They found some irregularities with the BMS operation. They even suspect some the the battery-powered APUs could have been wired incorrectly. (These potential root causes are mostly independent of battery electrochemistry, so these are relevant data for this discussion.)



While we will never know how the Boeing lithium ion batteries failed, you can be sure that the battery chemistry, components, and construction were analyzed and tested to understand their operating windows. The BMS would have been tested and modeled and pushed to failure during design. The APU itself would have had to have performance guarantees. But yet, somehow these systems failed--multiple times! If it can fail an American-made commercial aircraft with all their built-in redundancies, it can fail anywhere.



Humboldt, you seem to have researched your product pretty well. If you're convinced you're safe, then go camping and have fun. As for me...as fun as it would be to build a home-brew Li-ion battery system for my Airstream when it's time to replace my AGMs, I will most likely purchase whatever products have been proven in the marketplace at the time I'm ready.


Okay, I feel like Iím getting a handle on what youíre saying.

Lithium chemistry batteries are more inherently at risk of catastrophic failure than lead acid tech.

I agree that many lithium batteries are more prone to catastrophic failure, but LifePo4 chemistry seems much more stable.

If the argument is for one over the other in safety terms I think that lead acid wins. You can combust a LifePo4 cell if you put a conductor through it. You canít combust a lead acid cell.

LifePo4 is going to have a good track record also. So many people are using them in their homes, boats, RVs and tons of other applications.

Many more battery techs are ahead of us. The more power you cram into a tight space the larger the danger!!!
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Old 05-11-2021, 10:17 PM   #13
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Originally Posted by Humboldt Air View Post
Okay, I feel like Iím getting a handle on what youíre saying.

Lithium chemistry batteries are more inherently at risk of catastrophic failure than lead acid tech.

I agree that many lithium batteries are more prone to catastrophic failure, but LifePo4 chemistry seems much more stable.

If the argument is for one over the other in safety terms I think that lead acid wins. You can combust a LifePo4 cell if you put a conductor through it. You canít combust a lead acid cell.

LifePo4 is going to have a good track record also. So many people are using them in their homes, boats, RVs and tons of other applications.

Many more battery techs are ahead of us. The more power you cram into a tight space the larger the danger!!!


Iím sorry, one correction. LifePo4 isnít combustible and not prone to thermal runaway. Just for the record.
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Old 05-11-2021, 11:29 PM   #14
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Its also pretty clear if you watch any of the 'tear-down' videos on Youtube that the pre-assembled batteries are built from OEM components, so in many ways self-assembly is better because you can 'pick and mix' and use higher quality components where you prefer, rather than save a few bucks to keep the assembled price low.

Depends if you want everything in a neat box that looks like a lead acid battery.
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Old 06-07-2021, 05:06 PM   #15
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LiFePo4 is one of the safest Li chemistry out there. Reason being LiFePo4 is a natural occurring minerals. All the scary stories are from other Li combos. There’s lots of YouTube videos of LiFePo4 batteries being intentionally abused to show how safe they are. Even lead acid will explode and catch on fire is properly abused. Yes, buyers beware!!!! You are playing with electricity and many ways to screw up.
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Old 06-07-2021, 06:25 PM   #16
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Its also pretty clear if you watch any of the 'tear-down' videos on Youtube that the pre-assembled batteries are built from OEM components, so in many ways self-assembly is better because you can 'pick and mix' and use higher quality components where you prefer, rather than save a few bucks to keep the assembled price low.

Depends if you want everything in a neat box that looks like a lead acid battery.
Hi

Getting *detailed* information on the BMS modules is pretty much impossible. Yes, they say this or that. It's all pretty superficial stuff. The details you really need to evaluate the safety of one are at least two or four layers deeper.

Bob
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