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Anyone ever used 38120 ?
#1
Anyone ever used 38120 cells ?

Their specs are LiFePo4 3.2V 8-10Ah. Pretty good capacity.
I definitely can think of some applications for them but I never tested something like that.

I'd be interested in how well they maintain capacity over time and if they could be an alternate solution for high capacity 18650 builds.
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#2
38120, 38140 and 40152 are very popular formats for LFP cells, mostly offered by Headway. They are very good, high quality cells and easy to use because of the M6 screw terminals. Cycle life, among other specs, should be specified in their datasheets and certainly will be on par with what you'd expect from LFP cells. I can't remeber the figures from the top of my head.

There might be other manufacturers making cells in this format obviously. If they are any good depends on each individual case. The format alone doesn't tell you anything.
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#3
I'm interested primary in their reliability over time, compared to Li-ion.
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#4
There is no difference in reliability.
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#5
Maybe some more information about the different types will help you decide which type is the best for you. In general, we differentiate between LiFePO4 and the other Li-ion batteries because of the different nominal voltage (3.2V / 3.7V).
On this site is a good explanation of the different types of Lithium Ion batteries:
https://batteryuniversity.com/learn/arti...ithium_ion
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#6
As I understand it, LiFePO4 is a less volatile chemistry than most of the other Li-Ion variants.  Not likely to suffer a "vent with flames" incident if mistreated or damaged.  So perhaps not more "reliable" but somewhat "safer."

Cycle life is also accepted to be much higher, with figures from 2000 cycles at 100% DOD (depth of discharge) to 8000 cycles at 30% DOD claimed.  (Before capacity reaches 80% of new.  Of course, they can still be used after this point.) Lots of wild claims abound on the Interwebs - YMMV.

Like all Lithium cells, they are best kept cool where possible as high temperatures (especially if combined with high states of charge) are detrimental to capacity/life.

Apparently the Headway cells are popular with ebike users.  Their quality is considered to be high.

I have 48 of the Headway 38120s at 10Ah.  So far, I have made 8 cells into a 12V 4s2p pack without BMS.  I did fit a balance lead and only balance charge with a hobby charger using a buffer battery between my solar source and the charger.  I use an RC "screamer" alarm if I am running heavy loads or I think I am getting close to discharged.  
Ideally I will fit a BMS - when I find something suitable.
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#7
I have a pack I built with Headways I purchased form Alarm Hookup. They are the ones with a 25C 8AH rating. It was a 8S2P 24V pack with a much higher discharge rating for the purpose of powering a 24V RC controlled device I built. The pack performed as it should although that project has now gone south. It was more expensive to build with the Headways but it did perform to spec. I have now reconfigured that pack to a 4S8P 12V that I am using as a power source for my Kweld spot welder. And that pack is also performing to spec.

The pros of the Headways are they are easy to build with and reconfigure. The cons are they are more expensive from what I have seen.
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#8
Quote:"LiFePO4 is a less volatile chemistry than most of the other Li-Ion variants.  Not likely to suffer a "vent with flames" incident if mistreated or damaged.  So perhaps not more "reliable" but somewhat "safer."
I had an incident with an A123 26650 lifepo4 which I shorted out which punched a hole in it, the fire on it with comparable to a blowtorch. I would not choose lifepo4 if safety from fire was a main consideration its not any safer then li-ion. I still use the A123 cells but treat them with the same respect as I treat 18650. I think the 38120 lifepo4 would be as safe as the A123 26650.

The drawback from these larger lifepo4 cells is they take up too much space for the amp hour they deliver. Even the 26650 A123 I use them to build jump packs to jumpstart my car. Using 26650 cells I built a 4s6p 10ah, with high quality 18650 I could build 3s16p 40ah pack and both packs would take up about the same space.

I used the 32650 lifepo4 cells to build my 220ah house battery, those are huge heavy cells. Next time I just use the 18650.
size difference between 18650 and 32650
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#9
(02-25-2019, 06:49 PM)DarkRaven Wrote: There is no difference in reliability.

LiFe batteries tend to have a higher cycle life compared to Li-Ion.

However, you could potentially get a longer life out of Li-Ion by reducing the depth of discharge, and charge voltage. This is not really feasible with LiFe as the discharge curve is fairly flat.
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