LiFePO4(lfp), not LiCoO2(what’s in your phone). LiFePO4 offers less energy density than LiCoO2 but offers better stability. LFP offers a better energy per weight ratio than sealed lead acid, along with a high discharge rate.
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Sealed Lead Acid Batteries suck. FIRST still insists on using them, though there are alternatives that can be used in this modern day, with greater energy per mass ratios, higher sustainable discharge rates, etc.
The most promising of these is probably the LFP (LiFePO4), or Lithium Iron Phosphate battery. You might say, well David, this seems like a horrible idea, lithium batteries catch fire easily and violently. This is not true in the case of LFP batteries, with are different than the batteries used in your phone (LiCoO2). LFP batteries are “virtually incombustible due to chemical stability of their Iron Phosphate cathode material.” https://www.gliderpilotshop.com/lfp_vs_lead_acid
Since LFP cells are naturally 3.2v per cell, which means 4 cells together would give 12.8v, close enough to be a replacement for your lovely sealed lead acid battery.
Along with fine safety characteristics and easy adaptation to FIRST, these LFP batteries support discharging below 50% without serious detriment to the battery, as well as they last for 5000 charge cycles and have a shelf life of 5-7 years, which are very helpful since the sealed lead acid batteries we use currently are pretty much shot after one season due to how they are charged, along with the high discharge rate when in a robot drawing upwards of 300 amps at any moment.
So with options like LFP on the table is there incentive to switch to something other than the SLA that has been abused for years by FIRST teams?
Further Reading and Sources:
https://www.gliderpilotshop.com/lfp_vs_lead_acid
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I completely understand the differences. Although LiFePO4 is more stable it is still far too dangerous to utilize without an overhaul of the electrical system( they can’t just be a drop in replacement). In 2016 I saw two SLA batteries short and swell at one event, in 2017 I saw 3 punctured batteries at the same event.
These occurrences could have resulted in circumstances far worse than a dead battery, a used container of baking soda and a mess if LiFePO4 is used.
Also LiFePO4 is still far higher in cost than SLA and they are much harder to air transport.
Where are you seeing affordable LiFePO4 batteries capable of supplying 400 amps?( actually interested)
There are lots of advantages( minimal sag during discharge is a big one), but they are also lots of disadvantages.
Like Alastair posted in another thread: where do you get a LFP battery that’s affordable and is capable of 400A?
Didn’t say it was perfect, though cheap isn’t necessarily needed when the shelf life of 5-7 years with 5000 charge cycles…
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I figure it would be something like CTRE, a company sees a location where there is demand for a product and produces it. FIRST is also a large enough organization that Im sure something could possibly be figured out for sourcing a battery.
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Merged/Moved posts from 2018 Parts Thread to avoid cluttering up that discussion.
Cheap is still something that is needed. Yes for an established team that knows it can sustain itself for another 5 years at least, it makes sense. But for a new team with limited budgets (most new teams are limited in their budget) having to invest vast amounts of money into new batteries is a hard sell. We just purchased another $400 in new batteries for champs, and I for one would not be very happy if they were no longer usable next season. If First were to do this they would need to give teams at least 1 seasons notice in advanced to the change, if not more.
Cheap may not be needed, but affordable is. Pick a battery, give us an actual model number and specs to look at, not just a description of a hypothetical one that’s “better”. Let us look at price per battery, battery capacity, durability. How many batteries would a team need to get through a competition? What are the odds that you’ll damage one (we lose at least one battery a year due to damage)? Damaging it and putting it out of commission makes that whole 5-7 year thing kinda pointless. And finally, can you show testing done on that battery to highlight the failure modes when shorted, punctured, and dropped?
http://products.batterytender.com/Batteries/480-CCA-Lithium-Engine-Start-Battery.html 480amps, ~$200 depending on who you look at for it. Run 28-35 LA equivalent amp/hrs, along with only being 3.75lbs.
Regarding lifespan/cost over time on a larger scale:
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Current batteries:
~$45
80% Depth of Discharge: 225 Cycles
18 Ah
80 A discharge continuous
250 A discharge for 5 seconds
Most comparable LFP battery I found from a quick Google Search:
$124
80% Depth of Discharge: >1000 Cycles
20 Ah
40 A discharge continuous
200 A discharge for 10 seconds
Cost wise in terms of cycles/$, the LFP battery is actually cheaper. The continuous discharge rating is only half of that of the SLA though.
I know there are tons of safety considerations and testing required before considering for FRC and I don’t really have an opinion in the debate of should we switch to lithium ion. I’m just putting an example of a semi-comparable battery out there.
EDIT: Got beat to it. A battery with a more comparable discharge rate is posted above
Why can’t we run LiPo batteries? Easily accessible, dirt cheap once you get chargers, and very nice power output.
Them exploding is sorta an issue.
When have you ever seen a LiPo that was being used properly explode?
Exactly the problem
I for one like the durability and affordability of the lead acid batteries and I hope they stick around for several more years.
I have seen people forget to unplug them when they walk away and find a nice puffy battery when they come back the next day. On the flip side, my senior design team has used the battery tender Lithium Iron Phosphate battery posted above without an issue for a while.
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“Phosphates are not prone to thermal runway and will not burn even though abuse occurs. Therefore lithium ion batteries made by phosphate as cathode are very safer as compared to other lithium ion batteries.” http://www-scf.usc.edu/~rzhao/LFP_study.pdf
I think there is some misinterpretation here between the differences in Lithium-ion the ones used in phones and such(LiCoO2), the exploding type, and Lithium Iron Phosphate batteries(LiFePO4), the non-exploding type due to the Phosphate group.
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Let me put it this way:
CHARACTERIZE your preferred battery in an FRC environment.
You think we abuse SLAs? Let’s see, they only get shorted, dropped, picked up by the terminals, possibly impaled, and oh did I mention transported in nice toasty cars/trucks which can do a number on their life expectancy. And I think I forgot about the whole “improperly charged” problem, including speed charging, using alligator clips instead of Andersons, and “hey this one is the fullest, grab it and go!”
Now, let’s see, take a battery that costs 4x as much and give it that treatment. Trust me, it’ll get it. Everything in the above list. How long will it last? Right. About that. Now whether it’s a big meltdown/explosion/fire may depend on the type of abuse…
The question you should be asking is: Do I want to spend $200 on one unit of somewhat unknown technology when I can go to AM and get 4 units of known technology and a charger for that much?
So it wasn’t being used properly? I was referring to cases of LiPos exploding when people don’t do something stupid.