Figuring Lead vs LFP's pricing delta

[john61ct]

To clarify how **I prefer** to do this,

also accounting for the difference in "usable amps" between the two chemistries.

Split off from this previously hijacked thread
http://www.skoolie.net/forums/showthread.php?p=364614

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eBay search for pricing data
https://www.ebay.com/sch/i.html?_nkw=180Ah+CALB+LiFePO4

at writing, two options for a nominal 12V bank including delivery and at 900Ah, pretty small for running aircon more than a few hours:

$4100 from a USA seller, $4.86 / Ah
$3212 from the Chinese one, $3.57 / Ah

in theory both equally covered by eBay's NQAMB guarantee, but for the Chinese one you have to pay for the return shipping if they turn out to be sub-par, but in eBay's opinion still "as described"

That shipping cost would end up being thousands, so, in effect a very risky purchase.

In fact, I would not purchase from either seller, only from a known trust-worthy vendor as reported by a friend or multiple trusted forum members having dealt with them satisfactorily in the past, and proven stable over time.

Most sellers through platforms like eBay, Amazon, Ali Express, Taobao.com, Tmall.com and 1688.com*are selling less than brand new Grade A factory output, many even used as if new.

So of course you need to be able to do a proper accurate capacity benchmark upon arrival to judge whether they're worth keeping, before the warranty return period is finished.

Buying from the factory direct is really the best strategy, but so far that's always turned out to be more expensive.

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The relationship between average DoD% and cycling lifespan is proportionally similar for LFP, shallower cycling yields 3-5x more cycling, can easily get to 10,000 - barring user error, bad design, failure of protection gear or accidents.

But, even if you're happy with only 4-5000, never let resting voltage get near 3Vpc, and the stop-charge setpoint should stay around 3.45Vpc, depending on the C-rate.

That works out to around 70-75% DoD on average, or 630-675 usable.

The GCs are well under $1200 for six pair, yielding 1290Ah, or around 650Ah usable

So comparable ballpark usable capacity.

Note the Deka GCs are every bit as good as say Trojans, or Superior, Crown and US Battery.

Very few would spend the extra money on Rolls / Surrette, mostly yacht owners looking for 15-year lifespans, cruising where replacements are just not available.

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You also need a known-accurate and reliable BMS, perhaps

separate balancing gear,

DMM & ammeter and

ideally a variable-voltage and current-limiting power supply,

along with the high-current charger you'll need for routine daily usage when shore power or an AC genset is available.

Not counting the voltage-adjustable and current-limiting gear required for charging your LFP bank off alternator while driving, and/or panels and solar controller, which may not be needed atall.

If you have to ask how much you can't afford it all.

Only a tiny number of which if any are required using the Deka GCs, and much cheaper versions good enough as opposed to with LFP.

You **might** get away with less than $2,000 for these infrastructure components, but I doubt it, even $3k won't get you the usability & security when shooting for being "certain" of over a decade's lifespan.

And if you don't have the confidence (skilz, knowledge) to select install configure maintain all these components, you'll want to either buy a (**much** more expensive per Ah) pre-packaged "systems solution" from Lithionics, Victron or Mastervolt, or

hire a trusted / recommended professional to help your DIY efgorts, and those are pretty thin on the ground, especially in North America.

Not so bad in Europe, Australia etc, where local LFP distribution channels are **much** more mature, and good quality deep cycling lead banks are also **much** more expensive

thus tipping the scales much more readily in LFP's favour.

[kazetsukai]

I've found used EV batteries to be the cheapest in terms of price per watt hour. Various brands' common models have enthusiast followings with popular configurations for use in off grid and grid tied applications. I needed the capacity and the cost savings, and was willing to jump through the necessary hoops to go this route.


Once you really start scaling up your system there's a line you eventually cross where you're no longer in hobby-land. 400W-500W of panels with 1.2kWh-5kWh of capacity is serious enough to be practical, but when you triple that you really have to pay attention. Add Lithium to the mix where you have to find and implement a BMS...


Anyone even thinking about this has got to be willing to manually monitor their system, checking performance every single day.

[john61ct]

Originally Posted by kazetsukai

I've found used EV batteries to be the cheapest in terms of price per watt hour

LI chemistries other than LFP or LTO should not be used, risk of thermal runaway far too dangerous in a mobile living use case IMO.

Especially secondhand from scrapped EVs, now orphaned from their engineered TMS, even if the BMS has been reverse engineered.

Maybe for a science project, in a back yard shed far from where humans live.

Let's please keep this thread to LFP vs FLA only.

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Yes, never charge without constant manually monitoring.

But for LFP you can relax a bit more.

A good setup makes monitoring the key variables easy.

[joeblack5]

Haha, I have seen that text now about 10 times.


If you want to limit your thread to lead acid to LFP and then new also...then their is not much to be gained or learned..... It is always going to be to expensive.

I would think people who convert old defunct buses would be more helped by figuring out how they can get the best result for the $$...



Almost would think scrapped ev batteries are more dangerous then a tank of gas next to a campfire.


I think it would be better if you would explain when and why thermal is to be expected in a low power environment like bus life.


It will be pretty difficult to run a chevy volt battery in a thermal runaway with a 1000 watt solar array and 1C discharge currents. a voltmeter on each of the 4 cell banks required to get to a 12 V equivalent battery ( 16volt) gives plenty of time to monitor cell imbalance and you certainly do not have to look at that more then once every month.



The cell matching especially from EV batteries is way better then any LFP you can buy. So use the cells from one already chevy volt pack and do not mix without testing and understanding.


A chevy volt pack can be had for $ 2000 +/- 1000.
assuming wear and tear about 12 KWH. for a 48 Volt system that would be 250 AH available used . Try to charge that in a bus environment with solar above 1 C , not going to happen.. or discharge that in an normal use with more the 1C .. So just fuse each of the 5 parallel string with a 20 to 40Amp fuse.


The chevy volt comes in easy to use 48 volt modules , and some 24 volt as well. The cells in one pack are matched better then anything an individual can come up with. So for the full pack capacity this would have to be a 48Volt system.


If you want a lower voltage system then go to Nissan leaf. Then you can assemble in 8 volt modules. That means a minimum of 2 in series becoming a 16 volt battery ( full) . All 12V automotive electronics can accept 16 volt since that is about the same as a car battery under charge in very low temperatures.


Thermal runaway can occur for some chemistries above 150 celsius. So do not install these batteries above or net to your exhaust system.
If you physically damage cells, shot a bullet in them, vehicle accident then it is possible that because of short circuit current the temperature inside the damaged becomes to high and so a thermal is started.
Kind of similar to a leaking fuel tank, leaking gas cylinder.. life is dangerous.


Thermal runaway from heating because of charging / discharging currents is not possible in our bus application when fused properly. That is because the capacity of a full pack is way larger then the charge currents from solar or discharge current from a 5 KW inverter. Nothing against a temp probe for monitoring so that you get a feel where temps are.



So left over is the max voltage protection and the low voltage cut of.




I have used both to replace lead in my DIY electric vehicles and I am happy i did. If the time is there.. meaning my current lead acid bites the dust.. then for sure it will get replaced by an EV pack.



Read up on it and come to your own conclusion.


Sorry John, I am starting to sound like you... repeating the same thing over and over... maybe it would be good if you explain your fears about thermal runaway of EV batteries in more detail if they are used in bus applications so that interested people can compare and can by knowledge decide what is acceptable for them.



Good luck, Johan

[kazetsukai]

Originally Posted by joeblack5

Haha, I have seen that text now about 10 times.

Thanks joeblack. I've seen this kind of response quite often as well but didn't really have good push back. Especially the bit about comparing them to gasoline. You've inspired me a bit. Therefore,

Originally Posted by john61ct

Let's please keep this thread to LFP vs FLA only.

Especially considering you are trying to perform a kind of cost/benefit analysis: Why? Given:

Originally Posted by john61ct

Yes, never charge without constant manually monitoring.

And:

Originally Posted by john61ct

A good setup makes monitoring the key variables easy.

I just don't see why other lithium technologies are _any different_ in this application. The bits about thermal runaway, or "being designed for X" when used for Y, it all sounds like FUD to me. All Lithium batteries have low resistance relative to lead acid, meaning they'll discharge more. That being said if you asked if I was more afraid of my Tesla packs or the D-cell sized capacitors you'd find in a microwave, I'd say the latter. When I said:

Once you really start scaling up your system there's a line you eventually cross where you're no longer in hobby-land. 400W-500W of panels with 1.2kWh-5kWh of capacity is serious enough to be practical, but when you triple that you really have to pay attention.

I meant _any_ chemistry. I've seen cables heat up until they smoke on AGM batteries, situations that had they been left alone, would have started fires. Are we really going to run 10A, 15A, or 20A 110V, 220V AC service lines all over our rigs and pretend they're somehow less dangerous than outlets you'd find in a house simply because they're battery powered? Even with a single 12V battery you are often playing with fire.



So yeah, I object to the idea that the EV Lithium options are somehow inherently more dangerous, given you understand how the system and their components work, you are properly monitoring performance and understand the possible failure scenarios/conditions like you should in any other similarly sized system. I went this route and have been testing against Tesla batteries for almost two years now. The system is stable, it works. I don't care what the naysayers have to say about it, I'm not going to believe someone's FUD over my own lying eyes.



Now there is such a thing as more forgiving technology and AGM would fit that bill to an extent, but really once you start getting serious with your setups I say that forgiving nature just makes people more prone to negligence and thus failure.


...and it doesn't make sense to leave the most cost effective solutions out of a cost benefit analysis.