A lithium iron phosphate battery is a type of lithium ion battery that uses
LiFePO4 as the cathode material and a graphite carbon electrode with a metallic
backing as the anode.
A lithium ion battery is a battery that mainly relies on the movement of
lithium ions between positive electrode and negative electrode to work. Lithium
ion batteries use an intercalated lithium compound as an electrode material. At
present, the commonly used cathode materials for lithium ion batteries are:
lithium cobalt oxide (LCO battery), lithium manganate (LMO battery),
lithium-ion ternary (NCA, NMC battery), and lithium iron phosphate (LiFePO4
battery).
On Monday, March 8, 2021, 9:57:24 AM CST, jerry freedomev via EV
<[email protected]> wrote:
Hi Lee, Dan and All,First I agree BMS is best but one needs to look at all
the facts. One I've found is high C rate cells are very stable and last far
longer the low C cells and only works for Li-ion, not LFP which has completely
different charge profile.Vs Li-ion is much closer to lead in that voltage is an
indication of charge allowing much easier monitoring.My Volt pack after 2.8 yrs
of charging abuse including accidentally charging 20% above rated Kwh the
cells are STILL within 1/100 of a Volt of each other. Using a timer or set
voltage power supply stops charging abuse.So I'll likely still use the good
parts that were not shorted out in the crash as I'm frugal. And let's remember
this was in a Volt for 3 yrs before I got them.So near 7 yrs old and NO
deviation from 1/100vdc balance. At some point one has to admit that is how it
is vs previous thoughts.I don't use the Volt BMS as would need several
different size ones and there are no good choices and those that are, are more
prone to fail than the cells are data clearly shows on LG cell modules..Since
NO change in balance 6 yrs old one should except that will be the trend though
continue to check and verify. I expect another 5 yrs from them but we'll
see.You are correct about temp variations and why I told Dan to use the cooling
system if nothing else but to keep each cell the same temp in such heavy use.Vs
I didn't in my 700 lb EV trike pickup but such light use unlikely any temp
difference as high rate cells don't make much heat and never run or charged at
high rates. Though certainly others with high power and charging. I'm cooling
air my Bolt pack because of the way it is set up.So if you cool and limit max
charge voltage to 4.12/cell, there is about nil chance of fire. From Tesla
data, a medium C rate of 4-6c depending on yr EV battery life is way beyond
our dreams at 300k miles.I think the Volt modules might be million mile cells
their trend says as no detectable degradation in the ones I've went through 5-7
yrs old.7 yr old ones lab tested every yr showed the same 1k amp output each
yr.As for costs let's compare them to lead the cost is about the same as as
well bargained/shopped lead golfcart batteries but 35% of premium like Yt/kwh
so even if they only last 5 yrs they are cheaper, superior in every way even
without a BMS my, other's data shows.If you pay full list for GC batteries
Volt modules cost 30% less/kwh.So overall I find the Volt modules a bargain and
very safe inside voltage, temp specs even without a BMS we shouldn't ignore as
a great low cost way to upgrade from lead or for a new EV. Yes you have to
monitor them but saving $2-5k, that is worth it.I hope the Bolt, 2020 US made
NIB, other LG cell modules do as well.Luckily Tesla, some other BMS have
been hacked so you can and should use them. And anyone using Leaf module MUST
use a BMS as a low c-rate cell and easily degrades, gets out of balance.Thus I
don't use Leaf modules.That's what I have to say, found.Jerry Dycus
Dan Baker via EV wrote:
> I guess where the Volt pack is so reliable you can go without an electronic
> BMS although it sounds like a terrible idea.
The Volt *does* have a BMS. It's in the battery pack. GM is no fool;
they would face all sorts of expensive problems under warranty if it
didn't have one!
When people re-use a Volt pack in their own projects, they might leave
the BMS in place and still operating; they might leave it in place but
not fully operating; or they might take it out altogether.
I don't know which option Jerry chose; perhaps he can tell us. It sounds
like he left the BMS connected to the batteries so it could shunt small
amounts of excess charging current; but it was *not* connected to the
controller or charger, so it could not prevent running the cells dead or
overcharging them with an overly exhuberant charger.
Now... if you're going to go without a BMS, it's better to do so with
*quality* cells. The automakers do a lot of testing, so their cells are
much better balanced than random vendors on ebay. They will survive
better even without a BMS.
But all batteries age. They will gradually drift farther and farther
apart. With no BMS to "herd" them together, they will eventually wander
far enough apart to cause problems. And with no BMS to *warn* you that
there's a problem (no "idiot" light), you're headed for a disaster!
> I suppose one could write a pre-flight checklist like a plane/boat to
> ensure all systems are checked including some kind of manual BMS check.
Jerry did say he had one of my batt-bridges on his pack. This is a
quick-n-easy LED indicator that lights if the voltage of one half of the
pack doesn't match the other half (indicating that something is wrong).
It tells you something is wrong; but it doesn't stop you from driving
anyway.
And like David Roden said, Jerry was acting as his own BMS -- a manual
BMS, if you like. I used to do that, too. But it gets old, and you forget.
You can read up on my battery balancing experiments here:
<http://sunrise-ev.com/balancer.htm>
> Everyone that owns an ICE vehicle should check their oil regularly and the
> there really is no safety to that-by the time the oil light flickers lots
> of damage is likely already done.
Older cars had an oil pressure gauge or "idiot" light. It would tell you
the pressure was low, but it didn't stop you from driving anyway.
Most newer cars have interlocks to prevent you from driving with no oil
pressure, or no water, or some other catastrophic problem. I suspect the
manufacturers had too many warranty claims from people "driving their
cars to death".
People like my uncle: He bought a new car every few years, and just
drove it with no maintenance. No oil changes, no checking the tires; no
dealer visits at all. Most of his cars managed to run for 3 years OK. He
bragged about how much he was saving on maintenance and repairs.
Then one of them had some problem that caused it to run out of oil. He
ignored the warning light and kept driving until the engine seized. The
dealer wouldn't cover it under warranty. So he sold the car (at a big
loss) and just bought another one... and kept doing the same thing.
> Sometimes safety systems actually do more harm than good.
Yes, that's true. People tend to buy the cheapest BMS they can find.
Then *it* fails, and destroys the pack.
> I can't find one article where a Volt caught fire sitting on a
> charger or for any cause other those that were in accidents.
That's because the Volts all have an effective BMS.
Lee Hart
--
There is a computer disease that anybody who works with computers knows
about. It's very serious, and interferes completely with your work. The
trouble with computers is that you 'play' with them! (Richard Feynman)
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
--
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