I did not find reference to this Panasonic patent with a quick glance over the forum and use of the search function. If this has been discussed already, then please point me to it!
NOT Attached is a patent by Panasonic in which describes methods of detecting bad cells in long battery strings and how to replace them - it's too big for the forum rules!
Here is a link to it instead: https://www.endless-sphere.com/forum...e.php?id=40422
The described techniques could be helpful for repairing the Insight batteries.
In the Prius NHW10 Yahoo group it is generally believed that the patent is directly related to the NHW10 battery - and they are the same cells as in the Insight.
Below is a (IMHO) sensible summary of some interesting core points, written by a member of the yahoo group:
I don't find the patent vague (or at least, no more so than
patents usually are). Here's my take on what it means when
it describes the pretreatment of cell modules before they
are put into use.
Firstly, it is important to be aware that newly manufactured
NiMH cells, or NiMH cells that have been kept in storage for
some time (a few months or more), don't deliver their best
achievable performance when you begin to use them. To overcome
this it is necessary to exercise them by charging and discharging
them a few times, a process that I know of as "conditioning".
In the patent, what I have just called "conditioning" they are
referring to as "activation". (I suggest we continue to use
the term "conditioning" as it appears to be a term widely used
among battery technologists).
The main thrust of the patent is that it is not necessary to
replace an entire defective battery, but instead it is sufficient
to locate and replace only the defective cell modules. (No
surprises here - it's what many people on this group have been
trying to do for a while now
The need for conditioning arises from the fact that the stock
of replacement modules may well have been sitting unused
for long enough to lose condition, or might even be freshly
manufactured modules that have never yet been conditioned.
If a replacement module which has not been conditioned is
fitted to a battery which has recently been used, the new
module will not match the remainder of the battery and
will limit the performance of the battery, possibly giving
the impression that it is still defective. So it is
necessary to carry out a "pretreatment" process to "activate"
the module before it is installed in the battery being repaired.
There are two options for carrying out the pretreatment -
1) Repeatedly charge and discharge the module until a total
of 450% of the nameplate capacity of the module has been
fed into it and drawn from it. This is not one single
huge charge/discharge cycle (which, needless to say, wouldn't
work because the module does not have enough capacity).
Rather, it is a series of smaller charge/discharge cycles,
of gradually increasing size as the module becomes conditioned
to its best achievable capacity.
On those occasions when I have monitored the conditioning
of a NiMH cell string, I saw approximately these capacities
as the conditioning progressed:
first cycle - 60% of specified capacity
second cycle - 80% of specified capacity
third cycle - 90% of specified capacity
fourth cycle - 95 % of specified capacity
fifth cycle - 98 % of specified capacity
That sequence totals up to 423% of specified capacity, so
the patent's recommendation to condition using at least
450% of specified capacity looks sure to bring the module
up to tip-top condition.
2) Store the module for five days at 50 degrees C or more.
The patent asserts that this is an alternative way of
conditioning the module which has a smaller energy
requirement than charge/discharging cycling it.
So, the patent is not directing us to both cycle the module
and heat it, but instead you can choose which of the two
conditioning methods to use.
After the replacement module has been fitted to the battery,
the patent says that a post-treatment process is needed. This
process is the same as what we have been calling an equalisation
charge - that is, deliberately charge the entire battery up
above 100%, to ensure that every cell in the battery is at the
same state of charge before it is put into use.
Consequently, I don't think there is any value in heating an
entire battery (as described in other recent posts) unless the
battery has been left unused for long enough to lose condition.
Even then, I would be tempeted to condition it by charging and
discharging it rather than heating it, because this would give
me the chance to slip in an equalisation charge without any
extra effort.
Too good to remain hidden in a unsearchable location!
As far as I know the patent is in the public domain, but if anyone thinks posting it here is some sort of copyright breach then please remove it!
This is what this group has found over the years and many of us are utilizing on an ongoing basis. Nothing new here, except maybe the heating process which I would have hesitation about doing.
__________________
Jim Isbell
2000, 5 speed, 250,000 miles
"If you are not living on the edge, well then,
you are just taking up too much space."
Patents are public, their nature is to allow for recourse if someone is using your process or design, etc. so that you can get money from them in a predatory fashion for infringing on their patent. US Patents are fairly easy to find if you know the right keywords through the United States Patent and Trademark Office site or the newer Google Patents.
I'm not in huge support of heating the cells to 50 degrees C. I am looking over the Endless Sphere thread and trying to figure out why they are blasting charge through them at 60 degrees C or more and thinking this isn't damaging. 45 degrees is about the limit for me and if I stop when I measure 45 degrees C, sometimes I'll see it rise to 50 degrees C which is my 'never exceed' point. They are doing it at fairly low currents too, not sure why they are continuing a charge that long to get them hot, it's not a good idea to do push them to 60 degrees C and continue to batter them.
I'm sure 50 degrees was chosen by those who created the patent because it was about as hot as you could get them without damaging them. ...while charging though they could be hotter inside than the apparent temperature on the outside.
Patents are public, their nature is to allow for recourse if someone is using your process or design, etc. so that you can get money from them in a predatory fashion for infringing on their patent. US Patents are fairly easy to find if you know the right keywords through the United States Patent and Trademark Office site or the newer Google Patents.
I'm not in huge support of heating the cells to 50 degrees C. I am looking over the Endless Sphere thread and trying to figure out why they are blasting charge through them at 60 degrees C or more and thinking this isn't damaging. 45 degrees is about the limit for me and if I stop when I measure 45 degrees C, sometimes I'll see it rise to 50 degrees C which is my 'never exceed' point. They are doing it at fairly low currents too, not sure why they are continuing a charge that long to get them hot, it's not a good idea to do push them to 60 degrees C and continue to batter them.
I'm sure 50 degrees was chosen by those who created the patent because it was about as hot as you could get them without damaging them. ...while charging though they could be hotter inside than the apparent temperature on the outside.
The heating of the battery to that excessive level was a one-off deliberate experiment to check what happens and if the charger would terminate charging. I designed and built that charger and if I want to use it with little or no supervision, then I need to know what happens at the extremes of temperature range. In summer it can get this hot inside the car if parked in the sun without any charging going on. It's not an unrealistic scenario at all!
I have spent so much time on figuring out these batteries - and I have spares - that I can afford to destroy a battery more than I can afford to waste more time by being too careful!
I would not want the batteries to be exposed to such over-charge in regular operation or use! That is the whole idea behind the multiple safety mechanisms in the charger design. It ensures that the charger never runs when the cooling impeller is not drawing current, and it has a last resort safety stop by switching off the charge current if the resistance of the PTC strips rises too much. But it needs to get hotter than 65degC, I know that now! (As Fechter says on ES: A test is worth a thousand opinions!)
A single extremely hot (75degC should be hot enough due to the steeply exponential characteristics of the PTC strip) will also shut down the charger, whilst continuing to run the cooling impeller.
Until I ran that test I have also been very conservative and stopped charging at around 40degC, even earlier, but found over the last 2 years that the NiMH cells are "tough as" and seemingly need to be taken to the extremes every now and then to keep them keen!
The battery seems to do very well so far, it is the next one in line for cycling and testing in a vehicle. I'll know more in a few weeks or months!
I have edited the post on Endless Sphere to make this more obvious.
It would seem to me that if heating a battery would improve it then the batteries that sit in closed cars in junk yards for a year would be the good ones. I dont think that is the case.
__________________
Jim Isbell
2000, 5 speed, 250,000 miles
"If you are not living on the edge, well then,
you are just taking up too much space."
Not saying that it necessarily is good for batteries to be heated, but the battery in my dark blue Prius had been standing in the car for several years in the Australian heat before I "resurrected" it! And apart from a single bad stick it is again in great shape!
Is this Battery as dead as a Dodo?
...
...
This is going to be interesting!
The battery is very flat and many would assume that it cannot be restored at all.
But I believe that the NiMH technology will quite likely showcase it's resilience here once again; and that the battery might well be fine once I have pampered and cycled it a few times!
Here are the open voltages:
HP1: Open voltages (mV) : Entire 120s: 11230mV (yes, millivolt!)
Best stick 2.2V, worst stick 0.007V - what do you think?
Who wants to hazard a guess if this battery is dead as a dodo, or not?
Very basic schematic of the NHW10 battery is attached.
.
I wonder if the intended effect of the heating to 50degC for five days suggested in the patent may actually be accelerated self discharge to zero SOC.
The self discharge rate is very high at such high temperatures. It might be the easiest way to discharge all cells and bottom balance them (if you have a temperature controlled oven for it and you are doing this to many batteries).
IIRC, the "Battery University" website recommends discharge of NiMH cells to 0.4V at low current to re-condition them. That's what I did with the 102s NiMH battery in my Vectrix, with good results. But for the 240s battery in the NHW10 Prius this is prohibitively tedious! Heating the cells may be an easier way to achieve the same goal.
But I have not tested this!
Again, I'm not claiming it works, just speculating how it might work!
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Method of Replacing Secondary Battery Patent
