PTC

[IamIan]

The 120 cells are all in contact with a PTC ( Positive Temperature Coefficient ) strip.
This strip is wired in series among each of the 20 subpacks.

The strip will give a Ohm reading relative to the packs temperature.
The higher the temperature of the pack the higher the ohms of the strip.
If any one individual cell out of the 120 cells in the pack gets very hot it will raise the Ohms.

So far I have completed 4 tests on the PTC strips as part of my much larger scale battery testing that I have been doing.
I hope to over time add more tests to the data set... but a trend seems clear already.

A graph of the results I have posted for others who are interested to see it here:
http://www.geocities.com/ian_p_george/PTCStrips.jpg

The strips are not all identical ... but are close to each other.

I am hoping to narrow the variation down more with additional testing.

For example with 20 of the strips from subpacks all wired together a 120 cell pack at ~95 F will be ~40 Ohms, give or take... but if any one of the 20 strips gets above 170 F it will be ~40 Ohms all by itself... this exponential Ohmic increase with temperature means that a single cell that gets overly hot can result in significant increase in the total series resistance of the whole strip.

Of course the BCM was not built to check the individual resistance of each subpack... so it won't know exactly where the problem is.. but the PTC combined with the other temperature probes give the BCM enough data not to fry the pack... and thus make it safer to hit with such high currents and still expect it to last for so many miles.

I posted this to share my results so far.

[leomorgan]

Thanks for the post. I am in the process of analyzing the individual subpacks from my old IMA battery I took out last summer (I got a replacement from a junkyard). I have 5 subpacks that perform poorly; the rest return 92% or better of the factory rating of 6500 MAH when charged at 110% of that rating (unless peak voltage kicks in, which it always does on a good subpack; normally around 6800 MAH). My intent is to take the best subpacks from the old pack and, should the junkyard replacement pack fail, take the best subpacks from it and make a single decent IMA pack (for free). I have been using a Triton 2 battery cycler; it takes over 30 hours to cycle the pack 10 times, so it has taken over a month to get through all the subpacks. If you feel there is a better way to distribute the temp probes, I'd be very curious to hear what you have to say about it (after your full analysis, of course).

Keep us posted.

Leo

[IamIan]

Glad to hear there are others out there.

Make sure you keep a log of your data and settings as you go in your testing.

The thing to remember about trying to recondition NiMH batteries is know what exactly you are trying to treat... there are different things that can have the same symptoms...

When you charge and discharge NiMH cells rapidly the electrons follow / find the path of least resistance... so the harder you push the battery for amps in or out... the less of the whole cell chemistry is being used... this can in time lead to a voltage depression that behaves allot like the memory effect from NiCd batteries... also remember the chemistry inside the battery is not as fast as the electronics or electrons ... it is much slower...

The Triton you are using is a great tool.

If you still have the battery subpacks available you might want to run the conditioning test gentle to see if you can get a better result... by gentle I mean don't charge at more than 100mA , charge no more than 8Ah , give it at least 24 hours after charging to rest before discharging , and don't discharge at more than 1Amp.... this is unfortunately a painfully slow process but depending on the details of what is going on inside the cell as few as in ~3 of these very slow cycles can sometimes do more than any number of faster cycles ever could...

In the end unfortunately it depends on what exactly is the cause of the loss of capacity some things can not be treated.

I have been doing battery tests for months now... it will be a long time before I have finished all the tests I want to do... but I figured I might start posting the results I have so far for other to take advantage of.... but it is likely to be several more months at least before I am even close to being done with all of my testing.

[uhtrinity]

Pretty much the same results I got in this thread:
viewtopic.php?f=4&t=7527&p=70386&hilit=ptc+strips# p70386

Once you get above 170 - 200 degrees you quickly get into the high K-ohm to Meg ohm range. That in turn triggers a P1449 code with the stock trigger point being about ~410 ohms.

[IamIan]

sorry I had forgotten about that thread.... if I had remembered I would have just posted my finding in the same thread to have them all together....


anybody know if there is a way to merge the two now ???

[leomorgan]

Is there a way to use the Triton2 to perform any conditioning or balancing on the entire battery pack as a whole? If not, is there a device on the market that is affordable and can do that kind of work?

Thanks...

Leo

[IamIan]

Originally Posted by leomorgan

Is there a way to use the Triton2 to perform any conditioning or balancing on the entire battery pack as a whole? If not, is there a device on the market that is affordable and can do that kind of work?

Thanks...

Leo

Triton... no.. it would fry and the magic smoke would get out if you connected it to the full pack voltage... the triton and like products can only take pieces of the pack at a time.

If you have electronic and HV skills you can build a basic unit yourself.... there are 2 or 3 threads on IC that talk about options for this.... but if you do it wrong you can kill yourself , the car , or both.

If you want to buy one premade... the word affordable has to be removed for your request... as in you would have to spend a couple thousand dollars to get one... you would need to combine a HV EV charger... a HV EV instruments to track what is happening... and some method of safely and properly discharging that HV power.... if you want all 3 devices to talk to each other and be able to do programed cycles like the triton ... then I would expect you would be in the $10+ range.... no easy way out unless money is no object.

[leomorgan]

Well, shoot. Thanks for the advice. Money is always an object. I've put more money and sweat in this car than it's high book value... can't help it though, I think it's the coolest car I've ever owned (and I've owned some cool cars). I bought the car with 156,000 miles (just out of warranty) and the IMA battery died 1,000 miles later. So, I bought another IMA battery from a salvage yard (along with BCM and MCM) and replaced the originals. Now, 5 months later, I can tell that this battery is on it's way out. Since removing the old battery, I have been cycling the subpacks with the Triton2. I can tell which ones are faulty; I have maintained a spreadsheet and the weak ones really show up on a graph. My intent was to take the best subpacks from the old pack and use them to replace the weakest ones in the second pack, making one good pack. I've seen several posts on balancing/reconditioning; I'm having a hard time knowing which one I should be doing. These are the parameters I've been using:

7200 MAH max charge (according to Triton2 instructions, the max charge should be 110% of rated MAH - 6500 X 110% = 7150)
7 AMP Charge
3 AMP Discharge
5.4 Volt Minimum Charge (0.9 volts X 6 cells = 5.4 volts)

Most subpacks had increased their output by the time I had cycled them through this routine 10 times. A few had low output and did not improve. My questions is, are these not the most optimal parameters for trying to revive a subpack? Many of the packs produced over 6000 MAH by the time I had completed these routines...

Thanks,

Leo

[IamIan]

Balancing the pack deals with the usage of the pack... not trying to recover anything from it...

If the pack is out of balance when the car tries to use it the BCM will protect it by using the safe range... if one subpack has 1Ah more or less stored energy than any other subpack you effectively loose 1Ah of capacity from the whole pack... because the BCM will not over charge or over discharge the rest of the pack... and because the BCM has no OEM method to charge or discharge one subpack more or less than another.

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Now reconditioning a battery deals with trying to teat some of the effects that happen to the battery over usage and time.

If you want me to go into detail... let me know... I have learned most people dislike it when I go into great detail....

In short ... to recondition a NiMH battery you charge it up as close to 100% as you can while observing as many of the proper NiMH battery charging issues as you can ... then give the chemical cell ( Battery ) some time for the chemical reactions to finish up and catch up with the much faster electronics ... then discharge as close as you can to 0% while still observing as many of the proper NiMH discharge issues as you can.

As you get closer to the top and closer to the bottom SLOWER rates of charging and discharging become more and more important...

The more cells you try to do at one time the harder and harder it is to properly and carefully 100% charge ( without over charging ) and the harder and harder it is to properly discharge to 0% without causing cell reversal.

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As for your specific parameters... they are pretty good... thanks for doing some homework on it.... optimal is a strong word... That word suggests that there is no better way to do it... and there are some options / ways to improve what you are doing for the battery... BUT ... there is always another side... the other methods have issues like taking much much longer... requiring you to spend more time ... or getting more instrumentation / better tools... etc...etc... for me there is always a better way to do it.... we just make some "reasonable" assumptions ... decide how far we are willing to go in time, money, hassle ... for how much additional gains.

If you get the subpacks to give you 6+Ah that is enough capacity for what the Insight will use it for...

Of course there are other things... other issues ... but, there is also diminishings returns.

[leomorgan]

I have a couple of questions for you. Most of the subpacks I have been cycling are similar from a charging/discharging capacity perspective. However, a couple of them have individual cells that get extremely hot (the good packs seem to get evenly warm across all 6 individual cells). I assume these hot cells are experiencing "cell reversal". Is there any way to recover from that? Such as discharging to zero and slow recharge? I just purchased an HCH battery pack and most of the subpacks are good, so I'll have enough good subpacks to rebuild the Insight battery even if I can't recover every single subpack from the HCH. But I would like to know that they CAN be recovered and how to do it...

Also, once I have cycled and re-installed all of the good subpacks, what charge level should the individual subpacks be at when I re-install the battery pack back in the car? Should I:

a) charge each subpack fully with the Triton2 just prior to re-installation or
b) discharge each subpack down to 5.4 volts and let the car charge the entire pack after re-installation.

Keep in mind when answering this question that the only viable chargers I have available to me are my Triton2 and the Insight itself...

Thanks for your help,

Leo