NHW11 Traction battery autopsy

Diagnostic Trouble Code:

http://priuschat.com/forums/generat...03-classic-prius-scanguageii.html#post1180085

What vincent1449p pointed out is the default 'codes' reported by the ScanGauge are emissions related. This is the same problem the over the counter scanners have . . . they just report emissions related trouble codes. In contrast, our NHW11 ECUs have three storage locations for Diagnostic Trouble Codes, the "P" and "C" codes that let us diagnose what is going on. The "C" codes come from the brake ECU.

BTW, I was thinking about the module pair that always show up high, #1, because it highlights a problem with unbalanced charges. A module that has a slightly higher state of charge can reach 100% charge before the others. It then begins generating gas and a higher internal pressure and the stresses the terminals from the higher, internal pressure. Part of the pressure comes from the increase in temperature.

There has been reference to something called a 'balancing charge cycle' or 'charge equalization cycle' and as explained the TechStream can force a higher than 80% charge on the traction battery, deliberately forcing the higher charged modules to generate gas. Then left alone, the H{2} and O{2} recombine in these modules and in theory all slightly over charged modules return closer to the lower SOC modules. But we know the NHW11 modules have weaker terminal seals than the NHW20 modules. If it leaks a little electrolyte, there would be a path to ground, the source of a P3009.

Personally, I would prefer to take the case off, measure the two modules at position 1, adjacent to the electronics, and using a load, moderately discharge the higher voltage modules to bring them inline with the next lower pairs. A controlled discharge that does not risk gas generation. In a perfect world, all higher charged modules would be fractionally discharged to equalize the charge . . . but this is very experimental stuff.

At the same time, I would use a pH test (aka., pool test kit) to look for evidence of electrolyte leakage. Clean it up and the P3009 path is gone. . . . Speculation on my part but the chemistry and physics makes sense.

Bob Wilson

 

Perhaps this will help:

I don't normally pay any attention to SOC but by happy accident, recorded some data while testing the Auto Enginuity:

• 5:27:19 - 5:29:19 - initial start-up. In the first ~45 seconds before the cats light up, the car runs on traction battery if gentle throttle is used. So you can see the decrease in SOC even as the speed increases. Once I reach cruising speed ~35 mph, I shift into "N", no further charging, to minimize the traction battery load. Of course the car continues to use the traction battery for 12 V electrical power.
• 5:29:19 - 5:31:19 - brief speed dip approaching and making a right turn so I engaged "D" for regeneration and acceleration which put a charge back into the traction battery.
• 5:31:19 - 5:33:19 - traffic light stop so I shifted into "N" while waiting. By now, the ICE temperature had reached 70C and I could go into "Stage 4" or hybrid mode.
• 5:33:19 - 5:45:19 - normal driving
• 5:45:19 - 5:47:19 - when I approach home, I keep my speed low so the car will maximum use EV mode until it is parked. The SOC reached a low point

Bob Wilson

 

KUDOS! This is some of the best data and exceeds my efforts. The spreadsheet is awesome. We have a new battery master!

Now your photo shows a black material on module #33. The 'o-ring' is black and it would be great if we can match the material. The other hypothesis is the KOH reacted with the sealant material. Regardless, #33 is certainly interesting. I also noticed the copper corrosion particles. I suspect the corresponding buss bar looks pretty ugly.


I'm in the spreadsheet and will post what I see:

• #8, #12 - clearly the lowest voltages and weakest charge mAhr, these are likely FUBAR. It may make sense to do another charge-discharge cycle but I seriously doubt they can be recovered.
• #29 - an exception, the initial voltage is in the 6 V range but the charge-discharge cycle looks bad. This one is interesting to see if it can be recovered or does it represent the threshold between a self-discharged to failure or a hard failure.
• #5, #12, #13, #16, #20, #22, #24, #31, #32, #35, #38 - these are the 6 V range modules that have mAhr capacity similar to what the Dept of Energy measured in their endurance testing of the NHW11 traction battery after 160,000 miles.
• #1, #2, #3, #4, #6, #7, #9, #14, #15, #16, #17, #18, #19, #21, #23, #25, #26, #27, #28, #30, #33, #34, #36, #37 - these are the 7.2 V range and they look strong, reusable for another pack. However, some of these modules have poor charge/discharge data.

I had forgotten this profile from a failed module:

You'll notice a failed module, one with a hard-failed cell, can show high charge voltages that appears nearly instantly as the failed cell appears as a non-linear, back-EMF cell on charge but as soon as it starts to discharge, it suffers a very rapid drop.

This is a great effort and I fully appreciate what we're seeing.

Here is one pattern that looks interesting:

My eyes see these groups:

• Group A - these look to be excellent traction batteries that could easily be used to replace marginal ones in another pack. The terminals need to be inspected to check for any evidence of weakness. Preserve these modules with a tickle charge, (1, 3, 4, 6, 7, 9, 14, 15, 23, 25, 26, 28, 33, 34, 36, 37).
• Group B - not so great, they show significant loss of capacity. These are excellent candidates for water rehydration, (2, 18, 27).
• Group C - even weaker capacity, at least they still show full voltage indicating all cells are 'still there.' I've seen similar modules respond well to water rehydration. However, they also show the rapid loss upon discharge. These would need testing and/or rehydration, (17, 19, 20).
• Group D - shows loss of one cell voltage. It isn't clear if these can be recovered either through multiple cycles or a combination of water rehydration (5, 10, 12, 13, 16, 21, 22, 24, 30, 31, 32, 35, 38)
• Group F - the low capacity strongly suggests these have reached the end. The full voltage suggests they may still be usable but between Group D and Group F, these are the modules least likely to be recoverable with water rehydration and/or multiple charge-discharge cycles (8, 11, 29)

I'm not done with the spreadsheet but I'm beginning to see patterns that may allow us to classify modules into groups. Some should go directly to a recycler to reclaim the NiMH material, Group D and F? Others may be reconditioned with a combination of rehydration and charge cycling, Group B and C. Then there is the good group that can readily be used to replace failing modules in other packs if there is no external evidence of a problem, Group A.

This is top quality data and is revealing information not previously available. Thanks "oldnoah" . . . you're making a real contribution to our knowledge.

Bob Wilson

 

Hummm, this is interesting. Looking at the photo of #33:
The second photo shows the gasket material around the terminal base of a failed module. This module had a failed cell and did not respond to rehydration.

When we look at #33 and #32 metrics:

	Column 1	Column 2	Column 3	Column 4	Column 5	Column 6
0	#	V several days	charge mAhr	discharge mAhr
1	32	6.66	2	419	1	272
2	33	7.76	3	510	1	924

Oldnoah table.

Was #33, B+ terminal the only one with the black material?
Can you characterize the black material . . . rubber like?

Thanks,
Bob Wilson

 

	Column 1	Column 2
0	module	group
1	2	B
2	5	D
3	6	A
4	11	F
5	12	D
6	29	F
7	30	D
8	31	D
9	35	D
10	36	A
11	37	A

There is good correlation with Group D and F or adjacency. Note that 37 is adjacent to 38, Group D. I know KOH has amazing ability to 'wick out' or travel.

BTW, you can see that any two leaks to the case within one bank will provide resistance path to begin partially discharging some of the modules through the case. It is very likely that the current flow electrolyzes the water leaving a non-conductive path. But KOH is hydroscopic and normal humidity will make it slightly conductive again. Over time, the modules 'leak' discharging will become unbalanced and that is death to a series battery.

I knew this but was wondering if when the battery originally failed, were you lucky enough to get any codes in the initial diagnosis?

Pure KOH is a white powder and in solution, clear. I think you've identified the bulk of the black around #33.

I am not sure we know what it is but I suspect it will have to be mechanically removed. You might try a flat screwdriver. I don't remember it adherhing to the plastic case. I've tried using JB Weld to seal holes and it has a hard time making a quality seal.

I'm convienced that sealing the case requires plastic welding of a matching plastic with attention to a clean, KOH free surface and that is a challenge. That KOH is wicked stuff.

I've not done that yet but I understand it is not that difficult. The standard Toyota battery swap ships the modules with new buss bars and the control electronics are swapped. One user reported it took him about 5-6 hours.

I can't emphasize what wretched stuff KOH is to work with. When it gets on your fingers, it feels slippery because it combines with the fats in our skin to make a soap. It 'climbs' surfaces and digests any and all organic material. It 'eats' aluminum, copper, and just about anything except stainless steel, glass and some plastics.

Make sure you have a water basin nearby, wear old clothes, and safety goggles. Gloves may not be necessary but be sure and washup afterwards. Did I mention it is wicked stuff?

Bob Wilson

 

I've thought about a 'plug-in lite' for the Prius traction battery based upon using a series, shunt regulator. This would not only put an 80% charge on the traction battery but also equalize the SOC of the 19 module pairs. The tricky part is when all modules achieve equal SOC, the power source, typically a constant current, needs to step down to a trickle level. It can be detected by a boost in charge voltage over the peak, series value.

You'll notice the sense wires go to a strange, custom connector. My thinking is a pair of 25-pin D connectors could intercept the voltage sense wires so the plug-in lite charger could do its stuff. It would also need to energize the middle relay and have an interlock so it 'steps out' should someone try to start the car.

Bob Wilson

 

I've removed the Bty ECU numerous time when I was troubleshooting my problem back in Feb. You don't have to take the frame apart, you just need to remove the 3 nuts that are holding it down.

I did not take photos. Here are some photos from web.

Remove the 2 nuts on the top and bottom of the white sockets:



Remove the 3rd nut at the base:



Tilt the Bty ECU towards the SMR and then lift it upwards.

More instructions can be found here:

http://techno-fandom.org/~hobbit/cars/TIS/ileaf/toyssc/toysspdf/sscsourc/2004/40g/40gtech.pdf

My HV Bty did not have sealant so can't offer any suggestion. However, I did use vinegar to neutralize the KOH spillage. You can also use dilute boric solution (800 grams boric acid to 20 liters water or 5.5 ounces boric acid to 1 gallon of water.)

 

One of the good things about a photo is being able to go back and see things otherwise missed on a first glance:

The traction battery is split into two banks, roughly in the center, 9 pairs in one and 10 pairs in the other. When the car is not in operation, these banks are isolated. But a DC current typically will have a different corrosion pattern depending upon which is the cathode and the anode. A DC current is used in electroplating so metal is removed from the anode, B+, and added to the cathode, B-. So looking at one side, my eyes see:

	Column 1	Column 2	Column 3	Column 4
0	module #	type	group
1	2	redish	worse	B
2	11	discolored	less bad	F
3	12	discolored	less bad	D
4	21	redish	worse	D
5	22	redish	worse	D
6	29	discolored	less bad	F
7	30	discolored	less bad	D
8	31	discolored	less bad	D
9	35-36	dark (?)	D-A

But this is just one side, the trunk side, of the traction battery case. If I were expecting one side to be more exposed to moisture, it would be the trunk side. Notice how the outside end, module is in the better, A and B, groups. So I would expect the modules in the middle of each bank to be in worse shape as these are the ones most likely to suffer discharge over time. The ones at the 9 and 10 bank boundary should also be relatively better than the middle ones of the 9 bank and 10 bank.

Could we get a similar photo of the other side or possibly both sides in one photo? The traction battery case is effectively a full-mesh, resistance network. Seeing the leakage patterns on both sides can help us understand the current flows. It would also help to know where the most positive and negative terminals were located.

Also, is it possible to get some close-ups of the different corrosion styles? The redish color suggests a rust.

If you have a sensitive instrument, do you have a way to measure the resistance say bolt-hole #1 to #38 on each side and #1, across, and #36, across? I suspect the resistance is very much less than an electrolyte leak. What this does is give a way to model how multiple leaks might flow current. Heck, if we could find a SPICE expert, ask them model it. <grins>

I'm also see two patterns. The more easily detected matches the width of the modules. The curious ones appear to be points midway between two anchor bolt holes.

Great photos!

We may have found a 'tell' of how to evaluate traction battery health and status. The ratio of voltages of the middle pairs compared to the end pairs may be what is needed to identify relative unbalance of a traction battery:

	Column 1	Column 2	Column 3	Column 4
0	module-pair #	description
1	1	left pair	base
2	4	5	6	left pair middle
3	19	right pair	base
4	16	15	14	right pair middle

I have some past surveys of traction battery voltages and this may help us understand the status.

The next test would be to see if we can get a 'balance charge' exercise done and see the results. I'm not fond of this approach because it can stress all modules, especially the better ones.

One lesson learned is if there are going to be leaky terminals, more module isolation and possibly a non-conductive case would be a desirable option. Instead of having fasteners to the metal case, the modules could fit in slots that the top and bottom halves would hold the modules fixed in place. This is just speculation, not a commitment to a new style battery case.

Bob Wilson

 

The dilution is suggested by Toyota for dismantling a Gen2 HV Bty.

 

You are bring a systems approach to the traction battery, the very thing missing and very impressive! When I bought my salvage battery, I was interested in the modules as the control electronics had been swapped and the old buss bars were gone. This was too narrow.

This also explains why we've had scattered reports of Prius traction battery failures after having sat idle for a long period of time. Speculation, the module imbalance from electrolyte leakage could easily explain what happened.

I have tried parallel wiring with smaller numbers of modules with copper hookup wire only to discover it was 'eaten' by the KOH three months later. I have a 100 ft. spool of nichrome wire, .01 x 0.02, that might make a better parallel connector buss:

• resistive - minimizes initial surge current from small voltage differences
• corrosion resistant - it should tolerate any KOH residuals
• heat tolerant - it was planned for an 'in-pan' transaxle heater

Send me a PM and I'll mail a 10 ft. section.

As for measuring trickle charge for a massive, parallel battery assembly, this is new territory.

Bob Wilson

 

and better wear eye protection goggles at the first place