Analyzing, refurbishing/repairing a dead hybrid battery pack (2000 Honda Insight)

[MetroMPG]

Halftime report...

Well, I'm at the halfway point in testing. The 10th subpack goes on "auto cycling" this evening for an overnight run.

So far I've found 2/9 subpacks that seem below average - max. discharge capacity in the mid-5500 mAh range, vs. mid-6500 range for the rest.

Mr Smalls relayed to me that Ron at hybrid-battery-repair considers 5500 and below worth replacing. So, if the trend holds, perhaps 4 sticks will need replacing in total.

In other news, I found a grid charger to buy from another EcoModder member who sold his Insight, so once this all goes back in the car it can be kept better balanced.

[MetroMPG]

Found another dud in the pack - worst so far: stick #12 topped out at 4979 mAh discharge capacity.

Lucky #13 cycling now...

[MetroMPG]

Home stretch

I can see light at the end of the tunnel. The last stick is cycling, should be done early this evening. I'm still collecting self-discharge data, and will also do the internal resistance test IamIan recommended.

So... how bad is the pack?

You can see the results in the google spreadsheet.




The worst stick (the one with the lowest "restored" discharge capacity) appears to be #19, at 4879 mAh.

Since the capacity of the pack is limited by its weakest stick, that puts the pack at 75% of original, nominal capacity of 6500 mAh.

That really doesn't seem too horrible. Out of curiousity, I'm tempted to put it back in the car just to see how it behaves, while properly balanced.

If I replace all the sticks with sub-5500 mAh discharge capacity, as has been recommended, that would mean 6 or 7 (depending on how this last one turns out) sticks to replace.

With the weakest stick at 5500 mAh, that would mean the pack has 85% of its original capacity.

[IamIan]

Originally Posted by MetroMPG

Since the capacity of the pack is limited by its weakest stick, that puts the pack at 75% of original, nominal capacity of 6500 mAh.

With the weakest stick at 5500 mAh, that would mean the pack has 85% of its original capacity.

I agree with your idea to after the other testing is done to test a SoC balanced pack in the car to see how it performs.

Then you will have all the information to decide if you want to replace sticks or not ... and what the potential gain would be ... and now you know how much work and such would be involved doing so.

If you plan on occasionally doing some type of SoC balancing ... Grid Charging or whatever ... then the Self Discharge rate will be a minor issue ... but if you don't do some type of occasional SoC balancing , it is only a mater of time before differences in self discharge rate significantly reduce the usable capacity ... like how your saw in the start with a large gap in SoC.

Capacity differences kind of always effects the total effective capacity ... like you said weakest link in the chain.

Resistance differences are most significant the higher the IMA currents used ... so how important that is ... is kind of up to how you choose to drive.

[rmay635703]

Originally Posted by MetroMPG

Home stretch

I can see light at the end of the tunnel. The last stick is cycling, should be done early this evening. I'm still collecting self-discharge data, and will also do the internal resistance test IamIan recommended.

So... how bad is the pack?

The worst stick (the one with the lowest discharge capacity) appears to be #19, at 4879 mAh.

That really doesn't seem too horrible. Out of curiousity, I'm tempted to put it back in the car just to see how it behaves, while properly balanced.

With the weakest stick at 5500 mAh, that would mean the pack has 85% of its original capacity.

Have you tried quick discharge to 1v then recharging that one bad cell repeatedly?

I was told a while ago that some of the NiMH can be restored somewhat if discharged quickly (but not too low) then recharged several times.

Also if you build a grid charger you can probably live with the issue at near full capacity, the one cell will be pulled into the low range but as long as you recharge every night it should last quite a while anyway.

[MetroMPG]

All the sticks were cycled repeatedly until their capacities stopped improving, which ranged from 4 to 8 cycles. (I used a ~1% guideline - if the improvement was around 1% or less, I stopped cycling it.)

You can see the results in the google spreadsheet.



But maybe I'll try cycling one of the lower ones a few more times to see what happens.

Of course if the stick IS as good as it is going to get, I'm just shortening its lifespan with "unnecessary" cycling...

[MetroMPG]

But maybe I'll try cycling one of the lower ones a few more times to see what happens.

FYI: 4 more cycles on stick #18 - no improvement.

[MetroMPG]

Originally Posted by IamIan

If you plan on occasionally doing some type of SoC balancing ... Grid Charging or whatever ... then the Self Discharge rate will be a minor issue ...

That's the plan - I have bought a grid charger from a former Insight owner. It's in the mail.

Resistance differences are most significant the higher the IMA currents used ... so how important that is ... is kind of up to how you choose to drive.

Understood.

In fact, one of the first mods of 2012 for this car will be the clutch switch hack to disable assist on command. I don't plan on using aggressive assist generally.

[MetroMPG]

Originally Posted by Old Mechanic

A tactical graph of all of the individual sticks should show you where the sticks tend to suffer the most and where they suffer the least.

Not sure if these tea leaves are meaningful (representative of other people's battery packs), but here's how it turned out:




It sure seems like the top row is a better place to live than the bottom row.

And in terms of the series "string" of sticks within that layout, here's how they're connected:

Top row stick #'s: (empty), 1, 2, 3, 4, 5, 6
Middle stick #'s: 13, 12, 11, 10, 9, 8, 7
Bottom stick #'s: 14, 15, 16, 17, 18, 19, 20

Photo of the LEFT side:

[ncc74656m]

#thingsIamimpressedwith

Metro, all I can say is that this is amazing. It seriously makes me want to go out and try to find an old Insight with a "dead" pack. I've always thought they were oddly gorgeous. Obviously though, a great deal of your savings came from pure luck, I suspect, given that not all lot owners would know that a dead batt can be revived like this.

What, roughly, do the tools you used (Super Brain?) and a Grid Charger cost if I decided to play with this.

I'm comfortable enough with things that can kill me, so I believe I'm competent to work on the IMA pack without shorting me or it out. Seeing as how the car can be safely driven without the IMA if you're careful (minding the 12V issues), I'd love to try this out. It'll also give me a good excuse to dump my Corolla, which I've felt almost nothing but apathy for since I got it.