Could you post some instructions and pics for your grid charger? I'm only finding a parts list in your signature and that's not enough for me to have the confidence to do it.

 

Do you mean the 12V car battery tester I linked?

Have you balanced and measured the capacity of all your sticks?

If you haven't "reconditioned" your sticks with a top balancing charge and a discharge to 6V or lower at low current, then the load test will not give you reliable results.

Be cautious of the information you get from this site and others. Some of it is outdated, some of it is suboptimal, and some of it is just wrong. I'm pretty active in these efforts on an ongoing basis for both IMA and Prius packs. If you have a question about something you've read, just ask here, and I'll try to clarify it.

I'm not the final word on this, but I own 5 hybrids and 11 packs...

 

I found what I was looking for in your spreadsheet regarding the grid charger. I didn't see the second sheet when I was originally looking. Thanks for your caveat of warning. I'm taking heed. I've been reading lots. I had my brother, a physicist and electrical engineer look at what I am doing and thinking so far. I appreciate your willingness to help.

I put a timer shutoff of 680 minutes on my chargers, I have 5 of them. After depleting the sticks to 6V and leaving an hour or so I charged the sticks for 680 minutes a piece. The first 5 gave me readings of apprx 8.8V fully charged with capacities on charging of around 7200. They never reached the delta peak of 4mV that I had set. I switched them immediately to discharge after they timed out so that I can hopefully get an accurate reading of their discharge capacity. All of this has been a learning curve.

I will take IR measurements when I top these off for use. I will use your suggestion of waiting 1 hour after a full charge and using the connections as you suggest. Grid charging looks like a strong possibility.

Jen

 

What was your charge current?

Charging tells you only vague information on the capacity of a NiMH cell/battery. The charging process is inefficient, so the input is always greater than the output. You only care about the output.

You were charging at too low a rate for too short a period. I'm guessing you were charging at around 0.6-0.7A. Please confirm.

All your charges went to the same mAh because you were charging at a near constant current for exactly the same time. C/10 charges are recommended for 15-16 hours for a full formation charge.

For DeltaV to be reliable, you need to be close to 1C. For a 6.5Ah battery, that's 6.5A. 6A and even 5A is close enough if your cells are reasonably balanced.

Due to the charging inefficiencies, it's almost certain your sticks aren't full. I recommend you conduct ANOTHER 5-6A (higher is better) charge on each stick and let it hit deltaV cut off. That will help ensure you are at 100% SoC. Monitor cell temps and do not worry too much. Damage will not occur until the cells are uncomfortably warm (I mean, they are uncomfortably warm to touch, not that it makes you nervous). The car is outright abusive to them compared to what you can do.

Rest each stick for 1 hour before IR check or discharging.

I'm still concerned that you have not adequately "reconditioned" the sticks. Deep or semi-deep discharge is key, and if you've only gone to 6V, you might not have gone far enough.

What was the lowest current you used to discharge to 6V?

Steve

P.S. if your electrical engineer physicist brother has any corrections, please let us know.

 

The knowledge that the car abuses these batteries more than I can helps me have more confidence. Sorry about the line about my brother. He didn't spend much time on my config. He just said that batteries should be discharged at C/10. I will have another conversation with him. I was charging at .7 amps. They all charged to about 8.8V and did not gain any significant voltage for the last 80 minutes. At the end of the charging the voltage started to vary by one or two tenths of a volt on all of the sticks so I was guessing that the chargers may have begun their "re-peak" function right before they timed out. No information was given to this effect though. I had no idea that C/10 would go 15 to 16 hours. I thought 11 hours was bad enough.

I am now discharging them at 0.8 amps to 6V. I'm really bored with these batteries right now... I can charge at up to 6 amps and discharge at up to 2 amps. When these batteries finish this 0.8 amp discharge cycle I will charge them at 6 amps. Then I will do one more 0.8 amp discharge to 5.4V and call that capacity the final one, charge them up, and test them. What do you think?

Thanks,
Jen

 

No need to apologize. I was being serious about your brother.

The ANSI standard for testing capacity is:

C/5 discharge to 1V/cell
C/10 Charge for 15 or 16 hours (can't remember which)
C/5 discharge to 1V/cell

The final discharge determines the capacity of the battery; however, the above is mostly for consumer grade cells in electronic devices. Due to the extremely high charge and discharge currents these cells experience, higher discharges are necessary to confirm they will perform. No, they can't deliver their entire capacity at 100A, but they can deliver about 90% of it at 20A, and they get subjected to 20A routinely.

To save time and accomplish the same thing, I recommend you use your rapid discharger to go to 6V. Then use the IMAX to discharge to 5.4V @ 500mA. The high current discharge won't hurt them, and it will shave hours off your discharge time per stick. You can't get a capacity off that, but you can get a discharge time, which will be as good as a capacity measurement for comparison purposes.

I get that you're bored with them. That's why I discourage anyone from stick work without doing the grid charge/discharge first. You can be done with the grid charge/discharge in a long weekend with 3 hours of actual touch time.

Lastly, to summarize a few posts and expand detail:

1. Fully charge sticks @ 5-6A to deltaV peak (following your 680 minute charge).
2. Allow to rest for 1 hour or more
3. Record resting voltage and IR (take at least 3 readings)
4. Discharge with your 20A discharger to 6V, record time for comparison purposes (you may want to monitor it to make sure it cuts off at 6V and so you can get an accurate time, 20A goes quick)
5. Discharge with your IMAX to 5.4V @ 500mA
6. Recharge the stick at 0.7A for 30 minutes as soon as possible after 5.4V discharge.

Do all of the above on all sticks before proceeding.

1. In a single sitting, on the same day, Charge all sticks @ 5-6A to peak deltaV.
2. Let them sit overnight (at least 8 hours)
3. Conduct 30 second discharge test with 12v Automotive load tester on each stick (monitor voltage with separate voltmeter). Note that you may need to change the time of the test. Don't go past 60 seconds as that will be very hard on the tester unless you let it cool several minutes between tests. The 30 seconds is my best guess based on the anticipated load of the tester. It could be as short as 10-15 seconds if it can actually load 100A on the lower voltage stick.

Consistency in the 20A discharge test (same discharge time ±10%) and consistency in the 100A load test will tell you if you're there. If you have any sticks that stand out on the low side, you may want to do some more refurbishment efforts on them (more cycles, lower discharge).

BTW, what prompted you to take this on? Did your IMA light come on suddenly, or had it been on for some time?

Steve

 

Thanks so much! I took this on because my HCH1 died: transmission slipping, engine leaking oil... but the check engine light was on and was throwing the codes for the battery, I don't remember them off the top of my head, and codes for 2 emissions sensors even though I had recently replaced them. The IMA light was not on but my gas mileage had fallen from 45 to 37mpg also. I'm curious as hell so I took the battery out before I junked the car. I sold the inverter, dc-dc converter, and the IMA computer on eBay. I figure I'll find this battery a happy home as soon as I am confident it will perform well but I want to learn everything about this. Its my nature.

 

Ah. Well, since the IMA light was not on, then the pack is probably functional as-is. The stick refurb and load tests will just confirm it.

Steve

 

Ok, my first five sticks are finished. They all measure between 7100mAh and 7500mAh at 0.8A discharge and between 6.2mAh and 6.5mAh on a 100A load. They have gained considerable capacity but I am unable to express this adequately since my first few cycles were done differently than my last two. I will report the gain in capacity on the second set of five sticks so that the comparison is available. - Jen

 

I forgot to state that the capacities were measured from peak voltage to 5.4V when discharged at 0.8A and from resting voltage (about 12 hours after charging to peak) for 30 seconds (since I didn't come close to 5.4V on any of them) for the 100A test.

I take it that 30 seconds is the test length because 80A (because of inefficiencies) divided by 6.5Ah = 360 seconds per hour divided by 29.25 seconds? Please correct if I am understanding this wrong. - Jen