Battery reconditioning voltage measurement
#61
01-19-2016, 07:02 AM
Re: Battery reconditioning voltage measurement
I tried this discharge method of 500W to ~135V and then 120W to about 35V on a pack that was recalling multiple times on each drive and I haven't had a recall since (three days of driving as of this post).
Thanks for this reconditioning method!
Thanks for this reconditioning method!
Jen,
I'm very sorry you've gone down this path. There is so much evidence of the benefits of grid charging/discharging that render stick work unnecessary except in the cases where sticks must be replaced. That requires high current discharge testing on the order of 36X (180W vs. 5W) the power the Imax can deliver.
I have a dozen of the chinese Imax knock-offs. They are terrible at deltaV detection and frequently cut out well before the stick is close to full. It has nothing to do with voltage bounce of the sticks, it has to do with them being crappy pieces of crap. You can sometimes get some use out of them by setting the deltaV detection to 20mV and keep your charges under 3A. You may have to go as low as 0.7A.
While the SkyRC is a quality product, it is terrible for this application. You should see an improvement in correct charge termination. The best move would be for you to return it/them and obtain something with a useful rate of discharge.
Voltage bounce is normal and desirable in NiMH cells. In your case, when you start a discharge after fully charging the sticks, the capacity is the number the Imax reads when the discharge terminates at 6V and ~0.8A, that's the capacity of the stick... at 0.8A.
The issue with the B6 is the discharge rate is way too low to tell you anything useful about the health of the sticks. They can only identify the most crappy of sticks. The car subjects the sticks to a 100A load for short duration and 20-50A routinely. Sticks perform at 50A+ much differently than they do at 0.8A.
I recommend the following:
The above process will accomplish what it will take 2-3 weeks to do with your IMAX B6 (assuming you only have one that works). 3 of them would get you down to one week, etc., but that would require that you time your cycles perfectly and don't lose any time or have any false charge terminations.
The grid charger takes about 30 minutes to put together.
If it doesn't work, you have a sick stick or two or more, and you'll likely never find it with the Imax.
Good luck,
Steve
I'm very sorry you've gone down this path. There is so much evidence of the benefits of grid charging/discharging that render stick work unnecessary except in the cases where sticks must be replaced. That requires high current discharge testing on the order of 36X (180W vs. 5W) the power the Imax can deliver.
I have a dozen of the chinese Imax knock-offs. They are terrible at deltaV detection and frequently cut out well before the stick is close to full. It has nothing to do with voltage bounce of the sticks, it has to do with them being crappy pieces of crap. You can sometimes get some use out of them by setting the deltaV detection to 20mV and keep your charges under 3A. You may have to go as low as 0.7A.
While the SkyRC is a quality product, it is terrible for this application. You should see an improvement in correct charge termination. The best move would be for you to return it/them and obtain something with a useful rate of discharge.
Voltage bounce is normal and desirable in NiMH cells. In your case, when you start a discharge after fully charging the sticks, the capacity is the number the Imax reads when the discharge terminates at 6V and ~0.8A, that's the capacity of the stick... at 0.8A.
The issue with the B6 is the discharge rate is way too low to tell you anything useful about the health of the sticks. They can only identify the most crappy of sticks. The car subjects the sticks to a 100A load for short duration and 20-50A routinely. Sticks perform at 50A+ much differently than they do at 0.8A.
I recommend the following:
- reassemble pack
- build DIY grid charger and discharger in my sig (about $85-90)
- grid charge to peak voltage for 8 hours but do not exceed 24 hours. Blow a box fan through the pack for cooling.
- discharge to 135V with 2X 200W or 250W bulbs
- switch to 60W bulbs and discharge to 60V or 12V as time permits.
- Grid charge to peak voltage for 8 hours but do not exceed 24 hours
- Install in car
The above process will accomplish what it will take 2-3 weeks to do with your IMAX B6 (assuming you only have one that works). 3 of them would get you down to one week, etc., but that would require that you time your cycles perfectly and don't lose any time or have any false charge terminations.
The grid charger takes about 30 minutes to put together.
If it doesn't work, you have a sick stick or two or more, and you'll likely never find it with the Imax.
Good luck,
Steve
#62
01-19-2016, 07:34 AM
Re: Battery reconditioning voltage measurement
Good to hear. Note that while it's not referenced in those specified steps, I mention it elsewhere, including the DIY grid charger/discharger sheet, the bulbs should be wired in series.
When bulbs are wired in series, the voltage drop occurs across both bulbs where they effectively see only half the voltage. Their power is not additive, it is halved. 2X 250W bulbs in series are actually the same as a single 125W bulb. If they are wired in parallel, then yes, it's 500W. The 2X 60W are really like a single 30W bulb.
I have since changed my method to further limit current at low voltages. This greatly increases the discharge time, but the risk of damage from reversals is significantly reduced.
The use of 2 bulbs in series is intended to minimize bulb replacement as pack initial voltage can well exceed the bulbs ratings. Single bulb configuration can fail quickly.
Any reasonable wattage to ~1.1V/cell (135V HCH1, 145V HCH2), even 2X 500W halogen bulbs would be fine. Below that, 2X 25W appliance bulbs in series. The conservative current threshold for deep discharges is 200mA. The dual 25W bulbs in series are between .12 and.17A from 85-175V, respectively.
If you were experiencing recalibrations without an IMA light, I would expect good results for 1-2 months, maybe more. When you start to get regular recalibrations again, try a grid-charge only and see how long that lasts. Once you know those two numbers, your 3rd should be another grid charge/discharge. If you recorded the time from the previous discharge, I would expect the second discharge to take longer, and that's a good sign.
When bulbs are wired in series, the voltage drop occurs across both bulbs where they effectively see only half the voltage. Their power is not additive, it is halved. 2X 250W bulbs in series are actually the same as a single 125W bulb. If they are wired in parallel, then yes, it's 500W. The 2X 60W are really like a single 30W bulb.
I have since changed my method to further limit current at low voltages. This greatly increases the discharge time, but the risk of damage from reversals is significantly reduced.
The use of 2 bulbs in series is intended to minimize bulb replacement as pack initial voltage can well exceed the bulbs ratings. Single bulb configuration can fail quickly.
Any reasonable wattage to ~1.1V/cell (135V HCH1, 145V HCH2), even 2X 500W halogen bulbs would be fine. Below that, 2X 25W appliance bulbs in series. The conservative current threshold for deep discharges is 200mA. The dual 25W bulbs in series are between .12 and.17A from 85-175V, respectively.
If you were experiencing recalibrations without an IMA light, I would expect good results for 1-2 months, maybe more. When you start to get regular recalibrations again, try a grid-charge only and see how long that lasts. Once you know those two numbers, your 3rd should be another grid charge/discharge. If you recorded the time from the previous discharge, I would expect the second discharge to take longer, and that's a good sign.
#63
01-19-2016, 07:41 AM
Re: Battery reconditioning voltage measurement
Thanks for the info (I was an aircraft electrician for many years, so I understand the electrical part). I'll try your advice when I start getting regular recalls with just a grid charge and see how that goes.
#64
01-21-2016, 08:28 AM
Re: Battery reconditioning voltage measurement
Additionally, a big disadvantage to the carbon pile tester is the difficulty setting a specific load. It's a great tool, but it's a tough one to master.
I think the tone the unit emits is after 10 seconds at a set load. If that's a more convenient target point for you, that's fine too. Just make it consistent.
Steve
I think the tone the unit emits is after 10 seconds at a set load. If that's a more convenient target point for you, that's fine too. Just make it consistent.
Steve
Newbie question: When using this tester is it ok to zero the load in on one stick and then leave it set at that setting for all the rest of the sticks, clamping and unclamping the tester to turn it on and off?
Jen
#65
01-21-2016, 08:44 AM
Re: Battery reconditioning voltage measurement
If you don't mind the violent spark of 90A, it's not a problem; however, you will find that as each stick responds a little differently, so does the tester.
A better solution is to remove the master switch from the subpack and attach it to the end of the stick. You can then use the master switch to turn on and off and tweak the current as needed.
I can't stress it enough... don't try to catch a falling voltage. If it's still dropping fast as you hit the tone or whatever mark you choose, it's best to let it settle. Don't go more than 30 seconds though.
And again... after this discharge, about 60 seconds later, measure or feel the temps of the cells. they should be at least a little warm. What will get you is if one is significantly warmer than the rest - higher internal resistance.
A better solution is to remove the master switch from the subpack and attach it to the end of the stick. You can then use the master switch to turn on and off and tweak the current as needed.
I can't stress it enough... don't try to catch a falling voltage. If it's still dropping fast as you hit the tone or whatever mark you choose, it's best to let it settle. Don't go more than 30 seconds though.
And again... after this discharge, about 60 seconds later, measure or feel the temps of the cells. they should be at least a little warm. What will get you is if one is significantly warmer than the rest - higher internal resistance.
#66
01-23-2016, 04:27 AM
Re: Battery reconditioning voltage measurement
Hi Steve,
It took me about 28 hours after grid charging the pack before I was able to test the sticks. The pack charged to 170.1V. Immediately before the test each stick measured within 0.05V of each other. Most of the sticks measured 8.1V. I did what you said about using the master switch inline with the battery, great idea thanks. I was able to load 80 amps for the 10 seconds before the tone sounded. All of the sticks dropped to about 6.4V immediately and then slowly. 15 of the sticks dropped to 6V, three of the sticks to about 6.1V and 2 to 5.8V. Good enough?
Jen
It took me about 28 hours after grid charging the pack before I was able to test the sticks. The pack charged to 170.1V. Immediately before the test each stick measured within 0.05V of each other. Most of the sticks measured 8.1V. I did what you said about using the master switch inline with the battery, great idea thanks. I was able to load 80 amps for the 10 seconds before the tone sounded. All of the sticks dropped to about 6.4V immediately and then slowly. 15 of the sticks dropped to 6V, three of the sticks to about 6.1V and 2 to 5.8V. Good enough?
Jen
#67
01-23-2016, 07:18 AM
Re: Battery reconditioning voltage measurement
Sounds great. The healthiest sticks I've tested at 90-100A for 15 sec are in the 5.4-5.7V range.
Just to make sure you weren't "catching" voltages, grab the 6.1V stick and check it for 30 seconds noting voltage at the 10, 20 and 30 second marks.
Just to make sure you weren't "catching" voltages, grab the 6.1V stick and check it for 30 seconds noting voltage at the 10, 20 and 30 second marks.
#68
01-23-2016, 09:28 AM
Re: Battery reconditioning voltage measurement
I retested the 6.1V stick. It dropped immediately to 6V then at 10 secs to 5.7, 20 secs to 5.6V and 30 secs to 5.4V. So I'm pretty sure I wasn't catching the voltage reading in the first set. Besides they really were dropping slowly by the time the tone sounded. Thank you so much, Steve! 
#70
02-14-2016, 05:59 AM
Re: Battery reconditioning voltage measurement
Good Morning,
Ok about a different pack...
If a battery discharges substantially faster the second time it is grid- discharged to 132V what does it mean? I will post a spreadsheet of my measurements for this pack but basically it discharged unevenly to 130V very quickly (the speed "broke" after 2.5 hours) the second time. After this happened I deep discharged it to 60V. This was slow and even in speed but the sticks discharged unevenly.
https://docs.google.com/spreadsheets...it?usp=sharing
I measured the tap voltages after discharging. I don't think I would have had the courage to discharge the pack to 60V if I had known how low some of the tap voltages were reading. All of the sticks rebounded relatively well considering.
This seemed to have fixed the pack since I got nice tight readings upon charging... a low standard deviation, and a low spread of tap voltages. This pack is now in my HCH1. There are no codes any more. It doesn't have very good gas mileage yet (33 mpg) but the temperatures are below zero here right now and I'm still getting reacquainted with a stick shift.
Jen
Ok about a different pack...
If a battery discharges substantially faster the second time it is grid- discharged to 132V what does it mean? I will post a spreadsheet of my measurements for this pack but basically it discharged unevenly to 130V very quickly (the speed "broke" after 2.5 hours) the second time. After this happened I deep discharged it to 60V. This was slow and even in speed but the sticks discharged unevenly.
https://docs.google.com/spreadsheets...it?usp=sharing
I measured the tap voltages after discharging. I don't think I would have had the courage to discharge the pack to 60V if I had known how low some of the tap voltages were reading. All of the sticks rebounded relatively well considering.
This seemed to have fixed the pack since I got nice tight readings upon charging... a low standard deviation, and a low spread of tap voltages. This pack is now in my HCH1. There are no codes any more. It doesn't have very good gas mileage yet (33 mpg) but the temperatures are below zero here right now and I'm still getting reacquainted with a stick shift.
Jen
Last edited by jjh1; 02-14-2016 at 07:09 AM. Reason: clarity
