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MIMA Pack Whack /rebalancing the battery pack
|  | | | Whack the pack to erase the cell memory and fix recals |
The MIMA pack whack could be a huge new advantage to owning MIMA for the many people struggling with limited capacity battery packs due to recalibration's.
As many of you know, I have been using MIMA on my pack since 80K, and as I approach 140K, the pack still runs fully from top to bottom, on each cycle. Since I do not have recal's, it is something that I was not able to examine. On my trip to Hybridfest, I flew out to MI,to ride out with Ed Zandee,a very savvy auto technician who owns his own service center in Grand Rapids. Ed purchased a used 2000 Insight with 130K on the clock.Like many older Insights, he was getting a typical recal whenever his pack reached 5-6 bars from the bottom. Ed Installed a MIMA system the day before we drove the 350 miles to Madison. I drove some of the way, and got to experience recals first hand for the first time. Ed and I started to experiment and analyze what was happening. We noticed that the recal point seemed to move up the scale one bar as the pack temp increased.We also found that full regen could be applied with MIMA, even though the SOC guage was showing full and limiting the standard IMA regen.
I have since confirmed that my pack will stop MIMA charging near the top bar, so it is synchronized with the SOC display.
Most of us with MIMA will stop regen when the SOC is at the top, since we fear overcharging.
This is where we do the PackWhack.
Just let the ABC keep charging until it is limited, even though the SOC is at max.
Drain it down till no assist is available, and you have given it a stop to stop full charge.
On the way back, we again took turns driving,We decided to push past the SOC top end and using MIMA we continued to freely charge, for quite some time while the SOC was pegged at the top. A good pack will stop excepting charge from MIMA when full,even if the MIMA system request it, so this was a new experience for me.
We decided to keep jambing charge into the pack to see if it would eventually start limiting, and eventually it did, but only after putting in the approximate equivalent of charging to about 6 more bars.
We then switched on PIMA, and started running a lot of assist. We were drawing full assist for several minutes, before the SOC finally began to drop, and it dropped smoothly to the recal point, and then recalled as normal, but this time, even with no bars of SOC, we were able to draw the full 100 A of assist for several minutes as the photo shows, until the assist finally became limited. We ran the pack through the cycle another time, with the same results.
We got back to Ed's place, feeling that the pack was outputting a lot more capacity than before.
The real surprise came the next day, when Ed brought me back to Detroit for my flight home.
The recals were gone. We cycled the pack several times, and the SOC ran from the top,right to the bottom.
Ed will do some more test runs with his Honda factory scan tool and get us more information. Making some assumptions which still need to be tested, my read of this experiment is that the SOC limits that stop normal IMA action at both ends are different that the BCM top and bottom limits which are based on actual voltage measurements on both ends.
When a pack starts having limited capacity issues due to the memory effect, the SOC in normal IMA mode will stop regen when the guage is at the top,even though the pack is really not charged fully. The MIMA forced charge is limited instead by the BCM when it determines that the battery voltage has reached the max. So this MIMA PackWhack as Ed and I began to call it, allows the pack to be fully charged past the SOC gauge limited point that the standard IMA is limited by, and is only stopped when fully charged, therefore doing the equivalent of a equalization charge on a lead acid based pack.
I suggest that any of the MIMA owners that have recals give this a try. Just stay in an ABC forced charge, or manually do regen until the charge is limited even though the SOC bars are full. Then do assist with PIMA or MIMA until it starts to be limited on the bottom end.
Do several of these cycles, then see what happens with your recals the next day.
Of course you are doing this at your own risk, as it will take some time to see if this effect is temporary.
This blog will be where we will put the results of further testing of this experimental procedure.
All recals are not the same, so this procedure is for the standard regular recal at a specific SOC that seems to be the most common.
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Insight Battery pack charger/rebalancer
|  | | | Danger this HV panel can electricute you |
Many Insight battery packs develop an imbalance.
Sitting at a constant SOC for a long time without charging or exercise will allow the individual cells to self discharge due to internal leakage. This leakage is usually slightly different on each cell, so given enough inactivity time, the pack will develop a big difference in charge between the cells.
The Insight system stops charging at 80 % SOC, so the imbalance never gets fixed by an equalization charge.
If you fully charge a pack with a constant current of 85 -255 MA, this constant current will bring up the weaker cells by giving all cells a 100% charge.The cells are rated for 500 or more full cycles, so an occasional one or two will not effect the pack life.
It is very likely that many packs that have become imbalanced, and were frequently recalibrating before throwing an IMA code can be revived by rebalancing.
I am designing a solar pack charger that provides the required current at sufficient voltage to do this recharging and re-balancing.
The solar charger needs to be able to produce 180VDC to fully charge the battery.The panel output terminals with no load will be at 250VDC. this panel delivers about 15 watts of power.
Using this procedure exposes you to the full pack voltage, so you can get electrocuted if you get your self across the HV, of either the pack, or the solar panels.
Any body want to be a tester of the charger/balancer, should contact me to discuss it, electrically savvy people only.
(Posted 6/23/2008 by mikey) |
Equilization test #1
|  | | | Equilization charge at 300ma |
Ian and I took one of my 7 Seven subpack Prius based packs and after discharging it to lower the SOC by 10-20%, set up a constant 300MA charge system, and logged the voltages across each subpack. We spread the packs out so that cooling would be the same on each, and measured the temp of each cell when we took the voltage measurement. The initial condition showed a max of about .07V difference between the subpacks. The charge ran for 14 hours before I saw the sides of the cells start to bulge, but I never saw any measurable temperature rise.
The Subpacks seemed to equalize starting at 7.85V/subpack, where all of the subpacks were at that exact voltage. I continued to charge up to 8.47V/subpack where all the subpacks remained at the exact same voltage.
Next I will discharge the series string and log the voltages during discharge.
(Posted 11/19/2007 by mikey) |
Battery pack rebalancing?
|  | | | HV taps WARNING this will fry you. |
WARNING, the batterypack can and will kill you if you contact the hot terminals, so do not try this if not fully comfortable with working on HV DC circuits.
A look at the Saturday workshop efforts will show that Ian has rebalanced the silver Insights battery pack using the Triton smart charger. A lot of work, as the pack must be pulled and disassembled. James Frye from Reno, has duplicated the procedure for his consistantly recalibrating pack, and we await the results.
Another approach to this rebalancing has been suggested by Armin Kusig who has been grid charging his battery pack each night with a gentle 300MA charge. Since the info on NIMH batteries would indicate that a low current charge of the batteries should not do any damage or substantially reduce the life of the batteries, it may be a better way to do a rebalancing.
The battery pack current control/interconnect board allows access to both ends of the battery pack, and therefore is the best place to connect a series charger. The indicated points are only HOT when the main switch is on.We will be building up a constant current charge system to give this a try, and will report the results here.
(Posted 11/17/2007 by mikey) |
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