grid charger/balancer

[MN Driver]

Originally Posted by Mike Dabrowski 2000

If the top voltage is set below the max that the pack will reach when completely full, yes the current will drop, but I am suggesting that the max voltage should set above what the pack will ever reach, so the 350ma is available to allow the weakest cells to get 100% full. The max voltage that the final settling reaches is a variable that will change based on the condition of the subpacks.
I have seen some cells top off at .1V more than others. You will see this when I put up the tracings of all 20 of my sticks.
.1V X 120 cells, and we have 12V on the whole pack. Most cells are much closer than that, but you get the idea.
The key thing to remember here is that the 350ma will not damage the pack,especially with the fan running, and if the pack is not allowed to fully balance, buy setting the max volts too low, you are not really balancing the cells that need it the most.

I agree, I have no plans on controlling a 'max overall voltage' when charging them since they can easily absorb an overcharge at 350mA.

[MN Driver]

In reference to post #350, I'm referencing the entire post but don't want to quote the whole thing, since it is rather long

Originally Posted by crx_rogus

But the BCM can only look the cells 12 at a time; I hope it can detect the voltage collapse of a single cell in each of those 12-cell strings.

...

Fast Charger:
Charge C-rate: 1C
Charge time: 1h+
Temp range: 50 - 113 deg.F (10 - 45deg.C)
Termination method: NdV responds to higher settings; uses dT/dt, voltage plateau, absolute temperature and time-out-timer.

If the Insight's cells are 6.4Ah rated, 1C = 6.4A, 0.5C = 3.2A, 0.3C = 1.92A, 0.1C = 640mA unless I'm clueless.

Before the table, it mentions "NiMH batteries should be rapid charged rather than slow charged. ... Because a NiMH battery does not absorb overcharge well, ... The recommended trickle charge for the NiMH battery is a low 0.05C [320mA in our case if I have my numbers right]."

That suggests our packs shouldn't even see the 350mA as a real charging current, but that defies observed reality. It also suggests that beefing up the chargers and making them temperature-sensitive would be a good idea. Beefing them up to where the cells overheat even with a full 12V to the fan would however not be a good idea. As weather changes, I suspect acceptable sustained charger power levels should also change.

The only issue that I have with fast charging these that I've come across is in order to charge 1C, there are some cells on a stick that get hotter than others. I just charged a stick at slightly under .5C of it's discharged capacity, at 3 amps the two far outside cells didn't even get to 30C, two of them got to 40C and one to 45C which after I noticed this and terminated the charge, it went to 50C within about 10 minutes. I've charged this stick at a lower rate followed by a trickle charge and I've manually measured voltages and they all experience voltage drop and at lower rates they seem to raise temperature in a uniform fashion within the same stick to where if I stop charging with the coolest stick at 35C, the hottest is at 40C with the odd part of this being that every time I cycle it's not always the same cell(s) that ends up the hottest either.

The cells are rated at 6.5Ah. They seem to take a 2C charge pretty well at the stick level but grid charging that at the pack level without temperature monitoring can get them hot enough to hit 45C if a charger doesn't terminate through dV, which with an unbalanced pack will not happen in time to prevent an overheat with the cells at a lower SOC since they are still rising in voltage and dV isn't pronounced enough at lower currents either for effective detection, which is where we are sitting at around C/20. I've read that they can handle the overcharge through recombination with C/20, ideally it shouldn't be done without a purpose for longer than it needs to be done as you eventually reach the point where all cells are topped off and energy is being wasted as heat. It would be nice to have a 1 amp charge with an end of charge detection scheme but I think that the closest that we can get easily without popping over our packs and throwing temperature sensors all over and to monitor things or wire into the PTC strips(which would likely be much easier) is to have the charger trip off with Mike's design at a predefined voltage that occurs somewhere near a full charge.

Mike, The switchover point of your charger being lower than the ending final voltage of the pack at 350mA might be too low considering that the higher rate would have a higher terminal voltage, we might need to find a way to calculate an ideal voltage for that switch-off of the higher current to occur, granted after they are balanced would be the safest time to do that but if it's done too early, it might take a significant time for the ending top-off. I'm not sure how exactly to measure this other than playing with my hobby charger to find the numbers but many(if not most) of my sticks are damaged, worn out, or below capacity, and likely wouldn't produce a reliable result in testing. ...although the average Insight pack might have its fair share of bad apples even if it performs as if it were perfectly healthy. I figure that once the 'full pack voltage at 350ma' is figured out and the pack trickled a few times for a long enough duration to have a pretty safe idea that things are balanced that raising the voltage of the switch over to lower current could be done. If the full pack voltage at 350mA sticks at, say, 170 volts or so, if we end at 170 volts when charging at 1050mA, I think it's got some distance to go with charging once it drops down to 350mA. I'm just not sure how much though. I'm looking to find out however since if I go with a NiMh buddy pack instead of a LiFePO4 pack replacement, I'll want to be able to get a full charge within a reasonable period, I figure if I can manage a full charge, or close to it in about 10 hours I would be set, I think this is pretty easy to achieve though, 1 amp per pack, if not completely empty would be about 6Ah, charging to a termination point where it has all but around 1Ah in, drop to 350mA and cut the charge after about 5 hours of that would likely ensure a full charge in 10 hours or so, right? That's considering that when slow charging that the factor is 1.6 or 16 hours to fully charge at .1C since the charge efficiency drops with lower currents, not sure where things stand at .05C though.

I'll be thinking about this, I'll eventually get the time to play with the concept of finding a decent termination voltage that leaves about 1Ah left over.

[Mike Dabrowski 2000]

Your correct that the dual rate charger will exceed the 350ma max when still not charged with the 1A rate, that's why the relay is latched, and will not reactivate the 1A when the voltage settles back. The voltage rise between 1A and 350 ma is not huge. I expect that the best procedure would be to set the 1A to 350ma charge cutback conservatively low for the first few cycles to see where your pack top's off. No need to do all the work at the 1A rate.

I spent the afternoon putting up all the 20 subpack traces, lots of information there.
I charge at 5-6A, and can hit it with A 30A charge. The voltage rise between the two rates is indicative of the cells Internal Resistance.
MIMA Honda Insight Modified Integrated Motor Assist - What actually goes wrong with the batteries????
Feel free to try and explain what we see, I am still trying to figure out the various things that the graphs show as well as trying to come up with a standard test sequence.
I think that subpack 10 and 12 are my IMA code setters.
No such thing as waste heat when you need to heat the house. consider it an electric heater that also charges the batteries.

[crx_rogus]

Originally Posted by Mike Dabrowski 2000

... MIMA Honda Insight Modified Integrated Motor Assist - What actually goes wrong with the batteries????
Feel free to try and explain what we see, I am still trying to figure out the various things that the graphs show as well as trying to come up with a standard test sequence.
I think that subpack 10 and 12 are my IMA code setters.
No such thing as waste heat when you need to heat the house. consider it an electric heater that also charges the batteries.

It can't get any clearer that a 350mA to all 120 at once for huge hours is occasionally needed to let the healthiest cells catch up for a real balancing charge to avoid an eventual occasional excessive discharge condition in them. C2 of SP9 is still at a low voltage after 9.5 hrs of 350mA, yet I gather holds its charge better than any other cell in the subpack, ending up at a higher voltage afterwards.

C3 of SP12 and C4 of SP10 show clearest that high IR goes along with excessively high charge ending voltage, likely skyrocketing in temperature in heavy (M)IMA use. They end up relatively hogging the charging power at the 5A end charge, whereas the clearly healthy C3 of SP7, C4 of SP3, and C2 and C4 of SP1, end with 5A charge voltages above their companion cells. Most of the time one could guess that dendrite formation from overcharging limits end voltages, except for the C3 of SP12 and C4 of SP10 outliers with their very high IR...

I'm curious how much those two self-discharge. If they self-discharge a lot, their high IR despite the high self-discharge suggests they are highly cooked into uselessness. Maybe the IR is more from occasional polarity reversal, leaving overcharging responsible for dendrite formation, which makes some sense following the "self-discharge is from lack of deep cycling via oversize sharp-edged crystals/dendrites puncturing the membrane" idea. If they don't self-discharge much, then perhaps they are leading examples of what happens to super-healthy cells allowed to fall down into chronic discharge, their needed charging power increasingly hogged by lesser-capacity cells, eventually flipping them into death by polarity reversal.

C5 and to a lesser extent C4 of SP19 do not technically do a -dV, but it looks like it could be masked by their higher voltage rise under charging. If they're higher-capacity cells that fell behind, certainly explaining C4, then C5's climbing so relatively high could be dismissed as "not that high" vs. the other sticks, with 1.48 - 1.52V being a basic end voltage range at 5A, or 1.43V at 350mA for SP9 (=> 180, 171.6V end pack voltages). (Odd that about 3hrs into SP9's 350mA the voltage slopes all suddenly increased... The current is too small to track, but I wonder if it changed. If it did, say from a charger voltage increase when the cells had nearly matched the earlier lower voltage, then it's a great demo of how strong cells can't catch up with a low charger voltage setting that allows the weaker cells to hog the available charger power.)

Goodness there's a lot of data there.

[Mike Dabrowski 2000]

Thanks for the feedback, it is always helpful when looking at this much information to have another point of view.
Since this discussion has more to do with discovering what goes wrong with the subpaacks than grid charging, I will finish my answer in that thread so we don't get the two related but different issues confused.

[buzzard]

As much as I hate to follow a highly technical discussion of battery management technology with a simple "newbie" question, I think this might be the best place to ask it. Mike Dabrowski has moved the discussion of NiMH battery charging rates to another thread, so I'll try my question here.

As a new kid on the block who has owned an Insight only 4 months and only installed MIMA and a grid charger a couple weeks ago, I'm just learning to use and program MIMA. As I reported on another thread, Mr. Honda was kind enough to install a new IMA battery under warranty a couple months ago. Presumably, my battery doesn't need balancing yet, so I don't have a need for the grid charger which I built before the battery was replaced.

I've noticed that, using MIMA (what a blast!), I tend to "burn down" the SOC indicator when I return home to the top of the mountain leaving 2-5 bars on the SOC. This is especially true of short local trips. Yesterday, I fired up the 350 mah grid charger for about 4 hours just to see what it would do. The SOC showed a positive recal about two miles into my local run after charging.

Do you experienced people recommend occasional shorter charges from the grid charger to keep up the SOC level (and save fuel since there would presumably be less ABC on the next drive, wouldn't there?). Or should the grid charger be reserved only for longer balancing charges after the new battery begins to age? What would be best to maintain the health of the NiMH pack over time?

Thanks.

[uhtrinity]

Mima begs for either a) more battery capacity, and b) plugin charging. Without plugin charging you end up wasting fuel to replace what charge you lost.

[uhtrinity]

This week I started 'playing' around with the ebayed Meanwell 48 volt power supplies. First, they will not operate on a battery without current limiting. The supply stays in a tripped state. Adding a 50 ohm current limiter resulted in ~200mA @170volts. The battery I'm charging started at 160 volts.

A few notes. Without diode isolation the power supply leds come on when connected to the pack. They also come on when plugged in in. At most they are slightly warm to the touch at the current levels mentioned. the set voltages of these supplies is also very stable without any fluctuation.

I haven't set up a final charger yet as I'm waiting for the led driver / 300mA current limiters to come in. The battery I am playing with is the battery from the car we picked up from RHDInsight. That battery appears to be less than a few years old and is testing at full capacity. It even has the yellow shrinkwrap on the subpacks. I'm pretty sure it had been replaced under warranty.

[TRI]

Originally Posted by buzzard

Do you experienced people recommend occasional shorter charges from the grid charger to keep up the SOC level (and save fuel since there would presumably be less ABC on the next drive, wouldn't there?). Or should the grid charger be reserved only for longer balancing charges after the new battery begins to age? What would be best to maintain the health of the NiMH pack over time?

My battery pack is weak and I only can drive the car without frustration if I charged it overnight with a grid-charger. Even with a new battery I'd charge it before the next drive after a longer non-use of the car, let's say one week to keep it healthy and balanced.
If you're battery is nearly empty until you arrive at home it gets charged while you're going downhill next time you drive it, no?
Orelse you could charge it with a solar panel.

[Jivko57]

Originally Posted by uhtrinity

This week I started 'playing' around with the ebayed Meanwell 48 volt power supplies. First, they will not operate on a battery without current limiting. The supply stays in a tripped state. Adding a 50 ohm current limiter resulted in ~200mA @170volts. The battery I'm charging started at 160 volts.

A few notes. Without diode isolation the power supply leds come on when connected to the pack. They also come on when plugged in in. At most they are slightly warm to the touch at the current levels mentioned. the set voltages of these supplies is also very stable without any fluctuation.

I haven't set up a final charger yet as I'm waiting for the led driver / 300mA current limiters to come in. The battery I am playing with is the battery from the car we picked up from RHDInsight. That battery appears to be less than a few years old and is testing at full capacity. It even has the yellow shrinkwrap on the subpacks. I'm pretty sure it had been replaced under warranty.

Please post or send me instructions how to build one , i am in dire need of a grid charger (cannot believe that honda is not selling one at least as an accessory)
seems my driving style does not allow enough charging so every couple of days the battery starts recalls and forced charging which hurt my mileage.

I found one solution where I drive in third up to 85 mph, then coast till it falls to 60 (charging the battery a little ) then accelerate in third gear back to 85 and so on for 25 miles (my commute home) the mpg suffers but the battery is charged...

So instead of creating havoc on the road I would rather charge the battery at home every couple of days if I could


I am not much experienced, but have some basic electrical /electronic knowledge and can follow instructions if details are well covered.

I have a set of the ebay Meanwells and can get the other needed parts online.
thank you