Balancing question
 

I apologize in advance if I'm posting in the wrong forum, or if this has been answered in another place.

I took the battery apart and charged the 20 sub packs over this past winter. I recorded the discharge and charge values. I also recorded the final voltage and then the voltage it was a week to 2 weeks later.

Its time to put it back together and I entered all the numbers into excel. I then realized I have no idea how to determine which battery is good and which is bad. Can someone please help! The numbers to me say they are all good, but I don't believe this to be the case.

Thanks for the help!

I was hoping someone knowledgeable would answer your question because I'm curious too.

In my experience with Roomba batteries, simply knowing the charged and rested voltage along with capacity was not enough to determine which cells were bad. I believe you also need to know what the internal resistance is for each cell, and I'm less clear on how to determine this.

It would be good to know more details, such as what hybrid pack you are dealing with, and what the symptoms are that caused you to dig into them in the first place.

what are your units of charge value?
 

It looks like subpack #3 is bad by your data--all the rest settled down to 8.1-8.2 except that one dropped to 7.5, it's not holding.

i have done cell capacity checks on some batteries, the largest pack being 44 cells of lifepo4 with 100Ahr capacity.

For example i recorded voltage, current, temperature and time while discharging at 30 amps until the voltage reached 2.5V, then recorded same while charging at 25 amps until the voltage reached 3.6. After resting the voltage settled to 3.33-3.34, which is considered the 100% state-of-charge voltage for this chemistry. The cell capacity is calculated by the current multiplied by the time, e.g. 30Ax3.4hrs=102Ahr.

You need to get the specific upper and lower limits for your cell chemistry, the cell capacity rating, the charging procedure, etc to make sure you stay within the box and don't damage them.

There is not a real resistor in the battery that you measure, but a so-called internal 'resistance' can be calculated as the difference between the unloaded and loaded voltage divided by the load current. For example if a 12 V battery drops to 10V with a 100A load, then Ri is 2/100 = 0.02 Ohms. Some people swear by it, but i haven't found it as useful as actual cell capacity, especially when trying to determine expected range.

I have a 03 civic hybrid. When I purchased the car 2 years ago, I was getting 48-50 mpg.

I park my car during the winter months, and last winter I forgot to start the car the entire winter. I think this hurt the battery pack. Sometime during the summer I started to get IMA lights. the light would come and go. but the Umph that the electric assist used to give has weakened. Then the O2 sensors went out, and my mpg dropped to 40. I replaced all 3 o2 sensors this spring and it only brought the MPG to 43.

So I'm trying to rebuild the pack to get my MPG back up and get rid of the IMA light all together.

It is also worth noting that last year the Honda dealership took it upon themselves to update the firmware on my car. And I can't shake the feeling that in doing so it changed my MPG too.


As far as calculating the internal resistance, you say I need a load put on it. Do you have a good way of putting a load on the cells? Or would it not matter just as long as the test is consistent with all cell packs?

Your right about the firmware update. My mileage dropped about 5% after the last recall update. Honda claims this was done to preserve battery life, in other words, the computer will not allow the battery to discharge fully, so this in turn increases the work for the ICE, and decreases MPG.

If it makes the battery last longer, I can live with the decreased MPG.

Im not an expert, but there are plenty of the insightcentral forum that do this for fun. They use a super brain charger to cycle the sticks and record the results over 5 cycles. This gives an amp capacity and in many cases just cycling the stick rehabs it into better shape.

Still the load of the super brain is nothing to what it faxes in real life and a bad stick can pass this procedure with flying colors if it has a high internal resistance. :eek:

I used a super brain 989 for all my reconditioning. I did 4 cycles on most. (I know it should have been more consistant, but from what I read on other forums, 3 was plenty, I just wanted to be extra sure.)



It sounds like I should be set with just replacing stick #3 then. I hope it helps. There feels like theres a lot to do in reconditioning...

Thanks for the help, if no one else replies to this post I'll try to update it in a couple months. (Still have a foot of snow in my backyard so getting the Civic out for another few weeks is not going to happen.)

Yeah, thats fine. Also pair off the sticks good with a bad one so the "taps" are seeing an evenly distributed voltage. If any of the taps sees a lower than collective voltage that triggers a negative recalibration where the car starts recharging for a preset time. Some feed signals to these taps sing a resistor matrix and such to gain more performance out of the system as well as a move to lifepo4 batteries. :eek:

Another dimension you can add to this cycling is to use a laser themerstotat to check the temp while the stick is being cycled.

Typically the first signs of problems with a hybrid is from 1 bad cells. Once that is found the next problems are either another bad cell or an overall worn battery.

Since you got some time on your hands you could try another set of cycles on your sticks. :turtle:

I ended up ordering a new to me stick to replace #3. That should be here next week. Its been at least a month and I checked all the voltages, they are all sitting near 8v. #3is 7.3

Im cuurrently charging all the batteries my question is do I need to let the batteries rest before I check internal resistance or can I use the Peak voltage after a charge, and apply the load?

Nevermind. I suck
 

SO right after I posted the above message, I decided to answer myself and use the voltages that have been at rest for a month, calling that the full or 100% SoC.

Long story short my 7th stick, I hooked up the Super brain with the wrong polarity. Yep fried a transistor. Next step is finding a replacement to put into the board. GRRRR oh well.

I'll keep you posted.