Firstly appologies to Peter for how over due I am in posting this!!
Battery rebalance - how to do it!!
Ok I know quite a few people have done this already on here, and there is a lot of good info regarding the procedure and equipment required etc. A lot of it however is hidden pretty deep inside other posts. So having done all the reading and seeking of advice over the last couple of months I finally got around to doing it. Now having completed it all and having it all fresh in my head I thought I’d put together a reasonably comprehensive post to help others in the future.
Firstly I must add a small disclaimer;
MY WRITING THIS DOES IN NO WAY HOLD ME ACCOUNTABLE OR LIABLE FOR ANY INJURY OR DAMANGE TO ANY PERSONS OR EQUIPMENT CAUSED BY ANY ONE ATTEMPTING THIS PROCEDURE. THIS IS A GUIDE ONLY, AND DOES NOT SUBSTITUTE LACK OF ANY ELECTRICAL KNOWLEDGE OR EXPERIENCE. THE IMA SYSTEM IS CAPABLE OF KILLING YOU IF THE CORRECT CARE IS NOT TAKEN.
Anyway moving on, the tools needed to complete the entire job are;
To remove the IMA battery from the car;
1. Digital multi meter - able to measure at least 200V DC.
2. Metric socket set including 8,10,12,13mm sockets, a ratchet, and 18” worth of extension bars.
3. Torx T30 bit plus something to drive it.
4. A selection of different sized Phillips and flat blade screw drivers – all must be in good condition!!
5. A couple of pairs of needle nosed pliers.
6. Some small containers to keep the various nuts and bolts that you will remove in.
7. A rag!
8. A strong friend to help lift out the IMA battery assembly. If possible try to get the Honda lifting handle. Or make your own if you have the time and materials. I just got someone big to help me!!
To carry out the rebalancing procedure – in addition to the above;
1. Some form of smart charger ie a Triton or Robitronic Overloader. If you have the means, buy or borrow 2. It makes life much easier. The overloader is by far the best, I will explain later!!
2. A 12v power supply to power the above charger. (This can be as simple as a 12v lead acid battery with a car battery charger connected to it. I used a regulated 0-20v 0-5A bench power supply however that cost me £50).
3. Some device to measure temperature accurately. I tried a simple digital thermometer with a small probe. This was useless. I bought a cheap infra red thermometer instead which worked far better. Depending on what charger you have this is not strictly necessary (The over loader comes with one for example) but it is still handy to have.
4. A cooling fan. I just had a really cheap 10” oscillating desk top fan.
A bit of background info on me and my car before I carry on. I am an electronic engineer for the British Military with almost 10 years of experience. I am also a rather good car mechanic who has built from the ground up various race cars and motorbikes. Im not saying you need to be of the same background as me to do this, but some prior knowledge of cars and electrical systems will defiantly help.
Right Im not going to describe how to remove the battery assembly from the car. This is described very well in the workshop manual. If anyone doesn’t have one of these but wants to see the pages I’ll happily scan the relevant pages for you.
Here are just a couple of pics of the process of getting it out of the car. From start to finish this bit took me about 2.5 hours. I just about managed to get the battery pack out by myself but if you can get a friend to help do so. It is heavy!!
The Honda manual stops once you’ve got it out of the car, so I’ll carry on from here.
Firstly remember this thing still has 144v at various points potentially on both ends of the pack. Be very mindful of where you stick your fingers and screw drivers!!
Ok I started at the end with the circuit breaker and fuses etc. You’ll need to remove this panel to get to the subpacks. To remove it you need to remove the 3 bolts at the top, the 3 at the bottom, and the 4 hidden behind the little gray rubber bungs as you can see in the picture. This end assembly then lifts up and clear of the battery pack. You’ll be left with this.
You need to be very careful with this next bit. You need to remove all the little screws that hold down the ends of the temperature monitoring strips and very very gently bend them out so that the big orange board can be slid off over them. Do this on both ends obviously. Lastly remove the bolts that secure the subpacks to the orange boards from each end. You should be here now.
Now gently and squarely pull off the orange boards to reveal all your subpacks
I took out the 4 subpacks that are connected together by the temp strips first, I put them to one side. Then take the rest out and put them somewhere safe so they can’t roll away and risk damaging the temp strip ends. I numbered all mine straight away so I knew the positions they were originally in.
Ok now the fun (read boring) bit starts. Peter had very kindly lent me a few spare subpacks to use should any of mine be beyond recovery. I cycled a couple of these before doing any of mine so I know how to work the equipment and what results to expect.
To start with I was hoping that identifying a dead cell would be a nice simple fix, and I should be able to tell this by the voltage across 1 subpack being substantially lower (i.e. aprox 1.2V) than the rest. Unfortunately they were all virtually the same.
So I began the cycling and rebalancing of them all. To begin with I only had one power supply and a Triton. The Triton can only discharge at 3A and charge at 7A so I set it to that for one initial cycle on one subpack to see a. how long one complete cycle would take, and b. what temperature I could expect to see as the subpack neared full charge. Before I did this I charged the subpack right up, till the triton stopped charging it, at what I now know to be the delta v point.
Regarding the settings I used for the Triton I was a bit confused to start with. It asks for the number of cells it is dealing with (6 obviously) and the overall capacity, which I set to 6500mAh. On the charge cycle of its first cycle it put exactly 6500mAh in which I thought to be a bit odd. It obviously didn’t fill it to the delta v point. After consultation with Peter he suggested that because the charger wasn’t 100% efficient that I should set the capacity setting to 7000mAh.
So I performed another cycle on the subpack after giving it about 15 mins to rest. This time on the discharge cycle I noticed it appeared to already have more capacity than on its first effort, about 5850mAh vs 5650mAh if I remember correctly, but I didn’t record this as I was still experimenting. What I did notice though was that the subpack did get rather warm during the last 500mAh of its charge phase. I therefore adjusted the charging current to 6A
Anyway I carried on experimenting with settings and timings and came up with the following routine;
1. Charge the subpack as far as the triton would allow (up to the delta v point)
Cycle the subpack 3 times, 3A discharge first then 6A charge. I would then record the discharge and charge capacity for the final cycle along with start and finish times. The Triton was also set to have a 10 min wait between each bit of the process. This process takes about 12 hours per subpack.
2. Towards the end of the first charge cycle (in step 2) I monitored the temperatures of each individual cell to look for any anomalies, ie a cold or abnormally hot cell. After that I would leave it to crack on and complete the rest of the cycles.
3. I would then immediately start on the next one.
4. After I had done 3 (ie after 36 hours, 24 from completing the first) I put the first one on just a charge cycle again to see how much charge was required to top it up. This in my mind would give the self discharge rate.
5. As you can see from my table of results that the rates appear to be rather high, in the order of 800mAh in 24 hours. In hindsight I don’t think this was the best method. After I had completed about 10 subpacks, out of interest I performed a discharge cycle on one after being stood for 24 hours and it delivered almost the same amount of charge as it did previously. I continued to record the self discharge rates the way I had been doing however due to lack of time to start again, and I would still be able to hopefully spot an anomaly.
6. Once I had done 3 full cycles and a self discharge rate on about half of the subpacks I began to get an idea of which the better of the subpacks were. I then formulated a remedial action plan to try to bring them all to a similar level. I wanted all to deliver at least 6000mAh on the discharge cycle. Some did on their first time, but most did not.
7. At this point I realized that the triton alone would not be enough to complete everything in the time I had available, I had a holiday to Bulgaria booked!!! So I bought the overloader and another DC power supply.
8. Anyway the subpacks that did achieve 6000mAh on the first 3 full Triton cycles had one cycle on the overloader. The ones that did not had multiple cycles, up to 3 in some cases, until the came up to my desired spec. I altered the settings slightly, this time I charged and discharged at 6.5A. The overloader also gave me the internal resistance readings for the subpacks.
MAKE SURE YOU DON’T ISOLATE THE POWER FROM THE TRITON BEFORE YOU HAVE TAKEN THE READINGS YOU NEED!!!!!
It does not keep them in memory!!
Anyway this is the table of results I generated, to me it makes sense, but if you have any questions fire away.
To be continued in part 2…………………
Battery Reballancing how to
