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Got retepsnikrep LTO Interrigator in last nights mail. Used it today to find CANbus ID on my 16 CANBus BMS boards. Really neat piece of equipment. Did all 16, complete with making tags, in about 30 minutes.

Now on to a little extra experimenting. I want to test how close my PL8 charger correlates with the Honda BMS voltage measurement.
 

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Discussion Starter #802
Didn't even realize they got the BMS boards actually working and readable. I'm going to have to get this. Good thing I didn't spend big bucks on an aftermarket BMS. I'm sure the BMS will be quite accurate because honda seems to use very good electronics in all its cars.
 

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Good thing I didn't spend big bucks on an aftermarket BMS. I'm sure the BMS will be quite accurate because honda seems to use very good electronics in all its cars.
We aren't there yet. So far it is only possible to read the cell voltages. It has not been determined yet how to use the boards to actually balance the cells :(
 

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Discussion Starter #804
View attachment 84539

I'm sorry but that's really crispy and probably dangerous. If you have to have it on the front put it here with one of these marine power receptacles with the lid. This is on my car, it's not for the IMA, this is for oil pan and transmission heat pads and a block heater. They really do help with MPG.

Don't use the switch I have in this photo, use a waterproof one, which I bought to replace the one in this picture after this photo was taken. Honestly you probably don't even need a switch.

I will mention that you'd think this area gets wet, but over the last year and a half I've never seen it wet.
While I agree it does seem dangerous I do not think it is so. The reason is that no electricity will be live in that connector at the front of my car unless it is plugged into from my house. The flap will keep almost everything out of the plug. Even if some water got inside, or even salt water which would be far worse, it could potentially cause a short but that is highly unlikely and would just blow the fuse block in my house.

Worse case that could happen is I burn out the connector and if that happens then I will replace it with something better. I do not think it could ever cause a shock hazard.

That being all said, putting the charge port at the front of my car was the best thing I could have done. It is so easy to charge my car now. It takes me 5 seconds to take the computer extension cord, which I leave plugged into my house all the time, and quickly just plug it into that connector at the front of my car. The only thing that would be easier is if I had my car wireless charged from the concrete below my car as I parked.

It is so convenient that I charge my car all the time now. What I do is keep my max charge voltage lower, so I charge my LTO cells to 3.38 volts, and I usually charge when I'm around 2.18 volts. This keeps me using my pack around 65-35% of capacity which is the best voltage range for cell longevity. With regular lithium cells you increase cycle life from 500 to like 2000 cycles by charging between a 40-60% range. I don't know how much this matters when these cells are rated at a 20,000 cycle life.

The reason I need to charge often is I'm using the current hack + the IMA Boost device which allows me more assist. This really drains the battery but gives me much more power from the car.
 

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Discussion Starter #805
We aren't there yet. So far it is only possible to read the cell voltages. It has not been determined yet how to use the boards to actually balance the cells :(
Not a big deal to me because I've used my car for around 2 years now and not a single cell needed to be balanced. If you need to balance any of your cells then you have cell issues and will probably need to bypass or replace that bad cell. It seems that once a cell starts to go bad, it really goes bad quickly after that. usually it will have a bad smell if you smell it closely.

It is more important to read the the cell voltages and to know when a cell starts to go bad. If the OBDIIC&C automatically shuts down the pack if your highest and lowest cell divert too much that would be perfect.
 

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Just wanted to give an update about the IMA error codes I was constantly getting while using my car. I decided to poke around all my connections, pulling and pushing all the wires when my car was on to see if I can throw an IMA error. It did not happen. I saw no issues with any of my connections by doing a pull test on many of the wires. Usually a bad connection will have the wire pull out of the solder if you have a bad connection.

Then I decided to disconnect my Current Hack as that has the most connections. I drove the car for a few days without any issues. The car felt so weak and was not nearly as fun to drive without the current hack so I decided to reinstall the current hack.

I have now driven for a few days with the current hack installed and have not had any issues. I have drove over many hard bumps in the road and everything seems normal. Before I was getting IMA errors a few times per ride, usually when I drove over any bump in the street.

I have no idea what the issue is because everything is back normal. It is most likely a connection issue and I must have moved something in a way for it to stop. Since everything is working fine now there is nothing I can do but just wait and see if I have trouble again.
 

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Not a big deal to me because I've used my car for around 2 years now and not a single cell needed to be balanced.
What is the best to worst voltage spread after 2 years of cycling? That would be useful information to rest of us.
 

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Discussion Starter #808
All my cells seemed to not have had any drift. At least not more than .001 volts in a cell. This cells are quite amazing in how well they stay balanced. The reason for this is that they are protected very well in a hard shell case.

I had lipo pouch cells in my electric bike which I didn't take much care to secure them proprely. So many of them were out of balance. Many of them got puffed up. The reason was they got damaged because the pouch cells were not protected and pouch cells are easily damaged. I had 18650 cells in a new electric bike build and they stayed perfectly balanced without any balancing for over a year.

The big issue will be that odd cell that seems to have issues and most likely it was a defect in manufacturing and it had issues from the very beginning and just slowly got worse.

I would think after 2 years of cycling your cells should be all perfectly balanced and there should be no deviation other than your voltage tester rounding up or down.
 

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Discussion Starter #809
I wanted to let you guys know I did a capacity test comparing a pack in my car, to a pack that I never used. Actually I split the pack in two so they are definitely a matched pack.

Here are my findings which does not add up.

Original capacity of the pack from 2.7 volts to 1.5 volts at 4 amp discharge. = 21.5 Amp Hours taken around October 2017.

Pack that was sitting in basement unused = 20.1 amp hours

Pack that has been used in car for 2.5 years = 20.4 amp hours.

This was about 2.5 years since I last did the capacity test.

You are probably wondering why would the pack sitting in my basement unused lose more capacity then the pack that has been used and cycled in my car for 2.5 years?

Well here is what I think and I probably hurt my pack. I discharged the cells to 2.0 volts, but when I pulled it out of storage the volts ranged from .800 volts to 1.5 volts per cell. The pack slowly discharged when not in use.

I would guess that perhaps the pack discharging to such low voltages and sitting at those low voltages may have made the pack deteriorate faster? Which is honestly surprising because the pack was sitting in my cool basement and I found on lithium ion cells that storing at lower voltages did not make the cells lose capacity faster.

Remember, it is always better to keep lithium ion cells at lower voltages as higher voltages are known to deteriorate the cells quicker. Maybe you can store the cells too low and the LTO may act differently than lithium ion chemistry.

What I suggest after this finding is that if you store LTO cells, make sure you check voltages periodically and you keep the battery at around 2.2 - 2.3 volts per cell.

There is a chance the BMS is putting a parasitic load on all the cells as I have not found lithium ion cells to lose voltage with time.

Not the biggest deal in the world as I still have a good amount of capacity left and I hope to never have to use the backup pack. I am surprised about just how much capacity the packs lost in that time, I would have expected less capacity loss from the LTO chemistry.
 

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Well here is what I think and I probably hurt my pack. I discharged the cells to 2.0 volts, but when I pulled it out of storage the volts ranged from .800 volts to 1.5 volts per cell.
yup , I think you're right.

There is a chance the BMS is putting a parasitic load on all the cells as I have not found lithium ion cells to lose voltage with time.
I'd expect any BMS to have some parasitic load .. the energy it takes to run the BMS itself has to come from somewhere .. a good quality one should be very low / slow.

I have not found lithium ion cells to lose voltage with time.
Soo .. am I reading that correctly .. that the voltage drop you did see over time .. that those cells had a BMS on them over that time ?

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Any part will fail eventually .. it is just a question of , on average , which part is more likely to fail first ,.. and .. on average how long is reasonable to expect before failure .. Mean Time Before Failure (MTBF).

A BMS .. the manual human kind , or the automatic electronics kind .. will have a MTBF under some operating conditions .. a 48 cell battery will have at mnimum 48 places / points for a BMS to fail .. connected 24hr a day 365 days a year .. if the BMS's MTBF is 420,480 hrs , than it is reasonable to expect such a BMS to fail (on average) once per year .. if the BMS's MTBF is ~4.2million hours .. than it is reasonable to expect it to fail (on average) once every 10 years.

The batteries on their own have a MTBF , under some operating conditions .. same thing.

Which ever one fails first is the some that causes that system to fail.

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I have tested many types of Li batteries over the years for self discharge rates .. including these Toshiba SCiB LTO from Honda Fits .. and I have never yet seen any that has a truly zero self discharge rate .. I'll agree it is common in Li family of batteries to have a very slow rate of self discharge .. single digit % (of Ah or Wh) per year is common .. but I've never found one yet that is actually zero self discharge per year.

Self discharge rate usually changes at different cell SoC/SoE and Temperature .. slower at lower SoC/SoE , and slower at colder temperatures .. calendar ageing also is usually slower at lower SoC/SoE and lower temperature.

As for a specific amount .. my room temperature testing showed a minimum cell self discharge of 2.23 mAh per day .. and a max of 4.36 mAh per day .. I'd estimate it's safe to figure on an average of around ~6% per year at room temperature .. sure with a far more expensive (time & $) testing we could narrow it down even more .. but the testing I did of them was good enough for me.
 

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I'd expect any BMS to have some parasitic load .. the energy it takes to run the BMS itself has to come from somewhere .. a good quality one should be very low / slow.
The FIT LTO BMS is actively powered from the 12V side.

It does not have any measurable parasitic draw on the cells when unpowered.

I'm not saying it doesn't have any draw, just none I could measure even down to the microamp level.
 

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I think one problem with storing the used LTO packs at 2.0V is that the cells differ slightly in capacity. That begins to show significantly below 2V. The "tails" as I call them can cover a range of .3-.4V by time the weakest cell reaches 1.5V on a PL8. It will take very little self discharge of that weakest cell to start getting below 1.5V, if stored at 2V subpack average. Thinking it through a bit, if the subpack pack is stored at 2.0V/cell average or 24V, then the weakest cell is probably already at 1.6-1.8V. From there, it is a short trip to .8V.
 

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I am going to run more tests here. I actually have another half of pack that was stored at 2.00 volts per cell, and then I have the other half of that pack in my garage which had a bad cell that smelled so I placed the whole half of the pack outside. The recorded voltages on that half pack in my garage are around 2.2-2.1 volts per cell. This pack was my initial pack I bought that only had 20.5 amp hours when I got it.



This should tell me if storing them around 2.2 per cell fared much better in capacity then the cells which were stored at 2.00 volts per cell and then discharged to around 1 volt per cell.
 

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Well here is what I think and I probably hurt my pack. I discharged the cells to 2.0 volts, but when I pulled it out of storage the volts ranged from .800 volts to 1.5 volts per cell. The pack slowly discharged when not in use.
For LTO cells, 2.0V is just under 0% SoC! They should be stored around 2.18V/cell (30% SoC).
While the BMS does have leakage current, if it's well-designed, it should be about 100nA or less per cell. Even if it was 1uA, over 2.5 years it would drain only 0.1% of the cell's total capacity. The voltage drop is probably just from self-discharge.

Storing a battery at 0% SoC for 2.5 years and only having it lose 7% capacity is extremely impressive! :) LTO is just so good.
 

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Discussion Starter #816
When I got my initial batteries they were all around 2.45 volts. I figured that they were probably around the voltage the car charged them to before being removed. But maybe not, who knows.

If you want to capacity test your pack, charge a single cell to 2.7 volts, make sure it sits at 2.7 volts for at least 20 minutes as the voltage sags quickly around that voltage.

Then discharge it at 4 amps to 1.5 volts. This amp hour reading will give you a rough idea of how much your pack capacity is. 22 Amp Hour is probably what these packs were new. My packs were 21.5 amp hours. The first packs I got were 20.5 amp hours. Anything over 20 amp hours is probably good.

You will get at least 10 years out of these packs and will probably junk the car before the packs would need replacement.
 

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I think I really messed up those packs storing them at 2.00 volts a cell.

I did some more testing on the pack that initially had 20.5 Amp hours when I first bought it and stored around 2 years ago. I had stored half the pack in my basement at 2.00 volts and half the pack in my garage at 2.3 volts per cell and actually had varying cell voltages in that pack.

The pack stored in my basement at 2.00 volts per cell, which fell to 1.4 volts had 20.0 amp hours.

The pack stored in my garage at 2.3 volts per cell when I checked it, had 20.4 amp hours of capacity left. Which indicates it lost only .1 amp hours in over 2 years when stored at 2.3 volts per cell.

It would seem, that optimally you want to store these at 2.3 volts per cell. Now please understand these tests are running mostly single cycles. But I did run a test on two separate cells in the same pack and both were exactly the same amp hours. My testing is done at the same temperature, using precise voltages so it is a reliable test to be honest. I've used this charger for a lot of testing and it seems to be very accurate and consistent when keeping the variables the same.

Bummer that I screwed my packs up, the only saving grace is that it kind of closely matches the packs in my car and in another couple of years after I store them at 2.3 volts per cell there is a chance that the packs will match in capacity to the packs in the car.

Another thing to consider is that the packs which had the higher 21.5 fell to 20.1 amp hours per cell when stored at 2.00 volts per cell. The packs which were at 20.5 amp hours fell to 20.0 amp hours for cells stored at 2.0 volts per cell. This seems to indicate that as the pack ages it will lose less amp hours and that initial 21.5 amp hours seems to deteriorate quite rapidly.

To sum it all up, store the packs at 2.3 volts per cell unless you hear something differently and the packs will lose very little capacity. Do not store them at 2.00 volts or below.
 

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^ Your testing made me wonder about my 2.9Ah SCiB 12V battery, 5 cells, that I discharged to 2.25V/cell at 3A (essentially empty for these) about 3 months ago and left sitting.

I checked cell voltages and they are: 2.122,2.065,1.586,2.093,2.130

That 3rd cell was discharged the most during that last discharge operation, a little lower than others.

I didn't do an exact comparable cycle today to check 'capacity loss', but I did cycle them once and I see no major difference from the last discharge... I charged to 2.7V, put in 3050mAh, discharged to 2V at 6.5A and pulled out 2986mAh. That 3rd cell was the lowest, terminated the discharge. It's always been a little off though.

Keep in mind that what you're reporting as a capacity loss is still very small compared to the capacity of your cells. I'll give you the benefit of the doubt and presume your testing is tight and you can actually discern that small of a difference. But still, it's pretty darn small...

I'm gonna do a storage charge, charge about half way, and store it (i.e. I have no idea when I'll get back to it). When I got them new I'm pretty sure they were delivered at half charge, BTW.
 

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Discussion Starter #819
I've got pretty good equipment and voltage meters so I can somewhat accurately do these tests. It is also extremely important that the tests are done at the same temperature and voltage as that will have a huge impact on the results.

You also have to be careful about how you top of the cells. You have to make sure you get the voltage to three decimal places like 2.700 and make sure it sits at that voltage for at least 20-30 minutes.

If I take a cell and repeat the same tests on the same cell it will record very close numbers and that tells me it has a very good accuracy at reporting capacity.

If you did charge those cells to 2.25 and some fell to as low as 1.5 something is seriously wrong with those cells and you must have a current draw on them.
 

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If you did charge those cells to 2.25 and some fell to as low as 1.5 something is seriously wrong with those cells and you must have a current draw on them.
I discharged them to 2.25V, as I said essentially empty. These are a little different than the FIT cells, they're Toshiba's "high power" cells, with a 2.4V nominal. Sounds like you might be thinking they're the same as the Fit cells...
 
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