Francisco's Electric Pajero

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francisco.shi
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Re: Francisco's Electric Pajero

Post by francisco.shi »

About the quietness the inverter is running at 7khz and surprisingly there is no 7khz noise coming from the motor. I was very surprised. However when I lift the wheels and run it there is a lot more noise from the diff gears than I was expecting. I have to wait and see how noisy it is once it is driving.
At the moment I am only running it off 48v so it can't go very fast.

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JD Solar and EV
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Re: Francisco's Electric Pajero

Post by JD Solar and EV »

Good Job Francisco! Can't wait to hear more about it at this months meeting.
Current AEVA QLD Chairman

Check out my EV videos at JD Solar and EV YouTube Channel
https://www.youtube.com/channel/UCNMxXc ... bUTfpHU5LQ

francisco.shi
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Re: Francisco's Electric Pajero

Post by francisco.shi »

I have been working on the BMS today. I got 4 modules I have been using for testing to make sure there are no mistakes in the boards. I was assembling and calibrating the modules in sets of 5.
Here are some pictures of the boards in a subpanel.
15849701403783566395928291262880.jpg
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15849701078307081356832782851835.jpg
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I used different colours for the connectors because it is too easy to plug it in the wrong plug. The first time I made that mistake the com's wire burst into flames. The transmit has an optocoupler but the receive is connected to gnd. If I plug two receives together it shorts the battery thru the thin com's cable. With the different colours I just need to plug into sockets of the same colour and all is fine.
Here is a picture of the test pack.
Test module
Test module
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While I was doing the assembly I decided to balance the battery I have been using for testing. The cells were 88mv out of balance.
Before balancing at 6:40pm
Before balancing at 6:40pm
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I set the cutoff to 15mv difference.
After balancing 11:18pm
After balancing 11:18pm
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It took 4 and a half hrs to balance the 189Ah cells for a 55mv change. The energy recovery system seems to work well. The low cells charged up and the high cells discharged. The average battery voltage only went down by 10mv.

T1 Terry
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Re: Francisco's Electric Pajero

Post by T1 Terry »

What voltage is considered 100% capacity? In other words, at what voltage does the cell voltage rise rapidly yet only a small current going into the cell. LFP and LYP cells will voltage balance quickly below fully charged but that has nothing to do with the state of charge being balanced. The only points that balancing really counts is fully discharged or fully charged, and you can't have both, it's one or the other.
Top balancing for house batteries and bottom balancing for EV batteries seems to be the way to go, you never completely discharge a house battery intentionally, yet it is the norm for an EV.

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francisco.shi
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Re: Francisco's Electric Pajero

Post by francisco.shi »

4.2v is supposed to be full.
The bypass circuit dumps the energy at the pack's terminal. So I can balance at any time.
The way the balancing works is the master works out the average voltage of all the cells and it sets the target voltage to that value. Then if the difference between the max cell voltage and min cell voltage exceeds a certain value it issues the bypass command to all nodes.
If the cell voltage is higher than the previously set target voltage the node will bypass the cell. The energy goes to the pack which acts as a charger. So all the cells that are not being bypassed will start to charge (and increase in voltage) the ones that are being bypass will decrease in voltage.
So the balancing is always active regardless of the cell voltage or wether the pack is charging or discharging. The end result during charging is the cells with lower voltage will have slightly more charge current and the ones with higher voltage will have less charge current.
During discharge the cells with higher voltage will supply more current and the ones with lower voltage will supply less current.
So ultimately the stronger cells will supply/absorb more energy than the weaker cells so all the cells will reach top and bottom at the same time.

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4Springs
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Re: Francisco's Electric Pajero

Post by 4Springs »

T1 Terry wrote:
Wed, 25 Mar 2020, 11:04
What voltage is considered 100% capacity? In other words, at what voltage does the cell voltage rise rapidly yet only a small current going into the cell. LFP and LYP cells will voltage balance quickly below fully charged but that has nothing to do with the state of charge being balanced. The only points that balancing really counts is fully discharged or fully charged, and you can't have both, it's one or the other.
Interestingly, these NMC cells don't behave the same as the LFP that we're used to using. Within reason, you can actually use the voltage to figure out the state of charge. Here is the table from the spec sheet:
E63_table.jpg
E63_table.jpg (36.57 KiB) Viewed 116 times
The difference between 5% and 15% is 0.07V or so.
The difference between 90% and 100% is 0.1V or so.
So at a higher state of charge the voltage does move more rapidly, but nothing like LFP.

This means that the cells can be balanced over a very large voltage range. Which is great! Because holding at a high state of charge is somewhat detrimental to cell life. We can balance at pretty much any state of charge, and can do it while we're charging, discharging or resting. High bypass currents are not required, we can use low currents over long times.

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brendon_m
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Re: Francisco's Electric Pajero

Post by brendon_m »

4Springs wrote:
Wed, 25 Mar 2020, 16:12
Within reason, you can actually use the voltage to figure out the state of charge. Here is the table from the spec sheet:
E63_table.jpg
I tried to find a similar chart for my ex imiev cells and couldn't really find anything with actual values. Lots of small graphs that if you squinted you could get a voltage vs soc. I got a couple of hard numbers but nothing for the whole range of charge levels.
I ended up getting my own from readings from my outlander.
100% 4.1v
90% 4.05v
80% 4.01v
70% 3.96v
60% 3.93v
50% 3.9v
40% 3.86v
30% 3.83v

These figures were taken after driving without letting the pack rest so they're not exact.
Interestingly the manual states 3.75v is 30% and from the graphs I've seen I get
20% 3.5v
10% 3.25v
0% 3.0v
Dead flat danger zone% 2.75v
You just destroyed 1000's of $$% 2.5v

So the official Yuasa numbers match with your chart but my numbers from the outlander seem too high even with an unrested pack. I wonder if 30% (the minimum soc you can go in an outlander) is not 30% soc but 30% of allowable usage.

T1 Terry
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Re: Francisco's Electric Pajero

Post by T1 Terry »

4Springs wrote:
Wed, 25 Mar 2020, 16:12
T1 Terry wrote:
Wed, 25 Mar 2020, 11:04
What voltage is considered 100% capacity? In other words, at what voltage does the cell voltage rise rapidly yet only a small current going into the cell. LFP and LYP cells will voltage balance quickly below fully charged but that has nothing to do with the state of charge being balanced. The only points that balancing really counts is fully discharged or fully charged, and you can't have both, it's one or the other.
Interestingly, these NMC cells don't behave the same as the LFP that we're used to using. Within reason, you can actually use the voltage to figure out the state of charge. Here is the table from the spec sheet:
E63_table.jpg

The difference between 5% and 15% is 0.07V or so.
The difference between 90% and 100% is 0.1V or so.
So at a higher state of charge the voltage does move more rapidly, but nothing like LFP.

This means that the cells can be balanced over a very large voltage range. Which is great! Because holding at a high state of charge is somewhat detrimental to cell life. We can balance at pretty much any state of charge, and can do it while we're charging, discharging or resting. High bypass currents are not required, we can use low currents over long times.
Thank you for pointing that out, I hadn't realised the NMC cells had a sort of linear voltage that could represent the SOC. That would mean the 3.818v that the Pajero pack balanced at was actually some where between 65% and 70% SOC?

T1 Terry
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francisco.shi
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Re: Francisco's Electric Pajero

Post by francisco.shi »

That is correct. The batteries were not fully charged. The way the BMS is setup it will keep the cells balanced at any voltage no matter if the pack is charging or discharging. Because the bypass energy is recovered I can balance at any time without losing range if anything I will gain range because I can get the maximum energy capacity of each cell even if the cells are not all exactly the same capacity. Remember that the same capacity cells are only within 3 to 4% of each other. So if I used the conventional method of top or bottom balancing and one cell was 3% lower than the rest then I would get 3% less than the true potential of the pack.

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