I'm not sure where the voltage measurement on the dash comes from while supercharging. I has assumed it was measured by the car.
I was actually just now trying to find islandbayy's pics from his discharge adventure, but wasn't having any luck.
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I'm not sure where the voltage measurement on the dash comes from while supercharging. I has assumed it was measured by the car.
I was actually just now trying to find islandbayy's pics from his discharge adventure, but wasn't having any luck.
So, back to charging. I decided to up the input power to 30A. My input voltage is about 232V right now at that load which comes out to about 6.5kW out on the DC side from 6.9kW input, or about 93.3% efficient (PF 99.5%).
The pack voltage hadn't changed at all since I left it last night, so that's positive. Will check back soon.
The pack voltage hadn't changed at all since I left it last night, so that's positive. Will check back soon.
JRP3
Hyperactive Member
Kevin Sharpe has experienced a low brick with range loss, there's a thread around here somewhere. Doesn't seem to happen very often.
Yeah, you're right. For some reason I was thinking something along the lines of using the BMS to hold the under-powered module's voltage during top off of the remaining good modules, but that's probably not practical regardless.
Alright, so, I stopped charging with a final resting voltage of 370.1V. (3.855V per cell) The modules are actually all within about 10mV of each other now, interestingly enough. (I physically disconnected the main BMS board before I started.)
I'm comfortable storing it like this for now until I can get some more components for my project.
I'm comfortable storing it like this for now until I can get some more components for my project.
JRP3
Hyperactive Member
I would expect modules to remain close with no active management for quite some time. One of the advantages of using so many smaller cells is that individual differences are averaged out when paralleled, so you effectively have large single "cells" that are closely matched in capacity and charge/discharge diffusion rates. I use no active balancing in my car using 100 ah prismatic cells, which are essentially just smaller layers paralleled together. The cells in series after 4 years of use don't differ enough over time to worry about it.
So I figured out what the sharpie lines near some cells are. Looks like the cell level fuse was misplaced or something and manually repaired. Red for when the messed up fuse is found, blue for when it is repaired.
The pack I have only has 3 such occurences visible.
The pack I have only has 3 such occurences visible.
So in thinking about this... this voltage "baseline" is what seems to make the other numbers you are seeing "off" in terms of voltage vs. overall SoC/range.
Is it possible that when the charging rates are so high (1.0 - 1.6C) that the voltage potential of the supercharger is some degree greater than what the cell would be at rest?
IOW: at the low rates we use at home (fractions of a C), cell V roughly equals charger output V... but at 120+ kW there's a larger disparity?
islandbayy
Active Member
If you are reading the voltage while the current is being applied, then yes. However, their is a point at start of the charge on a SC where no current is flowing yet, and voltage is displayed, as well as when the pack is finishing charge when the current is practically nil, only time it would be off to any noticeable extent would be during the actual charging.
If I understand correctly, if you simply apply a greater voltage it doesn't necessarily allow faster charging and would just create more losses due to the voltage drop. I could be wrong, as I've never attempted this.
Continuing with more stuff about the pack...
The microcontroller that accompanies the CPLD ont he main BMS is a TMS which is probably an ARM processor by Texas Instruments, but I can't discern the rest of the writing to get a model number.
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It shouldn't be off by much at all, really. Most off-the-shelf single cell LiOn chargers apply the full charged voltage (4.2V) to the battery constantly, but if read while charging the voltage is within 100mV of the cell voltage, from experience. I've also seen this with 3-cells-in-series setups (11.1V batteries) with nearly the same result. So, extrapolating that out to 96 cells in series would be a difference of up to 9.6V. Probably incorrect thinking, but, I doubt there is a huge disparity in voltage readings during charging.
I'd have to say the supercharger pushing 404V (4.2083V per cell) makes some sense, since if the actual target voltage is 4.15V per cell (398.4V) then that's only 6V difference. I'd love to get some readings from an actual normally fully charged pack at rest though.
stopcrazypp
Well-Known Member
The NHTSA crash test of the 60kWh Model S (14 modules) lists a minimum operating voltage of 210V (2.5V*14 modules*6 series group per module) and max operating voltage of 350V (4.167V*14 modules*6 series group per module).
http://www.teslamotorsclub.com/show...ack-Pics/page2?p=449465&viewfull=1#post449465
Another point is that Tesla says the voltage window for the Roadster was 3.0V to 4.15V:
http://www.teslamotors.com/blog/bit-about-batteries
Not a whole lot of reason to change from this.
islandbayy
Active Member
I agree
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When my car shut itself down due to low charge, i do believe my 60kWh pack was at 262v. Visual tesla showed 2% remaining at shutdown (older firmware though). fully charged is 353.
OK, so, fully charged, assuming 4.2V per cell readout like I get when reading my Model S at the SC would lead to about 84 cells in series, or 14 modules. This fits with the images from the NHTSA I think, showing some modules with missing cells in the parallel portions presumably to make them 60kWh.
Applying this to the shutdown voltage of 262V puts the cells at 3.12V... much lower than what I saw at 12 rated miles which showed 352V, or 3.67V per cell. I'd be very surprised if there were a 0.55V per cell difference between 12 rated miles (3.6kWh) and "empty."
Whats the lowest seen for an 85kWh pack at a supercharger? 353V for me, 12 rated miles. (I've been down as low as 4 rated miles, but not at a supercharger.)
For perspective, the pack I have for my project was at ~313V / 3.26V per cell when I got it.
From the Tesla blog post about the Roadster battery... I'm not 100% sure the same applies to the Model S.
If they were the same batteries, I would go by this... but I think it's been determined they are not the same cells? (citation needed... forget source)
I'm skeptical about the 3.0V on the Model S, since I can not find a single source showing this level of discharge.
JRP3
Hyperactive Member
Roadster cells are LiCo, S cells are NCA, (LiNiCoAlO2). I'm not sure the operating voltages are significantly different.
To be clear, when you saw the voltage at 12 miles was current flowing into the pack? Because as soon as current flows the voltage is driven much higher, especially at a supercharger.
To be clear, when you saw the voltage at 12 miles was current flowing into the pack? Because as soon as current flows the voltage is driven much higher, especially at a supercharger.
islandbayy
Active Member
forgot about these,
both the 60 and 85
Hope they canhelp somewhat, though a number of firmware revisions ago.
both the 60 and 85
Hope they canhelp somewhat, though a number of firmware revisions ago.
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