[SteyrTMP]

Update: I haven't posted anything, but have been limping along as my dad is working on the charger/discharger. Over the holidays, I've been driving it as my daily, and it's been pretty steady at 1/2, according to the battery gauge. I have been in some hilly areas a few times, in which it'd drop to 2 bars or so, but I'd make sure to allow as much charging as possible during the drive back, and it'd go back up to half or so. I've had two 1449 codes, both times my ScanGuageII was able to reset them, which was not working last time. I have noticed some wierd behavior--a few times, when driving on level ground, it won't have the constant 3 bars of charging. Instead, I'd get assist, but no charging, unless braking, which will kill the battery pretty quickly. Again, I don't think there's any point of stressing over it, until I've tried discharging and recharging. That should tell.

This weekend, I'm going to his house, and we're going to do some poking around, and some more tweaking. I am thinking about 3D printing a permanent housing, when he's done with the microprocessor, that will fit and bolt into the gap on the passenger's side of the battery compartment. Maybe a door, flush with the aluminum plate, to have the power cable rolled and enclosed away from everything.

Today I cobbled together the voltmeters into their housing, and into the rear bulkhead. Tomorrow we'll wire them up with vampire clamps, into the BCM cable, to have constant, real-time voltage of the battery sticks (or every pair, at least). I was having finish issues with both ABS and PETG, as I do not have enclosures for any of my printers, but sanded the finish on the PETG bracket a little, and called it a day.

 

[engdahl]

Here is an update on the voltmeter system. I'm Nathan's dad, a retired firmware engineer, but I also know which end of a soldering pencil to hold. We connected the 10 voltmeters (something like these: https://amazon.com/CenryKay-4-5-30v-Digital-Display-Voltmeter/dp/B08PB5NDMC), via a set of multi-pole switches, to the dozen wires running from the battery pack to the BCM, like this:

When we tried driving the car it would shut down IMA and throw a code as soon as we switched on the voltmeters. I'm guessing there is a current-limiting resistor in the battery pack, like this:

The voltmeters have only two wires, which are used to both read the voltage of the battery, and also to power the voltmeter. Each voltmeter draws something like 25 milliamps. The sense taps can supply that much current, but the voltage changes a lot -- as the digit segments light up the load varies, which drags down the sense voltage and changes the reading yet again, which changes... The BCM does NOT like this one bit.

I'm building a differential buffer to read the voltage and drive the voltmeter.

Here is the board on OSHPark: OSH Park ~

At this point this is still in development and is untested.

 

[retepsnikrep]

Yes there are orange PTC resistors in each voltage sensing wire on the battery end board.
I can't remember the resistance off hand but maybe a couple of hundred ohms when cold.
This resistance shoots up in the event of a wiring/BCM short to prevent it all melting down.

As you found out you can't draw significant current from them for your LED meters.

Your buffer circuit will need 10 x isolated power supplies will it not.

Can you find and use self powered lcd meters?

 

[*sean*]

Here is an update on the voltmeter system. I'm Nathan's dad, a retired firmware engineer, but I also know which end of a soldering pencil to hold. We connected the 10 voltmeters (something like these: https://amazon.com/CenryKay-4-5-30v-Digital-Display-Voltmeter/dp/B08PB5NDMC), via a set of multi-pole switches, to the dozen wires running from the battery pack to the BCM, like this:
View attachment 101536
When we tried driving the car it would shut down IMA and throw a code as soon as we switched on the voltmeters. I'm guessing there is a current-limiting resistor in the battery pack, like this:
View attachment 101540

The voltmeters have only two wires, which are used to both read the voltage of the battery, and also to power the voltmeter. Each voltmeter draws something like 25 milliamps. The sense taps can supply that much current, but the voltage changes a lot -- as the digit segments light up the load varies, which drags down the sense voltage and changes the reading yet again, which changes... The BCM does NOT like this one bit.

I'm building a differential buffer to read the voltage and drive the voltmeter.

View attachment 101535
Here is the board on OSHPark: OSH Park ~

At this point this is still in development and is untested.

A tip - it's not the voltages that are interesting, it's the difference between the highest and lowest channel that matters. It shows up when you hit the gas or brake. It will be impossible to see this while driving unless it's a bar graph display. The BCM already does the conversion to low voltage. There are about a half dozen BCMs on car-part.com for less than $50.

I had more here originally, but in fact this takes someone with electronics and high voltage experience and an interest in safety, not just while building but also while driving. It should not be attempted otherwise. Electrocution during the build may kill or hurt the builder, but electrocution while driving may kill the family in the minivan driving the other way when the electrocuted driver lost control and crossed the center divider.

 

[engdahl]

The inputs to the meters are ground referenced and can't handle more than 36 volts. The original idea would have taken care of this if not for the current limiters. The voltmeters are junk, but if we were to buy quality voltmeters we might as well go buy a new battery pack and be done with it. (But a new pack would be twice what he paid for the car).

Isolation is not needed. The 100K/10K voltage divider provides high impedance so the BCM doesn't know we're doing this. It also brings the high voltage down into range of the op-amps, which are powered by a 12-24V converter (https://amazon.com/gp/product/B08J2JYLC6). The power for the op amps needs to be more than 12V to handle the up to 19V difference across each pair of sticks. For a 16V difference the output of the first stage would be 1.6V, which is too close to the rail, so the op-amps use 3.3V as a reference. The 20V zener protects the negative input of the op amp from floating too high when the power is off. The second op-amp multiplies the difference-over-10 by 10 and references it to 0V. The 2N2222 provides enough current to power the voltmeter. The gain of the second stage is adjustable because I assume the cheap voltmeters are not that accurate and they don't even have a calibration pot. The 1 uf cap makes the second stage a low-pass filter with a cutoff of 20 Hz in case there is noise floating around. I haven't tried this in real life yet, but PSpice says it should work.

For safety, the entire voltmeter system is inside the aluminum covers behind the seats. The idea is to mount a cell phone looking back at the meters and recording a video while driving. The video will include commentary, such as "now I'm flooring it up a hill", and will be analyzed later rather than trying to watch 10 voltmeters and drive at the same time.

 

[retepsnikrep]

The idea is to mount a cell phone looking back at the meters and recording a video while driving. The video will include commentary, such as "now I'm flooring it up a hill", and will be analyzed later rather than trying to watch 10 voltmeters and drive at the same time.

I like that!

 

[eq1]

^ Funny, I had been wondering about that earlier - didn't seem too practical to have a board of 10 VMs in the back...

 

[SteyrTMP]

^ Funny, I had been wondering about that earlier - didn't seem too practical to have a board of 10 VMs in the back...

My original idea was simply to have a passenger recording it. I did not want to cut into the dashboard, and there is no easy location up front to place 10 VM's. On top of that, I did not want any bright lights flashing while I am driving. This way, it will not interfere with night driving.

 

[eq1]

A tip - it's not the voltages that are interesting, it's the difference between the highest and lowest channel that matters...

Ohhh the voltages are interesting. And they matter. For instance, watch your device after you've cycled a fresh swath of charge state range (say a 10-15% range between nominal 55% and 70%), leave it at 70% when you park for the night, then watch again when you're discharging down to 55% the next morning. You should probably see much lower voltages (not due to temp differences). That type of difference happens in various conditions/circumstances/ways. Granted, they don't reflect outright failure/major degradation like a tap down below 12V would, but it's interesting, and I think important in various ways.

Probably the most important thing to watch for is the stability of voltages under a steady load: You should be able to hit a particular discharge current, say 20 amps, voltages should fall to a particular value, say 14.8V, and only fall a tiny bit as long as you hold discharge current steady. If you see any voltage seemingly dropping fast/er, never holding steady, that's a sure sign of degradation (of whatever kind). I really had to dig into the recesses of my memory, from when driving on crusty packs, to unearth that one. My old packs couldn't hold voltages under load, they'd always be falling pretty fast.

 

[SteyrTMP]

 

[SteyrTMP]

 

[SteyrTMP]

 

[eq1]

^ Are those actual tap voltages in that last image -- 14.5, 17.3, etc.? 18.6V??

 

[SteyrTMP]

Yes, they are. That's why I ordered another 8 sticks from HybridRevolt, as at least 4 of the original batch I bought aren't up to snuff with the others. True, I have not had time to do a IMA reconditioning, but after 24+ hours of charging to reach peak and balance, I still end up with the same numbers after a day or so of driving. I am doing an oil change, installing the Killer3Cylinder underplate (I hope, some of those old threaded clips are pretty rusty, we'll see how this goes), then I will try to get the battery out, swap sticks, and charge it for a day or so.

 

[eq1]

hmm, you might do better with a random pack of untested sticks, bumblebee batteries used to sell those, don't know if they still do or not. I think one problem with hybridrevolt's 'tested' sticks is that they've already culled the good ones for their own rebuilds, so what you get must have some problem... Mixing and matching sticks can be tough, I think it's easier to get lucky with a random code-throwing pack, maybe having to replace a stick or two, than to cobble together a disparate bunch.

I don't know, I guess my advice is simply to make sure you discharge every cell at a really low current before you do anything else. You can grid charge all day and night and still end up with barely charged cells, if they've never been fully discharged.

The other thing is self discharge. I've seen cells that simply can't hold a charge, you can't have any of those in your pack. Uneven self discharge of milder degree is a problem (like cells with 2x, 3x the SD rate of others). But, it's possible to work around those, you'd need to do more topping-up type driving, and then to undo the degradation that causes, you'd need to discharge to empty more often, too. You should be able to spot taps with faster self discharge cells, especially with your VM board, with the right kind of manual tests/checks, so, maybe it's not totally necessary to test for that before you rebuild (because it's hard, takes a long time, etc.)... To screen for super-fast SD cells, you can probably charge a stick to full (after you've made sure every cell has been fully discharged at low current), check voltages, then let it sit for a day, then check voltages again. My guess is that cells that drop below 1.32V aren't usable, they're super-fast SD. All cells probably shouldn't drop below 1.36V within that single day... I'm not positive about this stuff, but I'm pretty sure?, reasonably sure?, somewhat bullish? on the ideas...

Again, though, you must make sure every cell is completely discharged at low current before moving on to anything else. Otherwise you just end up going around in circles, tilling bad soil, you end up testing/working with trash... The way I used to do it is with a cell discharge rig, basically a stick holder that has clips for each cell, with I think it was a 37Ω resistor across each cell. You could just tape them there. Or you can discharge each stick till first cell empty, then do the other cells individually. I suppose you could attach a 6 X 37 ohm resistor across each stick and do one whole stick at a time. I don't think I'd recommend doing the whole pack like people do. Oh yeah, you can short your taps and do stick pairs, the PTC resistors in the orange end board serve as the load for each tap (you can only do 5 taps at a time, never adjacent)...