Someone PM'd me about grid charging his pack. I responded with kind of a summary of what I think about that stuff these days, including a couple links to some underlying nut n' bolts. I thought it might be useful as a new thread, despite the constant drip of that kind of thing around here already. Mainly, there's a few ways I look at it that seem important to me but aren't usually represented in what people advise to others, such as the limits of grid charging-only, how a healthy pack should actually perform, and the function of deep discharging... Here's most of that response:
In general, I'm not nearly the fan of grid charging that most other IC'ers are. I don't think it does most of what people think it does. Here's a link to a thread where I've posted some graphic representations of the process, grid charging and grid charging + deep discharging. https://www.insightcentral.net/foru.../65322-graphic-illustrations-grid-charge-deep-discharge-process.html#post724378
I feel pretty confident about the general sweep of what's claimed there, though a lot of the specifics are out-dated... The graphics should help you wrap your brain around the bare 'mechanics' of charging and discharging a pack of cells in series... The gist of it is, simply, that if you need to revive or recondition your pack, a grid charge alone isn't going to do much...
As far as what your voltage readings say about the health of your pack? They don't say much of anything. The Insight NiMH cells will settle at a voltage around 1.318V at a wide variety of charge states and conditions. So, your pack voltage suggests just about that -- 159-160V / 120 cells=1.329V per cell. It just doesn't tell us much. We might be able to say that it's unlikely you have a totally failed cell...
You can't tell pack health very well unless you read and/or log pack voltages under load under various circumstances. For example, if you can bring state of charge down below 50% nominal, hit the pack with say 20 amps of assist, with the pack around 60 degrees F, and voltage stays above about 141V, your pack is probably pretty good... If you can bring charge state below 50% and still get about 4 seconds of about 80 amps of assist, at full throttle, your pack is probably pretty healthy... Anything less than these levels suggests some degree of... funk.
This is what's problematic with stuff you see/read at IC: no one looks closely enough at their pack performance to really know how they're actually performing. Most people are like, 'it doesn't neg recal' or 'there's no IMA light' - 'my pack is working great!' No, a great working pack has to hit certain metrics, certain benchmarks, in order to qualify as working great...
This is also what's insidious about the stock management and feedback about IMA functionality in the car - it's next to non-existent, you just don't know how well or bad the IMA is performing unless you dig in and take a closer look. The way the car manages the pack masks both poor management practices and poorly performing packs.
I also think the stock management causes at least some of the degradation/poor performance that creeps in seemingly fairly quickly... It charges too much, too often, too high. From my experimentation and observations over the... years, I'm coming to the conclusion that you almost can't force the pack to operate at too low a state of charge; i.e. the more you do/you can force the car to use lower charge states the better. The problem is, though, I think most packs are probably already too 'crudded-up' to get charge state very low and to have useful power/energy down there, so some initial reconditioning is needed...
Personally, I'm a proponent of 'ultra deep discharge' - very low current, prolonged, as disaggregated as possible (i.e. less than whole pack) discharging, followed by a grid charge. With this strategy I don't think it matters whether you grid charge first or not, as the load used is so small and you're preferably only dealing with at most 12 cells in series rather than 120, that cell reversal isn't an issue... Here's a link to some theory underlying this 'ultra-deep discharging' process: https://www.insightcentral.net/foru...m-1st-gen-discussion/81778-tinkering-non-working-ima-battery-8.html#post1206666
In general, I'm not nearly the fan of grid charging that most other IC'ers are. I don't think it does most of what people think it does. Here's a link to a thread where I've posted some graphic representations of the process, grid charging and grid charging + deep discharging. https://www.insightcentral.net/foru.../65322-graphic-illustrations-grid-charge-deep-discharge-process.html#post724378
I feel pretty confident about the general sweep of what's claimed there, though a lot of the specifics are out-dated... The graphics should help you wrap your brain around the bare 'mechanics' of charging and discharging a pack of cells in series... The gist of it is, simply, that if you need to revive or recondition your pack, a grid charge alone isn't going to do much...
As far as what your voltage readings say about the health of your pack? They don't say much of anything. The Insight NiMH cells will settle at a voltage around 1.318V at a wide variety of charge states and conditions. So, your pack voltage suggests just about that -- 159-160V / 120 cells=1.329V per cell. It just doesn't tell us much. We might be able to say that it's unlikely you have a totally failed cell...
You can't tell pack health very well unless you read and/or log pack voltages under load under various circumstances. For example, if you can bring state of charge down below 50% nominal, hit the pack with say 20 amps of assist, with the pack around 60 degrees F, and voltage stays above about 141V, your pack is probably pretty good... If you can bring charge state below 50% and still get about 4 seconds of about 80 amps of assist, at full throttle, your pack is probably pretty healthy... Anything less than these levels suggests some degree of... funk.
This is what's problematic with stuff you see/read at IC: no one looks closely enough at their pack performance to really know how they're actually performing. Most people are like, 'it doesn't neg recal' or 'there's no IMA light' - 'my pack is working great!' No, a great working pack has to hit certain metrics, certain benchmarks, in order to qualify as working great...
This is also what's insidious about the stock management and feedback about IMA functionality in the car - it's next to non-existent, you just don't know how well or bad the IMA is performing unless you dig in and take a closer look. The way the car manages the pack masks both poor management practices and poorly performing packs.
I also think the stock management causes at least some of the degradation/poor performance that creeps in seemingly fairly quickly... It charges too much, too often, too high. From my experimentation and observations over the... years, I'm coming to the conclusion that you almost can't force the pack to operate at too low a state of charge; i.e. the more you do/you can force the car to use lower charge states the better. The problem is, though, I think most packs are probably already too 'crudded-up' to get charge state very low and to have useful power/energy down there, so some initial reconditioning is needed...
Personally, I'm a proponent of 'ultra deep discharge' - very low current, prolonged, as disaggregated as possible (i.e. less than whole pack) discharging, followed by a grid charge. With this strategy I don't think it matters whether you grid charge first or not, as the load used is so small and you're preferably only dealing with at most 12 cells in series rather than 120, that cell reversal isn't an issue... Here's a link to some theory underlying this 'ultra-deep discharging' process: https://www.insightcentral.net/foru...m-1st-gen-discussion/81778-tinkering-non-working-ima-battery-8.html#post1206666
