SpeedEBikes said:
Sorry if I came away with the wrong impression.
If you succeed in your mission you'll have a big thumbs up from me. But I think to do it right will be more difficult than you expect.
Oh, I know quite well how difficult it would be to do perfectly, and unless I can get someone to write the code for an MCU to process the data, I won't be able to actually do it the full way.
I also appreciate very much the thoughts you've provided here, as they have provoked more thoughts in the back of my mind, which as they percolate up I'll post about, perhaps in a thread dedicated to the idea of this meter concept I'd like to help create (because I know I cannot do it all myself).
Also, I apologize if I came off the wrong way; I'm just very used to lots of TL,DR responses to my detailed posts. I know that on most forums I visit, many people never even read what I post at all, if it's more than one line. When they do, often it's obvious from their replies that they didn't read it all, or didn't pay attention to the details (which I wouldn't put in if they weren't important, to me at least). So I sometimes get a little snappy when I see a response that appears to disregard the point of what I was saying, or the basic reason for it.
There are quite a few variables to account for. It's not at simple as keeping track of a fixed number of watt hours in and out with fixed multipliers.
I know. But it is a start, and better than what I (we) have at the moment.
Both charging and discharge efficiency vary with the internal resistance of each cell. Cell IR increases slowly over time as the cell degrades. It also fluctuates with temperature and current. In addition there is the internal self discharge of a cell. That is charge that disappears with time. The rate that happens can vary with the condition of the cell, with temperature and also with the state of charge. I'm sure there are other factors too.
And of course all of these things inter-relate with each other, causing even more variability.
Yeah, it's likely not going to be much fun figuring out how to do this the complete way.
And all of those factors will work quite differently for each battery chemistry. Even for cells of the same chemistry there will be differences based on how each cell was constructed.
Without doing any engineering, you can quite easily test this yourself. Just reverse your wattsUp or other meter when you charge. Instead of attaching the battery as the source, the charger is the source and the battery is the load. Track and manually record both the power in and out. Do it for a while and I expect you'll see quite a bit of variability over time with the ratios between what went in and what went out. I know you don't want to do this manually, you want it automatic. But if you do it manually and see that it doesn't work, you'll have saved yourself the trouble of trying to automate it.
The basic version of the offset split shunt will work well enough as an automated process for the little work I have to do to create it. The full version with all the variables accounted for will be much much harder, but that is definitely not in the plans for any near-future stuff.
Right now I don't even *have* a CA, WU, or even Turnigy meter (TM?), and no prospects of getting one soon as my financial situation seems to get worse every other week. With a little luck and a lot of hard work, I'll turn that around sooner or later, but it's been getting worse for years, so it could keep going for some time to come.
