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nicknorman

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nicknorman last won the day on July 18

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  • Gender
    Male
  • Location
    Aberdeen
  • Interests
    Electronics, gliding, motorbikes

Previous Fields

  • Occupation
    helicopter pilot - retired
  • Boat Name
    Telemachus
  • Boat Location
    Fazeley Mill Marina, Tamworth

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  1. I don’t think it will be too hard. An off the shelf alternator controller chip with LIN interface. A PIC micro to talk over LIN to the controller to set target voltage / max field current or whatever. Inputs from cell voltages, obviously (is there a BMS thing like the BG-8S that outputs serial data?); from battery current, maybe from alternator output current (neither needs to be particularly accurate); from alternator temperature; from battery temperature; Human interface to select max SoC. (I’m thinking a switch to select max 80% or (near) 100%). I’d probably go for a separate AH counting SoC gauge (BMV etc). Maybe a separate PIC to do emergency low and high voltage disconnect. Anything else? Edit: The AD7280A looks good for battery cell monitoring, has an SPI interface.
  2. Ordered, for £28. But not delivered until next Wednesday and anyway, we are away on the boat until end of next weekend. I’ll report back after that.
  3. TLDR. If you are going to write another article, can I suggest you crisp it up a bit. You are committing that unforgivable scientific sin of vigorously ignoring evidence that doesn't suit you - I am referring to the pictures of MtB’s 2 monitors. But I realise I am wasting my breath, despite the fact that we agree on much of it, it’s clear you resent anyone with an opinion on any aspect of it that is slightly different from yours, and instead of being able to debate around it, you see it as a threat. A modern ill, of course. I’ll leave you to it. At some point in the future when I have the time and when our Trojans conk out, I will get some lithium batteries. I won’t fudge it by having a massive bank of LAs left in place (no room, apart from anything else), I will have a (probably home made) alternator controller that goes to float when the batteries are at the desired SoC and allows us to continue cruising. Perhaps then you will regard my opinion with less contempt, but then again probably not. I’m tempted to buy one and open it up - they’re only £30!
  4. That is how it works! The device has to work when connected to anything between 1 and 8 cells (ie 3.3v to 26v) and as has been mentioned, it takes its power only from the first cell, ie a 3.3v supply. Can a mux/amp such as you describe, directly deal with a 22.7v and 26v differential input when powered from 3.3v? As you can probably tell, my expertise is mostly in digital electronics / software. I’m not very good at analogue electronics.
  5. It’s not just about the engine size, it’s as much or more about whether the cooling arrangements can cope with the engine running very fast for a long while without overheating. If the engine is adequately cooled then yes, although also depends on size of tide.
  6. Can’t be bothered to look it up but can an analogue multiplexer and DVM ic that are both powered from 3.3v, easily measure the differential voltage across 2 points one being 23v and one 26.5v, and give the result to the same accuracy as measuring across 2 points one being 0v and the other 3.3v?
  7. Well yes but it’s not quite that simple since you are not just measuring 8 voltages all referenced to 0v. You have to change the reference point for each cell since the cells are connected in series.
  8. This is turning out a bit like live aboard vs non-live aboard boaters, with the former claiming that the latter’s opinions are worthless because they don’t live aboard! When you say “his meter is known to be accurate” what does that mean? What accuracy and resolution of a meter was it tested against, just at one point or over a range of points? Much of the “explanations” he gives, whilst valid in themselves, are not relevant to the specific point about the discrepancies between your two meters. And as we mentioned, it is surely questionable that a £30 device can be more than about 1% accurate. That presumes that these meters are genuine - the Chinese have a habit of cloning stuff! “Observational” science is great up to a point, but can lead to misconceptions, eg “I’m standing on this grassy plain and I can see flat ground as far as the eye can see, therefore I deduce the earth is flat!”. It needs the reality check of some theoretical knowledge too. I’m afraid he lost a lot of technical credibility when he said authoritatively that having added (say) 10 AH to a 4S battery, in order to return a cell to the state it was before that charge was added, you have to remove 10/4=2.5 AH from that cell. An absolutely basic and fundamental error, and so far I’m not convinced he realises it.
  9. Yes i know all that (except for the memory effect suggestion, which seems questionable) but it’s not relevant. If you are going to preface every response with “you don’t know what’s going on” I am going to think that having an article published has gone to your head. Anyway all that is irrelevant to the key point which is that if you look at Mike’s photos of the two types of monitor which as I understand it were taken just moments apart and with no significant charge or discharge, you can see that there are significant differences in voltage, not just absolute voltage but also the relative voltages of the different cells. I can’t see any possible explanation for that except meter accuracy. Can you provide another explanation?
  10. Yes I understand that, but that effect would only be visible near the top and bottom, unless the cells had massively different capacities. Coming back to your post 28, as I understand it those two pics were taken shortly after one another? If so one can see a fair discrepancy between the two, not a fixed offset for all cells, but the cells are in a different order, eg cells 7 and 8. Displays to 3 decimal places are alluring, but when the accuracy is unlikely to be better than 1% tops, misleading. Edit: cell 8 seems to have around 0.04v difference which is 1%
  11. Seems a bit unlikely that the cell voltages would change a lot relative to each other. What is the mechanism for that? I’m sceptical because whilst I don’t doubt it is an effect you have observed, you are observing it via the el cheapo BMS and perhaps what you are observing is the inaccuracies of that BMS, not something fundamental going on with the cells. Can you prove me wrong?
  12. Obviously the SoCs are different and thus so are the voltages. But the relevant point is the relative voltages - the first pic has the cells roughly in order of voltage, the second the voltages are all over the place. If the measurements were accurate the cells would surely have roughly the same relative voltages? The knee is the point in the graph of voltage vs SoC during charging where, approaching fully charged, the voltage suddenly starts to rise rapidly. Ie an upward kink in the graph. Knee as in bent knee, not straight knee, obvs!
  13. It is about meter accuracy if you try to draw conclusions mid charge, as MTB has done!
  14. You just have to look at this post to see the inaccuracy of one or almost certainly both devices. He did compare the two, and there were obvious errors/inaccuracies. Obviously these devices have their uses - as the knee is reached the change in voltage is much greater and thus inaccuracies become less important. So they are fine for top balancing (or bottom balancing). But it would be a mistake to read too much into a mid-charge reading and worrying about seeming imbalance. As we know, the voltage stays very steady for much of the midrange and these meters aren’t sufficiently accurate to be able to determine that one cell is “flatter” or “less flat” than others and hence needs balancing. As I said, that can only be determined near full or empty.
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