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nicknorman

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Everything posted by nicknorman

  1. Picking up on this and having answered my previous question about why the field current % has to be so high for the tacho to work at low rpm: I was for some reason thinking an alternator was effectively a current source. But at the heart is Faraday’s Law which describes emf being a function of magnetic field and (effectively) rpm. So the alternator is fundamentally an emf generator, not a current generator. So in order to get a decent phase signal of say 10v pk-pk one might need quite a lot of field current at low rpm. But no current flows because the diodes don’t go into conduction, until the phase voltage gets to battery voltage + diode drops. For a given low rpm, if you ramp up the field, no current flows as the emf ramps up towards (say) 14v. Then just a slight increase in field current is needed to push the voltage beyond the battery voltage + diode drops, and suddenly the alternator is outputting current. So there should be a fairly wide margin of field current at low rpm to keep a modest voltage - but a voltage below diode conduction - on the phase output. The problem arises due to the rpm term in faraday’s equation, such that a wide range of field current is needed to maintain the “phase output live but diodes not conducting”, over a wide range of rpm.
  2. It matters if you want have an alternator warning light that would eg come on when the belt snapped. If the field current can fall to zero / no phase signal when things are spinning, that is indistinguishable from a rotation stoppage. And so in order to avoid false warning when the former occurs, the system has to be designed so that neither case brings on the warning light. Again, this is not great design. As you imply, if you can only specify a max duty cycle then the actual field current will vary according to temperature. But what you want is to specify a max output, which corresponds to a max field current, not a max duty cycle. Which is why I use the max field current setting, not the max duty cycle setting (which is also available). The only thing I don’t understand is why so much field current is required to maintain a phase output. If the phase output is close to zero, the diodes don’t conduct and no current flows. In fact no current flows until the diodes start to conduct and that is with a phase voltage swing of battery + 2 diode drops, say 14v at least. Until the diodes conduct, the power output of the alternator is more or less zero. So I would have thought it would just take an extremely small % of field current to get the phase voltage up to the point of diodes almost conducting. I must be missing something if you need 20-something %.
  3. Thanks for that detailed description. It does seem very crap for something that cost £800+. You say “This overall problem is not unique to the Zeus, it's something we have to deal with in all external regulators which are capable of reducing the alternator voltage to float.” but I say that it doesn’t have to be like that. I know that you and DMR probably don’t want to hear this, but the regulator I built around an £8 chip deals with keeping the phase /tacho output “alive” with zero load on the alternator, flawlessly. From the data sheet: 15 Phase regulation This function avoids losing phase signal amplitude for proper regulation when the voltage in the board harness is higher than the set point value (case of load shedding, or set point below battery voltage). The regulator monitors the voltage levels of the phase signal and checks if the phase oscillates between VTH_L and VTH_H, ensuring phase amplitude is sufficient for regulation. Phase failure is detected if there is no PhaseOK rising edge for more than 30 ms. In this case the phase regulation is started. The phase regulation function is performed by applying 100 % duty cycle current to the rotor, so the phase amplitude can build up. This 100 % duty cycle is stopped, either when the rising edge of PhaseOK is present again, or when the maximum duration of phase regulation is reached (this timing is determined by programming the tONBOOST parameter, max on time for phase boost). If the PhaseOK signal recovers, then fails again before the end of tONBOOST timer, another tONBOOST time is initiated. If the phase is still not OK after tONBOOST, the device goes back to regulation mode and starts a 300 ms ‘failure’ timer. When this 300 ms timer has elapsed, if there is still no PhaseOK rising edge for the next 30 ms, the phase boost function is active again for a maximum duration of tONBOOST. The number of retries is not limited. In other words, it increase the field current just enough to keep the phase signal working. The actual min. field current will thus vary according to rpm. None of that is anything to do with my design, I just send the regulator the set voltage and field current limit, along with configuration data for the load ramp. The reg sends back rpm and there are a couple of failure flags for mechanical and electrical failure, which I use to operate the warning light. The reg also sends back the actual field current, duty cycle etc but these aren’t useful, just slightly interesting. It does seem odd to me that both Wakespeed and the Zeus have started with blank sheets of paper and re-invented the wheel, not particularly well. Why do that as a small low budget company, rather than using the cheap tried and extensively tested product from one of the several gigantic automotive electronic design companies with enormous budgets, experience and expertise. I just don’t get why people want to make life so difficult for themselves. Just on you point about the low initial field current, my reg does that too and I think it is a good thing. If you have a large alternator it is helpful to have it briefly disabled or at least creating only a light load whilst the engine is starting up. And as you say, why pump 4A into the field when the engine isn’t running?
  4. No I don’t think this is implied or likely. The inverter washing machine is probably more “electronics heavy” than a standard one and so the devil will be in the detail of what the electronics has been designed to cope with. As usual I’m afraid it will be a matter of “suck it and see”.
  5. Deffo. I sold 4 T105s to the scrappy, got around £50 for them. Price was I think 48p/kilo and they weighed 112kg
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  9. Norton Canes boatyard (Glascote basin) sells Winterblaze which is the best stuff IMO, very little ash compared to other stuff.
  10. We are of course only hearing one side of the story and not the words or demeanour of the OP’s communication with the trip boat skipper. Personally I think that if abuse is hurled at a passing boat, it is not too unreasonable to respond in kind, it is just human nature, although of course I have no idea if this relates to the OP’s communication or not and certainly am not intending to make any accusations. It is an annoying feature of modern life that people feel empowered to rudely shout orders to passers by - but only if they can do so without fear of physical retaliation by being isolated from the other party - eg by water, vehicle etc. Once again I will make it clear that I am not accusing the OP of bad behaviour, I am just commenting on the general situation.
  11. This won't have done the gearbox much good, but probably not too much harm either since you didn't run it for very long. Just as well he didn't forget to put oil in the engine! Personally I would never trust routine maintenance to a "professional" because as you have discovered, they often don't really care and just want the money and to get on with the next job. The old saying of "if you want a job doing properly, do it yourself" is true! Obviously this can be tricky if you are not mechanically minded but you can go on training courses to be shown how to do basic stuff like changing the oil. You will then be empowered to DIY and you will take more time and trouble over it than a "professional", and you will get to know your engine so that it is a friend rather than something to be frightened of.
  12. The canal is quite deep there so whilst those trip boats do seem to pass fairly quickly, it has never been an issue for us. Please bear in mind that the canals are a transport system and it is up to you to moor as best you can, rather than expecting everyone else to pass extremely slowly so that a badly-tied up boat doesn't move. We often see badly tied up boats with for example, ropes at roughly 90degrees to the boat/bank. Ropes quite loose so that the moored boat can "pick up speed" prior to the ropes snatching tight. Of course we weren't there to see how your boat was tied up nor how fast the trip boats were moving, but bearing in mind we have often moored there and never had a problem - in fact I can't remember the last time we had any issues with a boat passing too fast - my suspicion is that you could tie your boat up better. Sorry if you don't like the sound of that but sometimes one has to be cruel to be kind! Please ensure your ropes are tight and not at right angles. As so often is the case, we find the rings in Birmingham at the wrong distance apart so if we just use 2 lines then the boat is not really restrained in the fore/aft direction, which is the main way the boat wants to move when another boat passes. You have to use 3 lines, with a line going both fore and aft from either the front or the back. This holds the boat stationary in the fore/aft direction. Then you just need one line at the other end to keep the boat into the side. NEVER use the centre line to tie you boat up, this just makes it heel alarmingly. Once you are moored properly you will find that passing boats are not a problem however fast they go (within reason) and your life will be much more relaxing!
  13. Just to clear up this point there are two types of alternator, a 9 diode machine like the one in your pic. This requires current through the warning light bulb into the D+ terminal to get charging going. Then there is a 6 diode machine, this does not require a warning lamp to be connected in order for it to work. It is not uncommon for the smaller engine alternator to be the latter type.
  14. Yes I suppose an obvious point is - are you familiar with how to rev your engine whilst keeping it in neutral? The way this is done varies according to the type of engine control but sometimes involves pulling out a knob or some such. Is it possible that this knob(if there is one) remains out from when the mechanic did the service?
  15. If you had an issue with the selector shaft seal, this is usually due to too much travel on the cable which flexes the shaft and wears the seal. Replacing the seal only fixes the immediate symptoms, not the cause. So I would check to see if there is signs of oil leaking from the shaft again, and check the gearbox oil level. The gearbox is operated by oil pressure and so if the oil gets low, the gears won’t engage.
  16. You can’t access the database directly, other than via eg the CRT website if you have a licence with them. Or maybe the EA website.
  17. The info will be on the BSS database, maybe try phoning the BSS office?
  18. Let’s hope the leaves being grabbed aren’t yew.
  19. Limiting the max duty cycle is one way of avoiding alternator overtemp, but it doesn’t take into account the ambient temperature of the engine room - which even with your setup could probably vary by at least 20C - or the fact that the alternator can run flat out for a short while before overheating. Using a temperature sensor is of course the better way to do it.
  20. The inductance doesn’t matter for steady state, it only affects the max dI/dt. 100% duty cycle will put the battery voltage (13.whatever) across the rotor. Which is fine and will give max alternator output for the rpm. There is a reasonably close correlation between % duty cycle and % rotor current. The limit vs rpm is to reduce load at low rpm by reducing the duty cycle (very useful if you have a large alternator) whereas the max duty cycle puts an overall cap on the max output. Not sure why you would want to do that other than to establish a rough max current into a battery in the absence of a shunt, although as I said before it seems unlikely that you would want to put a blanket reduction on max output regardless of eg alternator temperature. Then again I do remember when I said our alternator (before the advent of my controller) could stuff in 180A into our 450Ah of Trojans at the beginning of charging. You said I was cruel! Trojan of course recommend a max of 20% C charge current and that was 40%. But that was crappy old lead acid batteries, who uses them these days?
  21. Yes the rotor is a surprisingly resistive load (bearing in mind all the whirly round magnetic bits in an alternator). Of course it has inductance too but in the longer term, the current is based on ohms law. So if eg you want to limit the alternator output to about half, you could specify a max of 50% duty cycle. Certainly this would work fine for an rpm vs load map to reduce mechanical load at low rpm, or to control max temperature. In my case the chip had field current measurement built in (measuring the voltage drop across the FET probably) and I use that, having identified that the alternator max field current was about 4.5A with 13v across it. Obviously that made it “tuned” to my specific alternator, but that isn’t a problem for me. In fact having just checked, I see I can read the instantaneous duty cycle but I can’t set a duty cycle limit. Only a field current limit in amps. This seems to be the industry standard for a LIN interface alternator controller. Anyway, it works fine for me!
  22. Well done for just continuing to read this thread. It is a geeky thread for geeky people, but spectators are of course welcome!
  23. No. In order to set an alternator load vs rpm curve, you use the rpm and a max field current limit as the axes on the curve. Otherwise, if you were foolish enough to use the alternator current instead of the max field current, when there was a sudden load on the alternator there would be transient overswing on the alternator current and hence on the mechanical load. Which is bad design. Why go for the added complexity of requiring a shunt to measure alternator current so that you can make a bad design, when instead you can use a field current limit that doesn’t require an external shunt, and make a good design with no load overshoot?
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