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nicknorman last won the day on January 23

nicknorman had the most liked content!

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    Electronics, gliding, motorbikes

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    helicopter pilot - retired
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    Fazeley Mill Marina, Tamworth

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  1. Well hopefully, 3 1/2 years later, the OP has fixed the problem.
  2. No, moving iron ones pass all the current themselves. Generally not a particularly good idea for a boat with a large alternator/inverter etc.
  3. I’ve got all the individual bits of my regulator working as far as I can do without actually testing it on an alternator (but the actual regulating bit should just “work” because it’s handled by the chip). So being able to set the regulated voltage, set the field current limit, read the rpm and actual field current, measure voltage, measure remote temperature (alternator temperature), receive CANBUS data from the Mastervolt system, control the alternator warning light etc. Next step is to create the “state machine” ie what behaviour actually arises from the different sensors etc. But it occurs to me that a simpler and intermediate step might be to have a digital input that simply selects between two regulated voltage levels, eg 14.2v and 13.4v, the latter being a “float” voltage that would allow the alternator to continue to supply boat loads without further charging the batteries. You folks using BMVs could use one of its alarm outputs to switch over to the float voltage at the set SoC or cell voltage alarm.
  4. I don’t think they are trying to say you shouldn’t cruise at night as a general point, it is that you shouldn’t cruise at night to get around the Coronavirus-related instruction to not move at all unless essential. Which would be a bit like using your car for a non essential journey at night, when it is disallowed during the day. Kind of daft!
  5. Yes, the principle of conservation of energy answers a lot of questions!
  6. The energy doesn’t go anywhere, in theory. And yes it can happen, consider a capacitor connected across the mains. The current and voltage waveforms are (theoretically) 90 deg out of phase and so the power dissipated by the capacitor is zero. Replace the capacitor with a resistor of a value to give the same current, and the voltage and current are now in phase, so lots of resistor-frying power is dissipated. or consider a resonant circuit comparing an inductor and capacitor in parallel. Once you put energy in by way of alternating current at the resonant frequency into the circuit, that energy continues to circulate (theoretically) indefinitely and is not dissipated. I say “theoretically” in the above examples, because in reality a device like a capacitor does have some resistance and so the current will generate some ohmic heating / wasted power. And this is why electric companies don’t like loads with power factor away from unity - it creates a lot of pointless current circulating in the distribution lines that, due to their resistance, causes power loss from ohmic heating for no benefit.
  7. It occurs to me that certainly for boating use, all heavy mains consumers are virtually pure resistive loads (washing machine heaters, tumble driers, kettles, hair dryers, cooking elements etc). One doesn’t normally power heavy duty electric motors etc from an inverter. And aren’t domestic appliances that have eg motors all supposed to have power factor correction? All of which makes advertising a 1.6kw inverter with the headline of 2kva a right con!
  8. Whilst a night time panel is like a reverse biased diode, I think it is a pretty leaky one, hence a “normal” diode to fully block the reverse leakage flow. On the general subject, there is a simple explanation of diodes here: https://www.altestore.com/blog/2016/09/bypass-diodes-blocking-diodes-solar-panels/#.XocPmC_TWhA It also mentions that most (but not all cheap PWM) solar controllers have built in diodes to prevent reverse flow at night.
  9. As I understand it (and we don’t have any solar) you can put diodes across an entire panel. When the panel is producing juice, the diode is reverse biased and so does nothing. If that panel gets shaded, the other panels trying to force more current through the string than the shaded panel can take, results in that panel becoming reverse biased and blocking the flow. At that point, the normally reverse biased diode would go into conduction and bypass that entire panel. Obviously the output from that panel is lost but the output from the other panels in the string remain effective. Just thinking about it, this would only work with a series set up - the MPPT can happily adapt to the reduced string voltage. If you had series -parallel into one MPPT then the loss of one panel in one series string would mean that string did nothing, so no point in fitting the diode. For the avoidance of confusion panels normally have diodes in series, so that at night current doesn’t flow backwards from the battery through the panel. I think this is complementary to MP’s point which is that individual sections within a panel can have diodes built in to give a similar effect on a smaller scale.
  10. To some extent, but the problem with a big inverter is that it pulls the system voltage down when under heavy load which might cause the thing to shut off. Current draw stops, system voltage rises, inverter goes back on again and so the cycle repeats. The settings recommend a 1v difference between the shut off and turn back on voltages, which will go some way to alleviating this problem and of course lithium batteries suffer much less than LA batteries from voltage drop under load, but there is still drop in the wiring, connections, isolator switch etc. When 250A is flowing, it doesn’t take much to drop a volt or two. You would end up with a system that shut off early when under heavy load, much later when under light load. The other thing to bear in mind is that presuming the Li cells are top balanced, unless their capacities are all identical they will not be bottom balanced and so one cell will become catastrophically flat before the others do, its voltage crashing. I think one doesn’t really want to ever get to that stage and so the monitoring of individual cell voltages is better, and (bearing in mind the very flat voltage curve of Li) some sort of SoC determination (eg Ah counting) to shut things off when SoC of worst cell gets to 10%, 20% or whatever. Lead acid has a much more progressive fall off in voltage and so having a minimum overall voltage setting works, even though it’s not ideal due to the load dependence. I am not convinced it would work well for Li.
  11. With MPPT from an electrical point of view it is generally better to have panels in series, thinner cable is needed because the current is less. But definitely not to exceed the maximum controller voltage at all. And you need to bear in mind that the panel Voc is temperature dependant - it is often quoted at say 25degC but will be significantly more on a cold bright morning. Another upside of series is that you stand a better chance of getting some juice out of it over winter when the panels are doing virtually nothing. A downside is that if one panel of a series chain is shaded, it kills the flow in the entire chain, whereas with a parallel setup only the output from that panel is lost. Life is a compromise! In you case probably series-parallel is best.
  12. Firstly it definitely can’t be used with a Combi as it is for unidirectional current only. Secondly I’d guess, as suggested, it is to do with the switch-on inrush current. The first time I disconnected our Combi to move some wiring, I got a right shock (metaphorically, not electrically) when I reconnected it. A massive fat noisy spark almost as if I’d shorted the batteries. I hadn’t, but what I had done is to connect the batteries across now-discharged very large capacitors inside the Combi. These present an effective short circuit for the few milliseconds they take to charge up, so a very large current flows. Even though this is only for a short time, semiconductors junctions even for 220A devices are small with little thermal mass and thus heat up nearly instantly. And it is not just the inrush current with the device’s semiconductors switched on, there is also a (very short) period when the device is in the process of turning on - it doesn’t go from off to on instantly (although it is very quick) and as the FETs are going from open circuit to conduction, they pass through a period of resistance for a microsecond or two which adds to heat dissipated. The 220A device quotes a peak current of 600A but the instantaneous current on reconnection of a big inverter will be much more, albeit for a very short duration. If you can manually control when the device will reconnect, you could “bodge” it by means of a push button and resistor bypassing the isolator. You would press and hold the button for a few seconds prior to switching the isolator on, to recharge the capacitors. I would expect it to be fine when disconnecting the load with high current flowing. I know all this because I have been working with electronic devices since the 3rd century BC.
  13. Dunning Kruger effect strikes again! Anyway, enough bickerfest, folk will find it tiresome.
  14. When was the last time you understood the relationship between power factor, va and watts? Weilding a few spanners, screwdrivers and wiring something up in accordance with the manufacturer's instructions hardly makes you an expert on the science behind it. Unfortunately for you, this post says it all.
  15. 1/ Yes, due to voltage drop and inefficiency and it being a nice round number, I tend to use 10v. Perhaps slightly pessimistic but I'd use no more than 11v unless the engine is running with a powerful enough alternator to keep the system voltage well up. 2/ Not sure what that is. No I think the relay will be fine provided you don't overload it. I must have misread earlier, I thought you said you weren't doing low voltage disconnect 3/ Yes. However it doesn't take into account human error, and not all humans making the error will be you! But as you say, the 200A fuse will help. 4/ No, I dont think so.
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