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Coulomb

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Coulomb last won the day on June 8

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About Coulomb

  • Birthday January 5

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    Brisbane, Australia
  • Interests
    Solar energy systems with storage; firmware for inverters and chargers

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  1. Congratulations. Technically, the firmware is the LFP flavour of patched firmware version 73.00e; the "1" comes from the "U1" settings label for main firmware versions, when they are non-patched. Other firmware versions have labels U2 through U4; only U2 on your model (and only when there is PV power available to power the Solar Charge Controller).
  2. There is no such thing as an Axpert King MKSIII; perhaps you meant three models, the King, the MKS III, and the VM III? The King is an unusual model, in that it is the only one with dual conversion from AC-in to DC, and DC to AC-out. Thus, it can offer zero transfer time (between the loads being powered by the battery and by AC-in). It's also one of the now relatively few models that has a 145 V absolute max Solar Charge Controller (SCC). It can be paralleled. The Axpert MKS III, also known as the PIP-MGX, is a version of the Axpert MKS II with a removable display. This model has a high voltage (450 or 500 V max) SCC. It can be paralleled. The Axpert VM III is a "value line" machine, which can't be paralleled and has a few other minor limitations. It also has a high voltage SCC. So it's like a cheaper version of the MKS III / PIP-MGX. All the above models come in 3 kW and 5 kW versions. A 7.2 kW and 8 kW version of the Axpert MKS III is called the Axpert MAX. There are also the Axpert MKS models (without a II or III as part of the name). These have no removable display, have a low voltage SCC, and can be paralleled. An Axpert VM II is like an Axpert VM III without the removable display; it's a far less common model.
  3. It could be the inrush current, if you don't have any pre-charge arrangement. Any inverter larger than about 1 kW should really be started with a resistor in series, of a few ohms. That limits the in-rush current to a tolerable ≈20 A. Once the capacitors in the inverter have reached some 90% of the battery voltage, the resistor can be shorted, at which point it is safe to start taking load from the battery, or to charge it. The resistor has to be a special type capable of very high peak power, preferably about 25x its continuous rating. Usually, it will be rated for 50-200 W continuous (so 1250-5000 W of peak power). My system uses a 3.3 Ω resistor, rated at (from memory) 100 W. A small computer monitors the voltage at the inverter terminals, and turns on a contactor to short the resistor when the voltage is close enough. The contactors themselves have a large inrush current, so they are started in a staggered fashion. So my system starts up from cold with a rapid clack-clack-clack... sound (there are about 7 contactors total). These are all EV200s, capable of switching 200 A DC at lowish voltages (such as the nominally 48 V battery, or 100+ V of solar power). You mention that you eventually got the inverter started. It's possible that each attempt left the inverter batteries with a little more voltage than before, until finally the capacitors were close enough to the battery voltage that the inrush current no longer tripped the battery's over-current protection. My understanding is that many battery designs, including that of the Pylontechs, include MOSFETs for battery protection, and that these naturally or by design are able to limit the current out of the battery for a short period of time. The short time is because these MOSFETs would be dissipating the same energy in a short pulse of power that the pre-charge resistor would be, i.e. several kilowatts. They can withstand such power levels for a short period of time (less than a second), without needing impractically large heat-sinks. Perhaps the Shoto battery doesn't use MOSFETs, or doesn't employ them in such a fashion that they naturally provide a pre-charge or soft-start function.
  4. No, that's dangerous. The difference in panel voltage will result in current flowing from one set of panels to the other. It could cause a fire. When paralleling strings, they ideally should be identical in panel specifications, but if not, the total Vmp should match within 5%. You seem to be using Voc in (some of?) your calculations, but Vmp would be similar. You would have a mismatch of 115.8 vs 100.2 V, or over 15%. That's way too much mismatch. That's at least not dangerous, but you would be reducing the 450 W panels' performance to effectively something like that of a 295 W. So that's impractical. It may make more sense to use a separate MPPT for the new strings of 450 W panels, connected directly to the battery. It's a little tricky, but can be done. Just set the external MPPT voltage settings one or two tents of a volt lower than the inverter's settings.
  5. You only have 1 now, by the sounds of it. You will need to get another one of the exact same model (not necessarily branded the same), and will likely have to update the firmware in one or both to make sure that they are the same revision. That's no problem at all. Yes, it's about 1 meter long. Basically, the two inverters need to be side by side, or very nearly so. Didn't a pair of paralleling cables come with the original inverter? Each paralleling card comes with one of each cable (one twisted pair, one white one with what looks like VGA connectors at each end). You need one pair of cables per paralleling card, so two pairs total for two inverters. The new card will likely only come with one pair. You may be confusing the paralleling board with the communications board; they live very close together. Note the four connectors (from https://www.communica.co.za/products/vp-mks-5kva-parallel-kit) : I'll let locals comment on what's available in South Africa. I use my removable 100 A fuses as isolators. You will need separate isolators for the two AC-outs as well. You probably have some way of isolating AC-in already; I don't use separate isolators for AC-in, although occasionally I wish I did.
  6. Are you running the 52.5 V bulk/absorb setting (setting 26)? If so, as an experiment, knock it down a notch to 52.4 V and see if that helps. Otherwise, change it to 52.5 V, as 53.2 V is way too high. My guess is that the battery is disconnecting due to excessive battery voltage. It will disconnect at 54.0 V, and Axperts have a propensity to overshoot the set voltage.
  7. OK, and since it's nearly the middle of winter, you should be OK with that voltage. That's the absolute maximum, never exceed voltage. You get zero power through at 145 V. Yes. Close, but OK. You don't need to rewire 2S. I don't know why you're getting a maximum of 60 A, unless setting 2 (maximum charge current) is set to that value, or solar balance is disabled (setting 31). Some have reported that the SCC runs hotter with 3S than 2S; can you see the temperature reported by the inverter on your monitoring software? Excessive temperature could reduce solar charging output.
  8. If your panels are 72-cell (330 W is about the transition between 60-cell and 72-cell), then the solar charge controller may be limiting power due to high PV voltage. What PV voltage are you seeing? If it's over about 134 V, you will be limited to ~75% of rated output, which would be 60 battery amps. If that's the case, the solution is to re-wire for 2P. Sadly, because you have an odd number of panels, that means getting an extra panel, or not using one of them. But you may get more power from 2S7P than 3S5P, and your SCC may well last longer. Unless your machine was made before about 2017, it will have an 80 A MPPT. I don't think you can easily obtain a replacement MPPT card.
  9. No, it will go to bypass on overload (unless disabled), but yes, the power still goes through the internal circuitry of the inverter-charger. The circuit is rated for 40 A (your wiring may not be), so there should be no problem unless the load exceeds about 9.2 kVA.
  10. That's a good point; especially when people don't use soft starting of their inverters, and use the fuse as an isolator, the splat when connecting can leave pit marks that could lead to high resistance. I've not had any trouble with mine, but I rarely disconnect the fuses, and I have pre-charge built in to my system. I use the fuses that are I think 18 mm or 22 mm diameter. They and their fuse holders are not cheap.
  11. But didn't the successful main firmware update happen through this "faulty" comms isolating board? Maybe it's just marginal, working only with certain removable displays. The most likely components to become marginal in my opinion are the two opto isolators, the two largest 4-pin components under the board. These can be ordered from Mouser or the like; shipping will likely cost 10x the cost of one part. I found a post where a reader replaced optos on a communications board and it fixed a similar problem (note: the Axpert MKS models have a very different comms board, which you can apparently buy from Mustek, but which probably uses the same opto isolators). I can't quickly find the part number for replacement optos; I'm pretty sure I posted it somewhere, probably in the repair and modifications topic.
  12. It's possibly me not understanding 24 V systems. My understanding is that 24 V is barely the start of where DC arcs become a problem, so that these "automotive" style fuses may actually be acceptable. Personally, I would not feel safe connecting a battery capable of thousands of amps to a fuse like that. I'd want to see a ceramic or sand-filled fuse that is capable of quenching a sizeable arc. But that's me. I would at least check the fuse's maximum current rating; I think it should be able to clear at least 2000 A. If you were using a large lithium based battery ongoing, it would likely have to be able to clear even more current than that. I emphasise that this is for short periods of time only, of the order of one minute, depending on the fuse characteristics. Some fuses are better at carrying short term overloads than others.
  13. It's very important that it's DC rated. Flat doesn't sound like it's DC rated.
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