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weber

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weber last won the day on November 9 2019

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  1. See Coulomb's excellent posts via the first 3 links here: https://forums.aeva.asn.au/viewtopic.php?t=4332#commands
  2. No. You should not let it go to 3.7 V. Use a headlight bulb to bring it down to where the others are.
  3. Yes. If you need to set the absorb voltage lower than your usual float voltage then you should set absorb and float the same. You typically won't be allowed to set absorb voltage lower than float voltage, so you'll probably have to set the float voltage down first.
  4. Only one cell needs to be above 3.4 V for it to be worthwhile doing balancing. It doesn't matter if the others are greater or less than 3.4 V. And you should stop (or the BMS stops you anyway) when any cell goes above 3.6 V. So you need to extend the time between the first cell going over 3.4 V and when it goes over 3.6 V. To do that, you need to reduce the charging current. Ideally, you would reduce it to the same as (or a little less than) the current that you are able to bypass around a cell by connecting a headlight bulb across it, which is typically 2 A for one filament. With th
  5. This is not mere theory. Coulomb and I do this with every new battery (set of cells). The typical 55 W headlight bulb draws about 4 A at 13.8 V, so you might expect it would only draw a quarter of the current at a quarter of the voltage, so about 1 A at 3.4 V. But in fact it will draw about 2 A at 3.4 A. This is because the filament has a much lower resistance when it is only glowing a dull red compared to when it is white hot. A fan will behave in the opposite way. i.e. it will draw much less than a quarter of the current at a quarter of the voltage. I doubt that the fan will draw enough
  6. One way is to use one or more car headlight bulbs with alligator-clip leads, and a multimeter. With the battery on charge, and close to full charge, clip the bulb(s) on to the cell(s) with the highest voltage(s), provided that voltage is greater than 3.4 V (for LFP cells), to burn off some charge and let the other cells catch up. You can leave the bulb on a cell until its voltage drops below that of the lowest voltage cell. You can also work in the other direction. If you have an adjustable-voltage current-limited power supply (a lab power supply) you can set it to 3.6 V, and when the who
  7. If this inverter accepts the same serial commands as its big brother, then I think it will reset its charging algorithm if you send it a command to change the float voltage or absorb voltage. You only need to change it by 0.1 V and then you could change it back. You could automate this, using Node-RED on a Raspberry Pi. The commands are PBFT and PCVV. http://forums.aeva.asn.au/uploads/293/HS_MS_MSX_RS232_Protocol_20140822_after_current_upgrade.pdf
  8. I thought I was a bit more nuanced than that. I did give at least one suggestion for making it work. https://powerforum.co.za/topic/4614-axpert-settings-for-lifepo4/page/2/?tab=comments#comment-70618
  9. I love how you wrote that with a straight face. The idea that an Axpert would have a 25% safety margin for anything, strikes me as hilarious.
  10. Yes. It's important, when designing a battery system, to try to predict the maximum storage requirement over the life of the batteries, and include enough capacity right from the start, preferably without paralleling. When this hasn't been done, some workarounds are: (a) Connect the new batteries to a separate inverter/charger and separate solar panels, and parallel the AC outputs of the two inverters. Unfortunately you can't do this with two Axpert inverters. To be able to parallel their AC outputs, they must be connected to the same battery. (b) Connect the new batteries to a
  11. Successfully paralleling strings of identical new cells is difficult enough. It requires extreme attention to detail. Successfully paralleling different makes, models or ages of cell is almost impossible. One string will end up carrying all the current during the middle of charge or discharge, and the others will carry all the current at the beginning and end. So they will all be abused, So it's pointless, unless the second lot of cells are free, or nearly so. More information here: https://powerforum.co.za/topic/2736-the-multiple-string-battery-riddle/?tab=comments#comment-43501
  12. Alternating the connections would be better than nothing. But you will need to swap it once a week (or once a day) for the entire life of the batteries. Otherwise one will age and die long before the other.
  13. @Adri, Sorry to take so long to respond. Using heavy cables isn't sufficient, because much of the resistance is in the crimps, the plug contacts and the bolted connections. If you have the same numbers of those on the path through each battery, then you may be OK. http://www.smartgauge.co.uk/batt_con.html As Chris Gibson shows in the above, there are only two ways to do it properly, his method 3 and method 4. He shows 4 batteries, not 2 as you have, but his method 4 is just "diagonal takeoff" applied hierarchically. Diagonal takeoff only works for 2, 4, 8, ... batteries (powers of 2)
  14. @Adri What you have may be fine. Diagonal takeoff isn't the only way to balance currents between two batteries in parallel. It will be fine if you are using one of these: https://www.redarc.com.au/anderson-parallel-cable-2 provided the cables going from it, to each battery, are the same length.
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