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  1. mcart117

    BMS Paranoia

    Yes, I think you are probably right :)
  2. mcart117

    BMS Paranoia

    I started out with one and really enjoy the luxury of having two, so I don't want either to fail or have to switched off while I wait weeks for a replacement BMS.
  3. mcart117

    BMS Paranoia

    Should probably be the subject of another thread, but your reply makes me think of charge controllers. Should they be oversized to handle noon sunlight and have redundant capacity morning and evening, or made to fit the softer sun and just burst at the seems for a couple of hours midday?
  4. mcart117

    BMS Paranoia

    Good strategy.
  5. mcart117

    BMS Paranoia

    I'm not sure I do either. When the battery is full and over voltage protection kicks in, it seems like a very flimsy device holding back a lot of current. I have manual isolator switches, and if I am home I switch off one array as the battery approaches full charge and the second array when it...
  6. mcart117

    BMS Paranoia

    I do actually have four spare LFP cells, which for me is half a battery. So I think it makes sense to have a spare BMS as well.
  7. mcart117

    BMS Paranoia

    Not that easy in Australia as discussed here
  8. mcart117

    BMS Paranoia

    Thanks for that. I think I'll order a spare for a rainy day.
  9. mcart117

    Solar power is not just for rich people.

    So, for the avoidance of doubt, by WA I meant Western Australia :)
  10. mcart117

    BMS Paranoia

    Can one afford a spare wheel on a car? Manufacturer's don't give them away any more, but I still carry one.
  11. mcart117

    BMS Paranoia

    Does anyone else lie awake at night worrying about whether their BMS is going to fail? And if so, do you always keep a spare on hand – just in case!
  12. mcart117

    Solar power is not just for rich people.

    Don’t you mean desiccate? It never rains!
  13. mcart117

    Solar power is not just for rich people.

    I am totally on your side. I had a builder put the first row on the roof, because I didn't want to fall off, but the rest are leaning against whatever is lying around. I think the tie it down for a cyclone mentality is for installers putting panels on rooves in crowded suburbs. You don’t...
  14. mcart117

    Keeping LiFePO4 Battery Banks cool in Australia

    I agree with you there :)
  15. mcart117

    Keeping LiFePO4 Battery Banks cool in Australia

    Not really measurable. The inverter is off during the day, and the battery doesn't seem to generate much heat while charging. I am just mitigating the external effect of the hottest days, without spending a fortune.
  16. mcart117

    Keeping LiFePO4 Battery Banks cool in Australia

    Under Australian law, what they call Tier 3 batteries aren't allowed anywhere near a dwelling or place where people sleep.
  17. mcart117

    Keeping LiFePO4 Battery Banks cool in Australia

    The ambient temperature goes over 40º on hot days. I'd worry about making the cells hotter, faster. This is a good strategy. The night time temperature might drop close to 10º, so I do run the fan from first thing in the morning to keep the battery as cool as possible for as long as possible...
  18. mcart117

    Keeping LiFePO4 Battery Banks cool in Australia

    It is a large shed with an open wall on one side. It gets hot, but not because of the inverter - because of the sun beating down on the tin roof. The battery is set to switch off at 36º, but with the cooler in place, it rarely gets there.
  19. mcart117

    Off grid solar project

    One of the things I have learnt with this project is that (second hand) solar panels are very cheap, but everything associated with them – solar rails, clamps, cables, connectors, isolators and labour – are quite expensive. My main motivation at this stage is science: how much energy can I...
  20. mcart117

    Keeping LiFePO4 Battery Banks cool in Australia

    Interesting idea, but I think I’ll build myself a wine cellar before I start excavating for a battery!
  21. mcart117

    Keeping LiFePO4 Battery Banks cool in Australia

    By way of an update, I have been using the cooler for about 4 months now. No sign of any corrosion, but the main problem is how feeble the cooling is. The physics of evaporative cooling is too complicated to waste a lot of time with, but the bottom line is that the best my cooler will achieve...
  22. mcart117

    Single cell jumping 400mV on charging

    Fair point. I thought it was a typo: I thought you were saying something is not right! But yes, all the people who said check the contacts seem to have been right, and I was being a bit stubborn.
  23. mcart117

    Single cell jumping 400mV on charging

    When I first assembled the battery, I used a torque wrench to tighten the nuts securing the bus bars and BMS contacts to the level of tightness recommended by the battery cell supplier. As I loosened four of these nuts to remove cell number 4 for testing, three of them still had the expected...
  24. mcart117

    Single cell jumping 400mV on charging

    Thanks for both of those. I'll check the connections. The cells are just 3 months old, but I will check the IR of Cell 4.
  25. mcart117

    Single cell jumping 400mV on charging

    Thanks for your input WindWizard. I'll have some time this weekend or over the holiday to remove this cell and run some tests. The only problem is my ZKE battery tester charges from memory at 5 amps, and as you rightly observe, the erratic behaviour kicks in when charging or discharging at 20...
  26. mcart117

    Single cell jumping 400mV on charging

    Thanks MisterSandals, I'll try that.
  27. mcart117

    Single cell jumping 400mV on charging

    OK. I appreciate all replies, but we seem to wandering off topic. I took a screen recording of the erratic behaviour of this MFP cell and tried to post it here but the forum doesn’t recognise the .mov format. I therefore posted three single frames, thinking it would be enough to explain what is...
  28. mcart117

    Single cell jumping 400mV on charging

    The settings in the first screenshot are mine. Continued discharge current is mine. Most of the rest are unchanged from shipment. The OP explained the screenshot you annotated was taken from a video showing the cell voltage is jumping from 3.336V when idle (ie after the cell overvoltage...
  29. mcart117

    Single cell jumping 400mV on charging

    When I went back later this afternoon, I was able to confirm that the BMS was reading true voltages. After "resting" a couple of hours the cell was not spiking as much, so the battery continued charging for long enough for the balancer to kick in. I then switched to discharge mode, and again...
  30. mcart117

    Single cell jumping 400mV on charging

    The BMS turns balancing on and off as needed, and I think it looks for a difference of 10mV, which thses cells didn't have when charging was turned off. I think the voltage of this one cells goes up so quickly that the cell over-voltage protection kicks in before the balancing function has time...
  31. mcart117

    Single cell jumping 400mV on charging

    I'll try moving the cell and let you know what happens. I have also replied to you in the general thread.
  32. mcart117

    Single cell jumping 400mV on charging

    The system has been running well for some time and is described in more detail here. The BMS has a section of the screen which I cut out, which I think answers your question: If there was a problem with the wiring I think it would show up as an anomolous resistance there.
  33. mcart117

    Single cell jumping 400mV on charging

    One cell out of eight in a 24v 8s LFP battery is jumping from 3.336V when idle to 3.791V as soon as the battery begins to charge. Any ideas as to why this might be? Is the BMS possibly giving false readings or does this cell have a serious problem? I made a screen recording of what happens when...
  34. mcart117

    suntech stp175s-24/ad unexpected male to female adaptor

    Probably a good idea, thanks.
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