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#11
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K2 battery endurance
Piet Barber wrote on 5/8/2020 6:37 PM:
On Friday, May 8, 2020 at 3:21:11 PM UTC-4, John Silverberg wrote: Hi, I'm hoping someone with experience with K2 batteries can help determine if mine are due for replacement. I have dual K2 batteries wired in parallel to supply avionics power. I have an LX9000, S8 and V8 varios, trig transponder, FLARM core, and becker com radio running off them. I'm guessing your LX9000 was the one making the complaints about the battery levels, right? Under the Hardware settings, what setting do you have for a battery? The LXNav flight computer doesn't have a "K2 Battery" setting. You should consider going into the setup page, go to hardware, select battery type and select "Custom" For the battery settings under "Custom" enter the numbers they have printed on the side of the K2 battery. The numbers, as listed on the side of the K2 battery a Discharge Voltage Cutoff | 10.0V That number is the absolute bitter end of the battery. I wouldn't recommend discharging your battery all the way to that level! But theoretically you can set the custom settings to that number for the "this whole system could shut off at any moment" value. Try playing around with the numbers to see what you can come up with that seems right. I remember going into this setting immediately after turning on the system, finding out what the maximum battery charge is. If you choose one of the other settings like Lead Acid, LiFe or LiPO, the numbers aren't quite right. I have a two seater, and like clockwork, I turn on the system and the passenger says, "Uh, the battery meter is already showing yellow" At 11.3 volts, the K2 battery should have very little charge left, less than 5%. The setting is OK as an endpoint, but you need to determine that the 9000 is measuring the voltage accurately. If not, fix the measurement, or adjust the 9000 alarm point until it alarms when the battery is 11.3-11.7. But, first measure the capacity of each battery. -- Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me) - "A Guide to Self-Launching Sailplane Operation" https://sites.google.com/site/motorg...ad-the-guide-1 |
#12
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K2 battery endurance
On Friday, May 8, 2020 at 8:29:23 PM UTC-7, Eric Greenwell wrote:
Piet Barber wrote on 5/8/2020 6:37 PM: On Friday, May 8, 2020 at 3:21:11 PM UTC-4, John Silverberg wrote: Hi, I'm hoping someone with experience with K2 batteries can help determine if mine are due for replacement. I have dual K2 batteries wired in parallel to supply avionics power. I have an LX9000, S8 and V8 varios, trig transponder, FLARM core, and becker com radio running off them. I'm guessing your LX9000 was the one making the complaints about the battery levels, right? Under the Hardware settings, what setting do you have for a battery? The LXNav flight computer doesn't have a "K2 Battery" setting. You should consider going into the setup page, go to hardware, select battery type and select "Custom" For the battery settings under "Custom" enter the numbers they have printed on the side of the K2 battery. The numbers, as listed on the side of the K2 battery a Discharge Voltage Cutoff | 10.0V That number is the absolute bitter end of the battery. I wouldn't recommend discharging your battery all the way to that level! But theoretically you can set the custom settings to that number for the "this whole system could shut off at any moment" value. Try playing around with the numbers to see what you can come up with that seems right. I remember going into this setting immediately after turning on the system, finding out what the maximum battery charge is. If you choose one of the other settings like Lead Acid, LiFe or LiPO, the numbers aren't quite right. I have a two seater, and like clockwork, I turn on the system and the passenger says, "Uh, the battery meter is already showing yellow" At 11.3 volts, the K2 battery should have very little charge left, less than 5%. The setting is OK as an endpoint, but you need to determine that the 9000 is measuring the voltage accurately. If not, fix the measurement, or adjust the 9000 alarm point until it alarms when the battery is 11.3-11.7. But, first measure the capacity of each battery. -- Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me) - "A Guide to Self-Launching Sailplane Operation" https://sites.google.com/site/motorg...ad-the-guide-1 One thing that comes to mind is how did you know that the batteries were fully charged? The charger may have shut off for some unknown reason. I never fully trust battery chargers and double-check their operation with a battery monitor: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 Most of the time the charger and the monitor agree within the margin of error, but occasionally there is a significant disagreement. And, speaking of battery chargers, which charger are you using? Tom |
#13
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K2 battery endurance
after a little over 5 hours I got a low battery warning with the batteries at 11.3 volts.
It might be worth checking at the batt terminals just to make sure something didn't get loose. |
#14
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K2 battery endurance
On Friday, May 8, 2020 at 3:21:11 PM UTC-4, John Silverberg wrote:
Hi, I'm hoping someone with experience with K2 batteries can help determine if mine are due for replacement. I have dual K2 batteries wired in parallel to supply avionics power. I have an LX9000, S8 and V8 varios, trig transponder, FLARM core, and becker com radio running off them. I'm not sure how old they are but they're at least 3 years old as this is my 3rd season with the ship. Yesterday, after a little over 5 hours I got a low battery warning with the batteries at 11.3 volts. I had all the above avionics on but did virtually no transmitting on the com, just listening. They were fully charged at takeoff. I'm not sure if this normal endurance for these batteries or not, any advice would be appreciated. Thanks, John S. Hi, Thanks for all the information, I have some good ideas to work from now. I use the proper K2 charger and usually charge the batteries overnight. Temperature may have been a player too as it was -17C at cloud base (over 10,000' very unusual for the Northeast) and the batteries are behind the rear bulkhead on a Ventus so I'm sure they were cold soaked. Thanks again for all the info. |
#15
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K2 battery endurance
On Friday, May 8, 2020 at 4:55:35 PM UTC-4, wrote:
There was a thread about this, K2's mentioned, a rew years ago that Steve Keorner replied too. He asked the K2 engineers about reduced capacity he was getting, IIRC, their answer was to leave them on the charger for weeks at a time so they can balancecout the cells with the BMS on board. CH Question: I don't know about K2 batteries and chargers specifically, but generally I thought the BMS in LiFePO4 batteries disconnects completely from the charger once some maximum battery voltage is reached. How, then, does leaving them wired together for "weeks" going to do anything? Perhaps over time the battery voltage drops back somewhat and the BMS re-engages with the charger? |
#16
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K2 battery endurance
On Sunday, May 10, 2020 at 10:06:53 AM UTC-7, wrote:
On Friday, May 8, 2020 at 4:55:35 PM UTC-4, wrote: There was a thread about this, K2's mentioned, a rew years ago that Steve Keorner replied too. He asked the K2 engineers about reduced capacity he was getting, IIRC, their answer was to leave them on the charger for weeks at a time so they can balancecout the cells with the BMS on board. CH Question: I don't know about K2 batteries and chargers specifically, but generally I thought the BMS in LiFePO4 batteries disconnects completely from the charger once some maximum battery voltage is reached. How, then, does leaving them wired together for "weeks" going to do anything? Perhaps over time the battery voltage drops back somewhat and the BMS re-engages with the charger? The internal BMS itself has a top balancer. It will detect when one or more of the cells are undercharged and very slowly discharge the others to first equalize them, then top them all off together. This may happen multiple times over a fairly long time until all cells are equalized since the undercharged cells themselves are unequally so. This can happen by passive balancing (resistive) or active (energy transfer from one cell to another). I have seen my charger cycle when charging my LFP batteries (it's not K2 though). There is no hard disconnect. Monitoring by the BMS is continuous. David |
#17
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K2 battery endurance
On Sunday, May 10, 2020 at 1:40:44 PM UTC-4, wrote:
On Sunday, May 10, 2020 at 10:06:53 AM UTC-7, wrote: On Friday, May 8, 2020 at 4:55:35 PM UTC-4, wrote: There was a thread about this, K2's mentioned, a rew years ago that Steve Keorner replied too. He asked the K2 engineers about reduced capacity he was getting, IIRC, their answer was to leave them on the charger for weeks at a time so they can balancecout the cells with the BMS on board. CH Question: I don't know about K2 batteries and chargers specifically, but generally I thought the BMS in LiFePO4 batteries disconnects completely from the charger once some maximum battery voltage is reached. How, then, does leaving them wired together for "weeks" going to do anything? Perhaps over time the battery voltage drops back somewhat and the BMS re-engages with the charger? The internal BMS itself has a top balancer. It will detect when one or more of the cells are undercharged and very slowly discharge the others to first equalize them, then top them all off together. This may happen multiple times over a fairly long time until all cells are equalized since the undercharged cells themselves are unequally so. This can happen by passive balancing (resistive) or active (energy transfer from one cell to another). I have seen my charger cycle when charging my LFP batteries (it's not K2 though). There is no hard disconnect. Monitoring by the BMS is continuous. David So you concur with the BMS-reconnects-over-time hypothesis. I usually charge my battery with my iMax B6 charger because it shows me what's going on, voltage and mAH. But when the battery reaches about 14.6V my battery's BMS disconnects - a bit before that charger would have stopped the charge anyway. And that charger then complains loudly about the connection being lost, and won't restart automatically. If I want to give the battery BMS time to balance the cells further, I'd need to put it on a different charger. Would connecting the battery at that point to a "dumb" fixed-voltage source of about 14V be a good idea? Would using an SLA charger that aims for a "float" at 13.6V or so be a good idea? |
#18
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K2 battery endurance
On Sunday, May 10, 2020 at 10:50:22 AM UTC-7, wrote:
On Sunday, May 10, 2020 at 1:40:44 PM UTC-4, wrote: On Sunday, May 10, 2020 at 10:06:53 AM UTC-7, wrote: On Friday, May 8, 2020 at 4:55:35 PM UTC-4, wrote: There was a thread about this, K2's mentioned, a rew years ago that Steve Keorner replied too. He asked the K2 engineers about reduced capacity he was getting, IIRC, their answer was to leave them on the charger for weeks at a time so they can balancecout the cells with the BMS on board. CH Question: I don't know about K2 batteries and chargers specifically, but generally I thought the BMS in LiFePO4 batteries disconnects completely from the charger once some maximum battery voltage is reached. How, then, does leaving them wired together for "weeks" going to do anything? Perhaps over time the battery voltage drops back somewhat and the BMS re-engages with the charger? The internal BMS itself has a top balancer. It will detect when one or more of the cells are undercharged and very slowly discharge the others to first equalize them, then top them all off together. This may happen multiple times over a fairly long time until all cells are equalized since the undercharged cells themselves are unequally so. This can happen by passive balancing (resistive) or active (energy transfer from one cell to another). I have seen my charger cycle when charging my LFP batteries (it's not K2 though). There is no hard disconnect. Monitoring by the BMS is continuous. David So you concur with the BMS-reconnects-over-time hypothesis. I usually charge my battery with my iMax B6 charger because it shows me what's going on, voltage and mAH. But when the battery reaches about 14.6V my battery's BMS disconnects - a bit before that charger would have stopped the charge anyway. And that charger then complains loudly about the connection being lost, and won't restart automatically. If I want to give the battery BMS time to balance the cells further, I'd need to put it on a different charger. Would connecting the battery at that point to a "dumb" fixed-voltage source of about 14V be a good idea? Would using an SLA charger that aims for a "float" at 13.6V or so be a good idea? With my battery (Stark Power) and charger (see below) this is not just a hypothesis. The BMS in all LFPs may not have the same functionality regarding balancing but at the very least they should start/stop accepting charge appropriately. Yes, my charger behaves like a dumb power supply with an LED that shows if the battery is drawing current (300mA) or not. All the logic is in the BMS not the charger. See photo he https://photos.app.goo.gl/gcC4gB98fNUag5g39 |
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K2 battery endurance
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#20
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K2 battery endurance
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