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05-27-2014, 05:26 PM | #1 (permalink) |
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Join Date: Jan 2012
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Powerlab 8 and LiFe
Why does my PL8 keep shortening the charge %? 1st time was charged to 98% and the next to 96% and now it's at 95%. I am charging using the A123 accurate preset. What's happening?
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[B]Phoenix Sim V5.5, Spektrum DX9, PowerLab 8, iKon 2 HD, SAB Goblin 770 |
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05-27-2014, 06:48 PM | #2 (permalink) |
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It's trying to tell you to spend less time charging and more time flying.
Hopefully Greg can provide a (serious) response to this one because my knowledge of the LiFe presets is not very good. I do charge a 2100mAh 2S LiFe transmitter pack with my DPL and have noticed that it generally doesn't read 100% on completion. [ramblings of a clueless know-it-all follow] What I have understood about LiFe from the research I've done is that getting them full enough to hold a 3.65V reading is potentially damaging since it requires providing a higher voltage input. A123 presets don't use a forced charge (constant voltage phase) to top the pack off like LiPo presets do. LiFePO4 batteries actually have a voltage plateau of 3.5V per cell but also have a much wider overcharge tolerance of about 0.7V (4.2V total). So even though we say they're not full until they hit 3.65V, really anything above 3.5V is 'full' with 3.65 serving as a safe overcharge middle ground. So the preset will run the charge at 3.65V until the pack stops taking more current and then stop. The subsequent sag from removing the input voltage is what I believe you're seeing read out on the display.
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05-27-2014, 08:54 PM | #3 (permalink) | |
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Quote:
Hemp is correct. LifeP04 tends to discharge extremely flat. The voltage changes very little during the discharge cycle. Once the charge current is removed, the voltage sag is considerably more than with LiPos. The fuel table depends on a very predictable voltage charge and discharge curve. LiFeP04 cells just don't behave as predictably a LiPos. As a result the fuel reported by the fuel gauge may or may not be accurate. Regardless, the charger does not use the fuel gauge to determine when to stop the charge cycle. So I would not worry about the fuel percentage being a little off. I would worry more about logging amount of mah you put back into the pack after a known number of flights. Because the discharge is so flat, its hard to know if you can get a few more flights on the pack (receiver pack) before it needs to be discharge. If you have a rough idea how much each flight takes out of the pack, you can estimate how many flights you can get on the pack before recharging. Round down and then start logging how many flights are each charge cycle.
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05-28-2014, 08:47 AM | #4 (permalink) |
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Join Date: Jan 2012
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Thanks for the answer. Do either of you know the cut off point for the voltage before it drops below safe levels?
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05-28-2014, 09:47 AM | #5 (permalink) |
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Min safe discharge level for LiFePo4 is somewhere around 2.8V per cell, however that's basically empty which is going to be a big problem for whatever you're trying to power with them. Practical limit is closer to 3.3V per cell. But like Greg said, you should judge capacity based on how much goes back in rather than voltage since the voltage will remain constant for most of the discharge.
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04-11-2015, 04:08 AM | #6 (permalink) |
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Join Date: May 2013
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I don't have preset for A123 Life pack charging in my PL8. For now I have been manually reducing the max voltage to 3.60 per cell for the charger to accept my life packs.
Is there any way around this?
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04-11-2015, 08:51 AM | #7 (permalink) |
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The Powerlab8 ships with 12 built-in A123/LifeP04 presets. If you don't see them on your charger's menu, they may have been hidden or replaced.
If you have the USB connector you can use the Powerlab software to review and change the presets. Any missing presets can be loaded from the preset library. If you don't have the USB connector, you can load all stock presets from the preset library using the console. Both options are covered in the manual under the presets section. Let me know if you have any questions.
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04-12-2015, 04:11 AM | #8 (permalink) |
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Join Date: May 2013
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You were right, the presets were hidden in my library. I just had to copy them into my main set of presets.
I don't have the USB cable now, need to order them separately
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