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Caution: Receiver battery drain

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Old 05-29-2007, 11:39 AM
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Default Caution: Receiver battery drain

I just lost a battery and hopefully this will save somebody else from making the same mistake. The 9V inline cutoff circuit for the diversity receiver has some internal semiconductor leakage, which will draw the battery down below the level that it can be charged. I checked the battery about a week ago and it was at 10.5 volts. Yesterday I decided to charge it up for a new round of activity and it was at 3.4 volts! The receiver being off, or even disconnecting the power plug from the receiver, will not stop the discharge. I just spoke to DFI and they confirmed the behavior. I couldn't find any reference to this in the docs - they might add a slip of paper into their manuals telling people to disconnect the power at the battery. That's always good practice, but I've never let good judgement stand in my way in the past. As Rosanne Rosannadanna said, "it's always somethin!"
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Old 05-29-2007, 01:44 PM
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Default RE: Caution: Receiver battery drain

How could power be drawn if the power is off or the battery is not connected to the receiver? I would try to recharge that lipo but in a safe place outside in case it does something crazy. A couple of mine have dropped to 8v and 7v but not for an extended period of time. I have successfully recharged them with no issues.
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Old 05-29-2007, 03:26 PM
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Default RE: Caution: Receiver battery drain

The battery can't discharge if it's not connected to anything, but if it's connected to the power cable with the 9 volt cut-off built into it, it will discharge regardless of whether that cable is plugged into the receiver or not, or plugged in with the receiver off. I had some hope for the battery since it climbed from 3.4v to about 5.4v a few hours after I unhooked it, but the charger still saw it as faulty and would not put a charge on it (green light on the yellow charger continued to blink, even after hooking up the battery). Supposedly if a LiPo drops below 3 volts per cell, it's toast. If you'd let your 7 or 8 volt cells sit around for a couple of hours after a run, I'll bet they would have climbed to at least 9 volts on their own. Maybe that's why they charged back up? I had 6 batteries, but I still hated to lose one. They ain't cheap.
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Old 05-29-2007, 07:01 PM
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Default RE: Caution: Receiver battery drain

Yep, I'd say your battery is see ya bye! So that protection circuit is creating resistence and killing the battery. How ironic is that? Is that a defect or inherent? Even if it's inherent, I would seriously talk to DFI about replacing that battery since there was nothing noted about that possibility. Either way, it's not your fault because DFI knew about it and you weren't made aware.

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Old 05-29-2007, 08:16 PM
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Default RE: Caution: Receiver battery drain

DFI cut me some slack on a new battery - can't complain. This is what's called a phantom load. As close as I can figure, the cut-off circuit looks like a 50K - 100K ohm load to the battery. It has to do with the semiconductors - either the battery sensing circuits, diode or gate leakage, or something. It's probably unavoidable. It's not enough of a drain for you to easily notice, but give it enough time and it will frap the battery for sure. Just wanted to tell everyone to disconnect the receiver power right at the battery connector when you're not using it.
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Old 05-29-2007, 08:23 PM
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Default RE: Caution: Receiver battery drain

I always unplug power sources from any of my gear anyway but thanks for the info, it's good to know. DFI needs to get that resolved and/or put a bright yellow caution tag on that connnector so you can at least know about what can possibly happen.
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Old 05-30-2007, 11:14 PM
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Default RE: Caution: Receiver battery drain

Since the battery was shot anyway, I thought I'd have a look at the cell balancing circuitry...
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