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Old Mar 03, 2012, 09:31 PM
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Originally Posted by erkq View Post
I have never heard this. Is this true? I've never lost a LiPo like that.
Yes it's true. Not having telemetry is a good example of the old saying ignorance is bliss. Ask some good pilots in your club who use telemetry how often they land early or cruise at low power to see if they can coax a LiPo up to strong voltage before going full power. I estimate that occurs with average age batteries on about 10% of warm weather flights and on 80-90% of chilly flights. More often if the C rating is marginal.

You can demand full amps from a cold or poorly charged battery that is sagging to 3.4 volts per cell right after take off, but that battery will likely be permanently impaired. If you let the voltage build to nominal as it warms in flight before you start hard use, it will fly more minutes on that particular charge and also deliver more charge cycles.
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Old Mar 03, 2012, 09:45 PM
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Originally Posted by sandy11 View Post
How would you know? Of course it is true.
Well, I would know because I've only lost one LiPo... the a fore-mentioned E-Flight 1800mAh that came with my Blade 400... lost a cell out of that one. I never took that one to Oregon, but many others have been flown in Oregon cold, hot-dogging right off the ground into vertical climbs and hard flying.

I'm not saying it's not true. It's just this is the first time I've heard it and I have had no experience with it. So... pulling lots of current from a cold LiPo will "trash that LiPo permanently"?... OK... I learned something from this exchange. What temp becomes bad? Usually it doesn't get below 55 or so when I fly in Nor Cal. Do I have to worry about warming them?
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Old Mar 03, 2012, 10:10 PM
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Originally Posted by erkq View Post
Well, I would know because I've only lost one LiPo... the a fore-mentioned E-Flight 1800mAh that came with my Blade 400... lost a cell out of that one. I never took that one to Oregon, but many others have been flown in Oregon cold, hot-dogging right off the ground into vertical climbs and hard flying.

I'm not saying it's not true. It's just this is the first time I've heard it and I have had no experience with it. So... pulling lots of current from a cold LiPo will "trash that LiPo permanently"?... OK... I learned something from this exchange. What temp becomes bad? Usually it doesn't get below 55 or so when I fly in Nor Cal. Do I have to worry about warming them?
I don't use a battery temperature sensor but that is an option. I use voltage because it is an indicator of a cold soaked or poorly charged battery and also any other problem. Yes, a cold battery sags a lot more with power demand, so you can tell when it warms up because it stops sagging. A lot of people warm up batteries in pockets and cars, that helps but it is obviously no substitute for knowing.

And warm batteries sag too. It is really a combination of factors that determine how nice you need to be to a battery in flight before it warms up, or even after it warms up. How the C rating services the power demand of the particular plane, the temperature, the charge quality, the state of discharge, and I'm sure other things I don't know about.

Having telemetry lets you match your power demand to what the LiPo is capable of delivering from the combination of all factors. I guaranty you that you are roasting a lot of batteries over the long haul if you aren't watching the amount of voltage sag. It happens on every flight with every battery, not just with bad or cold batteries. Good batteries perform like bad batteries as they discharge over the course of every flight. You really need to match your power demand to the available performance of each battery all the time if you want to maximize individual flight times and also get long term longevity.
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Old Mar 03, 2012, 10:23 PM
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I don't use a battery temperature sensor but that is an option. I use voltage because it is an indicator of a cold soaked or poorly charged battery and also any other problem. Yes, a cold battery sags a lot more with power demand, so you can tell when it warms up because it stops sagging. A lot of people warm up batteries in pockets and cars, that helps but it is obviously no substitute for knowing.

And warm batteries sag too. It is really a combination of factors that determine how nice you need to be to a battery in flight before it warms up, or even after it warms up. How the C rating services the power demand of the particular plane, the temperature, the charge quality, the state of discharge, and I'm sure other things I don't know about.

Having telemetry lets you match your power demand to what the LiPo is capable of delivering from the combination of all factors. I guaranty you that you are roasting a lot of batteries over the long haul if you aren't watching the amount of voltage sag. It happens on every flight with every battery, not just with bad or cold batteries. Good batteries perform like bad batteries as they discharge over the course of every flight. You really need to match your power demand to the available performance of each battery all the time if you want to maximize individual flight times and also get long term longevity.
Thanks for explaining all that. Now I, the guy who advocates discipline and procedure, am saying "That's too much work, I just wanna go fly!" I couldn't look at a voltage read-out that much. With the planes I fly, except for my Bixler, I can't take my eyes off them and do what I want in the flight. I'd get disoriented pretty quick, I think.
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Old Mar 03, 2012, 11:11 PM
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Originally Posted by erkq View Post
Thanks for explaining all that. Now I, the guy who advocates discipline and procedure, am saying "That's too much work, I just wanna go fly!" I couldn't look at a voltage read-out that much. With the planes I fly, except for my Bixler, I can't take my eyes off them and do what I want in the flight. I'd get disoriented pretty quick, I think.
Sure, you can't take your eyes off the plane, but you can set an alarm when the voltage sags below a certain value.
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Old Mar 04, 2012, 12:09 AM
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Originally Posted by erkq View Post
Thanks for explaining all that. Now I, the guy who advocates discipline and procedure, am saying "That's too much work, I just wanna go fly!" I couldn't look at a voltage read-out that much. With the planes I fly, except for my Bixler, I can't take my eyes off them and do what I want in the flight. I'd get disoriented pretty quick, I think.
You don't need to a parachute to skydive. You need a parachute to skydive twice. You don't need voltage telemetry to fly.
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Old Mar 04, 2012, 12:19 AM
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You don't need to a parachute to skydive. You need a parachute to skydive twice. You don't need voltage telemetry to fly.
Oh, now, that's just a way, way over the top comparison. You had me going some... but that. That's just completely out of reality. You're implying I need telemetry to fly twice? Really?? Reality is my argument against that one. I have flow thousands of times... thousands and I've never, ever crashed because of battery failure. Never. Simply never. In 30 years of flying. Never. All the way back to glow in the late 70's. Never. Even when that 1800mAh battery failed the chopper settled to the ground rather gently in a partial auto-rotation.
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Old Mar 04, 2012, 04:52 AM
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Originally Posted by sandy11 View Post
..........
You can demand full amps from a cold or poorly charged battery that is sagging to 3.4 volts per cell right after take off, but that battery will likely be permanently impaired. If you let the voltage build to nominal as it warms in flight before you start hard use, it will fly more minutes on that particular charge and also deliver more charge cycles.
The voltage will sag whatever you do, but how much it will sag depends on the current being taken and the state of charge. The voltage will also be affected by battery temeperature - in general the higher the temperature the higher the voltage, but too hot means a ruined Lipo. I use a heater or cooler if needed to keep my Lipos between 20 and 30 degrees C before use.

Have a look at the attached data log showing voltage sag and recovery during a quick burst of motor in the middle of a (for me) normal flight. Yes that is over 350A from a 3700 20C Lipo and it lasted for several years and many many flights.

Voltage sag to below 3v a cell is quite acceptable in some situations, so being dogmatic about voltage alarms is pointless. Some of us even deactivate the LVC on the ESC to stop it interupting a competition flight

Dick
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Old Mar 04, 2012, 07:06 AM
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Originally Posted by sandy11 View Post
And some don't work for thousands of people every day. Arguing that LiPos never quit earlier than expected is ridiculous. Anyone who believes that has no RC experience at all.

The plain truth is that voltage telemetry is a major advance in safe operation of RC planes and helicopters and every decent radio standard will have it built in within 10 years. Some offer it now and the rest are playing catch up.
You just ID'ed yourself as a Hitec employee.

I'm still waiting for my answer! How many dead or maimed modellers have you seen from Lipo failure crashes?
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Old Mar 04, 2012, 07:10 AM
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The voltage will sag whatever you do, but how much it will sag depends on the current being taken and the state of charge. The voltage will also be affected by battery temeperature - in general the higher the temperature the higher the voltage, but too hot means a ruined Lipo. I use a heater or cooler if needed to keep my Lipos between 20 and 30 degrees C before use.

Have a look at the attached data log showing voltage sag and recovery during a quick burst of motor in the middle of a (for me) normal flight. Yes that is over 350A from a 3700 20C Lipo and it lasted for several years and many many flights.

Voltage sag to below 3v a cell is quite acceptable in some situations, so being dogmatic about voltage alarms is pointless. Some of us even deactivate the LVC on the ESC to stop it interupting a competition flight

Dick

Thats cool. I was thinking of getting a data logger.
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Old Mar 04, 2012, 08:04 AM
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I had to re-check the thread title to make sure I was still logged into the Hitec vs Spektrum thread.

Sandy.... your logic is so far off with Lipos it's not even funny.
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Old Mar 04, 2012, 08:16 AM
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Wow, this is unique outside of LTUP - a forum with TWO dead horses!

Sandy, a simple voltage-only alarm is not the answer, as you already know. In the huge battery chargers I used to work on we monitored the voltage at multiple points in the battery string (typically every 12V), and we monitored the temperature. A low voltage doesn't mean your battery is dead if the temperature is cold. You need to measure both.

These large systems have a LVD (low voltage disconnect, basically a huge relay) which, get this, can be adjusted based on temperature. So if the string is cold, the LVD setpoint is adjusted downward because, guess what, it still has power it can deliver. Do you know what the other variable is?

TIME!

Andy
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Old Mar 04, 2012, 08:27 AM
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Originally Posted by JurassicJet View Post
I had to re-check the thread title to make sure I was still logged into the Hitec vs Spektrum thread.

Sandy.... your logic is so far off with Lipos it's not even funny.

I'm glad you said this. I was composing a 5 paragraph post but deleted it because I got mad for wasting my Sunday morning on this.
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Old Mar 04, 2012, 08:45 AM
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I had to re-check the thread title to make sure I was still logged into the Hitec vs Spektrum thread.

Sandy.... your logic is so far off with Lipos it's not even funny.
Agreed. Maybe someone could get a room.
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Old Mar 04, 2012, 10:11 AM
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I'm glad you said this. I was composing a 5 paragraph post but deleted it because I got mad for wasting my Sunday morning on this.
The choice to waste your time including the 5 paragraph post was 100 percent yours.
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