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Old Jun 14, 2012, 09:21 AM
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Battery amp draw hexacopter question

Hi,

I have a simple question. I have an hexacopter with AUW of 5.5kg 2x4S 5000mah batteries and a 12-13A per motor in hovering mode.

I have that cheap 3.3V alarm connected on both batteries (1 per battery)

When flying I never wait the alarm goes off because the battery is too low, but then whats the point of the 3.3V alarm? But at the same time whan the hexa is flying there is a voltage drop and when I land the voltage is different.

My question is, whats a safe (for "long" term battery life) voltage of the battery when not drawing current? (landed) and when flying, whats a safe voltage with amp draw?

I don't know if I made this questions the right way, its because I'm confused and what to have more flight time without putting the hexa in danger or damaging the batteries.
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Old Jun 14, 2012, 09:31 AM
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Quote:
Originally Posted by Reginak View Post
My question is, whats a safe (for "long" term battery life) voltage of the battery when not drawing current?
Do not go below 3.7 volts per cell no-load voltage and your lipolys will be happy and reward you with long service life.

Quote:
Originally Posted by Reginak View Post
...and when flying, whats a safe voltage with amp draw?
This depends upon many factors (internal resistance of lipolys, ambient temperature, current draw, etc.) so accurately predicting an appropriate cutoff voltage that will result in a rebounded no-load voltage of at least 3.7 volts/cell is a tricky endeavor. It's typically easiest to experiment with your particular packs and adjust as necessary. Even better would be to simply time your flights and land when your packs are depleted to no lower than 3.7 volts/cell resting voltage.

Mark
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Old Jun 14, 2012, 01:39 PM
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Additionally, you can check the milliamps returned to your packs when charging. Ideally you should not use more than 80% of the milliamps available. So if your 5000mah batteries are fully charged at the beginning of a flight then you should not use more than 4000mah during your flight. When you recharge your battery your charger should not tell you that it put more than 4000mah back into the pack. If it puts more than 4000mah in you are flying too long. BTW double those numbers if you parallel charge.

Glen
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Old Aug 02, 2013, 11:32 PM
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Originally Posted by mrforsyth View Post
Do not go below 3.7 volts per cell no-load voltage and your lipolys will be happy and reward you with long service life.



This depends upon many factors (internal resistance of lipolys, ambient temperature, current draw, etc.) so accurately predicting an appropriate cutoff voltage that will result in a rebounded no-load voltage of at least 3.7 volts/cell is a tricky endeavor. It's typically easiest to experiment with your particular packs and adjust as necessary. Even better would be to simply time your flights and land when your packs are depleted to no lower than 3.7 volts/cell resting voltage.

Mark
Are you saying I should rely on the resting voltage and not be as concerned of the voltage drops during flight?
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Old Aug 02, 2013, 11:42 PM
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Provided you do not exceed the current capabilities of your batteries, yes.
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Old Aug 02, 2013, 11:57 PM
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Originally Posted by mrforsyth View Post
Provided you do not exceed the current capabilities of your batteries, yes.
I guess what is getting me confused/frustrated is when I set my alarm (- on the hexacopter) to 3.7V, it triggers the alarm from the drops which are below 3.7V. After landing, I am back to 3.9V.

Should I set the alarm to 3.5V or 3.6V? The resting state will probably be 3.7V - 3.8V?

Thanks.
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Old Aug 03, 2013, 12:01 AM
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Yes, try 3.5 volts. From what you've described, this should work well for your specific packs / application.

Mark
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