Jul 12, 2013, 09:03 PM Registered User Joined Nov 2012 12 Posts Discussion DC motor current A DC motor drawing 20 amps current on a 1000mah battery should last half an hour theoretically but is giving more than an hour flight time. Any reasons?
 Jul 12, 2013, 10:20 PM Registered User Australia, VIC, Melbourne Joined Feb 2010 2,003 Posts Erm, 2A from a 1Ah battery would give 30mins, 20A would give 3mins. Only way I can see the plane staying up an hour is if it spent most of the time gliding
 Jul 13, 2013, 12:53 AM Registered User Staffs, UK Joined Nov 2003 11,340 Posts Because it's very bad at calculating . The obvious explanation is that it's not, on average, actually drawing the current you think it is while it's in the air. How did you decide that your motor is constantly drawing 20A ? Steve
 Jul 25, 2013, 02:28 AM Registered User Joined Nov 2012 12 Posts measured via a ampere meter on ground while motor is turned on
 Jul 25, 2013, 02:58 AM Registered User Staffs, UK Joined Nov 2003 11,340 Posts So which part of the your original post do you want to change ? 20A on 1000mAh should last 3 minutes NOT 30 minutes. If it's flying for over an hour on a 1000mAh battery then the AVERAGE current is less than 1A, not anywhere near 20A. So either your current measurement or your battery size are completely wrong or the motor is running at full power for less than 5% of the time the plane is in the air . Steve
 Jul 25, 2013, 03:46 AM Registered User Australia, ACT, Kambah Joined Feb 2001 3,640 Posts Can you tell us a bit more about the model; and as others have pointed out, 20A from 1000mAH is 3 minutes: it would take 10000mAH to predict 30 minutes. If you already know your flight time is about an hour, you know your average current must be a lot less than 20A. To estimate average current, I note flight time and how much it takes to recharge the battery. For example, if I recharge 6000mAH into (my hypothetical) 10000mAH pack, and I flew for 1 hour, I know my average current had to be 6000mAh / 1 hour = 6000 mA = 6A. For average power, I multiply by a nominal voltage roughly halfway between the pack's full and and after flight voltage, usually around 3.9V/cell, or 11.7V for a 3S pack. So 6A aerage would be about 70W average.
Jul 25, 2013, 04:42 PM
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Quote:
 Originally Posted by scirocco Can you tell us a bit more about the model; and as others have pointed out, 20A from 1000mAH is 3 minutes: it would take 10000mAH to predict 30 minutes. If you already know your flight time is about an hour, you know your average current must be a lot less than 20A. To estimate average current, I note flight time and how much it takes to recharge the battery. For example, if I recharge 6000mAH into (my hypothetical) 10000mAH pack, and I flew for 1 hour, I know my average current had to be 6000mAh / 1 hour = 6000 mA = 6A. For average power, I multiply by a nominal voltage roughly halfway between the pack's full and and after flight voltage, usually around 3.9V/cell, or 11.7V for a 3S pack. So 6A aerage would be about 70W average.
FWIW - To get 1 hour flight time from a 1000mah battery the average current has to be 1A no matter what motor or prop - it's the law.
Jul 25, 2013, 04:54 PM
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Quote:
 FWIW - To get 1 hour flight time from a 1000mah battery the average current has to be 1A no matter what motor or prop - it's the law.
To be a bit more precise, a one-hour flight with an average current draw of one amp would use exactly 1000mAh from the battery. When applied to the real world, we also have to consider that only ~80% of the pack's full capacity is available for use or else the battery will end up damaged... so a one-hour flight with 1000mAh available means the average current has to be 0.8A.

 Jul 28, 2013, 04:37 PM Kamikaze Ace USA, FL, Lakeland Joined Jan 2010 2,707 Posts Maybe it's one of those "special" set ups. It's got more magic smoke pumped into it to give those kinds of results. Only explanation with those spec and results. Oooor, the prop unloads some serious amount in the air, vs when tested statically, and the amps drop dramatically.