I am using 2 nos. of Brushed motors with the following specification for my boat setup..

Rated Voltage Current : DC 12V
No Load Current: 0.2Amps (Max ~1.2 Amps)
No load Power Consumption: 2.4 Watts (Max ~15 Watts)
No Load Speed: 6000RPM
Motor Shaft Diameter: 3.17mm
Mounting Screw Hole Diameter : 3mm
Distance between Screw Holes: 25mm
Diameter of the Motor: 36mm
Length of the Motor (Body): 50mm
Length of Shaft: 16mm
Main Color : Silver Tone
Material : Metal
Net Weight : 150gm
Cylindrical shape and with 3mm diameter shaft and 2 pin connectors.

I am using turnigy 30amp brushed ESC..the watt meter shows its consuming MAX 3.7 amps..
HOW LONG SHOULD a 5000Mah 3s battery last on full 4 amp load..??

What is the discharge rating of your battery (C rating) ?

more than an hour I guess.

Since this motor is consuming max 3.7 Amps, at full throttle (3.7 Amps), it would last 5.0/3.7 = 1.35 hours = about 1 Hour 21 mins on this 5Amp Battery.
Of course you should never discharge a LiPo completly. So until the Low Voltage alarm Kicks in, the realistic figure should be just a bit above 1 hour.

@sooraj.palakkad, Discharge rating is not required for this calculation since the power requirement of the motor in this setup is even less than 1C !

Thanks guys.. verry helpful..

But it depends on Ampere hour and also Discharge rating of battery

Hey, the discharge rating does not affect the battery life. It only tells you how much the battery CAN supply constantly. The 5Ah battery in your example CAN supply 100 Amps but at that draw it would run out in (60/20)= 3 minutes since you are running at 20x 5A you will get 1 hour/ 20 flight time.

Discharge rating only depicts "How fast the LiPo can discharge itself."
The capacity of a battery is limited and does not changes with the Discharge rating. In this case it's 5000mah.

So a 1Ah (1000mAh) 1C battery means it can yield 1A of current constantly for 1Hour, In that way, a 5Ah, 20C pack can provide 5*20=100A
True, but not for 1 hour. The time will decrease as per SK1701's explanation.

yeah I got it, was little confused on that matter !

Its irrelevant now...but still the battery is rated as 30c..

5000mAh pack will give you at least 1Hr playtime, even if the total current consumption is 5Amps constantly !!

Quote from: sooraj.palakkad on December 03, 2014, 06:46:22 PM
...even if the total current consumption is 5Amps constantly !!

Sooraj, You never discharge a LiPo Completly