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Minimag losing power in flight??

Old 06-18-2010, 12:22 PM
  #1  
Catalina
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Default Minimag losing power in flight??

Hi, been flying my minimag recently which has up too now been bulletproof. But now when I fly for approx 5 mins I lose my motor power. Still have control power however. When I land I check the battery voltage and it is up around 4.0V per cell. My ESC is 30A, Im using 2C 2450 lipos and a brushless inrunner. These are the same componates I have been using from day one without a problem. I have noticed that if I go back to 0% throttle on my transmitter, then go back up to power on, the motor will re-start. Any ideas? I am buying another ESC just in case.
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Old 06-18-2010, 01:19 PM
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RUSH
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Most likely your batteries are at the end of their life. Sounds like the low voltage cutoff is kicking in. A lot of ECSs require you to go to zero throttle before they will reset after the cutoff.

The resting voltage of the battery doesn't tell you anything about the voltage under load. If you have a watt meter, hook it up after this happens and see what the voltage of the pack is when the motor power is lost. How many cycles do you have on your battery packs?
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Old 06-18-2010, 01:21 PM
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Catalina
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Originally Posted by RUSH View Post
Most likely your batteries are at the end of their life. Sounds like the low voltage cutoff is kicking in. A lot of ECSs require you to go to zero throttle before they will reset after the cutoff.

The resting voltage of the battery doesn't tell you anything about the voltage under load. If you have a watt meter, hook it up after this happens and see what the voltage of the pack is when the motor power is lost. How many cycles do you have on your battery packs?

Thanks for your reply, both batteries I have for this plane were purchased at the same time and only have approx 8 cycles each. Each time only discharged to 3.8v. Im sure the batteries are not the problem.
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Old 06-18-2010, 03:16 PM
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Larry3215
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Originally Posted by Catalina View Post
Thanks for your reply, both batteries I have for this plane were purchased at the same time and only have approx 8 cycles each. Each time only discharged to 3.8v. Im sure the batteries are not the problem.
Im afraid thats mostly wishfull thinking

You wont know for sure unless you actually test the voltage under load. Thats the only way to tell if its the esc or the batteries.

The only other option is to "test" by buying new parts untill it starts working again

Its also possible your motor has a problem and is pulling more amps now than it was - again you need to test to find out.
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Old 06-18-2010, 03:50 PM
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philipa_240sx
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+1

You need a wattmeter to measure amp draw and battery voltage. I have an Eagle Tree eLoggger, but one of these would work very well:

http://www.hobbypartz.com/88e-aepm30...att-meter.html



Once you can measure amps & volts you will find one of 2 things:

1) The battery can't deliver the rated amps and the voltage is dropping. ie. a 2S 10C 2450mAh battery should be able to deliver 24A at about 7V. If it's closer to 6V, then the battery is finished.

2) The amp draw is through the roof (ie 30+ amps), then there is something wrong with the power system. Check the mechanicals (ie does the prop spin freely?), then all of your electrical connections. If in doubt, remove and re-solder all electrical connections.

Do you have specs of the motor, gearbox ratio, and prop so you can figure out the 'normal' amp draw for this motor?
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Old 06-18-2010, 06:25 PM
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You are getting great advice. I concur with my buddies -- you should use a watt meter to figure out what is going on.

Based on what I've read so far, you have flown your airplane 16 times. It's not like you've flown this power system in this airplane every day for a year, and it's suddenly having problems. It sounds more like the power system was flawed from the start, and you are just now realizing it!

Please do yourself a favor, and test your power system with a wattmeter before flying it again. If you post your motor, esc, and battery, along with the results of your wattmeter test, we can help you resolve your problem. Until then, we can only guess.
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Old 07-31-2010, 09:55 AM
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Catalina
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I forgot to post earlier, Found the issue with losing power. It was a bad solder joint at the end of the motor lead. These joints were pre made on the end of the motor leads when motor purchased. Cut, re-soldered and now all OK.
Didnt have to buy that new ESC now. Oh well, good for another project.
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Old 08-03-2010, 02:46 AM
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Wow, I would have agreed with what everyone else told you, from your description of the problem. The way you explained it was a text book example of Low Voltage Cutoff.

Still you should heed the advice to get a meter, it's the most important tool you can own when flying electric.


Thinking about your fix, it could still have caused a LVC to occur. Resistance in a poor solder joint will take more juice to get through, it will make the connection get hot, and could have maxed the pack because of it and caused the shut down. In the time to reset your system, the poor connection might have cooled enough to allow the pack to handle the load again.


Again keep an eye on it, if it starts acting up again, you really should get some meter readings on it. Best of luck to you thou.
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Old 08-03-2010, 07:56 AM
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Originally Posted by Glacier Girl View Post
Still you should heed the advice to get a meter, it's the most important tool you can own when flying electric.
I am just going to go ahead and fifth this recommendation. If you think it is expensive (around fifty bucks for a decent one), consider the price of a plane, motor, and ESC combined, which you could lose due to improper propping, overamping, ESC pooping out due to overheating etc.

It is really one of the best investments in electric flight. Mine has saved me many a motor/ESC/plane, and already paid for itself many times over!
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Old 08-03-2010, 10:21 AM
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Catalina
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Originally Posted by Numbthumbs View Post
I am just going to go ahead and fifth this recommendation. If you think it is expensive (around fifty bucks for a decent one), consider the price of a plane, motor, and ESC combined, which you could lose due to improper propping, overamping, ESC pooping out due to overheating etc.

It is really one of the best investments in electric flight. Mine has saved me many a motor/ESC/plane, and already paid for itself many times over!
I have just purchased one. See the link:

http://www.hobbycity.com/hobbycity/s...idProduct=6380

Looks like a reasonably good one.
Thanks again guys.
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