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Old Nov 18, 2012, 06:48 PM
Gilbert AZ
United States, AZ, Gilbert
Joined May 2012
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Twin Motor questions

I'm running two HURC power 80 motors 16 x 8 apc E props.
Combined I get 2000watts and 94 amps 6s 4000 mah 30c. Those numbers are not exact. When I run the motors Separately Im getting 1400 watts. Cant remember the amps. So why am I not getting 2800 watts when they are combined? I'm guessing the batteries cannot handle the amps even though they are 30c and sagging. I understand this isnt the Ideal battery because of short run times but I was expecting closer to 2800 watts.

Should I run two seperate batteries so each motor produces closer to 1400 watts? This way I get twice the Mah and more power. The airplane can handle the additional weight.

What problems will I have running two identical packs in the same condition? Should I parallel them? By paralleling them will the amps be split between both packs?

Thanks
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Old Nov 18, 2012, 07:11 PM
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pda4you's Avatar
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Correct your packs are not up to task. You need larger packs that are capable of the draw. I suspect you are seeing VERY short flights too. That is a lot of expectation from small packs.

I would use two (wired in parallel NEVER separate) larger, much larger packs.

Mike
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Old Nov 18, 2012, 07:49 PM
Gilbert AZ
United States, AZ, Gilbert
Joined May 2012
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The plane hasn't flown yet. I was just testing the motors. Can I run seperate 4000 6s packs.
What complications will I have?
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Old Nov 18, 2012, 07:56 PM
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Separate packs run in parallel will be fine.

You don't want to run them seprately as one motor may draw more and thus that "side" will reach LVC sooner. Not a big issue if you always time flights so long as you leave plenty of extra time.

I just feel it is better to run parallel.

Mike
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Old Nov 18, 2012, 07:59 PM
Gilbert AZ
United States, AZ, Gilbert
Joined May 2012
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So is the amps split between the two? Thank you.
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Old Nov 18, 2012, 10:15 PM
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Quote:
Originally Posted by azflyingguy View Post
So is the amps split between the two? Thank you.
Yes, to all intents a pair of packs in parallel behave the same way as a single pack of double the size (provided the packs are the same).
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Old Nov 18, 2012, 10:22 PM
Gilbert AZ
United States, AZ, Gilbert
Joined May 2012
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Thank you
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Old Nov 19, 2012, 04:27 AM
An itch?. Scratch build.
eflightray's Avatar
South Wales U.K.
Joined Mar 2003
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I assume you are using a wattmeter to read the amps and watts.

Also check the volts read out when under load, as that gives a good indication of the battery capability. A big volt drop shows the battery is not really up to the job.
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Old Nov 19, 2012, 08:21 AM
Gilbert AZ
United States, AZ, Gilbert
Joined May 2012
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Quote:
Originally Posted by eflightray View Post
I assume you are using a wattmeter to read the amps and watts.

Also check the volts read out when under load, as that gives a good indication of the battery capability. A big volt drop shows the battery is not really up to the job.
I think the voltage dropped to 21 volts under load WOT. I have to look again. I suspect its the batteries not up to the task. I just wanted to test run with this pack anyway. I will try dual Parallel packs and post results here.

Thank. you.
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Old Nov 19, 2012, 11:08 AM
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Chattanooga, Tennessee, United States
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30C 8000mAh should be able to supply about 80% of 30x8000 = ~192A. Separately your motors draw ~65A each.That parallel pack should be able to supply 130A total easily enough. [at 22v under load that gets you your 2800W]
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Old Nov 19, 2012, 11:56 AM
Gilbert AZ
United States, AZ, Gilbert
Joined May 2012
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Dr Kiwi thanks for doing the math. I never been good at it. I could use the extra nose weight anyway with two packs.
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Old Nov 22, 2012, 02:43 PM
Gilbert AZ
United States, AZ, Gilbert
Joined May 2012
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Ok I don't understand this.

Two 4000 Mah 6s 30C packs wired parallel

Combine twin motor run with wattmeter inline.

2005 watts 91amps 22 volts

Watt meter inline with motor #1 and battery

1170 watts
51amps
22volts

Watt meter inline with motor #2 and battery.

1250 watts
54 amps
23 volts.

All test runs were with both motors running. I just move the watt meter from one to the other.

So why am I not getting the combine watts and amps when the wattmeter is inline with both motors.

1170 + 1250 = 2420 watts
51 + 54 = 105 amps.

This is my first twin setup.
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Old Nov 22, 2012, 06:17 PM
Gilbert AZ
United States, AZ, Gilbert
Joined May 2012
1,617 Posts
Ok I think I know what is going on. It appears I'm losing something in the harness.

When I hook up both batteries directly to the ESC's I'm getting 1250 watts, 52 amps and 23 volts per motor. These numbers are exact but +- 10 watts of each other.

So I'm about to forgo the wire harness all together and just time my flights so one motor doesnt hit LVC before the other.
Maybe I have a bad solder joint.
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Old Nov 23, 2012, 02:27 AM
I think I'm inverted. Maybe.
acetech09's Avatar
United States, CA, Pacifica
Joined Apr 2012
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Or resistance/inductance losses, more likely. Try a very compact adapter instead of a wire harness, as close to connector-on-connector as possible.
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