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Old Aug 28, 2012, 10:53 AM
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STANG KILLA SS's Avatar
Killeen TX
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a .45V drop in cell voltage after only 20 seconds sounds REALLY excessive to me.
im also wondering if you esc is voltage cutoff is set to 3.7v?

a lot of people consider 3.7v per cell to be a dead pack. ie flight over, need to recharge.
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Old Aug 28, 2012, 11:17 AM
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Canada, BC, Surrey
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Eflite's manual for the controller indicates a 12v low voltage cutoff preset for when connected to 4s... It doesn't appear to be adjustable in that regard. Is it possible for a cell to be an open circuit intermittently? The batteries had always looked good on my Hyperion cell tester before and after the incident and during the additional bench tests.

Another thing I noticed in the manual is that the esc can accept 3-6 cell lipos. So why do people change out the esc when upgrading to 5s? Increased voltage means lower currents so it shouldn't drive it harder.
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Old Aug 28, 2012, 11:48 AM
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It can indeed take 6s, but only 60A. You're right about higher voltage and current, sorta. The one bit that's missing is that for the same power output as you get on 4s, you could run a 5s and pull a lower average amp rating. Go to full throttle though, and viola, you've got higher max amps. The problem is that ESC's are like switches - they basically go on or off only, and vary the 'on' pulse length depending on the throttle setting. If you're running half throttle, the ESC sees full power half the time, and 0 throttle the other half. Basically, on 5s the ESC would have to deal with 65A all the time, which might increase the chances of a failure.
More info here: http://www.castlecreations.com/suppo...eral.html#gen6
Hope that helps!
Josh
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Old Aug 28, 2012, 02:56 PM
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kalmon's Avatar
United States, MI, Grand Traverse
Joined Oct 2008
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Quote:
Originally Posted by WhalleyB0Y View Post
Eflite's manual for the controller indicates a 12v low voltage cutoff preset for when connected to 4s... It doesn't appear to be adjustable in that regard. Is it possible for a cell to be an open circuit intermittently? The batteries had always looked good on my Hyperion cell tester before and after the incident and during the additional bench tests.

Another thing I noticed in the manual is that the esc can accept 3-6 cell lipos. So why do people change out the esc when upgrading to 5s? Increased voltage means lower currents so it shouldn't drive it harder.
If all you do is increase the number of cells you're going to increase amps.
warning math ahead!
Watts = Volts x Amps
So a stock habu on 4S might look something like this:
14.8V x 3200kv = 47360 rpm
14.8 Volts x 45 Amps = 666watts

On 5S you're going to have a lot more power
18.5V x 3200kv = 59200 rpm
18.5 x 65Amps =1202.5 Watts!

The reason most planes using a higher cell count draw less amps is because the motor was sized (kv wise) for that battery. For example my 3DHS Extra can use a 4,5, or 6 cell battery. However you have to buy the right motor for each. for the 4S you need a 710-750kv motor, for 5s you want around a 610, for 6S 400-500. In this example the watts will be about the same for each configuration. Therefor the amps will be lower as the volts increase.

Back to the Habu, if you change nothing other than the volts(number of cells) you are going to increase both watts(power) and Amps(current).

-Brian
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Old Aug 28, 2012, 03:04 PM
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Nice math job! (coming from a math teacher )

I think what Whalley was asking was about was if one could get the same amount of power with less current if you use a higher voltage battery. The answer is a definite yes (but this change usually requires a corresponding change in prop pitch/diameter or EDF fan).
-J
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Old Aug 28, 2012, 05:18 PM
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Quote:
Originally Posted by kalmon View Post
Watts = Volts x Amps
So a stock habu on 4S might look something like this:
14.8V x 3200kv = 47360 rpm
14.8 Volts x 45 Amps = 666watts

On 5S you're going to have a lot more power
18.5V x 3200kv = 59200 rpm
18.5 x 65Amps =1202.5 Watts!
If all you're changing is voltage, how did 45 Amps become 65 Amps?
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Old Aug 28, 2012, 06:27 PM
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Birmingham (UK)
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Quote:
Originally Posted by kevinrc View Post
If all you're changing is voltage, how did 45 Amps become 65 Amps?
because...

Higher voltage = higher RPM

Higher RPM = higher load

Higher load = higher current
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Old Aug 28, 2012, 07:20 PM
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And at this point I guess you would want to modify your throttle curve to keep rpm/load values within managable numbers.
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Old Aug 28, 2012, 08:15 PM
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United States, TX, Garland
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Always overkill on ESCs in EDFs...always! And run seperate BEC in anything over 4s lipo.I fly by these 2 simple rules but thats just MO.....
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Old Aug 28, 2012, 09:31 PM
Happy Habu Hustler
Joined May 2012
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Thanks to both kalmon and ulogix. I realize this is very elementary, but ...

I see where you get the RPM. I understand that for the same motor higher RPM requires more current.

Where did the 45 amps and the 65 amps come from?

It seems to me that power would increase as voltage:

18.5V/14.8V = new power/666W, or 832.5W.
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Old Aug 28, 2012, 09:31 PM
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United States, MI, Grand Traverse
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Quote:
Originally Posted by kevinrc View Post
If all you're changing is voltage, how did 45 Amps become 65 Amps?
+1 Like ulogix said

The amps are measured from a meter hooked up to the plane. 45 seems to be about the average people on stock 4S get and 65 was what I've seen reported from the stock fan 5S people.

in your example above you show a good point. At any given Amp draw the higher voltage will produce more power. However there is no way to limit that current effectively. You can't use throttle because an ESC is like a switch and it sees all the power. This was explained a few posts back.

To clarify more. The motor will try to turn at its designed "kv". The motor will keep drawing all the available power it can to do so. So when you give it 18.5v it tries to turn faster. The weight of the fan, drag of the blades etc doesn't change. The faster a blade moves the more thrust it produces but this also requires more power to move that air. This "draw" increases the amps. There are many complex formulas that I don't understand for power required to turn a "x" bladed prop of diameter "d" with pitch "p", at "z" rpm. But that is for the aeronautical engineers. I just want to fly the plane

-Brian
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Last edited by kalmon; Aug 28, 2012 at 09:45 PM.
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Old Aug 28, 2012, 10:43 PM
Happy Habu Hustler
Joined May 2012
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Quote:
Originally Posted by kalmon View Post
The amps are measured from a meter hooked up to the plane. 45 seems to be about the average people on stock 4S get and 65 was what I've seen reported from the stock fan 5S people.
Thank you. I thought amperage was calculated and I couldn't imagine how.
Quote:
There are many complex formulas that I don't understand for power required to turn a "x" bladed prop of diameter "d" with pitch "p", at "z" rpm. But that is for the aeronautical engineers. I just want to fly the plane.
I resemble that, and I've decided to just fly the plane as is and put the ESC/fan/battery money into a new Corsair. My name is on the first one to arrive at the LHS.
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Old Aug 30, 2012, 04:33 PM
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Canada, BC, Surrey
Joined Jul 2011
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I called HH the other day regarding my Habu issues. I explained te power issues and how the lvc was coming on prematurely and causing the plane to drop out of the sky just after takeoff. I think the bec cannot handle the servos with the reccomended retracts and flaps... HH has asked that i send them the plane minus the flap servos and retacts for testing. I am a little concerned because the freight costs of shipping from Canada and the fact that they didn't say how they would handle this.
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Old Aug 30, 2012, 05:02 PM
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I'd call them again for clarification. I imagine return shipping will be free, but you never know until you ask.
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Old Aug 30, 2012, 05:36 PM
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@whalleyboy

Intermittent problems are the HARDEST to try and diagnose. I'm experiencing that right now with my girlfriend's car. Problems aren't there when the car is at the repair shop. If it was me, I wouldn't send the entire plane. Just the ESC. Just be prepared for them to say something like, "we checked it and it appears to be fine". Pain in the butt for sure. If that happens, I would just switch to maybe a 75amp ESC with a reliable switch mode BEC. That will give you the extra room of insurance.
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