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Author Topic: Amp range  (Read 686 times)

Offline Traian Dorin Morosanu

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Amp range
« on: July 27, 2017, 05:49:05 AM »
I am researching something here and was wondering what kind of Amp range do you see typical on a 60 size ship. I looked in the list setup and there is not much information on this subject.
If you can make a reply with Model weight wing area Prop and rpm set max Amp and level flight amp I would really appreciate any information you can provide.
Thanks Traian
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Happiness is the harmony between what you think and what you do. Mahatma Gandhi


Offline John Rist

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Re: Amp range
« Reply #1 on: July 27, 2017, 07:39:12 AM »
I would select the motor first.  I would look at a typical wet 60 size motor specifications.  In particular prop size and rpm and or HP.  Then find the electric motor that provides this amount of power.  Also you can look in the setup section and see what motors are being used for the size ship you are looking at.  Once you have a motor in mind look at the motor specks.  It will give current requirements for max power.  Based on this you can pick a controller.  To big is better than to small.  The only disadvantage of to big is more weight.  Not a direct answer to your question but this is the approach I have used in the past and so far it seem to produce a set up that has the correct power range and is reliable.
John Rist
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Offline Crist Rigotti

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Re: Amp range
« Reply #2 on: July 27, 2017, 09:33:16 AM »
Number of amps will depend on the number of cells used.  More cells used the less amps.
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Online Peter Germann

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Re: Amp range
« Reply #3 on: July 28, 2017, 02:34:13 AM »
F2B airplane 59 in span, 64 oz:
64 ft x 0.015 in lines
AXI 2826/12 Motor
APC 13 x 5.5 WEP Prop
9'720 RPM constant speed, governed
speed 5.2 sec / lap
flight duration 5:20
5 Cell 2'700 mAh 70 C battery
Average current 27 A
Peak current 39 A
2'000 mAh recharge after flight
Peter Germann

Offline Vitalis Pilkionis

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Re: Amp range
« Reply #4 on: July 28, 2017, 11:06:52 AM »
Modified Brodak T-Rex; 64.5 oz
67 ft x 0.015 in lines
Active timer by Igor
6 cells 2700mah
12x5 3-blade prop
at high rpm 10500
current 44.6 A
« Last Edit: July 29, 2017, 03:43:27 AM by Vitalis Pilkionis »

Offline Traian Dorin Morosanu

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Re: Amp range
« Reply #5 on: August 08, 2017, 06:16:17 AM »
Chris i think there is a difference between what i call upstream (batt to ESC) and delivery to motor. Sure Ideally you want to go to highest voltage impute supported by the ESC. I understand that.
Now for the downstream side that is the variable i am looking in to right now.
Peter thanks for the info. It looks like normal flight 27 hen when you go high demand jumps to 39A.
Vitalis is 44.6A the the peak or the average?

Thanks to all who helped.
Each goal you meet is a moment of happiness
Happiness is the harmony between what you think and what you do. Mahatma Gandhi

Offline Tim Wescott

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Re: Amp range
« Reply #6 on: August 08, 2017, 01:09:30 PM »
Chris i think there is a difference between what i call upstream (batt to ESC) and delivery to motor. Sure Ideally you want to go to highest voltage impute supported by the ESC. I understand that.
Now for the downstream side that is the variable i am looking in to right now.
Peter thanks for the info. It looks like normal flight 27 hen when you go high demand jumps to 39A.
Vitalis is 44.6A the the peak or the average?

Thanks to all who helped.

I think the numbers quoted are for the battery side, not the motor side.  And yes, in general the average motor current will be higher than the average battery current.
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Offline Traian Dorin Morosanu

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Re: Amp range
« Reply #7 on: August 12, 2017, 09:06:50 PM »
I was trying to see if we have options to go to 8S setup on our birds. but what i have in mind becomes heavy and does not handle the Amps.
Then I realized that most chargers go to 6S.
Did anyone try 8S?
Each goal you meet is a moment of happiness
Happiness is the harmony between what you think and what you do. Mahatma Gandhi

Offline Tim Wescott

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Re: Amp range
« Reply #8 on: August 13, 2017, 12:13:59 PM »
I was trying to see if we have options to go to 8S setup on our birds. but what i have in mind becomes heavy and does not handle the Amps.

You need to think in terms of watts, not amps.  For two systems of equal efficiency, an 8S setup should be about the same weight as a 6S setup, because as the voltage goes up by a factor of 4/3, the current would go down by the same factor.  The actual power required out of the cells, and the total energy stored in the cells, would remain the same.

So, for instance, a 64 ounce plane with a reasonably efficient system is going to use around 45 watt-hours.  Using the "75% rule" you'd want a battery pack that's rated for 60 watt-hours (this is conservative; mosts people with good-quality packs shave this figure).  Getting absurd, you could theoretically do this with a single 16200mA-h cell.  Or you could go with four cells of around 4000mA-h, five cells of around 3300mA-h, or eight cells of around 2000mA-h.

Money for new chargers aside*, the problem becomes one of efficiency.  The greater the mismatch between the battery voltage and the voltage the motor needs to run, the more switching losses the system incurs.  You want to more or less match the motor kV with the desired RPM and full battery pack voltage, to avoid switching losses in the system.  You also want to match the ESC's capabilities to your projected maximum current (lower with more cells) and maximum voltage (higher with more cells).  So a 5S system that works perfectly well may need a new ESC to work at all on 8S, and it may not run efficiently unless you find a same-size motor that has a lower kV to match the higher battery voltage.

* Lots of RC folks who fly 8S or 10S fly on two 4S or 5S packs, charged in parallel and flown in series -- but that takes more connectors in the plane, which incurs a weight penalty.
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Offline Jason Greer

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Re: Amp range
« Reply #9 on: August 13, 2017, 08:31:26 PM »
I think you'll be hard pressed to find an 8s 2000 combination that is comparable to the weight of a 6s 2700 pack. Like Tim said, you'll probably end up with two packs in series and that will consume extra space and require extra wiring. If you plan to run normal sized propellers in the standard rpm range, you'll also need to use a motor in the 500 kv range, which narrows your pool of motors to choose from. 
« Last Edit: August 14, 2017, 07:48:18 AM by Jason Greer »
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Offline Traian Dorin Morosanu

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Re: Amp range
« Reply #10 on: August 14, 2017, 09:31:21 AM »
Yes Tim I knew about the power "equality"
I was looking at round cells that can store a load of mAh that are in the 40-50g range but they do not have the C rating to keep up with the demand. As we look at 60 sized models that draw 45A then the cells would have to go up to 10C roughly and they are not capable to supply the demand.
I do not mind soldering a pack but as you already stated I am going to 6S after all. Also I am considering a 4250 600KV motor too.

As you might already know this is for the new project i am endeavoring and it will be a model at about 50-55oz range. SV11ish size but uber light.
Each goal you meet is a moment of happiness
Happiness is the harmony between what you think and what you do. Mahatma Gandhi

Offline Tim Wescott

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Re: Amp range
« Reply #11 on: August 14, 2017, 10:00:04 AM »
If the 11W/ounce rule holds for a plane that light, you should expect about a 30A draw from the batteries at peak with a 6S pack.  I'm not sure where your 45A comes from, unless the Igor-style timer demands a whole lot more current, or you're going with numbers for a much heavier plane.
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Offline Traian Dorin Morosanu

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Re: Amp range
« Reply #12 on: August 14, 2017, 12:53:28 PM »
Tim I was conservative as Vitalis T_Rex was peaking at 45A so there is where the 45 came from (worst case scenario)

I am looking at the specs on this motor Leopard LC4250-8T 550Kv  208G
9800rpm/550=17.8V
According to their prop data 12x6 at 18.5V uses 315W of power so level flight 17A Not sure where it will peak. But This is only a wild guess at this time. It does look to me, too good to be true. And also the math does not add up 18.5Vx17A is not 315W.

http://www.altitudehobbies.com/leopard/new_charts/4250_new_chart.htm
Each goal you meet is a moment of happiness
Happiness is the harmony between what you think and what you do. Mahatma Gandhi


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