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Old 09-01-2014, 11:33 PM   #1
weakcreature
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Default Max Trottle

So I decided to switch some more of my nitro planes to electric. But I bought the wrong batteries. I got a good deal on 8 5000mah 6s batteries but they are 20c. I bought 8 Castle Creation Phoenix Edge 120hv ESC's. But on my first setup my watt meter is telling me at 3/4 throttle Im going past my recommended discharge rate. Is there a way to "govern" the max throttle? By that I mean when Im at full throttle on the transmitter but Im actually only going 3/4 throttle. Im using a futaba 7C.
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Old 09-01-2014, 11:49 PM   #2
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I suppose you could set your throttle end points at 75% and see what happens. You could also try propping it down some, either by pitch or diameter.

Bigger question is will you have enough power to fly at only 75% either by reduced power or smaller props?

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Old 09-02-2014, 07:07 AM   #3
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Bear in mind that the batteries will have a higher burst rating, probably 30c for bursts.

Try full throttle and see what numbers you get. If you want to reduce amps you can always prop down a little.
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Old 09-02-2014, 08:03 AM   #4
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Originally Posted by weakcreature View Post
So I decided to switch some more of my nitro planes to electric. But I bought the wrong batteries. I got a good deal on 8 5000mah 6s batteries but they are 20c. I bought 8 Castle Creation Phoenix Edge 120hv ESC's. But on my first setup my watt meter is telling me at 3/4 throttle Im going past my recommended discharge rate. Is there a way to "govern" the max throttle? By that I mean when Im at full throttle on the transmitter but Im actually only going 3/4 throttle. Im using a futaba 7C.
If your plane can carry the extra weight, hook 2 5000mah 20 C lipos in parallel, for 10000mah 20c and 200 amps of power

I may be getting Older, But I Refuse to grow Up I am Having to much Fun to Grow Up LOL
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Old 09-09-2014, 08:08 AM   #5
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Originally Posted by weakcreature View Post
So I decided to switch some more of my nitro planes to electric. But I bought the wrong batteries. I got a good deal on 8 5000mah 6s batteries but they are 20c. I bought 8 Castle Creation Phoenix Edge 120hv ESC's. But on my first setup my watt meter is telling me at 3/4 throttle Im going past my recommended discharge rate. Is there a way to "govern" the max throttle? By that I mean when Im at full throttle on the transmitter but Im actually only going 3/4 throttle. Im using a futaba 7C.
5000 by 20c should be technically capable of 100A...... not that I would want to push that too much.

To be honest many set-ups exceed specs on power draw. Motors may say 40A or whatever max ... but often they are pushed well past that.

Using 'end-point' adjustment on Tax does work but as I read from others is not recc'd.

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Old 09-09-2014, 01:24 PM   #6
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Default Discharge Rate

I may have explained myself wrong. On the batteries they say 20c 40c max burst rate for 10 sec. So I can exceed 20c for 10 sec but after that I have the possibility to damage the batteries if I discharge the batteries at the high rate. If I fly at 3/4 (max) I should be ok.... but Ive decided to sell some of my ESC's so I can purchase some high discharge rate batteries ie 4s,5s and 6s 4-5000mah 40c+ and run them in series 20 accomplish 8s, 10s and 12s.
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Old 09-09-2014, 07:53 PM   #7
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Originally Posted by weakcreature View Post
I may have explained myself wrong. On the batteries they say 20c 40c max burst rate for 10 sec. So I can exceed 20c for 10 sec but after that I have the possibility to damage the batteries if I discharge the batteries at the high rate. If I fly at 3/4 (max) I should be ok.... but Ive decided to sell some of my ESC's so I can purchase some high discharge rate batteries ie 4s,5s and 6s 4-5000mah 40c+ and run them in series 20 accomplish 8s, 10s and 12s.
The main risk of pushing your batteries to hard is the resulting internal heat rise of your battery pack. Go much above an internal temperature of 140 degrees F, and your battery life can be drastically affected.

Note, it's the INTERNAL heat that is involved. If you really push your battery to hard, it takes a bit of time for the internal heat to reach the outside of the battery pack. And, others have indicated that the center cells of a battery pack can reach higher temperatures than the "outside" cells because of the lack of cooling area to this part of the battery pack.

Second issue is the batteries internal resistance. That resistance can be higher in those lower "C" rated battery packs. Higher internal resistance indicates lower output voltage to your motor, and higher heat rise of the battery pack.

One of those infra-red thermometers could help in this regard. If your battery is only luke warm after a flight, you might be OK.

As for running a two series 5 cell LiPo pack, that will power a giant scale model on the order of 15 pounds or so, given the proper motor and prop size. I'm flying two giant scale models, using the Hacker A60 series motors and those A123 battery packs. One pack is a 10S2P, second pack is a 12S2P. Both are pulling 75 Amps on the ground. Power output is on the order of 2400 Watts and 3000 Watts. Both power systems will haul their respective models straight up in the air, out of sight.

Take a look:
Great Planes Giant Big Stick Electric Conversion
http://www.wattflyer.com/forums/showthread.php?t=65052

Redwing MXSR Model
http://www.wattflyer.com/forums/showthread.php?t=72225

Also, IMHO, you should be using dual receiver power supplies for giant scale models, simply because of the amount of $$$$ involved.
Giant Scale Power System:
Battery Backup System

http://www.wattflyer.com/forums/showthread.php?t=63794

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Old 09-09-2014, 07:43 PM   #8
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I'm suprised that the 100A constant that the old batteries gave you wasn't enough for your purposes. As a single 6s battery 100A would have been about 2200Watts which is roughly equal to a 30cc gas engine. With two batteries in series you would be up to 4400 Watts which is equal to a 60cc gasser.

How big are your models?
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Old 09-09-2014, 08:10 PM   #9
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So is safe to say that (2) of my 6s 20c 5000mah will be ok? How about just one? The planes Im flying are Seagulls Percival and Sparrow hawk. Both have Tacon Big Foot 160/110 in them also a Sig Four Star 120 with a 160.
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Old 09-09-2014, 09:07 PM   #10
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Well, how many amps are your models pulling? I've been watching this thread and it seems so far we're all going on assumptions. If you want a good answer, you need to give good info. Right now, we're assuming you are going over 100 amps at 3/4 throttle. Is that correct? Just want to be clear.

To me, troubleshooting through the internet can be like trying to take a wide angle photo through a paper towel tube. You can't get the whole picture. My favorite example is on a tx thread, where someone got a fancy new tx and complained he kept losing signal and crashing. After pages of troubleshooting and him complaining what a crappy brand tx it was, it turned out he had a carbon fiber monitor clip attached to his tx antenna!

Not saying your issue is something like that. Just showing how easy it is to miss some critical piece of information.
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Old 09-09-2014, 09:40 PM   #11
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6S 5000 mah will fly the Sportsman Pattern Competition routine (about 5 min to 6 min) with a .90 glow-econversion model.

No info on the model being converted, but the majority of glow conversions that are appropriate for 6S will be fine using 20C 5000 mah or less.

That big EDF model in my avatar uses 12S 5000 mah 20C pulling 105 amp peak but getting 5 min avg flights.

Pulling 20C constant would be dead flat in 3 min and damaging the batteries from overdischarge.

If you get 5+ min with appropriate voltage left to not damage the pack you are fine with 20 rated packs.
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