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Old May 05, 2014, 08:04 AM
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DamonH's Avatar
United States, NM, Clovis
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Originally Posted by Madmax1965 View Post
GensAce 25 C packs will work just fine in EDF...I fly the 5500mah version in my Taft Viper.
5500mah is much different than 3800 and can supply more amps. I still think you would be pushing the 3800's.
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Old May 05, 2014, 01:49 PM
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If you would like to find out more about batteries and their limitations especially for applications such as EDF, you might want to check out the valuable work already done in the "Batteries" section of this forum by MSCGUY and others. In short...you can't take the specs too seriously!
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Old May 05, 2014, 01:52 PM
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United States, NM, Clovis
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Originally Posted by Levendis View Post
If you would like to find out more about batteries and their limitations especially for applications such as EDF, you might want to check out the valuable work already done in the "Batteries" section of this forum by MSCGUY and others. In short...you can't take the specs too seriously!
+1 agreed! That is a very informative thread.
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Old May 05, 2014, 02:25 PM
310mph Kolibri T25 Swist
henke's Avatar
Sverige, Kronobergs Lšn, Ljungby
Joined Jan 2001
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Quote:
Originally Posted by ozgur View Post
Is this a good idea to convert this viper to a turbine jet?
This is the best EPO sports jet I have flown so far. With T35 it's powerful yet light and capable of long flights. P20 makes it 1.5lb heavier and less power. Good for Asphalt, but a little heavy for grass, then go T25 or even T35.

The guys saying it won't hold together have probably not tried it them selves. Mine did 235km/h level flight with the T35. Allot of Viperjets are flying with our kits in them with great success.

This kind of planes are often something you buy and fly for a year and then change it for next seasons hot name. This year I fly the EPO Yak-130, but I miss the Viperjet too

Taft Hobby 90mm ViperJet (5 min 39 sec)


T25 of grass
Taft Viperjet Kolibri T25 grasstart. (0 min 22 sec)
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Old May 05, 2014, 05:23 PM
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bervic's Avatar
Spain, AL, Chipiona
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Quote:
Originally Posted by henke View Post
This is the best EPO sports jet I have flown so far. With T35 it's powerful yet light and capable of long flights. P20 makes it 1.5lb heavier and less power. Good for Asphalt, but a little heavy for grass, then go T25 or even T35.

The guys saying it won't hold together have probably not tried it them selves. Mine did 235km/h level flight with the T35. Allot of Viperjets are flying with our kits in them with great success.

This kind of planes are often something you buy and fly for a year and then change it for next seasons hot name. This year I fly the EPO Yak-130, but I miss the Viperjet too

https://www.youtube.com/watch?v=dRBrgJAUXjU

T25 of grass
https://www.youtube.com/watch?v=mq7Spp8k7J4


wonderful flight!
the best flight I could do with viper taft.
please can you give more info about your setup?

Thanks
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Old May 05, 2014, 05:56 PM
Watt me worry?
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Florida
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[I]5500mah is much different than 3800 and can supply more amps. I still think you would be pushing the 3800's.


Right...he is flying 8s so he will have no problem with those packs....maybe less flight time other than 4000mah.

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Old May 05, 2014, 06:09 PM
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Quote:
Originally Posted by Madmax1965 View Post
[I]5500mah is much different than 3800 and can supply more amps. I still think you would be pushing the 3800's.


Right...he is flying 8s so he will have no problem with those packs....maybe less flight time other than 4000mah.

Right, but in 8s series the voltage increases and not the amp output...it will still be 95 amps on the fully charged battery. Once you fly for a min or so you are now down to 2800mah (guessing) which then will only provide 70 amps but the motor will still want 90amps at full throttle. I agree that the 25c Gens Ace are probably underrated but it's not like they are the 5500mah that can supply over 137 amps with just the 25c rating and can provide over 90 amps for a longer period than the 3800. I will be interested to hear how they fare after a few flights...
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Old May 05, 2014, 07:53 PM
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USA, UT, Cedar Hills
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Quote:
Originally Posted by DamonH View Post
Right, but in 8s series the voltage increases and not the amp output...it will still be 95 amps on the fully charged battery. Once you fly for a min or so you are now down to 2800mah (guessing) which then will only provide 70 amps but the motor will still want 90amps at full throttle. I agree that the 25c Gens Ace are probably underrated but it's not like they are the 5500mah that can supply over 137 amps with just the 25c rating and can provide over 90 amps for a longer period than the 3800. I will be interested to hear how they fare after a few flights...
That's not how the math works with lipos.
The mah do not decrease, the voltage does and hence the amps drop. So, if a fully charged pack can handle the max amps it can continue to handle it as the voltage drops. This is the sag of the battery and is why you will see max and settled numbers when talking about the performance of a setup. Obviously, some batteries do this better than others. In this specific case, the 25c Gensace is more than adequate for his 8s setup.
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Old May 05, 2014, 07:56 PM
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Where can I find super snake horizontal horizontal stab

Where can I find super snake replacement plane parts (Horizontal stab)?
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Old May 05, 2014, 07:58 PM
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Originally Posted by swps View Post
That's not how the math works with lipos.
The mah do not decrease, the voltage does and hence the amps drop. So, if a fully charged pack can handle the max amps it can continue to handle it as the voltage drops. This is the sag of the battery and is why you will see max and settled numbers when talking about the performance of a setup. Obviously, some batteries do this better than others. In this specific case, the 25c Gensace is more than adequate for his 8s setup.
How do you figure the mah does not decrease? As you fly the mah depletes...this is why when you recharge your batts your charger (at least mine does) tells you how many mah was put back into your battery... As mah drop why flying so does the ability to provide the same amperage as with a fully charged battery.
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Old May 05, 2014, 09:09 PM
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Originally Posted by DamonH View Post
How do you figure the mah does not decrease? As you fly the mah depletes...this is why when you recharge your batts your charger (at least mine does) tells you how many mah was put back into your battery... As mah drop why flying so does the ability to provide the same amperage as with a fully charged battery.
They physical capacity of the battery does not change or shrink and neither does it's ability to supply the same amperage. If batteries did what you are describing, every battery would puff due to a WOT pass late in the flight. That doesn't happen because the ability of the battery to deliver the power is calculated off the capacity of the pack times the C rating, not the real time capacity at any given moment.
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Old May 05, 2014, 09:15 PM
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Ok... I give up, I'm not worthy. Good luck with the batteries. Someone else needs to chime in here.
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Old May 05, 2014, 09:23 PM
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Damon...no amount of explaining will help him.
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Old May 05, 2014, 11:02 PM
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I would expect the 3800mAH 25C will not be overly good to use.....
I have never had a GensAce, and have seen good stories about them, but even if they are up to specs it is still not good enough.

3.8 x 25 = 95Amps so that is good..... for a little while anyway.
"Continuous"... well that claim is pretty well always rubbish.....

The reason there is an issue that is a physical one.
A lipo is more or less a 'sea of paste' with an anode through it (or few). The paste is made up of molecules that get charged up and are happy to give that back out if the circuit is completed. When fully charged, every one of them is 'full' and ready to conduct current, and give out their charge easily. But as they deplete, they don't pass current as well - which is the Internal Resistance rising - and have less to give out. Plus some are more depleted than others, so they impede flow from 'better' ones too.

Basically after the initial 'perfect' state of fully charged, things go downhill.... in an escalating manner. This is why the heat rises in a escalating manner as it depletes too.

So after time X, the battery cannot even supply that "90Amps" anyway.... if you try to make it do so, it is under more duress than earlier on.
To make it simpler for now, I will ONLY talk about WOT.... as lower Amp needs are not as important anyway.

You yourself do not get to set what Amps will flow anyway. The balance of load, and thus motor impedance total, and the battery internal resistance sets that. So it is dynamic... it changes. More so the battery internal resistance as it depletes.
Thus the Voltage seen decreases ("sags"), because the 'voltage divider' of the impedances (resistances) changes. But note, the lipo does not fall to 10% of its voltage when it is 10% remaining capacity. The change is non-linear. So, say, by 50% depleted the original 90Amps of WOT is not going to be 45Amps... seeing the Voltage is still a much higher percentage. Let's say it will be more like 70 Amps....
The remaining 'paste with various charge levels' is trying to path this current flow through all the partially depleted paste, and some that are worse than others etc.
It is this escalating degradation = more heat, more and more stress to continue that current flow - even though the current flow is reducing, it is relatively harder for it to do it.

It SEEMS approximately right (by rough assessment over long term) to say "REMAINING Capacity times C" gives you what it can do without "Excess Stress" at any given time. If the setup demands more than that, by the Impedance balances 'asking' for that, then the battery stress is higher than when it was 'easier' like full charged capability.

If you go to WOT at 70% depleted, the volts will sag, but not to "30%" of the fully charged level, so that relative battery duress is higher.... and the battery will be very unhappy then! hehe

Even a 65C battery will be unhappy if driven to high currents as it heads near depletion. That in itself is more evidence that the CAPABILITY declines with capacity.

Effectively that 3800mAH 25C battery will only be capable of 50 Amps (or something) towards the end of charge. BUT the Impedance balances will still make WOT be 75Amps (or whatever) - they are just made up, 'rough guide' numbers to show what happens
You could say the 50Amps is X remaining Capacity of a 25C battery.... or the battery is 3800mAH (not remaining) of only 15C, etc. The real story is the battery's CAPABILITY has declined, so really it is the "C" that has reduced. Capacity is more like a bucket of water... you still HAVE 'enough' in there to keep the "pipes full and flowing"... but the 'drive' (thus resultant speed... Current/Amps) is diminished as the weight of 'water' is lower and thus gravity gives less pressure. It is pretty well exactly like that analogy (for different reasons though).

If you don't have MORE C to start with, then as it depletes the situation is going to be a lot worse at depletion level "X". (versus the 25C start).

One thing that "helps" a BIT, is how that increase in Internal Resistance does lower the Current ability - in a way that makes it a 'self regulating' power reduction. BUT, it is NOT 'fast enough'.... it is not enough reduction to stop the battery getting more and more stressed per depletion amount.

If you had 65C, you could go to 3.80v with "Great battery ease" - it would hardly know it hard 'worked' much.
If you had 25C then you will be under duress already by 50% depletion. So you better cut flights down to be much shorter than 80% depletion, and even volts still above 3.80v because that "still only down to 3.8v" is what is enough to keep Current levels high and over-stressing the battery.
So you can use 25C.... but you need to put much tighter constraints on how much, or how long you use it.

Sometimes you can viably use a lower C battery to 'help' reduce the max level of Power (Lower C, higher Internal Res, less motor power battery depletes slower, but you fly slower too) - but it then needs that greater attention to testing how the battery goes doing so.
90 Amps is quite a 'lot' in Lipo terms (seeing we are generally size/weight limited per a given plane size and can't just throw in a 'giant water tank' instead. eg huge Capacity Lipo), so at those levels you really want GOOD batteries!! 45C+... and pretty well the higher C the better with those numbers! (anything running at over 60Amps or so really)
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Last edited by PeterVRC; May 05, 2014 at 11:10 PM.
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Old May 05, 2014, 11:22 PM
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Sort of forget to add on the end..... if you START with more Capability, then as it reduces you still have more on hand than the lower C battery anyway.

Try 25C's and see how long they last..... and how often you get 'caught out' by over-heating them.
If you KNOW and are CAREFUL, you can make them work.... but that will mean using WOT less, especially using lower power levels as they deplete. Basically a notable compromise/hindrance to the plane's performance potential.
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