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xxx sct gets only 5-7 min runtime :( - 11/19/2012 1:34 AM   
Kenmtb


 

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From: Endicott, NY, USA
Status: offline 		Truck specs:
5900 mah 2s lipos
3500Kv 10T HW motor, 120 brushlesshobbies.com ESC
cutoff 3.2v/cell
88/17 gearing
Bats in great shape, no binding on the truck (wheels spin freely)

Hi-
My 2wd xxx sct is geting 5-7 min runtime. It dosent matter what battery I use. I get 15+
min on my T4.1 with the same packs on the same track. The truck has a lot of power and moves along well.

does anyone have any suggestions how to improve the current runtime?
Thanks


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RE: xxx sct gets only 5-7 min runtime :( - 11/19/2012 1:57 AM   
Johnnysplits


 

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Your lvc is too low. 3.4v per cell is the lowest you should have the hard cutoff set at. How many cycles have you run the batteries this way? You might have messed up your lipos.



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RE: xxx sct gets only 5-7 min runtime :( - 11/19/2012 2:16 AM   
nitrosportsandrunner



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quote:

ORIGINAL: Johnnysplits

Your lvc is too low. 3.4v per cell is the lowest you should have the hard cutoff set at. How many cycles have you run the batteries this way? You might have messed up your lipos.



1st, it aint to low. no reason why you cant run it at 3.2v. if you have high quality lipos, you can even set LVC at 3.0v

either way, increasing the lvc to 3.4v will not increase runtimes...will do the opposite.

runtimes are very low here. with that setup and that lipo...you should see anywhere from 25-30minutes.

how old is the brushless system? Its not unheard of for the LVD on a esc to go bad...cutting power WAY before the lipo gets that low. Its happened on more than one traxxas VXL unit ive owned. It would cut power after jsut 2 minutes on a freshly charged 2s 5000mah lipo.

If you are able to set the LVC on your esc, try changing the setting....maybe it will reset the system and it will work as it should.

also, how about the connectors? the battery to esc plugs...do they get hot? Poor connection there can fool the esc into thinking the lipo is low on power. Ive had that happen with deans connectors before.

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RE: xxx sct gets only 5-7 min runtime :( - 11/19/2012 2:23 AM   
SyCo_VeNoM



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Status: offline 		is the ESC overheating?
I have a 120A HW ESC on a 3500kv motor in my pede 4X4, and I know it gets way hotter on 2S than my similar ESC does on 4S in a heavier vehicle due to it having to pull more current for the motor.

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RE: xxx sct gets only 5-7 min runtime :( - 11/19/2012 2:30 AM   
Kenmtb


 

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Status: offline 		Hi-
The motor and ESC are brand new. The temps are low.
Is the gearing too high/low?
The esc punch was set to level 5

I would "kill" for 20 min runtime!!!!!!!!




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RE: xxx sct gets only 5-7 min runtime :( - 11/19/2012 2:30 AM   
Johnnysplits


 

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quote:

ORIGINAL: nitrosportsandrunner
 if you have high quality lipos, you can even set LVC at 3.0v



That's pushing it even with $180 lipo's.  3.0v / cell is too close to the lipo killing threshold.

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RE: xxx sct gets only 5-7 min runtime :( - 11/19/2012 2:48 AM   
Kenmtb


 

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Status: offline 		should I change the gearing or anything else?


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RE: xxx sct gets only 5-7 min runtime :( - 11/19/2012 4:49 AM   
phmaximus



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Status: offline 		Yeah I would, start with gearing, but I suspect its something els

Does it have more top end speed than the T4.1?

U really need a watt meter tho, only way to know for sure


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RE: xxx sct gets only 5-7 min runtime :( - 11/19/2012 5:17 AM   
Haddi Taha



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Status: offline 		I have my lvc set to 3.0v a cell, whenever it kicks in, I put the batteries on the charger and it usually says about 3.5v per cell

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RE: xxx sct gets only 5-7 min runtime :( - 11/19/2012 5:18 AM   
Kenmtb


 

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Status: offline 		The speed is close. I am not really sure which one has the highest top speed
but there is no big difference. I did read that someone recommended a24/84 for a velineon 3500.
Im thinking that the truck is way undergeared and may be wasting runtime spinning the motor excessively.


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RE: xxx sct gets only 5-7 min runtime :( - 11/19/2012 7:48 PM   
FahrtAutoRC



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Status: offline 		While not recommended, if you keep proper care of your batteries, you can still safely run it at this setting. Do you honestly believe it is a strict dead limit, one bit too low and the batt goes poof? I'm not saying it is 100% ok, you are cutting it short if your cells are out of balance, or something along those lines, but it should usually be perfectly fine.

As for the O.P., I second your runtimes being related to a bad LVC. If you have a friend who would let you run their ESC just for a battery pack, try that, cheapest way to see if the issue is from ESC problems or another source.


quote:

ORIGINAL: Johnnysplits


quote:

ORIGINAL: nitrosportsandrunner
 if you have high quality lipos, you can even set LVC at 3.0v



That's pushing it even with $180 lipo's.  3.0v / cell is too close to the lipo killing threshold.



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RE: xxx sct gets only 5-7 min runtime :( - 11/19/2012 10:09 PM   
phmaximus



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quote:

ORIGINAL: Kenmtb

The speed is close. I am not really sure which one has the highest top speed
but there is no big difference. I did read that someone recommended a24/84 for a velineon 3500.
Im thinking that the truck is way undergeared and may be wasting runtime spinning the motor excessively.



Hey I might be onto something there, try it


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RE: xxx sct gets only 5-7 min runtime :( - 11/19/2012 10:12 PM   
phmaximus



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quote:

ORIGINAL: Johnnysplits


quote:

ORIGINAL: nitrosportsandrunner
 if you have high quality lipos, you can even set LVC at 3.0v



That's pushing it even with $180 lipo's.  3.0v / cell is too close to the lipo killing threshold.


Yep that's you're opinion, not fact just opinion.

Why don't u create a thread so u can argue ur point in rather than hijacking this thread, if u were contributing that would be fine but ur not


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RE: xxx sct gets only 5-7 min runtime :( - 11/19/2012 11:11 PM   
nitrosportsandrunner



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Status: offline 		run a batt threw it again and then pop the lipo on your charger (or blinky balancer if you got one) and see what the cells read. If they read 3.7v or better, then chances are the LVD on your esc is bad and is cutting in way early.

Normally, even with cheaper lipos, if your LVC is set to 3.0 or 3.2, then your lipo should read around 3.5 when you put it on the charger. the LVC will cut in at its set point when the lipo is under load. when not under load, the voltage will read higher.

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RE: xxx sct gets only 5-7 min runtime :( - 11/19/2012 11:13 PM   
nitrosportsandrunner



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quote:

ORIGINAL: Johnnysplits


quote:

ORIGINAL: nitrosportsandrunner
 if you have high quality lipos, you can even set LVC at 3.0v



That's pushing it even with $180 lipo's.  3.0v / cell is too close to the lipo killing threshold.

you can charge lipos even if they get as low as 2.8v per cell. you may have to charge them on nimh setting for a bit 1st, but it will work.
Price of the lipo doesnt really effect what LVC you need. If the lipo's cells are balanced, then you can run a lower LVC. If they are not balanced well, then a higher LVC is needed.
But Im still betting the OP's LVC is cutting in way early. Not working right, like on some VXL esc's Ive had in the past.

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RE: xxx sct gets only 5-7 min runtime :( - 11/20/2012 12:33 AM   
Kenmtb


 

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Status: offline 		I got out to the track and tried a 22T pinion (22/88)
The runtime was timed at around 15-20 min. on 5900 2s packs.
One pack may have lost some storage.
Motor temp: 128, ESC: 70

The truck has not lost much acceleration if any and it gained some top speed
but not anything mind-boggling. I would say so far the runtime has roughly doubled.
It still seems like I get less time than my friends 4x4s but this is a good start.
Maybe investing in higher quality packs would improve things more. I have an SPC
5000 pack on order.



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RE: xxx sct gets only 5-7 min runtime :( - 11/20/2012 12:47 AM   
nitrosportsandrunner



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Status: offline 		I can swear I get 25 or so minutes on most brushless models with a 2s 5000mah pack...and its not a fancy pack either.

But if you are getting 20 minutes thats alot better than 5-7.

based on your temps, you could gear up. motor temps within 150=160 or decent. I prefer to keep it 140-150. I have run a vxl motor upto 190 without damaging it tho (rustler, high geared, big tires, tall grass, 3s lipo)

Can you set the low voltage cuttoff on your esc? if its set to 3.4v or so, and you are getting 20 minutes then that may be about right.
again, check the voltage of your lipo at the end of your run. based on what the voltage reads you get a good idea what the LVC is set to and if its coming on early or not.


Oh, also, whats the "C" rating on your lipo?

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RE: xxx sct gets only 5-7 min runtime :( - 11/20/2012 1:10 AM   
Kenmtb


 

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Status: offline 		The lvc is set to 3.2/cell. My estimate of 5-7 minutes was made without a watch. It may be closer to 10min. My friends can do 25 lap races at their track. With the extra runtime I could manage 15..but that is another estimate. Im still thinking the truck should run a bit longer.
I may try gearing up. The hobby shop track I race on is very tight so you don't want to go too high. It may come alive with a 24T pinion.

The packs I used today are GForce 5900KV 60C. Im not sure if the packs meet the advertized specs.

I wonder if the HobbyWing 3500 10T short course motors just eat batteries.


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RE: xxx sct gets only 5-7 min runtime :( - 11/20/2012 6:53 AM   
phmaximus



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Status: offline 		I personally would set the gearing to its limit motor temp wise, then u know the limit and can work backward from there to suit the track


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