Big Rock Short - very short run time

[maxgasmekl]

Hi - this looks like a very informative and cool forum. Looking forward to spending a lot of hours in here I recently bought myself a Granite and a Big Rock. They are both awesome trucks. My problem is that my two almost new DXF 5200mah 100c 3s batteries suddenly went from around 20 mins of run time - doing hard bashing on a well groomed grass field - down to around 10 mins of run time Same conditions. I should mention that I always put my batteries in store-mode after running. Nothing is binding in the trucks, all cells are equally balanced when fully charged (4.19, 4.20, 4.22), the charger seems ok. LVC between 3.5-3.8V. I guess I have had 10-15 runs on both batteries max. SO what is wrong? Are the batteries a low quality brand, or are they just bad? Is there an optimal way to charge the batteries that I should know about? Fingers crossed that its just me who does something wrong.

 

[GraniteFox]

My guess is batteries. Make sure you balance charge them. If a cell get unbalanced and one starts to sag it will hit LVC quicker. I’m not familiar with that brand or charger so don’t know for sure. Also LVC on the Arrma esc is sometimes set fairly high and cannot be adjusted. You could switch the LVC to NIMH will remove the LVC. Do so at your own risk and pickup a cheap lipo alarm to tell you when to stop the battery.

 

[gotnitro]

Hi - this looks like a very informative and cool forum. Looking forward to spending a lot of hours in here I recently bought myself a Granite and a Big Rock. They are both awesome trucks. My problem is that my two almost new DXF 5200mah 100c 3s batteries suddenly went from around 20 mins of run time - doing hard bashing on a well groomed grass field - down to around 10 mins of run time Same conditions. I should mention that I always put my batteries in store-mode after running. Nothing is binding in the trucks, all cells are equally balanced when fully charged (4.19, 4.20, 4.22), the charger seems ok. LVC between 3.5-3.8V. I guess I have had 10-15 runs on both batteries max. SO what is wrong? Are the batteries a low quality brand, or are they just bad? Is there an optimal way to charge the batteries that I should know about? Fingers crossed that its just me who does something wrong.

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That charger is one of the best chargers in RC ever. I own 2.

 

[maxgasmekl]

My guess is batteries. Make sure you balance charge them. If a cell get unbalanced and one starts to sag it will hit LVC quicker. I’m not familiar with that brand or charger so don’t know for sure. Also LVC on the Arrma esc is sometimes set fairly high and cannot be adjusted. You could switch the LVC to NIMH will remove the LVC. Do so at your own risk and pickup a cheap lipo alarm to tell you when to stop the battery.
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Thanks for the reply. I always balance charge my batteries. And its just weird as they are fairly new and didnt have more than 10 cycles before the problem occured. With the setting on lipo cutoff on the esc. As the lvc already stops the truck at 3.5v I would not risk to go lower with a lipo buzzer. Or would you recomend changing the setting anyway? Also what is acceptable in terms of voltage difference on the cells? Thanks

 

[GraniteFox]

I normally look resistance on each cell. If one is unusually higher resistance than the others then that cell is causing the issue. I’m far from a lipo expert. If one cell has a sag to it the lvc will
Kick in from the sag. I have run down to 3.2 or 3.3 with no issues.

 

[GRC]

Depending on the condition of the grass and how you run, that's normal run time for a 5200 mah battery.

 

[maxgasmekl]

Depending on the condition of the grass and how you run, that's normal run time for a 5200 mah battery.

Very short grass, hard ground, mostly wide open trottle. The strange thing is still that they worked fine (20 mins) to begin with

I normally look resistance on each cell. If one is unusually higher resistance than the others then that cell is causing the issue. I’m far from a lipo expert. If one cell has a sag to it the lvc will
Kick in from the sag. I have run down to 3.2 or 3.3 with no issues.

Very short grass, hard ground, mostly wide open trottle. The strange thing is still that they worked fine (20 mins) to begin with

I normally look resistance on each cell. If one is unusually higher resistance than the others then that cell is causing the issue. I’m far from a lipo expert. If one cell has a sag to it the lvc will
Kick in from the sag. I have run down to 3.2 or 3.3 with no issues.

How do you measure resistance? My buzzer only tells me the voltage pr cell

I normally look resistance on each cell. If one is unusually higher resistance than the others then that cell is causing the issue. I’m far from a lipo expert. If one cell has a sag to it the lvc will
Kick in from the sag. I have run down to 3.2 or 3.3 with no issues.

How do you measure resistance? My buzzer only tells me the voltage pr cell

 

[razorrc]

Is the ESC flashing green or flashing red when it cuts out?

 

[Diem Turner]

Hi - this looks like a very informative and cool forum. Looking forward to spending a lot of hours in here I recently bought myself a Granite and a Big Rock. They are both awesome trucks. My problem is that my two almost new DXF 5200mah 100c 3s batteries suddenly went from around 20 mins of run time - doing hard bashing on a well groomed grass field - down to around 10 mins of run time Same conditions. I should mention that I always put my batteries in store-mode after running. Nothing is binding in the trucks, all cells are equally balanced when fully charged (4.19, 4.20, 4.22), the charger seems ok. LVC between 3.5-3.8V. I guess I have had 10-15 runs on both batteries max. SO what is wrong? Are the batteries a low quality brand, or are they just bad? Is there an optimal way to charge the batteries that I should know about? Fingers crossed that its just me who does something wrong.

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This could be an indication of potential issues with internal resistance mismatching. I'm not saying that this is the cause for your runtime deterioration (though it might be indicative of another problem that might be the cause of it but I'm no battery surgeon so I can't say with certainty), but something worth keeping an eye on.

 

[GraniteFox]

I use a simple battery checker for resistence Tenergy 5 in 1 cell meter. There are quite a few batt checkers out there and they are pretty cheap. My charger also gives me cell resistence while charging HOTA D6+. I know there is an issue when I get something like 8-9-22. If the lipo is in good shape they should all be pretty even resistence give or take.

 

[maxgasmekl]

Is the ESC flashing green or flashing red when it cuts out?

Its flashing red so its not related to thermal problems