battery discharging question

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lx2008

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  1. Bashing
hi guys, been some time since i`ve got my elec. truck out to run. have a charging/discharging question.
i have been running an e-maxx with a 6s castle speed control. using 2- venom 7.4v 2s 5000mah 50c batts to run.
every time my run is over the one battery reads around 6.7 to 6.8v & the other ( and its the same one all the time)...
always has a voltage of 7.4 volts or so. why is the same battery always around 7.4 & the other around 6.8?

these have always been charged on a traxxas ID charger. the venoms came with a traxxas gen2 battery adapter so it would fit
in the ID charger. even though they can't be "i.d.`d" since the adapter does not have the balance wires built in like the real
traxxas batteries, the charger can be put in "advanced mode" to charge the batteries manually. ( with the balance plug in the balance port)

the charger charges these batts @ 1A automatically and then after about 2.5 hours or so it goes to 2A for a while longer.
but its all done auto & balances at the same time.

could someone explain what is going on with the differences in the discharge.

thank you. ( if you need further info please ask)
 
So, you run them til the low voltage cutoff kicks in and that is where they end up?

If that is the case, then I would have to guess the battery reading 7.4v after a run is experiencing voltage sag, and triggering the low voltage cutoff sooner. As LiPo's age, they can start to deteriorate. Especially if they weren't put away with a storage charge on them. When you have an amp draw on them, the voltage can drop pretty low, then bounce back up.

I am not familiar with that charger, but does it have an internal resistance meter? I kinda doubt it. But you need to find out what the IR is for your batteries. That is the best way to tell if your batteries are about to go bad on you. High IR readings means the battery is at a much higher risk of burning up while running your RC.
 
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yes i run it til it quits. i have this particular truck hooked up to their telemetry app and used it sparingly.
i guess i could check it to see how far the voltage has dropped while running but i thought since it has the cut-off
i would just run til it quits. and btw i`m ignorant to the term IR

thanx for the reply!
 
yes i run it til it quits. i have this particular truck hooked up to their telemetry app and used it sparingly.
i guess i could check it to see how far the voltage has dropped while running but i thought since it has the cut-off
i would just run til it quits. and btw i`m ignorant to the term IR

thanx for the reply!
You are very welcome.

IR = internal resistance. It is a reading some chargers will give you for each cell of your battery. When the IR starts to climb, it is a sure sign your battery is going bad. High IR can cause a LiPo to overheat while running... then poof! Your car is a molten pile of plastic.

Things that damage a LiPo...
If you run your battery too low (below 3v per cell), the cells can start to degrade, causing higher IR.
If you don't use them for a long time, the voltage can drop below 3v, and damage the cells, and they will degrade.
If you store the batteries fully charged, it can damage the battery. They should be stored between 3.7v-3.8v per cell anytime you are done running them.
And of course, road rash can damage them.

This is why I wouldn't recommend a smart charger, or smart batteries to anyone. There's nothing smart about them when people start using LiPo batteries and don't learn all this stuff. So it's great you're in here asking questions 😉
 
i have had an Onyx 260 for a couple of yrs now. still new in box. i`ll get it out and start using it.
 
That Onyx cgarger is old and outdated tech. It doesn't read IR either. I use this one.
Although outdated, my onyx 230 and kx80 chargers have been reliable.

Been thinking of the Hota you linked. I'm just not sure on wireless phone charging and all the connectivity on it. I guess I'm just getting old and technology is leaving me.
 
thanks for the link. i`ll try the 260 for a while and see how it functions and how my batts react to it.
i have four other new 2s 7.4`s i`ll try with it. the venoms i have had been put thru their paces and have
been really good so far...so i can't think i did anything to harm them to quickly as i have had lot of time on them.

thank you!
 
Well, as long as you take care of the batteries, there shouldn't be any issues. Having the ability to read IR is just an early warning to upcoming battery problems. But it is something I wouldn't want to be without now that I use it so much.
Although outdated, my onyx 230 and kx80 chargers have been reliable.

Been thinking of the Hota you linked. I'm just not sure on wireless phone charging and all the connectivity on it. I guess I'm just getting old and technology is leaving me.
Yeah, I still have Onyx stuff from years ago that still works great.

The connectivity stuff on the Hota is more for if you are out in the field charging your batteries I'm guessing. But I use it at home.
 
appreciate your knowledge & input.
 
We have the best hanging here @lx2008 , not me though, I'm just here for the comedy. :p
 
the thing is that battery that is running to a lower voltage will do so until you can bring internal resistance down. and with charger you have it will always run to a lower voltage. in order to bring ir down a battery must have a high charger rate not 1 amp then to 2 amps. Like 20 amps. Also the 50c batteries is not what motor is really wanting. Just my 2 cents worth. Add a 5$ battery buzzer to stop the lower voltage discharge. Plugs into balance plug
 
When running batteries in series like that you must use matched pairs or you'll run in to that problem of one LiPo getting discharged faster than the other one. You dont ever want to run a battery from a matched pair by itself or it will end up getting more usage than the other one and will cause the issue you are talking about. you're gonna have some variance even with a matched pair but that variance should be fairly minimal.

50C should be fine imho as long as the lipos are a good quality brand and matched.
 
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