lipo question

[bitton79]

Hi guys,
I have 2 questions regarding my lipo's:

I want to know if anyone meet the problem of a drop in the boat speed. the more run time the more the drop in speed. i have this prob in my bj26 brushless. the speed at the end of the run is approx 5 mph slower than the speed at the beginning of the run. is this normal?
I run 2x2s1p 5300 mah flightpower lipo's fully charged and balanced. all the boat is stock.

I want to ask also what should be the max temp of the lipo's at the end of a full hard run. i checked my lipo's with tempgun and i measured 58c. the engine wasn't even warm but the boats speed drops a bit. no water went in the hall as i run very dry.

Please assist anyone and thank's.

[Fluid]

It is normal for the boat speed to drop as the pack nears full discharge. But you do not want to fully discharge a LiPo pack since that will permanently damage the cells. Once you notice the speed dropping off, bring the boat back in immediately. If your ESC has a voltage cutoff, make sure it is set correctly for your pack; you do not want to go below 3.0 volts per cell.

Slight speed drops can also be caused by the motor heating up and losing efficiency, but I would not expect that to be 5 mph.

Quality LiPos seem to be fine if the maximum temperature does not exceed 140F/60C. Some cheap packs may not like it that hot and could de-solder their contacts.



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[bitton79]

Thanks'
I forget to mention that i have progremmed the esc using the proboat programming card.
I set the cut off voltage to high so the voltage didn't drop below 3v per cell before the esc kicked in.
I also noticed when i came home and balanced the packs that the voltage of the packs was not similer. on one pack the voltage was 3.1 and 3.15 on both cells. on the other pack the voltage was 3.5 and 3.45 v for each cell.
Could this be a problem in the esc maybe?
The motor temp after the run was about 50c only.

[TRUCKPULL]

For a stock setup on a BJ cat, it seems that your temps of 58C on the Batteries, and 50C on the motor are a bit high.
This ESC only puts out about 45 Amp
It would seem to me that you hace a bind in your drive, prop to big(not S+B)
or the boat setup is off.(too wet)

Larry

[Fluid]

I also noticed when i came home and balanced the packs that the voltage of the packs was not similer. on one pack the voltage was 3.1 and 3.15 on both cells. on the other pack the voltage was 3.5 and 3.45 v for each cell.
Could this be a problem in the esc maybe?The motor temp after the run was about 50c only.

The different pack voltages tell me that your packs are not well balanced together. Each cell in each pack is pretty close, although I'd like to see them closer than 0.01 volt. Either the two packs are from different lots, have different use histories, or there is a wiring harness issue. Were both packs fully charged on the same charger prior to the run?

The motor temperature is just fine, particularly if the run was long enough to exhaust the cells. Only if the motor temperature approaches 60C would I be concerned.



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[bitton79]

Thanks' guys a lot.