Low voltage detection

[andy4795]

Does anyone know at what volts the low voltage detection kicks in at, I have some 7.4 lipos and some 11.1 3s 5000 and the boat goes into limp mode far to quickly I think.

[orca44]

It should be set for 3.2 volts per cell and if in auto detection mode it will know how many cells.

[ksb51rl]

It should be set for 3.2 volts per cell and if in auto detection mode it will know how many cells.

It should be set for 3.4 volts per cell (minimum) and if in auto detection mode it will know how many cells.

[andy4795]

Thanks for info. So am I right in thinking that a 2cell 7.4v lipo will be useless after a one volt drop between the two cells ? As that 3.2 v each cell totals your 6.4v before low volt detection, just don't seem right

[ksb51rl]

2S LiPo packs are 8.4 volts fully charged, not 7.4 volts.

What do you think they "should" discharge down to?
Batteries don't discharge to 0 volts. Alkalines, for example, start at 1.6± volts. At about 1.4 volts, they are "dead" and useless for all but the lowest-draw devices.

[Ken125]

. Voltage and Cell Count:
LiPolys act differently than NiCad or NiMH batteries do when charging and discharging. Lithium batteries are fully charged when each cell has a voltage of 4.2 volts. They are fully discharged when each cell has a voltage of 3.0 volts. It is important not to exceed both the high voltage of 4.2 volts and the low voltage of 3.0 volts. Exceeding these limits can harm the battery.
The way to ensure that you do not go below 3.0 volts while flying is to set the low voltage cutoff (LVC) of your electronic speed control (ESC). It important to use a programmable ESC since the correct voltage cutoff is critical to the life of your batteries. Use the ESC's programming mode to set the LVC to 3.0 volts per cell with a hard cutoff, or 3.3 volts per cell with a soft cutoff. If your ESC does not have hard or soft cutoff, use 3.0 volts per cell. You will know when flying that it is time to land when you experience a sudden drop in power caused by the LVC.
If your ESC has an automatic lithium mode. Use it, it will correctly sense the number of cells and set the auto cutoff appropriately.
If you have previously been flying with NiCad or NiMH batteries, switching over to lithium polymer will result in a different number of cells being used. If you had 6 to 7 round cells then 2 lithium polymer cells will correctly duplicate the voltage of those cells. If you had 10-11 cells then 3 lithium polymer cells would be right for you. There are a lot of 8 cell flyer's out there that are stuck between 2 and 3 cells. In my experience the best option is to determine how many watts you were using before and duplicate that with your LiPos, Motor, and Prop. For example. If you were running 8 cells (9.6volts) at 10 amps on a speed 400 airplane, then you have 9.6 x10, 96 watts. So if you went with 2 lithium polymer cells (7.2 volts nominal) then you'd need to change your prop such that you used 13 amps. If you went to 3 LiPoly's (10.8 volts nominal) then you'd need to reduce the amperage to 8.9 amps. These estimates are approximate, and some experimentation is required for best results but conserving Watts is a good way to start.

[ksb51rl]

Was there a point to the above or did you just feel like performing a large cut and paste? Some rules for flying with LiPos do not apply to surface vehicles due to the difference in amp draws.

[SkidMan]

I run my spartan for the first time today...after 6-7 minute the lipo cut-off goes ON.I check my batterie and the voltage on my Gen Aces 3S 5000mah is 3.84v/cell..........when i run my Emaxx Bruhless i go to 3.2-3.3V/cell and give me better runtime.Can i change de lipo cut-off voltage of my spartan??

P.S.I have the old spartan ESC version not the Castle!!

[hog]

I don't believe the cutoff is programmable on either Spartan ESC.

I don't know where the LVC is set on your Emaxx, but boats draw higher amps than ground vehicles. Assuming both LVC are set the same, the Spartan may cut in sooner if your batteries don't have high enough C rating.

Internal resistance in the batteries may prevent full voltage from being available under heavy load, causing the LVC to sense a low voltage even though the batteries may still have some usable charge left in them.

hog

[SkidMan]

My battery pack is Gens Ace 5000mah 40C 3S......on my E-Maxx the LVC is set to 3.2V/cell!!

[ksb51rl]

My battery pack is Gens Ace 5000mah 40C 3S......on my E-Maxx the LVC is set to 3.2V/cell!!

And once again, that is too low of a cutoff value...IMO.

[SkidMan]

I never have issue with my LVC set at 3.2V on my maxx after one year!!When i test the cell i see 3.3-3.4V.

[hog]

Cell voltage is only one indicator of discharge. You also want to have 20% of your capacity left in your batteries, so on a 5000mah battery you should have approx. 1000mah of capacity remaining at LVC.

So when you charge your batteries your charger should show that you are "adding" 4000mah or less to the battery to reach full charge.

Also remember that the voltage you are seeing is "at rest" voltage. When you are putting a load on the battery the voltage will drop lower than the at rest voltage.

My experience is; on a properly discharged battery, I have 20% or slightly more capacity remaining, and my at rest voltage is usually around 3.6-3.7 volts per cell.

hog

[SkidMan]

Ok!Thanks!

[Erland]

It is interesting to watch the TQi readings on voltage as you go because your voltage levels really "falls like a rock" when you hit the throttle... Going neutral and you can see the voltage increasing again... After resting the batteries a few minutes you can see the voltage slightly increasing (supporting Hog's experience on LPC cut off at 3,4 byt rest voltage when charging being 3,6-3,7).

I'm by no means a battery expert but it sounds reasonable...

I have runed my Spartan with LPC off as my cheap 30C batteries just cuts off due to voltage drop as described but with the TQi checking it works... It will fail at last but I just got my new batteries so I will stop that practice ;-)