Lipo Cutoff setting question - RC-Monster Forums

marcus · **Lipo Cutoff setting question -** 02.27.2009, 12:41 PM

I've seen the general feeling that setting the lipo cutoff to a value iinstead of 'auto' is preferrable.
If however you're out in the field and perhaps switching between 4S and 6S that becomes the perfect thing to forget in the heat of the moment and/or a PITA.

What's the deal with the 'auto' setting? And if it's so unsuitable why is it even there?

BrianG · 01:29 PM

It's really for the lower 2s and 3s cell counts.

Depending on the charge level of a cell, the auto setting could read a mostly discharged 6s pack (~18v) as a 5s pack, and a mostly discharged 5s pack (15v) could be read as an almost full charged 4s pack. The only way for this to work right would be for the ESC to assume that the user is plugging in a fully charged pack where the voltage is >=4.0v/cell, but I know there would be people out there that would plug in a partially discharged pack and end up damaging it.

Then there's cell chemistry. A123s voltages are different than regular lipos. How does the ESC know the difference?

The only way to be sure would be to add connectivity of the balance plug to the ESC, and then set the cell type and desired per cell LVC point in the ESC. Only then can the ESC be sure what is hooked to it.

Yeah, it's not ideal.

marcus · 02.27.2009, 01:35 PM

yea, i figured [hoped] that the ESC would assume the first voltage read would be from a full pack and therefore be able to calculate the cell count.

I further assumed that the ESC, like me, doesn't give a hoot about heavyass A123 cells

rabosi · 02.27.2009, 06:47 PM

Quote:

Originally Posted by BrianG

........Depending on the charge level of a cell, the auto setting could read a mostly discharged 6s pack (~18v) as a 5s pack, and a mostly discharged 5s pack (15v) could be read as an almost full charged 4s pack ......... .

This can be gotten around if in auto-lipo mode. The mamba monster & max esc will beep for the number of cells detected, ie 5 beeps if 5s detected. If attention is payed when the esc is turned on you can tell if your pack is detected correctly. To be extra safe you can stop driving as soon as a noticeable drop in performance is detected.

SpEEdyBL · 02.27.2009, 10:38 PM

The main reason people don't use it is because the cutoff is two low. CASTLE, MAKE IT 3.2 VOLTS INSTEAD OF 3.0 IN THE NEXT VERSION OF CASTLE LINK! Or adjustable by the user.

Pdelcast · 02.28.2009, 01:50 AM

Quote:

Originally Posted by SpEEdyBL

The main reason people don't use it is because the cutoff is two low. CASTLE, MAKE IT 3.2 VOLTS INSTEAD OF 3.0 IN THE NEXT VERSION OF CASTLE LINK! Or adjustable by the user.

Well, we will be adding an adjust to a future version of the software, so that the cutoff threshold can be changed.

As it is, the cutoff is closer to 3.1V than 3.0V right now, and Lipo chemistry doesn't actually start any damage until a cell hits about 2.4V -- so there isn't any problem with using 3.0V as a cutoff.

And yes, the auto-lipo mode assumes that the batteries are at full charge. HOWEVER, the Monster controller ALSO beeps back the number of cells to the user -- so the user can verify that the number of detected cells is correct. (you will hear the normal power-up beep, followed by beeps for the number of detected cells, and then followed by the arming tones.)

jhautz · 01:32 PM

Quote:

Originally Posted by Pdelcast

Well, we will be adding an adjust to a future version of the software, so that the cutoff threshold can be changed.

As it is, the cutoff is closer to 3.1V than 3.0V right now, and Lipo chemistry doesn't actually start any damage until a cell hits about 2.4V -- so there isn't any problem with using 3.0V as a cutoff.

Glad to hear this will be a option in the future. Very welcome update.

As for the cells not being damaged.... tell that to my puffed flightpower 4350 25c pack that I puffed in my buggy using the auto lipo setting. Since switching to maual setting of 3.2v/cell I have not had another problem. The auto setting as it currently is allows the battery to drain to low and stresses the cells. This is my opinion.

SpEEdyBL · 03.01.2009, 05:35 PM

It also eliminates possible voltage reading variance by the esc. My eagletree data recorded a sustained voltage of 12.39 volts under a load when the cutoff was set to 13.0 volts.

**6s auto lipo?? -** 03.14.2009, 01:40 AM

i have an e revo on 6s two 5000mah 11.1v maxamps and have been running it on auto lipo, can anyone tell me what voltage setting i "should" have it on????,i also want to say a big Thanks to patrick and all at CC , i was in the waiting period for 5 months for my mmm,i couldnt be happier,i now own two mmm's and a mamba max ,they all are running flawless,..also thanks for the t- shirt "Connie" is HOT,....thanks joe,,,,,hi kristi

lincpimp · 03.14.2009, 02:44 AM

Quote:

Originally Posted by erevo15151y

i have an e revo on 6s two 5000mah 11.1v maxamps and have been running it on auto lipo, can anyone tell me what voltage setting i "should" have it on????,i also want to say a big Thanks to patrick and all at CC , i was in the waiting period for 5 months for my mmm,i couldnt be happier,i now own two mmm's and a mamba max ,they all are running flawless,..also thanks for the t- shirt "Connie" is HOT,....thanks joe,,,,,hi kristi

19.2v is what I run, that is 3.2v per cell.

brushlessboy16 · 03.14.2009, 07:30 AM

Has anyone verified how accurate the voltage cutoff is, i run my truck on 5200mah 2s lipo's and when they start to hit cutoff i shut the truck down... but when i put them on the charger the cells are still at 3.5-3.6v each.. My cutoff is set to 12v for 4s.

SpEEdyBL · 03.15.2009, 03:49 AM

The cells will rebound as they are removed from a load. So your 4s pack is probably hitting the cutoff under a load, and rebounding to whatever your charger reads.

Though ACCURATE? My eagletree elogger confirms that my MMM is letting my packs go about 0.8 volts lower than what set it at.

brushlessboy16 · 03.15.2009, 07:56 AM

Ah, never though about it that way, your right. dropping my cutoff from 12v to 11v gave me another 2minutes of runtime

and the cells are still at 3.4 when im done running

Jeremy1976 · 03.15.2009, 03:30 PM

I will have to pay attention then when I get my MMM. I should have it tomorrow and plan on running 2 2s packs and a 3s pack on it. I will have to verify I am getting the correct beeps. I dont want to ruin a pack. Especially when I have a brand new 3s Poly R/C pack coming.