kistner

My Feedback: (10)

So my nephew asked me if he could buy an rc from me so I fixed up a Rustler I had laying around. I threw in a Quark Roadster esc that I also had laying around. I went into programming and the default for lipo cutoff was 2.7/cell. That seemed low to me so I set it to the max available which was 3.0 per cell. Well that got me lurking around here again and noticed some guys saying 3.0/cell is way too low, you'll puff your batteries, etc. So I start thinking maybe I should get my nephew an lvc that cuts off or sounds at a higher voltage.

Well today my son says he wants to drive his rc (and by the way he's leaving in a 30 minutes) so I scramble to get his Rustler up to speed. Well there was trouble, it had been sitting for a while. I started messing with his esc, a 1st gen Castle sidewinder. I had it hooked up to the pc and the default cutoff is 3.0/cell. The issue with his was the receiver but that's a little off topic.

My question is what is the suggested cutoff voltage? is 3.0v/cell ok? Castle had that as default and the Quark had it as the max available in programming with default at 2.7v. I have a few other brand esc's but I haven't messed with them in a while to recall or know what their default cutoff is.

EXT2Rob

My Feedback: (1)

I've always read that with Lipo cells, anything below 3.0V was bad news for the battery chemistry and you risk damage thereby. It's not like you'll kill it right off, the damage is cumulative. I'm not aware of any modern ESCs that allow you to set cut off below 3.0V, and most of us set it no lower than 3.2V. 3.4V is more conservative. Get a new ESC.

kistner

My Feedback: (10)

Thanks. The sidewinder allows to set it higher and I already did. I'll probably just get an extra low volt alarm or cutoff for the quark. I wondered if we were getting into fiction versus fact with regards to the cutoff voltage. The quark is old enough that it was probably made right at the beginning of lipo use for cars and trucks, maybe they just didnt get it right.

RustyUs

Lithium batteries come in different "flavors" with different cutoff recommendations. I believe LiFe cells are fully "depleted" at 2.5v/cell. That being said, 3v/cell being the maximum setting on the Quark ESC's LVC, that would be okay for a LiPo pack. All my newer ESCs, my HobbyWings anyway, come set at 3v/cell by default for LiPo use. I use the 3.4v/cell setting for the so called longer battery life expectancy. The LVC normally senses the battery's voltage under a load. Let that pack sit for a minute and a person will probably see 3.2v~3.3v per cell.

kistner

My Feedback: (10)

Good points. thanks

mazpr

Mine are set at 3.5v in the ESC, and as a backup have installed a digital display set at 3.5v as well just in case the ESC fails for any reason. Mine is on a Blackout Pro stock ESC.

You can go ahead and test them out, if they are not in a hard case check temps as voltage drops, that usually is the giveaway (taking in consideration everything else is in order and not over-taxing the electeonics).

Steven35

Quick question on this topic. I bought my 2nd car last week and it only runs less than 10 minutes before shutting off. Redcat said low voltage shutdown at 6.4V . Isn't 3.8 - 4.2 V per cell full charge? 3.4 is their stock setting for shutoff. How can I get more run time out of a 2s 35C 5200mah? Thanks in advance..

RustyUs

Steven35, what balance charger are you using to charge your batteries? 4.2v/cell is fully charged for LiPo, unless you're using LiHV.

Using a good balance charger on your LiPo battery should be at top of list of getting the most outta your packs. Balancing LiPo batteries at safe/moderate charge rates, and not storing them fully charged will make "happy" LiPo packs most of the time. Storage voltage is 3.8v/cell. Some ESC's low voltage cutoffs (LVC) calibration can be off a bit from one ESC to another. You have to take voltage under load into consideration also. Some of my ESC's LVC are set at 3.2v/cell, but after it's tripped, and I test the pack's voltage, the batteries are usually close to 3.7~3.8v/cell after the pack has a chance to sit for 20 seconds or so.

Gearing, motor, condition of battery, bad bearings (any drag really), and driving style will all effect run times.

Some great links to read if you have the time:
http://www.rogershobbycenter.com/lipoguide/
http://www.rchelicopterfun.com/rc-lipo-batteries.html
Lipo battery Introduction - mrpositive.co.nz
RC Lipo Battery Guide: Explanation, Safety, and Care ? LearningRC
LiPo Batteries - A guide to using and looking after your batteries - Guides - DroneTrest
http://www.rcuniverse.com/forum/rc-c...batteries.html

EXT2Rob

My Feedback: (1)

Sounds to me like the Redcat ESC is set for NiMh batteries, not Lipo. Check the manual for how to change battery mode to Lipo.