mvigod

With all the new li-poly batteries how does one use existing BEC's which cutoff at 4.8 volts when a 7.2v li-poly or higher voltage pack needs a higher cutoff to be safe. Li-poly and Li-Ion packs cannot discharge to the lower voltages that nicads can so what is the trick here?

I have a li-poly pack at 7.2v I want to use in my electric sailplane to replace an 8.4v nicad pack. Do I just need to be ultra conservative with the li-poly and not let the pack run down since relying on a regular BEC cutoff isn't safe.

aeropenguin

My Feedback: (1)

Hello!
First of all, I cannot believe I am helping out the RCadmin!!!
Okay, sorry, but I had to say that...
I have not heard of any ESC that was directly made for Lithium Polymers, so no, none of them have a special cut off. Mostly, the cutoff was not really intended to save cells, but to save a little energy for the rudder/aileron/elevator controls.
But, you are not the first to think about this!
Bob Selman, who specializes in micro equipment, has a LBD - Low Battery Detector. It has an LED light, and it is always on when the voltage is above 5.8V. When under, it turns itself off. So, you just place it on a wingtip or uinder the fuselage, pointing down, and when it turns off, land! 5.8V is the exact voltage under which the battery must not get lower.

I am not sure of how bright the LED is, but it should be able to be seen from maybe 50ft max. Again, I am not 100% sure.

Peter Khor

My Feedback: (4)

Programmable LVC ESC's from CC:

http://www.castlecreations.com/produ.../airplane.html

So far it's only on the 7Amp, 20Amp and 35Amp ESC's for brushed apps. iirc all their brushless ESC have programmable LVC, nice touch.

The other way (which I still do for some smaller stuff on Li-ion), set a timer and land when it beeps! (trial and error, but on a 2C application 20 to 25 min is usually fine).

mvigod

this will be on a glider way up high so a LED probably won't work. I'm guessing I have to time the flights but there really isn't anyway to cycle the li-poly down to check its remaining capacity, is there? I have a triton charger and don't recall if that will discharge/charge a li-poly

aeropenguin

My Feedback: (1)

a Maha C-777PLUS, which is what I have, can. It can charge anything, literally, and well, too! Nicad, Nimh, Lipo, Li-ion.........

-aeroP

Fastlif

My Feedback: (2)

I seen a LVC for this application on FMAdirects website. You might want to check into that, as it seems they have what you are lookin for. I am in the same boat, with a flying wing, I just run it till it starts to fade some, call it good and land. Kinda crude, but heck I dont want to have to buy all new speed controls.

Matt Kirsch

My Feedback: (21)

FMA Direct does market a special LiPoly-ready ESC with a higher LVC. Many Castle Creations's ESCs have had programmable LVCs for a long time.

The easiest thing to do by far is be careful. If the power "feels" down, land.

mvigod

some first pics...arrived safe and sound and looks great just like the big brother.