Lipo LVC/LVA for radios

[BrianG]

I'm currently using 4 Turnigy LSD cells in my Spektrum radio and they work really well, but I'd really like to use lipos. A regulator is needed between the lipo and radio to give a solid 6v, but the radio's voltage display does not show the state of the actual lipo. So there has to be something that monitors the cells. A regular LVC circuit does not actually cut power, it just outputs a signal to the ESC that forces it to go to neutral, so that won't work. Seeing as how I like to tinker, I came up with a fairly simple LVC/LVA circuit to safely allow me to use lipos. It's basically just a couple of comparators.

The circuit inserts between the lipo and BEC and has two stages: When the cells get to ~3.5v/cell, it lights a warning LED telling the user voltage is getting low. Once the cells get to ~3.3v/cell, it shuts off power. The circuit is designed to completely cut power to itself and the radio to prevent parasitic drain once it shuts down (actually there still is some drain due to transistor leakage current, but it's in the low micro-amp range). However, this design requires the use of two extra momentary switches; one to turn on the radio and one to shut it off (the off button simply tricks the circuit into thinking the lipo is low and initiates the shutdown mode). The radio's stock on/off switch is no longer needed since the on/off function is done elsewhere.

The circuit works but I only made it for my particular use. If there is any interest, I can work on "mini-fying" it and can post the schematic.

[brainanator]

I run a 3S in my hongkong radio. I routed the battery wires to the top to a toggle switch so I can basically break the circuit manually. I was worried about draining it too far, but I found that even after 2-3 weeks of use the battery is barely drained and still reading around 11.5V.
I just pop it on the charger whenever I remember to. My radio also has an LVA that turns an LED red at 9V for NiMH. Never seen it red, but I assume it'll work as an emergency reminder for me.

I would however be interested in seeing your circuit.... :) if you have the time.

[Arct1k]

What about using one of the switches the punk dig has (google it) ?

Any way of keeping the existing on/off switch with the other off being an over-ride in a LVC.

[BrianG]

Originally Posted by brainanator

I run a 3S in my hongkong radio. I routed the battery wires to the top to a toggle switch so I can basically break the circuit manually. I was worried about draining it too far, but I found that even after 2-3 weeks of use the battery is barely drained and still reading around 11.5V.
I just pop it on the charger whenever I remember to. My radio also has an LVA that turns an LED red at 9V for NiMH. Never seen it red, but I assume it'll work as an emergency reminder for me.

I would however be interested in seeing your circuit.... :) if you have the time.

Your radio must require 8 NiMH cells then? If so, plugging in 3s lipo is a breeze. This is more for people with radios that take 4 NiXX cells. and still want to use lipo. But since 1s lipo is too low, and 2s lipo is too high, a regulator is needed. I personally like the peace of mind knowing that the cells aren't being drained too low.

Yeah, I'll post the schematic, but I have to redraw it out since it's on scraps of paper at the moment. I also want to clean it up a bit.

Originally Posted by Arct1k

What about using one of the switches the punk dig has (google it) ?

Any way of keeping the existing on/off switch with the other off being an over-ride in a LVC.

I don't know how the dig switch would be used in this application. From the looks of it, it just decodes CH3 pulses and locks the desired motor by shorting it.

Things will probably make more sense once I post the schematic...

[Finnster]

FWIW, I turned on my Fasst radio after not being used in 6mos, and the voltage of the 3S batt was right around the storage voltage I left it at.

IDK how your radio turns on, the parasitic drain for my radio is nil with the built in hard switch.

[BrianG]

I was talking about the parasitic drain from a BEC and LVC circuit...

Ever thought of using a li-fe battery.Like hobbico Lifesoures(which doesn`t need a regulator) battery?

www.lifesourcebatteries.com

Also

www.rcgroups.com review

[BrianG]

Voltage is too high on a life cell, especially right off the charger at 7.2v (3.6v/cell). Nominal of 6.6v is still a tad high for a 4.8v-6v radio, but probably ok.