Technical information on the Undervolt sensor and how it
differs from other LiPo sensors on the market today.
The Undervolt sensor is designed to encompass
cell packs from 2 cells all the way up to 10 cells and is a manually programmed
system just like your speed controller so you only have to do it once and it
remembers the cells you have.
Speed controller voltage
detectors are mostly hard-wired comparator type sensing devices that are ‘dumb’
type sensors so they are prone to going off at false readings and have no
intelligent loaded voltage sensing.
The advantage of the
Undervolt sensor is that it uses a 10bit analogue to digital converter and
digital signal processing to determine an accurate ACTUAL loaded voltage. This
will be further explained next.
Normal mode voltage
detection:
LiPo Batteries have a
specific voltage that is the minimum manufacturers recommended voltage
threshold of 3.1 volts per cell.
We all like to fly our
models and some of us right to their limits and we don’t want to have warnings
going off unless it is necessary. The Undervolt sensor utilises something
called change in voltage over change in time algorithm to enable the flyer to
get the most out of their Li-Po’s safely.
In this diagram we can see that when our LiPo Cells
get low, around the 3.1 Volts per cell range we can see that is quite easy to
get dips and glitches due to battery loading at these levels which will trigger
other voltage sensors.
The Undervolt sensor will
have a look to see if the sensed voltage has an overall dip at 3.1volts per
cell or below. If this voltage level is consistent for a period of greater than
5 seconds then it will latch the alarm. The Undervolt sensor samples the
voltage at 10Hz or 10 times in one second for fast voltage sampling so nothing
gets past it for an accurate change in voltage over change in time reading.
Diagnostic mode detection:
This mode is for those that
want to know what voltage your cells reach when you fly, data loggers do a
great job at analysing your flight systems after you land, but sometimes you
simply want to ‘see’ what your heli / plane is doing while you are flying to
determine what manoeuvres put more stress on the LiPo Cells or if there is a
problem with binding and judge more accurately when you need to land.
This diagram shows a typical discharge curve for
Lithium Polymer cells from full to empty. From a fully charged pack it can be
seen it takes quite a while to reach 3.2v per cell. This is the normal flight
envelope or ‘flight range’. From this point on things start to happen a lot
quicker and the critical voltages are reached faster. In Diagnostics mode the
sensed voltage is represented immediately by the alarm when it reaches a loaded
3.1v/cell.
The great advantage of this
mode is that as soon as the voltage reaches 3.1v/cell the alarm will start. If
the voltage recovers, the alarm will stop.
As mentioned in the
instruction manual, the alarm has a different sequence according to the voltage
it senses so there is no need to program a singe voltage as in other sensors,
with the Undervolt sensor you can ‘see’ all of the critical voltages as they
happen.
If the sensed voltage
reaches 2.9v/cell a solid on signal alarm turns on and remains ON for a minimum
hold period of 20 seconds. This enables the flyer to manoeuvre the heli/plane
to an easy to see distance to determine if the sensor has reached that voltage.
This is valuable information to diagnose how much you are loading down your
cells during certain manoeuvres and conditions.
The 3.0v/cell to the
2.9v/cell is only a small window and may pass by too quickly for you to see the
changes before the cell voltage gets too low so a hold time will let you know
it has reached that point before the cells have a chance to recover.
Logic Electronics strives to
make the BEST possible dedicated accurate diagnosis and warning tool for your
Lithium Polymer cells.
We will be releasing a more
comprehensive voltage/current/power logger with a graphing interface in the
near future so if you require a more detailed analysis of your flight after
landing so stay tuned.
Thanks for taking the time
to read this page.
If you have any suggestions
or feel the need to email me about my sensor please feel free to email me at: mailto:xdata@iinet.net
Thanks again
Dave.