Changing from Lead Acid to Lithium Iron Phosphate (LiFePo) battery... change of battery voltage and current range settings?

[ssbn608]

I recently changed from a lead acid battery to a LiFePo battery for my main aircraft battery. Specifically, I installed an Earth-X ETX-680C battery. Compared to a 12V lead acid battery, the 12 v lithium battery has a different resting voltage, and different charge/discharge characteristics This suggests that I should be changing the red, yellow and green bands for the battery voltage on my SkyView display, and possibly for the ammeter, if the ammeter shunt is installed in position A for reading of battery charge/discharge current to/from the battery.

So, the question is.... what are the values I should be using?

The following is an excerpt from the Earth-x manual... I'm not sure exactly how this would translate into red, yellow, and green band settings, or alarm values for a voltage indicator on SkyView..

Voltage Monitoring Alert Recommendation (Existing Aircraft Equipment if applicable) The table below shows the recommended user alerts based on voltages when in flight. This pertains to existing equipment, and is not applicable if existing low or high voltage alerts do not exist or are not adjustable. The low charge level is very different from a lead acid battery, for a lithium battery is completely drained at approximately 11.5V, and the normal resting voltage is 13.3V. '
Note: this table pertains to existing voltage level warning equipment and is NOT associated with the Fault monitoring LED.

>15V High voltage warning
<13.5V Alternator off-line alert
<12.6V Low charge level warning

 

[DBRV10]

Just like you, I have been here before. My guess is the following;

RED 14.7 > 15
YEL 14.5 > 14.7
GRN 13.3 > 14.5
YEL 12.6 > 13.3
RED 0 > 12.6

As for Shunt position, and I know someone will disagree, but for the life of me I cannot accept any good reason for any position other than Position A.
You will want to set up a typical 60A alternator current colours as below (or similar) with an EarthX
RED 60 > 80
YEL 50 > 60
GRN 0 > 50
YEL -10 > 0
RED -40 > -10

Hope that helps.

 

[ssbn608]

My guess is the following;

RED 14.7 > 15
YEL 14.5 > 14.7
GRN 13.3 > 14.5
YEL 12.6 > 13.3
RED 0 > 12.6

First, thanks for the reply.

Second... what about the Earth-X suggested " <13.5V Alternator off-line alert"? 13.5 volts is in the low part of your green band. I was thinking that would be the transition between green and the lower yellow band....

 

[airguy]

I have the ETX900V in my airplane, and what I did for the low yellow threshold was to throw ALL my electrical load at the system at the same time, on a single alternator (I have a primary and a backup), and note the voltage - 14.0 in my case - at normal flight RPM. Then I set the top of the yellow at 13.9 volts. I have red and aural alerts set at 13.0 volts and 25 amps discharge. My normal system voltage is 14.4 in flight. I have an all-electric airplane, including electric fuel pumps (no mechanical), electric ignition, electric injectors, and all glass in the instrument panel - so my electrical load is certainly higher than most. Adjust your numbers as appropriate.

I agree with David above - Position A for the shunt, where you are reading current in/out of the battery, is the only position that really makes sense. It's the one piece of current-flow data that you really NEED in the event of an electrical issue in flight.

 

[DBRV10]

Nothing wrong with even running your RED up to that 13.5 mark, but you may get nuisance alarms, as any measuring device is not going to be 0.1v perfect unless its a Fluke meter and calibrated.

I like a small margin and if the resting voltage is 13.3, once loaded up it will dip into the YEL range. Test your and see. But remember the YELLOW is going to highlight the parameter, but you will not get an alarm until you hit RED. So if you want it to alarm at say 13.1v you need your RED to start there.

Airguy has a sensible setup that he has tested on his aircraft and his loads. Try that even.