cubflier
MEMBER
Palmer, AK
I recently opened up an EarthX ETX36D to further my learning about how these batteries work. The battery showed 10V which if you divide by 4 (the series pack count of a 12V LiFePO4) gives 2.5V which makes sense in that the battery must be teetering at the Over Discharge Protection limit. This first photos are how the inside of this EarthX is arranged. This LiFePO4 which is referred to as 4S2P for 4 in series 2 parallel.
Next I disassembled one of the packs in parallel to separate each LiFePO4 pouch cell. The next two shots show all that stuff after it was taken apart.
Testing the voltage of both packs showed cell #3 at 0V and all other cells at 3.33V which was different from what I expected.
The BMS circuit board was very simple so I went drew up a schematic ( to the best of my ability) to see if I could understand what's going on.
It's a fairly simple circuit that serves to balance the cells and that's about it. There is no Over Discharge Protection at all. Both the EarthX Manual and Marketing literature on the ETX36D claim the following features:
Exclusive Features:
–Over discharge protection (#1 killer of all batteries and other brands do not protect against this and void the warranty)
–Over charge protection (Other brands do not protect against this and void the warranty)
–Built in cell balancing technology (Other brands must use a special balancing charger in order to level the charge of each cell. Your vehicle is what charges the battery most of the time, if you do not have built in cell balancing technology, how is your battery balanced while using it?)
– Short circuit protection up to 1,000 amps (Other brands void the warranty if you short the battery)
–Excessive cranking protection (Lithium technology is different than a lead acid battery and needs to be protected from heat)
This battery was purchased in 2013. I had always assumed that the features listed above applied. They do not. The important take away from this is if you have an ETX36D in your airplane that was purchased in 2013 there is very little in the way of the safe guards listed in the EarthX ETX36D literature. If you ever leave the master on it will possibly go flat on you. This is when they can get dangerous if you try to pump them back up. What I cannot say is whether EarthX made a change the BMS for this model of later years. I suspect this is case.
In any event I was always curious what these batteries looked like inside and thought I would share what I discovered in case any of you had the same curiosity.
Jerry
Next I disassembled one of the packs in parallel to separate each LiFePO4 pouch cell. The next two shots show all that stuff after it was taken apart.
Testing the voltage of both packs showed cell #3 at 0V and all other cells at 3.33V which was different from what I expected.
The BMS circuit board was very simple so I went drew up a schematic ( to the best of my ability) to see if I could understand what's going on.
It's a fairly simple circuit that serves to balance the cells and that's about it. There is no Over Discharge Protection at all. Both the EarthX Manual and Marketing literature on the ETX36D claim the following features:
Exclusive Features:
–Over discharge protection (#1 killer of all batteries and other brands do not protect against this and void the warranty)
–Over charge protection (Other brands do not protect against this and void the warranty)
–Built in cell balancing technology (Other brands must use a special balancing charger in order to level the charge of each cell. Your vehicle is what charges the battery most of the time, if you do not have built in cell balancing technology, how is your battery balanced while using it?)
– Short circuit protection up to 1,000 amps (Other brands void the warranty if you short the battery)
–Excessive cranking protection (Lithium technology is different than a lead acid battery and needs to be protected from heat)
This battery was purchased in 2013. I had always assumed that the features listed above applied. They do not. The important take away from this is if you have an ETX36D in your airplane that was purchased in 2013 there is very little in the way of the safe guards listed in the EarthX ETX36D literature. If you ever leave the master on it will possibly go flat on you. This is when they can get dangerous if you try to pump them back up. What I cannot say is whether EarthX made a change the BMS for this model of later years. I suspect this is case.
In any event I was always curious what these batteries looked like inside and thought I would share what I discovered in case any of you had the same curiosity.
Jerry