Ecotrek battery knowledge base

[markopolo]

From BMS specification page Mewyeah

Working power: 0.15A * 24hrs = 3.6Ah
Output control drive current listed at 0.5A could be a limitation and if so that could explain the 5 relays shown in this photo: (Note: Just my guesses below, please correct if wrong.)
ecotrek relays.jpg
Looks like:
1 & 2 are contactors (heavy duty relays)
3, 4 & 5 are automotive type relays

The drive current for the contactors could be 1.5A or more. If so, each would need an automotive type relay. BMS controls small relays which in turn controls a large contactors.

The 5th relay, not necessarily #5 in the photo, could be the heater control relay.

If you add it all up:
0.15A + <0.5A + <0.5A + >1.5A + >1.5A = 4A or so.
Also, 40W heaters if needed so another <4A including relay. The relays and contactors would give off heat too.
Plus there appears to be two small modules that would use power.

Note: Just my best efforts guessing at what's in the box and what it's for.

[markopolo]

I was curious about the charge to 13.8V coupled with the 12.4V discharge cutoff in the "KS2 Lithium Battery Guide- Rev 2 - June 2020.pdf" : http://home.roadtreking.ca/Manuals/F...une%202020.pdf

GU
ks2 GU avg user.JPG

Solar
ks2 solar.JPG

The 12.4V discharge cutoff leaves around 5% of a lithium battery's capacity remaining. That may vary a bit depending on discharge rate etc. I arrived at that 5% estimate by first discharging a battery to 12.4V then ran a discharge test from there down to 11V and got another 5% out of the battery.

I ran two tests at 0.7C charge rate. The first test was to charge to 13.8V and then discharge to 12.4V with no absorption period after reaching 13.8V. 70% of the battery capacity was able to be used. Add the unusable 5% below the cutoff and charging to 13.8V with no absorption period should result in around 75% SOC.

The second test was to charge to 13.8V again but with absorption held until tail current was down to C/30, then discharge to 12.4V. 92% of the battery capacity was able to be used. Add the unusable 5% below the cutoff and charging to 13.8V with absorption to C/30 tail current period should result in around 97% SOC.

I'd estimate that it would take around 2hrs per 200Ah module to charge from 5% SOC up to 97% SOC using 13.8V and starting charging current at .7C. The batteries will accept full charger output current for a long while but that does taper off as the battery nears 13.8V if the charger output is CV mode (constant voltage). My .7C initial charge current to 13.8V held until C/30 test on a smaller battery took 2hrs and 10 minutes. CC mode charging would be faster.

200Ah battery example:
.7C = 140 amps
C/30 = 6.68 amps
Operating within 97%<--->5% range = 184Ah usable capacity
Operating within 75%<--->5% range = 140Ah usable capacity

[cruising7388]

Originally Posted by markopolo

I was curious about the charge to 13.8V coupled with the 12.4V discharge cutoff in the "KS2 Lithium Battery Guide- Rev 2 - June 2020.pdf" : http://home.roadtreking.ca/Manuals/F...une%202020.pdf

GU
Attachment 10812

Solar
Attachment 10813

The 12.4V discharge cutoff leaves around 5% of a lithium battery's capacity remaining. That may vary a bit depending on discharge rate etc. I arrived at that 5% estimate by first discharging a battery to 12.4V then ran a discharge test from there down to 11V and got another 5% out of the battery.

I ran two tests at 0.7C charge rate. The first test was to charge to 13.8V and then discharge to 12.4V with no absorption period after reaching 13.8V. 70% of the battery capacity was able to be used. Add the unusable 5% below the cutoff and charging to 13.8V with no absorption period should result in around 75% SOC.

The second test was to charge to 13.8V again but with absorption held until tail current was down to C/30, then discharge to 12.4V. 92% of the battery capacity was able to be used. Add the unusable 5% below the cutoff and charging to 13.8V with absorption to C/30 tail current period should result in around 97% SOC.

I'd estimate that it would take around 2hrs per 200Ah module to charge from 5% SOC up to 97% SOC using 13.8V and starting charging current at .7C. The batteries will accept full charger output current for a long while but that does taper off as the battery nears 13.8V if the charger output is CV mode (constant voltage). My .7C initial charge current to 13.8V held until C/30 test on a smaller battery took 2hrs and 10 minutes. CC mode charging would be faster.

200Ah battery example:
.7C = 140 amps
C/30 = 6.68 amps
Operating within 97%<--->5% range = 184Ah usable capacity
Operating within 75%<--->5% range = 140Ah usable capacity

At some point KS2 revised the charger adding a LiFePO4 setting which set bulk and absorption to 13.6V and eliminating a trickle charge.

[markopolo]

13.6V (3.4VPC) should give results similar to 13.8V (3.45VPC) -> https://www.powerstream.com/lithium-...ge-voltage.htm - just 1% or 2% less resultant SOC if in absorption mode long enough. It would take longer to charge though.

This is what Nordkyn Design -> Marine lithium batteries in operation | Nordkyn Design <- has to say about 3.4VPC (13.6V):

Charging at reduced voltages, down to 3.4V/cell, only increases the absorption time and therefore the overall charging time, but achieves strictly nothing in terms of preventing the battery from getting fully charged and then overcharged. It only takes longer for this to happen. Furthermore, low-voltage charging opens the door to severe longer term performance issues which arise from memory effects in the cells.

[markopolo]

Another test started. Discharge to 12.4V then charge at 13.6V at .7C rate to C/30 tail current.

The charger stayed in CC mode for only 6 minutes then switched to CV mode. After another 5 minutes current started tapering! At around the 15 minute point, current had already reduced to .6C ....... this method of charging will take a few hours, maybe twice as long as a more effective method.

The charger I'm using regulates its output to maintain the selected voltage at its output. It doesn't have remote voltage sensing so the voltage at the battery terminals is a bit lower. I measured 13.578V at the battery terminals and that is slowly but steadily increasing. The battery terminal voltage will eventually get to 13.6V. If the charger has remote voltage sensing capability then it would speed things up a bit.


update: 3 hrs 10 mins to get down to C/30 current. Voltage at battery terminals: 13.605V. That's 1 hour longer than charging to 13.8V & C/30 current.


Edits: editing instead of making new posts

[markopolo]

The discharge test after charging to 13.6V yielded 1.5% less capacity than charging to 13.8V did. That was expected.

As previously noted, charging to 13.6V with .7C charge rate current limit set and C30 tail current took 3 hours & 10 minutes. I thought it would be useful to charge to 14.4V for comparison. The AGM in the Ecotrek setups would benefit from seeing 14.4V I'm sure. Same .7C charge rate and C30 tail current goal. It took just under half the amount of time that charging to 13.6V did. 1hr 33 minutes so, much faster. Full .7C current accepted for 80% of the time on the charger during the 14.4v test compared to only 3% of time during the 13.6V test.

Additionally, I'd guess that 2% to 3% more capacity would be restored by the 14.4V recharge compared to the 13.6V recharge.

[Moto vita]

I joined this forum to learn more about my Ecotrek 400 system in my 2017 CS adventurous, and I've learned a lot.
One remaining question is how do I know my Ecotrek batteries are working properly? It seems there is no way to verify that an Ecotrek 200 battery is charged and operating other than a blue LED on the batteries rocker switch. The voltmeter on my control panel shows system voltage that always includes the underhood AGM battery and I see no way to evaluate the voltage, or even operation, of the individual Ecotrek batteries.
Am I missing something?

[Winston]

Originally Posted by markopolo

. . . in parallel with the charge side of the lithium battery . . .

Guess we haven't been following "modern" technology . . . "charge/discharge" sides of a battery??? Maybe someone can bring us up to speed. Why do we have two sides? And electronically, what's the 'circuitry' separating the charge/discharge terminals and the battery itself? What's the perceived need for such a split?